Jay Quade

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Books

• Quade, J., & Dettinger, M. (2014). Calibrating and testing the volcanic glass paleoaltimeter in South America.. Geological Society of America Special Paper..
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  In: DeCelles, P.G., Ducea, M., Kapp, P., and Carrapa, B., eds., The Geodynamics of a Cordilleran Orogenic System: The Central Andes of Argentina and northern Chile. Geological Society of America Special Paper. published online Nov. 20, 2014; doi19.1130/2015.1212 (15).
• Quade, J., Dettinger, M., Carrapa, B., DeCelles, P., & Murray, K. (2014). The Growth of the Central Andes 22-26°S.. Geological Society of America Special Paper..
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  In: DeCelles, P.G., Ducea, M., Kapp, P., and Carrapa, B., eds., The Geodynamics of a Cordilleran Orogenic System: The Central Andes of Argentina and northern Chile. Geological Society of America Memoirs, published online Nov. 20, 2014; doi19.1130/2015.1212 (15).

Chapters

• Reiners, P., Thompson, S., Vernon, S. N., Willett, S., Zattin, M., Einhorn, J., Gehrels, G., Quade, J., Murray, K., Pearson, D., & Cavassa, W. (2015). Low-temperature thermochronologic trends across the central Andes, 21°S-28°S.. In The Geodynamics of a Cordilleran Orogenic System: The Central Andes of Argentina and northern Chile.(pp 215-249). Geological Society of America Memoir 212.

Journals/Publications

• Quade, J. (2017). Isotopic Characterization of late Neogene travertine deposits at Barrancas Blancas in the eastern Atacama Desert, Chile.. Chemical Geology, 46, 51-56.
• Quade, J., & Hudson, A. (2017). Stable and clumped 18O and 13C isotope systematics and 14C geochronology of shoreline tufas and other terrestrial and lacustrine carbonates from the Chewaucan closed-basin lake system, northern Great Basin, USA: implications for paleoenvironmental reconstructions.. Geochimica et Cosmochimica Acta, 212, 274-302.
• Quade, J., & Neilson, J. (2017). Significant impacts of increasing aridity on the arid soil microbiome.. mSystems, 2(3), e00195-16.
• Quade, J., Leary, R., & Decelles, P. G. (2017). Evidence from paleosols for low to moderate elevation of the India-Asia suture zone during mid-Cenozoic time.. Geology, 45(5), 399-402.
• Scott, S., Kleinsasser, L., Quade, J., Levin, N., McIntosh, W., Dunbar, N., & Semaw, S. (2015). Late Miocene hominin teeth from the Gona Paleoanthropological Research Project Area, Afar, Ethiopia.. Journal of Human Evolution, 81, 68-82.
• Steponaitis, E., Andrews, A., McGee, D., Quade, J., Hsieh, Y. T., Broecker, W., Shuman, B. N., Burns, S. J., & Cheng, H. (2015). Mid-Holocene drying of the U.S. Great Basin recorded in Nevada speleothems.. Quaternary Science Reviews, 127, 174-185.
• Davis, M., Matmon, A., Placzek, C. J., McIntosh, W., Rood, D. H., & Quade, J. (2014). Cosmogenic nuclides in buried sediments from the hyperarid Atacama Desert, Chile. Quaternary Geochronology, 19, 117-126.
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  Abstract: The evolution of Terrestrial Cosmogenic Nuclides (TCN) from an alluvial section in the Atacama Desert is examined. We reconstruct a burial history for the last ~10Ma using 40Ar/39Ar dating of volcanic ash layers interbedded with alluvial sediments; this independent dating allows us to distinguish between the effects of erosion, post-burial subsurface production, and radioactive decay during burial on TCN concentrations. Our TCN results show significant post-burial production, which is the result of the extremely slow sedimentation rate (~3m/Ma) and the old age of the sediments. Although distinct differences in TCN concentrations are apparent between the lower and upper parts of the sedimentary section, we show that these differences are most likely related to post-burial production and age, and not to changes in bedrock erosion rates or changes in elevation due to tectonic activity. Our approach provides a test to the applicability of the two-isotope cosmogenic burial dating system (26Al-10Be) in regions of extremely slow sedimentation rates. Our results reveal geomorphic stability in terms of erosion and sedimentation rates for the late Miocene-Pliocene in the Atacama Desert. © 2013 Elsevier B.V.
• Hudson, A. M., Olsen, J. W., & Quade, J. (2014). Radiocarbon dating of interdune paleo-wetland deposits to constrain the age of mid-to-late holocene microlithic artifacts from the zhongba site, Southwestern Qinghai-Tibet Plateau. Geoarchaeology, 29(1), 33-46.
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  Abstract: Microlithic artifacts, some found in situ, are abundant in the Zhongba archaeological site in southwestern Tibet. The site environment consists of extant wetlands and paleo-wetland deposits found in depressions between sand dunes derived from the Yarlung Tsangpo floodplain. Constraining 14C dates from wetland vegetation and shell from one site fall between ca. 6600-2600 cal. yr B.P., while a second site is dated 3400-1200 cal. yr B.P. A significant and variable 14C reservoir effect-up to 1400 14C yr-limits these ranges to terminus post quem constraints. The in situ artifacts are supplemented by surface collections fully characterizing raw material and typological variability for each site. Raw material found at Zhongba is chert and chalcedony likely sourced from Cretaceous bedrock near the site. Typologically, microblades are nongeometric and are derived from conical and wedge-shaped cores similar to those identified in the Qinghai Lake Basin and the Chang Tang Nature Reserve of similar or greater age. The later occupation period at Zhongba is broadly contemporaneous with sites on the Qinghai-Tibet Plateau containing bronze and iron artifacts, indicating microlithic technology remained an important tool-making strategy in western Tibet late into the protohistoric period. © 2013 Wiley Periodicals, Inc.
• Pigati, J. S., Rech, J. A., Quade, J., & Bright, J. (2014). Desert wetlands in the geologic record. Earth-Science Reviews, 132, 67-81.
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  Abstract: Desert wetlands support flora and fauna in a variety of hydrologic settings, including seeps, springs, marshes, wet meadows, ponds, and spring pools. Over time, eolian, alluvial, and fluvial sediments become trapped in these settings by a combination of wet ground conditions and dense plant cover. The result is a unique combination of clastic sediments, chemical precipitates, and organic matter that is preserved in the geologic record as ground-water discharge (GWD) deposits. GWD deposits contain information on the timing and magnitude of past changes in water-table levels and, therefore, are a potential source of paleohydrologic and paleoclimatic information. In addition, they can be important archeological and paleontological archives because desert wetlands provide reliable sources of fresh water, and thus act as focal points for human and faunal activities, in some of the world's harshest and driest lands. Here, we review some of the physical, sedimentological, and geochemical characteristics common to GWD deposits, and provide a contextual framework that researchers can use to identify and interpret geologic deposits associated with desert wetlands. We discuss several lines of evidence used to differentiate GWD deposits from lake deposits (they are commonly confused), and examine how various types of microbiota and depositional facies aid in reconstructing past environmental and hydrologic conditions. We also review how late Quaternary GWD deposits are dated, as well as methods used to investigate desert wetlands deeper in geologic time. We end by evaluating the strengths and limitations of hydrologic and climatic records derived from GWD deposits, and suggest several avenues of potential future research to further develop and utilize these unique and complex systems. © 2014.
• Quade, J. (2014). A forager-herder trade-off, from broad-spectrum hunting to sheep management at Aşıklı Höyük, Turkey.. Proceedings of the National Academy of Sciences doi/10.1073/pnas.1322723111..
• Simpson, S. W., Quade, J., Levin, N. E., & Semaw, S. (2014). The female Homo pelvis from Gona: Response to Ruff (2010). Journal of Human Evolution, 68(1), 32-35.
• Hudson, A. M., & Quade, J. (2013). Long-term east-west asymmetry in monsoon rainfall on the Tibetan Plateau. Geology, 41(3), 351-354.
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  Abstract: Variations in the strength and duration of the Asian Monsoon affect more than half the population of the planet, and there is intense interest in where, and how much, rainfall amounts will change regionally in response to warmer climate conditions. The modern monsoon region is divided into distinct subsystems, so the response may be regionally heterogeneous. Northern Hemisphere monsoon systems intensified during the early to mid-Holocene, increasing summer rainfall and creating wetter conditions across much of eastern Asia. In this study we use the area encompassed by high shorelines of early Holocene paleolakes in Tibet to reconstruct paleorainfall (and hence paleomonsoon) patterns during this very wet period. We found that the early Holocene relative paleolake expansions of 130 closed-basin lake systems in the central Tibetan Plateau display a strong east-west gradient. Paleolake areas expanded by approximately fourfold in the western plateau, compared to approximately twofold expansion in the eastern region. This early Holocene pattern mirrors the modern west-east climate division on the plateau: rainfall in the west is closely tied to the Indian summer monsoon (ISM) subsystem, and in the east is closely tied to a probable mix of ISM and East Asian summer monsoon (EASM) subsystems. Our results suggest that these modern climate divisions are an enduring feature of the plateau and that ISM rainfall increased much more than EASM rainfall in response to the same insolation forcing. © 2013 Geological Society of America.
• Hudson, A. M., & Quade, J. (2013). Long-term east-west asymmetry in monsoon rainfall on the tibetan plateau: REPLY. Geology, 41(12), e312.
• Mentzer, S. M., & Quade, J. (2013). Compositional and Isotopic Analytical Methods in Archaeological Micromorphology. Geoarchaeology, 28(1), 87-97.
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  Abstract: Resin-impregnated sediment blocks are a by-product of micromorphological sample processing. These blocks can be further studied using a variety of destructive, nondestructive, and minimally destructive geochemical techniques. X-ray fluorescence microanalyses conducted on sediment blocks yield semiquantitative major and trace elemental abundances that can be used to generate compositional maps, and to illustrate compositional change within or between archaeological strata and features. Sediment blocks can also be drilled to obtain small sediment samples for stable oxygen and carbon isotopic analyses. Both elemental and isotopic analyses can be conducted in conjunction with micromorphological analyses to yield a holistic picture of archaeological sediment composition, source, and depositional processes. The integration of micromorphological, compositional, and isotopic analyses is used here to aid in the differentiation of calcareous ash and lime plasters from the Neolithic site of Asi{dotless}kli{dotless} Höyük, Turkey. © 2012 Wiley Periodicals, Inc.
• Placzek, C. J., Quade, J., & Patchett, P. J. (2013). A 130ka reconstruction of rainfall on the Bolivian Altiplano. Earth and Planetary Science Letters, 363, 97-108.
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  Abstract: New efforts to link climate reconstructions from shoreline deposits and sediment cores yield an improved and more detailed lake history from the Bolivian Altiplano. On the Southern Altiplano, 10 lake oscillations have been identified from this new unified chronology, each coincident with North Atlantic cold events such as Heinrich Events H5, H2, H1, and the Younger Dryas. By coupling this new lake history to a hydrologic budget model we are able to evaluate precipitation variability on the Southern Bolivian Altiplano over the last 130. ka. These modeling efforts underscore the relative aridity of the Altiplano during the rare and small lake cycles occurring between 80 and 20. ka, when colder temperatures combined with little or no change in rainfall produced smaller paleolakes. Relative aridity between 80 and 20. ka contrasts with the immense Tauca lake cycle (18.1-14.1. ka), which was six times larger than modern Lake Titicaca and coincided with Heinrich Event 1. This improved paleolake record from the Southern Altiplano reveals a strong link between central Andean climate and Atlantic sea-surface temperature gradients during the late Pleistocene, even though today rainfall variability is driven mostly by Pacific sea-surface temperature anomalies associated with El Niño/Southern Oscillation. However, not all Heinrich Events appear to result in lake expansions, most conspicuously during the global cold interval between 80 and 20. ka when the Altiplano and Amazon Basin were relatively arid. © 2012 Elsevier B.V.
• Quade, J., Eiler, J., Daëron, M., & Achyuthan, H. (2013). The clumped isotope geothermometer in soil and paleosol carbonate. Geochimica et Cosmochimica Acta, 105, 92-107.
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  Abstract: We studied both modern soils and buried paleosols in order to understand the relationship of temperature (T°C(47)) estimated from clumped isotope compositions (Δ47) of soil carbonates to actual surface and burial temperatures. Carbonates from modern soils with differing rainfall seasonality were sampled from Arizona, Nevada, Tibet, Pakistan, and India. T°C(47) obtained from these soils shows that soil carbonate forms in the warmest months of the year, in the late morning to afternoon, and probably in response to intense soil dewatering. T°C(47) obtained from modern soil carbonate ranges from 10.8 to 39.5°C. On average, T°C(47) exceeds mean annual temperature by 10-15°C due to summertime bias in soil carbonate formation, and to summertime ground heating by incident solar radiation. Secondary controls on T°C(47) are soil depth and shading. Site mean annual air temperature (MAAT) across a broad range (0-30. °C) of site temperatures is highly correlated with T°C(47) from soils, following the equation:. MAAT(°C)=1.20(T°C(47)0)-21.72(r2=0.92)where T°C(47)0 is the effective air temperature at the site estimated from T°C(47). The effective air temperature represents the air temperature required to account for the T°C(47) at each site, after consideration of variations in T°C(47) with soil depth and ground heating. The highly correlated relationship in this equation should now permit mean annual temperature in the past to be reconstructed from T°C(47) in paleosol carbonate, assuming one is studying paleosols that formed in environments generally similar in seasonality and ground cover to our calibration sites.T°C(47)0 decreases systematically with elevation gain in the Himalaya, following the equation:elevation(m)=-229(T°C(47)0)+9300(r2=0.95)Assuming that temperature varied similarly with elevation in the past, this equation can be used to reconstruct paleoelevation from clumped isotope analysis of ancient soil carbonates. We also measured T°C(47) from long sequences of deeply buried (≤5km) paleosol carbonate in the Himalayan foreland in order to evaluate potential diagenetic resetting of clumped isotope composition. We found that paleosol carbonate faithfully records plausible soil T°C(47) down to 2.5-4km burial depth, or ∼90-125°C. Deeper than this and above this temperature, T°C(47) in paleosol carbonate is reset to temperatures >40°C. We observe ∼40°C as the upper limit for T°C(47) in modern soils from soil depths >25cm, and therefore that T°C(47) >40°C obtained from ancient soil carbonate indicates substantially warmer climate regimes compared to the present, or non-primary temperatures produced by resetting during diagenesis. If representative, this limits the use of T°C(47) to reconstruct ancient surface temperature to modestly buried (
• Uno, K. T., Quade, J., Fisher, D. C., Wittemyer, G., Douglas-Hamilton, I., Andanje, S., Omondi, P., Litoroh, M., & Cerling, T. E. (2013). Bomb-curve radiocarbon measurement of recent biologic tissues and applications to wildlife forensics and stable isotope (paleo)ecology. Proceedings of the National Academy of Sciences of the United States of America, 110(29), 11736-11741.
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  PMID: 23818577;PMCID: PMC3718084;Abstract: Above-ground thermonuclear weapons testing from 1952 through 1962 nearly doubled the concentration of radiocarbon (14C) in the atmosphere. As a result, organic material formed during or after this period may be radiocarbon-dated using the abrupt rise and steady fall of the atmospheric 14C concentration known as the bomb-curve. We test the accuracy of accelerator mass spectrometry radiocarbon dating of 29 herbivore and plant tissues collected on known dates between 1905 and 2008 in East Africa. Herbivore samples include teeth, tusks, soft tissue, hair, and horn. Tissues formed after 1955 are dated to within 0.3-1.3 y of formation, depending on the tissue type, whereas tissues older than ca. 1955 have high age uncertainties (
• Breecker, D. O., Payne, A. E., Quade, J., Banner, J. L., Ball, C. E., Meyer, K. W., & Cowan, B. D. (2012). The sources and sinks of CO ₂ in caves under mixed woodland and grassland vegetation. Geochimica et Cosmochimica Acta, 96, 230-246.
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  Abstract: We measured concentrations and stable carbon isotope compositions of carbon dioxide in the atmospheres of three caves in central Texas and one cave in southern Arizona in order to identify CO 2 sources and sinks. The vegetation above the caves studied is either savannah (two caves, above which vegetation has been minimally disturbed) or discrete patches of grassland and woodland (two caves, above which vegetation has been highly disturbed). We tested two hypotheses concerning CO 2 in the cave atmospheres: (1) cave ventilation by tropospheric air is the primary sink for CO 2 and (2) CO 2 is primarily derived from the deepest rooting plants growing above the caves. Within caves, we monitored CO 2 at individual locations on monthly and daily time-scales and measured CO 2 along transects with increasing distance from the cave entrances. We also measured CO 2 in the pore spaces of soils under grasses and trees above each of the caves. We calculated δ 13C values of respired CO 2 (δ 13C r) for all gas samples using measured δ 13C values and CO 2 concentrations. We then identified the sources of cave CO 2 by comparing cave-air and soil CO 2 δ 13C r values. At all locations in each Texas cave, CO 2 concentrations were highest (lowest) and δ 13C values were lowest (highest) during the summer (winter). Cave-air CO 2 concentrations consistently increased and δ 13C values consistently decreased with distance from the cave entrances. Similar but smaller magnitude seasonal variations in CO 2 concentrations occurred in the Arizona cave and no seasonal or spatial variation in the δ 13C of cave-air CO 2 was observed. The mean δ 13C r values of CO 2 in soils under grass were 3.5-4.5‰ higher than the δ 13C r values of CO 2 in soils under trees. In the caves under savannah, mean δ 13C r values of cave-air CO 2 (-24‰ in both caves) were within 1‰ of the mean δ 13C r values of CO 2 in soils under trees. In caves covered by large, contiguous areas of grassland, the δ 13C r values of cave-air CO 2 were similar to grassland soil values during the summer and were intermediate between grassland and woodland soil values during the winter. The observed spatial and temporal variations in cave-air CO 2 are consistent with density-driven ventilation controlled by seasonal surface temperature changes as the primary sink for CO 2 in the Texas caves. The consistent agreement between soil and cave δ 13C r values indicate that the same mixing and diffusion equations that are used to calculate δ 13C r values of soil CO 2 also apply to cave-air CO 2. Our results suggest that the majority of CO 2 advects or diffuses into these caves from soils as a gas rather than being transported in aqueous solution. Measured δ 13C r values and numerical production-diffusion modeling supports our hypothesis that the majority of gaseous CO 2 in these caves is derived from deeply rooted vegetation. The carbon isotope composition of groundwater and speleothem calcite used for paleoclimate records are therefore likely biased toward deeply rooted plants, even if sparsely present. © 2012 Elsevier Ltd.
• Copeland, A., Quade, J., Watson, J. T., McLaurin, B. T., & Villalpando, E. (2012). Stratigraphy and geochronology of La Playa archaeological site, Sonora, Mexico. Journal of Archaeological Science, 39(9), 2934-2944.
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  Abstract: La Playa archaeological site in northern Sonora, Mexico contains a long record of human activity that includes the Paleoindian period (terminal Pleistocene) and much of the Holocene. The size and complexity of La Playa has discouraged a systematic characterization of its stratigraphy and geochronology, a deficiency we redress in the study. We distinguished seven stratigraphic units ranging in age from >44,570 to 400 cal yr B.P. using 14C dates from charcoal and terrestrial gastropods found mostly in archaeological features. All of the buried (in situ) cultural remains are contained in Units B (4690-1580 cal yr B.P.) and C (1010-400 cal yr B.P.) and represent overbank deposition from the nearby Rio Boquillas. Occupation at the site peaks in Units B 4 and B 5, corresponding to the Cienega phase (2800-1800 cal yr B.P.) of the Early Agricultural period. This period coincides with the growth of early agricultural villages in the region and is marked at La Playa by thousands of archaeological features including roasting pits, human burials, and extensive canal irrigation systems. The presence of semi-aquatic and aquatic snails demonstrates that water was present year round in the canal systems constructed during this period. Stable and radiometric isotopic evidence suggests that early agriculturalists diverted ground water over several kilometers from the nearby Rio Boquillas. The extensive Cienega phase occupation ended after about 1700 cal yr B.P. with deep erosion of the site, an event also visible in alluvial records in southern Arizona that marked the end of the Early Agricultural period and significant changes in settlement organization in the region. © 2012 Elsevier Ltd.
• Díaz, F. P., Latorre, C., Maldonado, A., Quade, J., & Betancourt, J. L. (2012). Rodent middens reveal episodic, long-distance plant colonizations across the hyperarid Atacama Desert over the last 34,000 years. Journal of Biogeography, 39(3), 510-525.
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  Abstract: Aim To document the impact of late Quaternary pluvial events on plant movements between the coast and the Andes across the Atacama Desert, northern Chile. Location Sites are located along the lower and upper fringes of absolute desert (1100-2800m a.s.l.), between the western slope of the Andes and the Coastal Ranges of northern Chile (24-26°S). Methods We collected and individually radiocarbon dated 21 rodent middens. Plant macrofossils (fruits, seeds, flowers and leaves) were identified and pollen content analysed. Midden assemblages afford brief snapshots of local plant communities that existed within the rodents' limited foraging range during the several years to decades that it took the midden to accumulate. These assemblages were then compared with modern floras to determine the presence of extralocal species and species provenance. Results Five middens span the last glacial period (34-21ka) and three middens are from the last glacial-interglacial transition (19-11ka). The remaining 13 middens span the last 7000years. Coastal hyperarid sites exhibit low taxonomic richness in middens at 19.3, 1.1, 1.0, 0.9, 0.5ka and a modern sample. Middens are also dominated by the same plants that occur today. In contrast, middens dated to 28.1, 21.3, 17.3, 3.7 and 0.5ka contain more species, including Andean extralocals. Precordillera middens (c.2700m) show a prominent increase in plant macrofossil richness, along with the appearance of Andean extralocals and sedges at 34.5 and 18.9ka. Six younger middens dated to 6.1-0.1ka are similar to the modern local vegetation. Main conclusions Increased species richness and Andean extralocal plants occurred along the current lower fringes of absolute desert during the last glacial-interglacial transition and late Holocene. The absence of soil carbonates indicates the persistence of absolute desert throughout the Quaternary. Colonization by Andean plants could have been accomplished through long-distance seed dispersal either by animals or floods that originated in the Andes. We postulate that dispersal would have been most frequent during regional pluvial events and associated increases in groundwater levels, forming local wetlands in the absolute desert, and generating large floods capable of crossing the Central Depression. © 2011 Blackwell Publishing Ltd.
• Hynek, S. A., Passey, B. H., Prado, J. L., Brown, F. H., Cerling, T. E., & Quade, J. (2012). Small mammal carbon isotope ecology across the Miocene-Pliocene boundary, northwestern Argentina. Earth and Planetary Science Letters, 321-322, 177-188.
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  Abstract: The late Miocene expansion of plants using the C 4 photosynthetic pathway in South America has been documented by tooth enamel carbon isotope ratios (δ 13C en). However, a more detailed understanding of this ecological event is hampered by poor chronological control on the widespread fossil localities from which isotopic data are derived. This study develops a δ 13C en record from a single 2500m-thick stratigraphic section in subtropical South America. Strata at Puerta de Corral Quemado (PCQ), northwestern Argentina, span 9 to 3.5Ma in age, and existing paleosol carbonate data (δ 13C pc) document C 4 expansion across the Miocene-Pliocene boundary. Comparison of δ 13C en data with δ 13C pc data at high stratigraphic resolution refines understanding of this ecological event in South America. Small mammal δ 13C en data in particular are complementary to that of large mammal and paleosol δ 13C data. Small mammal teeth integrate isotopic data over much shorter temporal and spatial scales than large mammal teeth, providing a sensitive measure of local vegetation and placing constraints on the landscape distribution of C 3 and C 4 plants. Explicit consideration of the distinctive carbon isotope enrichment factor between enamel and diet for rodents (ε*en-diet=11‰, as opposed to 14‰ for large mammals) allows for unequivocal inference of C 4 vegetation ~1Ma prior to that inferred from large mammal δ 13C en data, and ~2Ma prior to δ 13C pc data. This multiproxy record demonstrates that C 4 plants were a stable component of the ecosystem hundreds of thousands of years prior to their major ecological expansion, and that the expansion of C 4 plants was pulsed at PCQ. Two periods of ecological change are demonstrated by δ 13C and δ 18O data at ~7Ma and 5.3Ma (coincident with the Miocene-Pliocene boundary). Development of small mammal δ 13C en records on other continents may provide similar insight into the early stages of the global C 4 event. © 2011 Elsevier B.V.
• McGee, D., Quade, J., Edwards, R. L., Broecker, W. S., Cheng, H., Reiners, P. W., & Evenson, N. (2012). Lacustrine cave carbonates: Novel archives of paleohydrologic change in the Bonneville Basin (Utah, USA). Earth and Planetary Science Letters, 351-352, 182-194.
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  Abstract: Records of past changes in lake levels and lake water isotopic composition in closed basins provide key insights into past variations in the hydrological cycle; however, these records are often limited by dating precision and temporal resolution. Here we present data from lacustrine cave carbonates, a previously unexplored class of carbonates that comprise a promising new archive of past hydrologic changes in the Bonneville Basin of the northeastern Great Basin (USA). These dense carbonates precipitated within caves, crevices, and other protected spaces flooded by Lake Bonneville during its highstand in the last glacial period. We report on deposits in Cathedral and Craners caves, located ~50km apart at similar elevations approximately 100m above the modern Great Salt Lake and almost 200m below Lake Bonneville's highstand shoreline. Carbonates from the two caves show similar chronologies, mineralogical transitions, isotopic compositions, and uranium concentrations. These findings suggest that lacustrine cave carbonates record changes in lake level and in the isotopic composition and chemistry of lake water. Importantly, the deposits can be precisely dated by U-Th methods, providing the first records of Lake Bonneville's water balance changes tied to precise U-Th ages. Close agreement between paired U-Th and calibrated 14C ages in the deposits suggests a minimal (
• Neilson, J. W., Quade, J., Ortiz, M., Nelson, W. M., Legatzki, A., Tian, F., LaComb, M., Betancourt, J. L., Wing, R. A., Soderlund, C. A., & Maier, R. M. (2012). Life at the hyperarid margin: Novel bacterial diversity in arid soils of the Atacama Desert, Chile. Extremophiles, 16(3), 553-566.
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  PMID: 22527047;Abstract: Nearly half the earth's surface is occupied by dryland ecosystems, regions susceptible to reduced states of biological productivity caused by climate fluctuations. Of these regions, arid zones located at the interface between vegetated semiarid regions and biologically unproductive hyperarid zones are considered most vulnerable. The objective of this study was to conduct a deep diversity analysis of bacterial communities in unvegetated arid soils of the Atacama Desert, to characterize community structure and infer the functional potential of these communities based on observed phylogenetic associations. A 454-pyrotag analysis was conducted of three unvegetated arid sites located at the hyperarid-arid margin. The analysis revealed communities with unique bacterial diversity marked by high abundances of novel Actinobacteria and Chloroflexi and low levels of Acidobacteria and Proteobacteria, phyla that are dominant in many biomes. A 16S rRNA gene library of one site revealed the presence of clones with phylogenetic associations to chemoautotrophic taxa able to obtain energy through oxidation of nitrite, carbon monoxide, iron, or sulfur. Thus, soils at the hyperarid margin were found to harbor a wealth of novel bacteria and to support potentially viable communities with phylogenetic associations to non-phototrophic primary producers and bacteria capable of biogeochemical cycling. © 2012 Springer.
• Quade, J., Reiners, P., Placzek, C., Matmon, A., Pepper, M., Ojha, L., & Murray, K. (2012). Seismicity and the strange rubbing boulders of the Atacama desert, Northern Chile. Geology, 40(9), 851-854.
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  Abstract: We found clusters of 0.5-8 t boulders worn to smoothness around their midsections in the Atacama Desert of northern Chile. We suggest that the boulder smoothing is the cumulative result of at least 1 m.y. of rubbing between boulders during earthquakes. 10Be exposure ages of boulder tops from these fields average ∼1.3 m.y., unsurprisingly old given the hyperaridity of the Atacama. During a visit to one major boulder site, we experienced an earthquake that rocked but did not tip the boulders, causing them to rub against each other for about a minute. This M W 5.2 earthquake was centered ∼100 km northeast of the site. In the seismically active Atacama, earthquakes of this energy or greater occur about once every four months, suggesting that the average boulder has undergone ∼40,000-70,000 h of abrasion over the past 1.3 m.y. This unusual evidence underscores the largely unrecognized role that seismicity probably plays in hillslope sediment transport in the nearly rainless Atacama Desert, and perhaps on other seismically active but now dry worlds like Mars. © 2012 Geological Society of America.
• Reynolds, A. C., Quade, J., & Betancourt, J. L. (2012). Strontium isotopes and nutrient sourcing in a semi-arid woodland. Geoderma, 189-190, 574-584.
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  Abstract: Sr isotopes are widely used as a tracer of Sr and Ca in surficial systems. Basalt flows ranging in age from 3ka (kiloyears ago) to>200ka from El Malpais National Monument (EMNM), New Mexico provide an ideal setting to examine strontium, and hence calcium cycling by plants in a semi-arid woodland. To gauge plant dependence on atmospheric dust versus local weathering products for strontium and calcium, we measured 87Sr/ 86Sr ratios in local bedrock and soils, and compared them to leaf/wood cellulose of four different conifers, a deciduous tree, three shrubs, an annual C 4 grass, and a lichen. Sampling sites varied by parent material (limestone, sandstone, granite, and basalt) and age (Quaternary to Precambrian), providing a wide range in end-member 87Sr/ 86Sr ratios, whereas the target plant species varied in physiognomy, life history, and rooting depth. On non-basalt parent material, the contribution from dust changed with the supply of weatherable Sr-bearing minerals in local bedrock. Soils developed on Paleozoic limestone showed significant bedrock contributions. On basalts, the Sr budget of soils at EMNM is dominated by atmospheric dust on young, 3ka flows, incorporates a mixture of basalt-dust in 9ka flows, and is basalt-dominated in 120ka flows. This is unlike the pattern observed in tropical soils developed on basalt in Hawaii, where basalt weathering dominates the Sr inventory of the youngest soils and aerosols dominate in older, deeply weathered soils. This contrast is mainly due to different water/rock (W/R) ratios: bedrock subjected to high W/R over short periods is quickly (
• Cartwright, A., Quade, J., Stine, S., Adams, K. D., Broecker, W., & Cheng, H. (2011). Chronostratigraphy and lake-level changes of Laguna Cari-Laufquén, Río Negro, Argentina. Quaternary Research, 76(3), 430-440.
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  Abstract: Evidence from shoreline and deep-lake sediments show Laguna Cari-Laufquén, located at 41°S in central Argentina, rose and fell repeatedly during the late Quaternary. Our results show that a deep (> 38. m above modern lake level) lake persisted from no later than 28. ka to 19. ka, with the deepest lake phase from 27 to 22. ka. No evidence of highstands is found after 19. ka until the lake rose briefly in the last millennia to 12. m above the modern lake, before regressing to present levels. Laguna Cari-Laufquén broadly matches other regional records in showing last glacial maximum (LGM) highstands, but contrasts with sub-tropical lake records in South America where the hydrologic maximum occurred during deglaciation (17-10. ka). Our lake record from Cari-Laufquén mimics that of high-latitude records from the Northern Hemisphere. This points to a common cause for lake expansions, likely involving some combination of temperature depression and intensification of storminess in the westerlies belt of both hemispheres during the LGM. © 2011 University of Washington.
• Cerling, T. E., Wynn, J. G., Andanje, S. A., Bird, M. I., Korir, D. K., Levin, N. E., MacE, W., MacHaria, A. N., Quade, J., & Remien, C. H. (2011). Woody cover and hominin environments in the past 6-million years. Nature, 476(7358), 51-56.
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  PMID: 21814275;Abstract: The role of African savannahs in the evolution of early hominins has been debated for nearly a century. Resolution of this issue has been hindered by difficulty in quantifying the fraction of woody cover in the fossil record. Here we show that the fraction of woody cover in tropical ecosystems can be quantified using stable carbon isotopes in soils. Furthermore, we use fossil soils from hominin sites in the Awash and Omo-Turkana basins in eastern Africa to reconstruct the fraction of woody cover since the Late Miocene epoch (about 7 million years ago). 13C/ 12C ratio data from 1,300 palaeosols at or adjacent to hominin sites dating to at least 6-million years ago show that woody cover was predominantly less than-40% at most sites. These data point to the prevalence of open environments at the majority of hominin fossil sites in eastern Africa over the past 6-million years. © 2011 Macmillan Publishers Limited. All rights reserved.
• DeCelles, P. G., Kapp, P., Quade, J., & Gehrels, G. E. (2011). Oligocene-Miocene Kailas basin, southwestern Tibet: Record of postcollisional upper-plate extension in the Indus-Yarlung suture zone. Bulletin of the Geological Society of America, 123(7-8), 1337-1362.
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  Abstract: The Kailas basin developed during late Oligocene-early Miocene time along the Indus-Yarlung suture zone in southwestern Tibet. The >2.5-km-thick basin-fi lling Kailas Formation consists of a lower coarse-grained proximal conglomerate and more distal fl uvial sandstone member, a lacustrine shale and sandstone member, and an upper redbed clastic member. Felsic tuffs and trachyandesite layers are locally present. De trital and igneous zircon U-Pb ages indicate depo sition of most of the Kailas Formation between ca. 26 and 24 Ma. The Kailas Formation was deposited by alluvial-fan, low-sinuosity fl uvial, and deep lacustrine depositional systems in buttress unconformity upon andesitic volcanic (ca. 67 Ma) and granitoid (ca. 55 Ma) rocks of the Gangdese magmatic arc. Abundant organic material, fi sh and amphibian fossils, and sparse palynomorphs suggest that Kailas lakes developed in a warm tropical climate, quite different from coeval basins in central Tibet, which formed at high elevation in a dry climate. Provenance and paleocurrent data indicate that the bulk of the Kailas Formation was derived from the northerly Gangdese magmatic arc (Kailas magmatic complex). Only during the latest stages of basin fi lling was abundant sediment derived from the southerly Tethyan Himalayan thrust belt in the hanging wall of the Great Counter thrust. Kailas basin stratigraphy resembles a classic lacustrine sandwich and is most consistent with deposition in an extensional or transtensional rift that developed along the suture zone some 30 m.y. after the onset of Indo-Eurasian intercontinental collision. Correlative coarse-grained syntectonic strata similar to the Kailas Formation crop out along a >1300 km length of theIndus-Yarlung suture zone, suggesting that the basin-forming mechanism recorded by the Kailas Formation was of regional signifi cance and not exclusively related to local kinematics near the southeastern end of the Karakoram fault. We propose that extension of the southern edge of the Eurasian plate was caused by southward rollback of underthrusting Indian continental lithosphere, followed by slab break-off. Alternating episodes of hard and soft collision, asso ciated with regional contraction and extension, respectively, in the Tibetan-Himalayan orogenic system may have been related to changing dynamics of the subducting/underthrusting Indian plate. © 2011 Geological Society of America.
• Fan, M., DeCelles, P. G., Gehrels, G. E., Dettman, D. L., Quade, J., & Peyton, S. L. (2011). Sedimentology, detrital zircon geochronology, and stable isotope geochemistry of the lower Eocene strata in the Wind River Basin, central Wyoming. Bulletin of the Geological Society of America, 123(5), 979-996.
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  Abstract: Shallow subduction of the Farallon plate beneath the western United States has been commonly accepted as the tectonic cause for the Laramide deformation during Late Cretaceous through Eocene time. However, it remains unclear how shallow subduction would produce the individual Laramide structures. Critical information about the timing of individual Laramide uplifts, their paleoelevations at the time of uplift, and the temporal relationships among Laramide uplifts have yet to be documented at regional scale to address the question and evaluate competing tectonic models. The Wind River Basin in central Wyoming is filled with sedimentary strata that record changes of paleogeography and paleoelevation during Laramide deformation. We conducted a multidisciplinary study of the sedimentology, detrital zircon geochronology, and stable isotopic geochemistry of the lower Eocene Indian Meadows and Wind River formations in the northwestern corner of the Wind River Basin in order to improve understanding of the timing and process of basin evolution, source terrane unroofing, and changes in paleoelevation and paleoclimate. Depositional environments changed from alluvial fans during deposition of the Indian Meadows Formation to low-sinuosity braided river systems during deposition of the Wind River Formation. Paleocurrent directions changed from southwestward to mainly eastward through time. Conglomerate and sandstone compositions suggest that the Washakie and/or western Owl Creek ranges to the north of the basin experienced rapid unroofing ca. 55.5-54.5 Ma, producing a trend of predominantly Mesozoic clasts giving way to Precambrian basement clasts upsection. Rapid source terrane unroofing is also suggested by the upsection changes in detrital zircon U-Pb ages. Detrital zircons in the upper Wind River Formation show age distributions similar to those of modern sands derived from the Wind River Range, with up to ~20% of zircons derived from the Archean basement rocks in the Wind River Range, indicating that the range was largely exhumed by ca. 53-51 Ma. The rise of these ranges by 51 Ma formed a confined valley in the northwestern part of the basin, and promoted development of a meandering fluvial system in the center of the basin. The modern paleodrainage configuration was essentially established by early Eocene time. Carbon isotope data from paleosols and modern soil carbonate show that the soil CO2 respiration rate during the early Eocene was higher than at present, from which a more humid Eocene paleoclimate is inferred. Atmosphere pCO2 estimated from paleosol carbon isotope values decreased from 2050 ± 450 ppmV to 900 ± 450 ppmV in the early Eocene, consistent with results from previous studies. Oxygen isotope data from paleosol and fluvial cement carbonates show that the paleoelevation of the Wind River Basin was comparable to that of the modern Great Plains (~500 m above sea level), and that local relief between the Washakie and Wind River ranges and the basin floor was 2.3 ± 0.8 km. Up to 1 km of post-Laramide regional net uplift is required to form the present landscape in central Wyoming. © 2011 Geological Society of America.
• Fan, M., Quade, J., Dettman, D., & DeCelles, P. G. (2011). Widespread basement erosion during the late Paleocene-early Eocene in the laramide rocky mountains inferred from ⁸⁷sr/⁸⁶sr ratios of freshwater bivalve fossils. Bulletin of the Geological Society of America, 123(9-10), 2069-2082.
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  Abstract: Reconstruction of the timing and pattern of exhumation of basement-involved uplifts during the Laramide is essential to the understanding of the mechanisms of crustal shortening and thickening in the region. We use reconstructions of the 87sr/86sr ratios of Late Cretaceous-early Cenozoic river water from fossil shells in six basins of the Rocky Mountains contextualized by modern riverwater Sr chemistry studies to trace the erosion of Precambrian basement cores in the Laramide ranges. The 87sr/86sr ratios and Sr concentration of modern river water in the Rocky Mountains are controlled by river bedrock lithology. Weathering of Precambrian silicate rocks in the cores of Laramide ranges produces high 87sr/86sr ratios in highland rivers. Weathering of Paleozoic and Mesozoic carbonates along the basin margins reduces the 87sr/86sr ratios and increases Sr concentration of rivers as they flow basinward. Lowland rivers that have headwaters in Precambrian basement mostly have 87sr/86sr ratios >0.711, whereas rivers confined to or with very long reaches in basins have 87sr/86sr ratios between 0.709 and 0.711. River-water d18O values do not change in response to changes in catchment elevation. Our results from fossil shells show that carbonate weathering dominated the riverwater Sr chemistry in the Alberta Foreland, Williston, and Crazy Mountains Basins, and that Proterozoic low-grade metamorphic carbonates in the Belt-Purcell Supergroup were not exposed in the Canadian Rocky Mountains during Late Cretaceous-early Paleocene time. Silicate weathering influenced the Sr chemistry of surface waters in the Powder River Basin during the late Paleocene and the Washakie Basin during the early Eocene, suggesting Precambrian silicate basement rock was extensively exhumed and eroded. The observation that Precambrian basement was eroded earlier around the Powder River Basin than around the Washakie Basin is consistent with a previous study that suggests Laramide ranges in northeast Wyoming reached high elevation earlier than the ranges adjacent to the Sevier thrust belt. Widespread basement erosion in late Paleocene- early Eocene time was controlled by tectonic exhumation, and may have been intensified by the wet and warm global climate. © 2011 Geological Society of America.
• Latorre, C., González, A. L., Quade, J., Fariña, J. M., Pinto, R., & Marquet, P. A. (2011). Establishment and formation of fog-dependent Tillandsia landbeckii dunes in the Atacama Desert: Evidence from radiocarbon and stable isotopes. Journal of Geophysical Research G: Biogeosciences, 116(3).
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  Abstract: Extensive dune fields made up exclusively of the bromeliad Tillandsia landbeckii thrive in the Atacama Desert, one of the most extreme landscapes on earth. These plants survive by adapting exclusively to take in abundant advective fog and dew as moisture sources. Although some information has been gathered regarding their modern distribution and adaptations, very little is known about how these dune systems actually form and accumulate over time. We present evidence based on 20 radiocarbon dates for the establishment age and development of five different such dune systems located along a ∼215 km transect in northern Chile. Using stratigraphy, geochronology and stable C and N isotopes, we (1) develop an establishment chronology of these ecosystems, (2) explain how the unique T. landbeckii dunes form, and (3) link changes in foliar δ15N values to moisture availability in buried fossil T. landbeckii layers. We conclude by pointing out the potential that these systems have for reconstructing past climate change along coastal northern Chile during the late Holocene. Copyright 2011 by the American Geophysical Union.
• Pelletier, J. D., Quade, J., Goble, R. J., & Aldenderfer, M. S. (2011). Widespread hillslope gullying on the southeastern Tibetan Plateau: Human or climate-change induced?. Bulletin of the Geological Society of America, 123(9-10), 1926-1938.
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  Abstract: Many drainage basins adjacent to the upper Tsangpo Valley on the southeastern Tibetan Plateau are pervasively gullied. These gullies expose a stratigraphic record alternating between slow aggradation and stability (i.e., soil development) for much of the Quaternary, suggesting that gullying is recent and unprecedented within at least the past 10-100 k.y. In this paper, we date the initiation of gullying at five sites in the region using optically stimulated luminescence (OSL). We also test alternative hypotheses for gully initiation usingnumerical landform evolution modeling. OSL ages constrain the initiation of gullying to be mid-to-late Holocene in age. This period coincides with the onset of pastoralism in the upper Tsangpo Valley. Numerical modeling suggests that a reduction in vegetation density during the colder, drier conditions of Pleistocene glacial intervals did not trigger gullying because the reduction in vegetation density and hence rates of colluvial deposition in valleys coincided with an unusually dry period less capable of significant fluvial erosion from valleys. As such, low-order valleys most likely did not incise prior to the mid-to-late Holocene because an approximate balance was maintained between colluvial deposition and fluvial erosion. Vegetation changes associated with the onset of pastoralism, however, may have triggered gullying because such changes lowered the rate of colluvial deposition in valleys and/or increased the rate of fluvial erosion in valleys. The results of this paper provide insight into the ways in which drainage basins respond to climatic and anthropogenic perturbations in semiarid climates of moderate relief and underscore the dramatic landscape responses that can occur when geomorphic thresholds are crossed. © 2011 Geological Society of America.
• Placzek, C. J., Quade, J., & Patchett, P. J. (2011). Isotopic tracers of paleohydrologic change in large lakes of the Bolivian Altiplano. Quaternary Research, 75(1), 231-244.
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  Abstract: We have developed an 87Sr/86Sr, 234U/238U, and δ18O data set from carbonates associated with late Quaternary paleolake cycles on the southern Bolivian Altiplano as a tool for tracking and understanding the causes of lake-level fluctuations. Distinctive groupings of 87Sr/86Sr ratios are observed. Ratios are highest for the Ouki lake cycle (120-95ka) at 0.70932, lowest for Coipasa lake cycle (12.8-11.4ka) at 0.70853, and intermediate at 0.70881 to 0.70884 for the Salinas (95-80ka), Inca Huasi (~45ka), Sajsi (24-20.5ka), and Tauca (18.1-14.1ka) lake cycles. These Sr ratios reflect variable contributions from the eastern and western Cordilleras. The Laca hydrologic divide exerts a primary influence on modern and paleolake 87Sr/86Sr ratios; waters show higher 87Sr/86Sr ratios north of this divide. Most lake cycles were sustained by slightly more rainfall north of this divide but with minimal input from Lake Titicaca. The Coipasa lake cycle appears to have been sustained mainly by rainfall south of this divide. In contrast, the Ouki lake cycle was an expansive lake, deepest in the northern (Poópo) basin, and spilling southward. These results indicate that regional variability in central Andean wet events can be reconstructed using geochemical patterns from this lake system. © 2010.
• Quade, J., Breecker, D. O., Daëron, M., & Eiler, J. (2011). The paleoaltimetry of Tibet: An isotopic perspective. American Journal of Science, 311(2), 77-115.
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  Abstract: Stable isotopes provide a valuable perspective on the timing of elevation change of the Tibetan Plateau. We begin our paper by looking in depth at isotopic patterns in modern Tibet. We show that the δ18O value of surface waters decreases systematically up the Himalayan front in central Nepal by about -2.8%/km, in agreement with the patterns documented and modeled by previous research. On the Tibetan plateau itself there is no apparent correlation between elevation and the δ18O value of flowing surface waters. Both surface waters and soil carbonates display a northward increase in δ18O values, of about 1.5%° north of the Himalayan crest, even though elevation increases modestly. The isotopic increase with latitude reduces the isotope-elevation gradient for water in the northernmost plateau to-1 to-2%/km. Carbonates in both soils and lakes form at higher temperatures than assumed by previous studies on the plateau. Temperature estimates from clumped-isotope (Δ47) analyses of modern soil carbonates significantly exceed mean annual air T and modeled maximum summer soil temperatures by 15.8±2.8° and 9.7±2.5 °C, respectively. Similarly elevated temperatures best account for the δ18O values observed in modern soil and lake carbonates. We recalculated paleoelevations from previous studies on the plateau using both higher formation temperatures and latitude-corrected isotopic values. With one notable exception, our revised model produces paleoelevation estimates very close to previous estimates. The exception is the reconstruction from late Eocene age deposits at Xoh Xil, for which we calculate elevations that are higher and much closer to the current elevation than previously reconstructed. Therefore, there is no evidence for northward progression through time of Tibetan elevation change. Instead, the available-but admittedly very scanty-evidence suggests that much of Tibet attained its modern elevation by the mid-Eocene. A truly robust test of the various geodynamic models of uplift await expansion and replication of isotopic records all across Tibet, especially in the center and north and for >15 Ma.
• Cerling, T. E., Levin, N. E., Quade, J., Wynn, J. G., Fox, D. L., Kingston, J. D., Klein, R. G., & Brown, F. H. (2010). Comment on the paleoenvironment of ardipithecus ramidus. Science, 328(5982), 1105d.
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  PMID: 20508112;Abstract: White and colleagues (Research Articles, 2 October 2009, pp. 65-67 and www.sciencemag.org/ardipithecus) characterized the paleoenvironment of Ardipithecus ramidus at Aramis, Ethiopia, which they described as containing habitats ranging from woodland to forest patches. In contrast, we find the environmental context of Ar. ramidus at Aramis to be represented by what is commonly referred to as tree- or bush-savanna, with 25% or less woody canopy cover.
• Pigati, J. S., Lifton, N. A., Jull, A. T., & Quade, J. (2010). A simplified In Situ cosmogenic ¹⁴C extraction system. Radiocarbon, 52(3), 1236-1243.
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  Abstract: We describe the design, construction, and testing of a new, simplified in situ radiocarbon extraction system at the University of Arizona. Blank levels for the new system are low ((234 ± 11) × 103 atoms (1 σ; n = 7)) and stable. The precision of a given measurement depends on the concentration of 14C, but is typically
• Pigati, J. S., Lifton, N. A., Jull, A. T., & Quade, J. (2010). Extraction of in situ cosmogenic ¹⁴C from olivine. Radiocarbon, 52(3), 1244-1260.
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  Abstract: Chemical pretreatment and extraction techniques have been developed previously to extract in situ cosmogenic radiocarbon (in situ 14C) from quartz and carbonate. These minerals can be found in most environments on Earth, but are usually absent from mafic terrains. To fill this gap, we conducted numerous experiments aimed at extracting in situ 14C from olivine ((Fe,Mg)2SiO4). We were able to extract a stable and reproducible in situ 14C component from olivine using stepped heating and a lithium metaborate (LiBO2) flux, following treatment with dilute HNO3 over a variety of experimental conditions. However, measured concentrations for samples from the Tabernacle Hill basalt flow (17.3 ± 0.3 ka4) in central Utah and the McCarty's basalt flow (3.0 ± 0.2 ka) in western New Mexico were significantly lower than expected based on exposure of olivine in our samples to cosmic rays at each site. The source of the discrepancy is not clear. We speculate that in situ 14C atoms may not have been released from Mg-rich crystal lattices (the olivine composition at both sites was ~Fo65Fa35). Alternatively, a portion of the 14C atoms released from the olivine grains may have become trapped in synthetic spinel-like minerals that were created in the olivine-flux mixture during the extraction process, or were simply retained in the mixture itself. Regardless, the magnitude of the discrepancy appears to be inversely proportional to the Fe/(Fe+Mg) ratio of the olivine separates. If we apply a simple correction factor based on the chemical composition of the separates, then corrected in situ 14C concentrations are similar to theoretical values at both sites. At this time, we do not know if this agreement is fortuitous or real. Future research should include measurement of in situ 14C concentrations in olivine from known-age basalt flows with different chemical compositions (i.e. more Fe-rich) to determine if this correction is robust for all olivine-bearing rocks. © 2010 by the Arizona Board of Regents on behalf of the University of Arizona.
• Placzek, C. J., Matmon, A., Granger, D. E., Quade, J., & Niedermann, S. (2010). Evidence for active landscape evolution in the hyperarid Atacama from multiple terrestrial cosmogenic nuclides. Earth and Planetary Science Letters, 295(1-2), 12-20.
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  Abstract: The Atacama Desert is one of the driest places on Earth. Multiple lines of evidence show that the Atacama has been hyperarid since at least the late Miocene, among these are cosmic-ray exposure ages indicating that individual clasts on some surfaces have been preserved for >9Ma and possibly since the Oligocene. Although these remarkably old ages indicate slow landscape evolution, it is not clear whether this pace is characteristic of the entire Atacama, or only of specific regions, landforms, or landscape elements. To address this question, we measured cosmogenic 10Be, 26Al, and 21Ne from a wide variety of landscape elements in a transect across the Central Atacama, where modern precipitation is at an extreme minimum, but where the concentration of cosmogenic nuclides in stable landscape elements has not previously been recorded. We find that the hyperarid core of the Central Atacama has substantially slower erosion rates than its eastern and western margins; however, even the driest part of this transect has erosion rates comparable to those of other deserts, ranging from 0.2-0.4m/Ma. The most stable landscape elements are boulder fields, with exposure ages of 1.5-2.6Ma. The vast majority of samples in the Central Atacama Desert, however, have cosmogenic nuclide concentrations corresponding to ages 5Ma documented elsewhere in the Atacama were not found in our area and appear to be limited to exceptionally stable boulders or cobbles in either the northern or southern extremes of the Atacama Desert. We suggest that the Central Atacama has been subject to episodic Pliocene and Pleistocene rainfall and geomorphic activity, perhaps due to intrusion of Pacific moisture. © 2010.
• Saylor, J., DeCelles, P., & Quade, J. (2010). Climate-driven environmental change in the Zhada basin, southwestern Tibetan Plateau. Geosphere, 6(2), 74-92.
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  Abstract: The Zhada basin is a large Neogene extensional sag basin in the Tethyan Himalaya of southwestern Tibet. In this paper we examine environmental changes in the Zhada basin using sequence stratigraphy, isotope stratigraphy, and lithostratigraphy. Sequence stratigraphy reveals a long-term tectonic signal in the formation and filling of the Zhada basin, as well as higher-frequency cycles, which we attribute to Milankovitch forcing. The record of Milankovitch cycles in the Zhada basin implies that global climate drove lake and wetland expansion and contraction in the southern Tibetan Plateau from the Late Miocene to the Pleistocene. Sequence stratigraphy shows that the Zhada basin evolved from an overfilled to underfilled basin, but continued evolution was truncated by an abrupt return to fluvial conditions. Isotope stratigraphy shows distinct drying cycles, particularly during times when the basin was underfilled. A long-term environmental change observed in the Zhada basin involves a decrease in abundance of arboreal pollen in favor of nonarboreal pollen. The similarity between the long-term environmental changes in the Zhada basin and those observed elsewhere on and around the Tibetan Plateau suggests that those changes are due to global or regional climate change rather than solely the result of uplift of the Tibetan Plateau. © 2010 by Geological Society of America.
• Broecker, W. S., McGee, D., Adams, K. D., Cheng, H., Edwards, R. L., Oviatt, C. G., & Quade, J. (2009). A Great Basin-wide dry episode during the first half of the Mystery Interval?. Quaternary Science Reviews, 28(25-26), 2557-2563.
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  Abstract: The existence of the Big Dry event from 14.9 to 13.8 14C kyrs in the Lake Estancia New Mexico record suggests that the deglacial Mystery Interval (14.5-12.4 14C kyrs) has two distinct hydrologic parts in the western USA. During the first, Great Basin Lake Estancia shrank in size and during the second, Great Basin Lake Lahontan reached its largest size. It is tempting to postulate that the transition between these two parts of the Mystery Interval were triggered by the IRD event recorded off Portugal at about 13.8 14C kyrs which post dates Heinrich event #1 by about 1.5 kyrs. This twofold division is consistent with the record from Hulu Cave, China, in which the initiation of the weak monsoon event occurs in the middle of the Mystery Interval at 16.1 kyrs (i.e., about 13.8 14C kyrs). © 2009 Elsevier Ltd. All rights reserved.
• Leier, A., Quade, J., DeCelles, P., & Kapp, P. (2009). Stable isotopic results from paleosol carbonate in South Asia: Paleoenvironmental reconstructions and selective alteration. Earth and Planetary Science Letters, 279(3-4), 242-254.
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  Abstract: We measured δ18O and δ13C values of paleosol carbonate nodules from a variety of sedimentary units in southern Asia in order to reconstruct paleoenvironmental conditions and to evaluate for possible diagenetic alteration. Paleosol carbonate nodules were collected from Lower to Upper Cretaceous strata exposed in two locations in southern Tibet, and from Lower to Middle Miocene strata in northern India and Nepal. Additional samples were collected from stratigraphically adjacent marine carbonate units to test for possible resetting of stable isotope values. Based on the implausibly low δ18O values (∼ - 13‰) of most of the marine carbonate samples, we interpret the δ18O values of the associated paleosol carbonate nodules as being reset, and therefore unreliable for paleoenvironmental or paleoelevation reconstruction. Importantly, the δ18O values of both marine and nonmarine carbonate samples have been altered irrespective of texture, including micritic fabrics, suggesting textural criteria alone are insufficient to determine whether primary stable isotope values have been altered. In contrast, δ13C values of marine carbonate rocks fall within the expected primary isotopic range, and so by association we interpret the δ13C values of paleosol carbonate from the same sections to have been unaffected by diagenesis. Using the δ13C values of paleosol carbonate nodules from Cretaceous strata in southern Tibet, atmospheric pCO2 is estimated to have been 1400-2000 ppmV between 130-120 Ma, and 2600-3200 ppmV between 100-90 Ma, consistent with previous estimates of pCO2 for these time periods. Paleosol carbonate nodules within early to middle Miocene strata in northern India and Nepal have average δ13C values of - 10.4‰, indicating virtually pure C3 vegetation and lower pCO2. © 2008 Elsevier B.V. All rights reserved.
• Ojha, T. P., Butler, R. F., Decelles, P. G., & Quade, J. (2009). Magnetic polarity stratigraphy of the Neogene foreland basin deposits of Nepal. Basin Research, 21(1), 61-90.
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  Abstract: The early Miocene Dumri Formation and middle Miocene-Pliocene Siwalik Group were deposited in the Himalayan foreland basin in response to uplift and erosion in the Himalayan fold-thrust belt. We report magnetostratigraphic data from four sections of these rocks in Nepal. Three of these sections are in the Siwalik Group in the hanging wall of the Main Frontal thrust, and one section is from the Dumri Formation in the hanging wall of the Main Boundary thrust (MBT). Thermal demagnetization experiments demonstrate that laminated siltstones yield palaeomagnetic data useful for tectonic and magnetostratigraphic studies whereas other lithofacies yield data of questionable reliability. Magnetostratigraphic data have been acquired from 297 sites within a 4200-m-thick section of Siwalik deposits at Surai Khola. The observed sequence of polarity zones correlates with the geomagnetic polarity time scale (GPTS) from chron C5Ar.1n to chron C2r.2n, spanning the time frame ca. 12.5-2.0 Ma. At Muksar Khola (eastern Nepal), 111 palaeomagnetic sites from a 2600-m-thick section of the Siwalik Group define a polarity zonation that correlates with the GPTS from chron C4Ar.2n to chron C2Br.1r, indicating an age range of ca. 10.0-3.5 Ma. At Tinau Khola, 121 sites from a 1824-m-thick section of the Siwalik Group are correlated to chrons C5An.1n through C4r.1n, equivalent to the time span ca. 11.8-8.1 Ma. At Swat Khola, 68 sites within a 1200-m-thick section of lower Miocene Dumri Formation are correlated with chrons C6n through C5Bn.2n, covering the time span ca. 19.9-15.1 Ma. Together with previous results from Khutia Khola and Bakiya Khola, these data provide the first magnetostratigraphic correlation along nearly the entire NW-SE length of Nepal. The correlation demonstrates that major lithostratigraphic boundaries in the Siwalik Group are highly diachronous, with roughly 2 Myr of variability. In turn, this suggests that the major sedimentological changes commonly inferred to reflect strengthening of the Asian monsoon are not isochronous. Sediment accumulation curves exhibit a 30-50% increase in accumulation rate in four of the five sections of the Siwalik Group, but the timing of this increase ranges systematically from ∼11.1 Ma in western Nepal to ∼5.3 Ma in eastern Nepal. If this increase in sediment accumulation rate is interpreted as a result of more rapid subsidence owing to thrust loading in the Himalaya, then the diachroneity of this increase suggests lateral propagation of a major thrust system, perhaps the MBT, at a rate of ca. 103 mm year -1 across the length of Nepal. © Journal compilation © 2009 Blackwell Publishing Ltd, European Association of Geoscientists & Engineers and International Association of Sedimentologists.
• Placzek, C., Quade, J., Betancourt, J. L., Patchett, P. J., Rech, J. A., Latorre, C., Matmon, A., Holmgren, C., & English, N. B. (2009). Climate in the dry central andes over geologic, millennial, and interannual timescales. Annals of the Missouri Botanical Garden, 96(3), 386-397.
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  Abstract: Over the last eight years, we have developed several paleoenvironmenlal records from a broad geographic region spanning the Altiplano in Bolivia (18°S-22°S) and continuing south along The western Andean flank to ca. 26 S. These records include: cosmogenic nuclide concentrations in surface deposits, dated nitrate paleosoils, lake levels, groundwater levels from wetland deposits, and plant macrofossils from urine-encrusted rodent middens. Arid environments are often uniquely sensitive to climate perturbations, and there is evidence of significant changes in precipitation on the western flank of the central Andes and the adjacent Altiplano. In contrast, the Atacama Desert of northern Chile is hyperarid over many millions of years. This uniquely prolonged arid climate requires the isolation of the Atacama from the Amazon Basin, a situation that has existed for more than 10 million years and that resulted from the uplift of the Andes and/or formation of the Altiplano plateau. New evidence from multiple terrestrial cosmogenic nuclides, however, suggests that overall aridity is occasionally punctuated by rare rainfall events that likely originate from the Pacific. East of the hyperarid zone, climate history from multiple proxies reveals alternating wet and dry intervals where changes in precipitation originating from the Atlantic may exceed 50%. An analysis of Pleistocene climate records across the region allows reconstruction of the spatial and temporal components of climate change. These Pleistocene wet events span the modern transition between two modes of interannual precipitation variability, and regional climate history for the Central Andean Pluvial Event (CAPE; ca. 18-8 ka) points toward similar drivers of modern interannual and past millennial-scale climate variability. The north-north east mode of climate variability is linked to El Niño-Southern Oscillation (ENSO) variability, and the southeast mode is linked to aridity in the Chaco region of Argentina.
• Placzek, C., Quade, J., Rech, J. A., Patchett, P. J., & Pérez, C. (2009). Geochemistry, chronology and stratigraphy of Neogene tuffs of the Central Andean region. Quaternary Geochronology, 4(1), 22-36.
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  Abstract: Tuff layers are vital stratigraphic tools that allow correlations to be made between widely dispersed exposures. Despite their widespread occurrence in the central Andes, tuffs from both natural exposures and sedimentary cores extracted from the region's extensive salars (salt pans) are relatively unstudied. Here we lay the foundation for a tephrostratigraphic framework in the central Andes (14-28°S) by chemically and morphologically characterizing ash shards, and in some cases dating 36 Neogene distal tuffs. These tuffs occur in lacustrine and alluvial deposits from the southern Bolivian Altiplano and adjacent Atacama Desert. All tuffs are calc-akaline rhyolites, consistent with their setting in the Central Andean Volcanic Zone. Five of the older tuffs were 40Ar/39Ar dated and yield an age range of 6.63-0.75 Ma. Organic material associated with tuffs deposited into paleolake sediments, paleowetland deposits, or urine-encrusted rodent middens provide constraints on the age of several Late Pleistocene and Holocene tuffs. These tuffs provide key stratigraphic markers and ages for lake cycles and archeological sites on the Bolivian Altiplano and for assessing rates of surficial processes and archeology in both the Atacama and Altiplano. While modern climate, and consequently questions about geomorphic processes and climate change, differs in the hyperarid Atacama and the semi-arid Altiplano, the most extensive air-fall tuffs covered both regions, placing the Atacama and the Bolivian Altiplano in the same tephrostratigraphic province. For example, the Escara B tuff (∼1.85 Ma), can be securely identified in both the Altiplano and Atacama. On the Altiplano, dates from the Escara B and E tuffs securely establish the age of the Escara Formation-representing the oldest expansive lake documented on the Bolivian Altiplano. By contrast, the presence of the Escara B tuff below ∼6 m of alluvial sediment at the Blanco Encalado site in the Atacama desert yields information about sedimentation rates in this hyperarid region. Indeed, most tuffs from the Atacama Desert are older than 600,000 years, even though they occur within fluvial terraces immediately adjacent to the alluvial fans that are still active. Most of these geomorphic surfaces in the Atacama also possess well-developed saline soils that, when combined with the radiometric ages of the distal tuffs, suggest slow rates of geomorphic change and exceptional landscape stability for this area during the Quaternary. In contrast, younger tuffs are more abundant in the more recent lake records of the Altiplano. The Chita tuff was deposited at ∼15,650 cal yr B.P., during the regressive phase of the region's deepest late Quaternary lake cycle-the "Tauca lake cycle"-which spanned 18.1-14.1 cal yr B.P. Two Holocene tuffs, the Sajsi tuff and the Cruzani Cocha tuff, are widespread. The Sajsi tuff was deposited just before 1700 cal yr B.P., whereas the Cruzani Cocha tuff appears to be mid-Holocene in age and shows some chemical affinities to a Holocene tuff (202B) deposited between 4420 and 5460 cal yr B.P. in a urine-encased rodent midden in the Atacama Desert. © 2008 Elsevier Ltd. All rights reserved.
• Quade, J., & Broecker, W. S. (2009). Dryland hydrology in a warmer world: Lessons from the Last Glacial period. European Physical Journal: Special Topics, 176(1), 21-36.
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  Abstract: It has long been recognized that the tropics were drier and mid-latitude deserts wetter during the Last Glacial Maximum (LGM). Until now there has not been a single, unifying explanation for this pattern. Recently, Held and Soden [34] suggested that ongoing global warming will cause the Earth's drylands to become progressively drier and its tropics to become progressively wetter. Because no suitable "warm world" analogue is available in the paleoclimate record, the best available test of Held and Soden's proposal is to look at records from the last glacial period in which drylands should have been wetter and the tropics drier. Our survey of the recent paleolake literature confirms that closed basin lakes located in the poleward limits (∼40) of the drylands in both hemispheres were far larger during the Last Glacial Maximum and parts of the tropics appear to have been less wet. While these observations are consistent with Held's prediction, evidence from the sub-tropical drylands (15 to 25°) is more complex. As with high-latitude drylands, lakes in subtropical drylands of South America and probably the Kalahari Desert were larger than present during the LGM. By contrast, lakes in the sub-tropical Sahara and Arabian Deserts of the northern hemisphere were largest in the early Holocene, but also apparently larger than today in the early LGM. What paleolake records show are that 1) a strong hemispheric symmetry in lake response occurred during the LGM, 2) a difference in response occurred during the latest-glacial, and 3) lake expansions occurred in response to shifts in the thermal equator related to Heinrich Events and insolation variation as well as to colder temperatures. © EDP Sciences and Springer 2009.
• Saylor, J. E., Quade, J., Dettman, D. L., DeCelles, P. G., Kapp, P. A., & Ding, L. (2009). The late Miocene through present paleoelevation history of southwestern Tibet. American Journal of Science, 309(1), 1-42.
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  Abstract: Recent research using stable isotopes of carbon and oxygen from carbonates and fossil teeth seems to support both a pre- and post-mid-Miocene uplift of the southern Tibetan Plateau. We examined this issue by analysis of well-preserved fossil mollusks and plant remains from the Zhada Basin in soudiwestern Tibet, which ranges in age from ∼9.2 to < 1 Ma. Based on δ 18O cc values from shell aragonite, we estimate that oxygen isotope ratios of Miocene - Pleistocene paleo-surface water (δ 18O psw) in Zhada Basin ranged from -24.5 to -2.2%. (VSMOW). The lowest of these calculated values are lower than δ 18O sw values [-17.9 to -11.9%. (VSMOW)] of modern water in the basin. The extremely low δ 18O psw values from fluvial mollusks and evaporatively elevated δ 18O psw values from lacustrine mollusks, show that the peaks surrounding the Zhada Basin were at elevations at least as high as, and possibly up to 1.5 km higher than today, and that conditions have been arid since at least 9 Ma. A decrease in elevation since the Miocene is not specifically predicted by any existing mechanical models for the development of the Tibetan Plateau. Paleoenvironmental modeling and physical evidence shows that the climate in Zhada Basin was cold and arid, indistinguishable from modern. The δ 13O pm values of well-preserved vascular plant material increase from -23.4 to -26.8 permit at the base of the Zhada Formation to as high as -8.4 permil above 250 to 300 m. This shift denotes the expansion of C 4 biomass in this high, arid watershed at ∼ 7 Ma, and thus corresponds to the C 3 - C 4 transition observed in Neogene deposits of the northern Indian sub-continent.
• Kleinsasser, L. L., Quade, J., McIntosh, W. C., Levin, N. E., Simpson, S. W., & Semaw, S. (2008). Stratigraphy and geochronology of the late miocene adu-asa formation at gona, ethiopia. Special Paper of the Geological Society of America, 446, 33-65.
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  Abstract: The Gona area includes many rich fossil localities that are of great consequence to the study of human evolution. The Adu-Asa Formation, containing the oldest of these fossils, consists of nearly 200 m of fossil-bearing sedimentary rocks in thin (≤30 m), laterally variable sections interlayered with abundant basaltic lava flows. These volcanic and sedimentary rocks dip gently to the east and are repeated by north-northwest-trending, mostly west-dipping normal faults that accommodate extension in the Afar Rift. The volcanic rocks in the Adu-Asa Formation are strongly bimodal. Basaltic lavas and tuffs are abundant, but we have also identified a rhyolite center and seven different silicic, or dominantly silicic, tuffs. Of these tuff units, we were able to identify four major tuffs across the Adu-Asa Formation at Gona by combining geochemical comparisons with detailed stratigraphic sections through fossil-bearing deposits: the Sifi, the Kobo'o, the Belewa, and the Ogoti Tuffs. New 40Ar/39Ar dates of these and other tuffs, as well as basalt flows, indicate that the formation spans the period from5.2 Ma to 6.4 Ma, although the oldest deposits within the Gona Paleoanthropological Research Project (GPRP) area have yet to be thoroughly surveyed. Known fossil localities within the Adu-Asa Formation at Gona are grouped into three temporal clusters, ranging in age from ca. 6.4 Ma to ca. 5.5 Ma. Copyright © 2008 Geological Society of America.
• Levin, N. E., Simpson, S. W., Quade, J., Cerling, T. E., & Frost, S. R. (2008). Herbivore enamel carbon isotopic composition and the environmental context of ardipithecus at Gona, Ethiopia. Special Paper of the Geological Society of America, 446, 215-235.
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  Abstract: Ardipithecus fossils found in late Miocene and early Pliocene deposits in the Afar region of Ethiopia, along with Sahelanthropus tchadensis from Chad and Orrorin tugenensis from Kenya, are among the earliest known human ancestors and are considered to be the predecessors to the subsequent australopithecines (Australopithecus anamensis and Australopithecus afarensis). Current paleoenvironmental reconstructions suggest a wooded habitat for both Ardipithecus kadabba and Ardipithecus ramidus but more open and varied environments for other hominids living in Africa during the late Miocene and early Pliocene. To further evaluate the environmental context of Ardipithecus, we present stable carbon isotope data of 182 fossil herbivore teeth from Ardipithecus-bearing fossil deposits in the Gona Paleoanthropological Research Project area, in the Afar region of Ethiopia. The sampled teeth include representatives of all major fossil herbivore taxa and the majority of the mammalian biomass that lived in the same time and place as the hominids. When compared to extant herbivores from East Africa, the spectra of isotopic results from herbivores found in late Miocene Ar. kadabba and early Pliocene Ar. ramidus sites at Gona are most similar to isotopic values from extant herbivores living in bushland and grassland regions and dissimilar to those from herbivores living in closed-canopy forests, montane forests, and high-elevation grasslands. The tooth enamel isotopic data from fossil herbivores make it clear that Ardipithecus at Gona lived among a guild of animals whose diet was dominated by C4 grass, and where there is no record of closed-canopy vegetation. Copyright © 2008 Geological Society of America.
• Quade, J., Levin, N. E., Simpson, S. W., Butler, R., McIntosh, W. C., Semaw, S., Kleinsasser, L., Dupont-Nivet, G., Renne, P., & Dunbar, N. (2008). The geology of gona, afar, ethiopia. Special Paper of the Geological Society of America, 446, 1-31.
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  Abstract: Deposits in the Gona Paleoanthropological Research Project (GPRP) area in eastcentral Ethiopia span most of the last ∼6.4 m.y. and are among the longest and most complete paleoenvironmental and human fossil archives in East Africa. The 40Ar/39Ar and paleomagnetic dates and tephrostratigraphic correlations establish the time spans for the four formations present at Gona: the Adu-Asa (>6.4-5.2 Ma), Sagantole (>4.6-3.9 Ma), Hadar (3.8-2.9 Ma), and Busidima Formations (2.7 to
• Quade, J., Rech, J. A., Betancourt, J. L., Latorre, C., Quade, B., Rylander, K. A., & Fisher, T. (2008). Paleowetlands and regional climate change in the central Atacama Desert, northern Chile. Quaternary Research, 69(3), 343-360.
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  Abstract: Widespread, organic-rich diatomaceous deposits are evidence for formerly wetter times along the margins of the central Atacama Desert, one of the driest places on Earth today. We mapped and dated these paleowetland deposits at three presently waterless locations near Salar de Punta Negra (24.5°S) on the western slope of the Andes. Elevated groundwater levels supported phreatic discharge into wetlands during two periods: 15,900 to ~ 13,800 and 12,700 to ~ 9700 cal yr BP. Dense concentrations of lithic artifacts testify to the presence of paleoindians around the wetlands late in the second wet phase (11,000?-9700 cal yr BP). Water tables dropped below the surface before 15,900 and since 8100 cal yr BP, and briefly between ~ 13,800 and 12,700 cal yr BP. This temporal pattern is repeated, with some slight differences, in rodent middens from the study area, in both paleowetland and rodent midden deposits north and south of the study area, and in lake level fluctuations on the adjacent Bolivian Altiplano. The regional synchroneity of these changes points to a strengthening of the South American Monsoon - which we term the "Central Andean Pluvial Event" - in two distinct intervals (15,900-13,800 and 12,700-9700 cal yr BP), probably induced by steepened SST gradients across the tropical Pacific (i.e., La Niña-like conditions). © 2007 University of Washington.
• Roman, D. C., Campisano, C., Quade, J., DiMaggio, E., Arrowsmith, J. R., & Feibel, C. (2008). Composite tephrostratigraphy of the Dikika, Gona, Hadar, and Ledi-Geraru project areas, northern Awash, Ethiopia. Special Paper of the Geological Society of America, 446, 119-134.
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  Abstract: Mapping and description of the Hadar and Busidima Formations in the northern Awash valley, Ethiopia, have been greatly aided by the use of tephrostratigraphy and tephra correlation in the Dikika, Gona, Hadar, and Ledi-Geraru paleoanthropological project areas. The Hadar Formation contains at least nine dated tuffs, many of which have been correlated across the northern Awash project areas, and all of which are easily distinguished from each other on the basis of major-element chemistry. The overlying Busidima Formation contains at least 35 distinct tuffs, many of which are firmly or approximately dated. Because of their discontinuous and compositionally similar nature, many of the Busidima Formation tuffs are not correlated across the northern Awash project areas. Trace-element compositional data or detailed stratigraphic information may be necessary for correlation or relative placement of many of the Busidima Formation tuffs. Differences in the frequency, chemistry, and extent of Hadar and Busidima Formation tuffs preserved in the northern Awash valley may ultimately be related to the tectonic evolution of the region throughout the Pliocene-Pleistocene, as well as to basin-scale geological processes. Despite a number of known issues in tephra correlation, the composite tephrostratigraphy assembled for the northern Awash valley demonstrates the effectiveness of this technique, which has played a key role in ongoing efforts to document the geological history of this unique and important region. Copyright © 2008 Geological Society of America.
• Simpson, S. W., Quade, J., Levin, N. E., Butler, R., Dupont-Nivet, G., Everett, M., & Semaw, S. (2008). A female Homo erectus pelvis from gona, Ethiopia. Science, 322(5904), 1089-1092.
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  PMID: 19008443;Abstract: Analyses of the KNM-WT 15000 Homo erectus juvenile male partial skeleton from Kenya concluded that this species had a tall thin body shape due to specialized locomotor and climatic adaptations. Moreover, it was concluded that H. erectus pelves were obstetrically restricted to birthing a small-brained altricial neonate. Here we describe a nearly complete early Pleistocene adult female H. erectus pelvis from the Busidima Formation of Gona, Afar, Ethiopia. This obstetrically capacious pelvis demonstrates that pelvic shape in H. erectus was evolving in response to increasing fetal brain size. This pelvis indicates that neither adaptations to tropical environments nor endurance running were primary selective factors in determining pelvis morphology in H. erectus during the early Pleistocene.
• Achyuthan, H., Quade, J., Roe, L., & Placzek, C. (2007). Stable isotopic composition of pedogenic carbonates from the eastern margin of the Thar Desert, Rajasthan, India. Quaternary International, 162-163, 50-60.
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  Abstract: Pedogenic carbonates in a 19 m-thick dune section (16R) at Didwana, and several shorter profiles from the eastern margin of the Thar Desert, Rajasthan, were studied for their stable isotope composition. Carbon isotope results show the C4 biomass (grasses?) has dominated local vegetation for most of the 250,000 years represented by the 16R section. Our results display a decrease in δ18O and δ13C values during the last interglacial and early glacial periods. The higher δ13C values in our dune records correlate to episodes in the strong upwelling and decreased sedimentation rates in Indian Ocean cores, probably the result of a strong Asian Monsoon. The high δ13C values may, therefore, denote the expansion of C4 vegetation in response to warm, wetter monsoon circulation. Conversely, low δ18O and δ13C values mark the expansion of C3 vegetation, probably caused by enhanced winter rains and lower temperatures. © 2007.
• Behrensmeyer, A. K., Quade, J., Cerling, T. E., Kappelman, J., Khan, I. A., Copeland, P., Roe, L., Hicks, J., Stubblefield, P., Willis, B. J., & Latorre, C. (2007). The structure and rate of late Miocene expansion of C₄ plants: Evidence from lateral variation in stable isotopes in paleosols of the Siwalik Group, northern Pakistan. Bulletin of the Geological Society of America, 119(11-12), 1486-1505.
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  Abstract: This study uses stable isotope variation within individual Mio-Pliocene paleosols to investigate subkilometer-scale phytogeography of late Miocene vegetation change in southeast Asia between ca. 8.1 and 5 Ma, a time interval that coincides with dramatic global vegetation change. We examine trends through time in the distribution of low-latitude grasses (C4 plants) and forest (C3 plants) on Indo-Gangetic floodplains using carbon (δ13C) and oxygen isotopic (δ18O) values in buried soil carbonates in Siwalik Series sediments exposed in the Rohtas Anticline, north-central Pakistan. Revised, high-resolution magnetostratigraphy and a new 40Ar/39Ar date provide improved age control for the 2020 m Rohtas section. Carbon isotope results capture lateral variability of C3 versus C4 plants at five stratigraphic levels, R11 (8.0 Ma), R15 (6.74-6.78 Ma), R23 (5.78 Ma), R29 (4.8-4.9 Ma), and upper boundary tuff (UBT; 2.4 Ma), using detailed sampling of paleosols traceable laterally over hundreds of meters. Paleosols and the contained isotopic results can be assigned to three different depositional contexts within the fluvial sediments: channel fill, crevasse-splay, and floodplain environments. δ13C results show that near the beginning (8.0 Ma) and after (4.0 Ma) the period of major ecological change, vegetation was homogeneously C3 or C4, respectively, regardless of paleo-landscape position. In the intervening period, there is a wide range of values overall, with C4 grasses first invading the drier portions of the system (floodplain surfaces) and C3 plants persisting in moister settings, such as topographically lower channel swales. Although abrupt on a geologic timescale, changes in abundance of C4 plants are modest (∼2% per 100,000 yr) compared to rates of vegetation turnover in response to glacial and interglacial climate changes in the Quaternary. Earlier research documented a sharply defined C3 to C4 transition in Pakistan between 8.1 and 5.0 Ma, based on vertical sampling, but this higher-resolution study reveals a more gradual transition between 8.0 and 4.5 Ma in which C3 and C4 plants occupied different subenvironments of the Siwalik alluvial plain. δ 18O values as well as δ13C values of soil carbonate increase up section at Rohtas, similar to isotope trends in other paleosol records from the region. Spatially, however, there is no correlation between δ13C and δ18O values at most stratigraphic levels. This implies that the changes in soil hydrology brought about by the shift from forest to grassland (i.e., an increase in average soil evaporation) did not produce the shift through time in δ18O values. We interpret the trend toward heavier soil carbonate δ18O values as a response to changes in external climatic factors such as a net decrease in rainfall over the past 9 Ma. © 2007 Geological Society of America.
• DeCelles, P. G., Quade, J., Kapp, P., Fan, M., Dettman, D. L., & Ding, L. (2007). High and dry in central Tibet during the Late Oligocene. Earth and Planetary Science Letters, 253(3-4), 389-401.
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  Abstract: The time at which the Tibetan Plateau rose to its present high elevation remains controversial, with estimates ranging from 40 Ma to more recent than 7 Ma. New stable isotope analyses of modern and accurately dated ancient paleosol carbonate in the Nima basin of central Tibet point to an arid climate and high paleoelevation (4.5-5 km, comparable to today's setting) by 26 Ma. Oxygen isotope values of ancient (26 Ma) soil carbonate are both very negative and indistinguishable-after modest corrections for changes in global climate-from the lowest (least evaporated) oxygen isotope values of modern soil carbonates in the area. Substantial enrichments in oxygen-18 in paleolacustrine carbonates, as well as high carbon isotope values from paleosol carbonates, indicate considerable lake evaporation and low soil respiration rates, respectively, and both are consistent with the present arid climate of the Nima area. Blockage of tropical moisture by the Himalaya and perhaps the Gangdese Shan probably has contributed strongly to the aridity and very negative oxygen isotope values of soil carbonate and surface water in the Nima area since at least the Late Oligocene. The maintenance of high elevation since at least 26 Ma suggests that any flow of lower crust from beneath central Tibet must have been balanced by coeval northward insertion of Indian crust beneath the Plateau. © 2006 Elsevier B.V. All rights reserved.
• Felton, A. A., Russell, J. M., Cohen, A. S., Baker, M. E., Chesley, J. T., Lezzar, K. E., McGlue, M. M., Pigati, J. S., Quade, J., Stager, J. C., & Tiercelin, J. J. (2007). Paleolimnological evidence for the onset and termination of glacial aridity from Lake Tanganyika, Tropical East Africa. Palaeogeography, Palaeoclimatology, Palaeoecology, 252(3-4), 405-423.
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  Abstract: Geochemical and sedimentological data in a continuous 60,000-year sediment core record from the Kalya horst region of central Lake Tanganyika provide a detailed history of paleoclimate-mediated weathering and overflow events from upstream Lake Kivu. Univariate (elemental profiles), bivariate (elemental ratios) and multivariate analyses of chemical trends show variations between the dry Late Pleistocene (32-18 ka cal yr BP) and the wetter conditions that both preceded and post-date that interval. This record places important new constraints on the timing of aridity in East Africa during the high-latitude Last Glacial Maximum (LGM) based on significant decreases in magnetic susceptibility and soluble cation concentrations coinciding with biogenic silica. Elemental indicators in the oldest portion of the sedimentary record (60-50 ka cal yr BP) characterize this interval as a comparatively wet period, similar to modern conditions. Our record demonstrates that the ensuing transition toward arid conditions in tropical Africa during high-latitude glaciation was a two staged event with intermediate levels of aridity occurring from 50-32 ka cal yr BP followed by intense aridity from 32-18 ka cal yr BP. The initiation of inflow from upstream Lake Kivu into Lake Tanganyika is evidenced at 10.6 ka cal yr BP through its influence on both elemental profiles (Mg, Ca) and through its effect on 87Sr/86Sr. Increases in elemental (Mg, Ca, Sr) concentrations coincide with the timing of the Lake Kivu overflow. Metal geochemistry suggests that the overflow from Lake Kivu into Lake Tanganyika may have ceased between 8 and 6 ka cal yr BP, suggesting a period of Middle Holocene aridity in East Africa. © 2007 Elsevier B.V. All rights reserved.
• Pigati, J. S., Quade, J., Wilson, J., Jull, A. T., & Lifton, N. A. (2007). Development of low-background vacuum extraction and graphitization systems for ¹⁴C dating of old (40-60 ka) samples. Quaternary International, 166(1), 4-14.
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  Abstract: At the University of Arizona's Desert Laboratory, we recently constructed new low-background vacuum extraction and graphitization systems that are dedicated to preparing old (40-60 ka) samples for 14C dating. These systems are designed to minimize the amount of contaminant carbon, specifically atmospheric carbon, that is introduced to a sample during laboratory processing. Excluding contaminants is particularly important for 14C dating of old samples because the impact of contamination increases with sample age. In this study, we processed 20 pretreated and 4 untreated aliquots of Ceylon graphite (a naturally-occurring geological graphite) to determine the total procedural background level, and hence the practical limit, of our systems. Samples were heated under vacuum at 240 °C for 1 h to drive off water vapor and other atmospheric gases, and then combusted in ultra-high-purity (UHP) O2 at 500 and 850 °C to monitor the removal of contaminants and to ensure complete combustion. After SOX, NOX, and halide species were removed, sample CO2 was converted to graphite via catalytic reduction of CO. Fe and Zn powders used in the graphitization process were oxidized, "scrubbed", and reduced with UHP O2, He, and H2, respectively, to remove sorbed atmospheric C species. Graphite targets were stored in UHP Ar until measurement by accelerator mass spectrometry (AMS) to avoid potential interaction with atmospheric gases. Based on the AMS results, the background level of our system is characterized by a nonlinear inverse relationship with sample mass (adjusted R2=0.75; n=24). For a 1 mg graphite target, the total procedural blank, including chemical pretreatment, combustion, cleanup, graphitization, storage, and AMS measurement, is 0.05±0.01 pMC (2σ), equivalent to a 14C "age" of 61.1±1.8 ka. This should not be taken as the upper limit of our system, however, because if the 14C activity of a sample is statistically indistinguishable from the appropriate mass-dependent blank value at the 95% confidence level (2σ), then its age is considered to be "infinite". Thus, for a 1 mg target, the practical limit of our system is actually ∼55 ka; for a 0.5 mg target, the practical limit is ∼50 ka. Although our extraction system can accommodate inorganic samples (e.g., calcite, aragonite), the above limits are only applicable to geological graphite, charcoal, and organic samples that are processed via combustion. Future work will be directed toward determining the appropriate background levels for inorganic materials. © 2007 Elsevier Ltd and INQUA.
• Quade, J., Garzione, C., & Eiler, J. (2007). Paleoelevation reconstruction using pedogenic carbonates. Reviews in Mineralogy and Geochemistry, 66, 53-87.
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  Abstract: Paleoelevation reconstruction using stable isotopes, although a relatively new science, is making a significant contribution to our understanding of the recent growth of the world's major orogens. In this review we examine the use of both light stable isotopes of oxygen and the new "clumped-isotope" (Δ47) carbonate thermometer in carbonates from soils. Globally, the oxygen isotopic composition (δ18O) of rainfall decreases on average by about 2.8‰km of elevation gain. This effect of elevation will in turn be archived in the δ18O value of soil carbonates, and paleoelevation can be reconstructed, provided (1) temperature of formation can be estimated, (2) the effects of evaporation are small, (3) the effects of climate change can be accounted for, and (4) the isotopic composition of the carbonate is not diagenetically altered. We review data from modern soils to evaluate some of these issues and find that evaporation commonly elevates δ18O values of carbonates in deserts, an effect that would lead to underestimates of paleoelevation. Some assessment of paleoaridity, using qualitative indicators or carbon isotopes from soil carbonate, is therefore useful in evaluating the oxygen isotope-based estimates of paleoelevation. Sampling from deep (> 50 cm) in paleosols helps reduce the uncertainties arising from seasonal temperature fluctuations and from evaporation. The new "clumped-isotope" (Δ47) carbonate thermometer, expressed as Δ47, offers an independent and potentially very powerful approach to paleoelevation reconstruction. In contrast to the use of δ18O values, nothing need be known about the isotopic composition of water from which carbonate grew in order to estimate of temperature of carbonate formation from Δ47 values. Using assumed temperature lapse rates with elevation, paleoelevations can thereby be reconstructed. Case studies from the Andes and Tibet show how these methods can be used alone or in combination to estimate paleoelevation. In both cases, the potential for diagenetic alteration of primary carbonate values first has to be assessed. Clear examples of both preservation and alteration of primary isotopic values are available from deposits of varying ages and burial histories. Δ47 values constitute a relatively straightforward test, since any temperature in excess of reasonable surface temperatures points to diagenetic alteration. For δ18O values, preservation of isotopic heterogeneity between different carbonate phases offers a check on diagenesis. Results of these case studies show that one area of south-central Tibet attained elevations comparable to today by the late Oligocene, whereas 2.7 ± 0.4 km of uplift occurred in the Bolivian Altiplano during the late Miocene. Copyright © Mineralogical Society of America.
• Quade, J., Rech, J. A., Latorre, C., Betancourt, J. L., Gleeson, E., & Kalin, M. T. (2007). Soils at the hyperarid margin: The isotopic composition of soil carbonate from the Atacama Desert, Northern Chile. Geochimica et Cosmochimica Acta, 71(15), 3772-3795.
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  Abstract: We evaluate the impact of exceptionally sparse plant cover (0-20%) and rainfall (2-114 mm/yr) on the stable carbon and oxygen composition of soil carbonate along elevation transects in what is among the driest places on the planet, the Atacama Desert in northern Chile. δ13C and δ18O values of carbonates from the Atacama are the highest of any desert in the world. δ13C (VPDB) values from soil carbonate range from -8.2‰ at the wettest sites to +7.9‰ at the driest. We measured plant composition and modeled respiration rates required to form these carbonate isotopic values using a modified version of the soil diffusion model of [Cerling (1984) Earth Planet. Sci. Lett. 71, 229-240], in which we assumed an exponential form of the soil CO2 production function, and relatively shallow (20-30 cm) average production depths. Overall, we find that respiration rates are the main predictor of the δ13C value of soil carbonate in the Atacama, whereas the fraction C3 to C4 biomass at individual sites has a subordinate influence. The high average δ13C value (+4.1‰) of carbonate from the driest study sites indicates it formed-perhaps abiotically-in the presence of pure atmospheric CO2. δ18O (VPDB) values from soil carbonate range from -5.9‰ at the wettest sites to +7.3‰ at the driest and show much less regular variation with elevation change than δ13C values. δ18O values for soil carbonate predicted from local temperature and δ18O values of rainfall values suggest that extreme (>80% in some cases) soil dewatering by evaporation occurs at most sites prior to carbonate formation. The effects of evaporation compromise the use of δ18O values from ancient soil carbonate to reconstruct paleoelevation in such arid settings. © 2007 Elsevier Ltd. All rights reserved.
• Cohen, A. S., Ashley, G. M., Potts, R., Behrensmeyer, A. K., Feibel, C., & Quade, J. (2006). Paleoclimate and human evolution workshop. Eos, 87(16), 162-163.
• Drees, K. P., Neilson, J. W., Betancourt, J. L., Quade, J., Henderson, D. A., Pryor, B. M., & Maier, R. M. (2006). Bacterial community structure in the hyperarid core of the Atacama Desert, Chile. Applied and Environmental Microbiology, 72(12), 7902-7908.
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  PMID: 17028238;PMCID: PMC1694221;Abstract: Soils from the hyperarid Atacama Desert of northern Chile were sampled along an east-west elevational transect (23.75 to 24.70°S) through the driest sector to compare the relative structure of bacterial communities. Analysis of denaturing gradient gel electrophoresis (DGGE) profiles from each of the samples revealed that microbial communities from the extreme hyperarid core of the desert clustered separately from all of the remaining communities. Bands sequenced from DGGE profiles of two samples taken at a 22-month interval from this core region revealed the presence of similar populations dominated by bacteria from the Gemmatimonadetes and Planctomycetes phyla. Copyright © 2006, American Society for Microbiology. All Rights Reserved.
• Placzek, C., Patchett, P. J., Quade, J., & Wagner, J. D. (2006). Strategies for successful U-Th dating of paleolake carbonates: An example from the Bolivian Altiplano. Geochemistry, Geophysics, Geosystems, 7(5).
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  Abstract: We report over 90 U-Th dates from carbonates deposited around paleolakes on the Bolivian Altiplano. Petrographic and chemical data for tufas and the siliciclastic detritus contained within them allow (1) assessment of possible diagenetic effects, (2) a development of a strategy for selection of carbonate samples with low initial Th contents, and (3) assessment of the uncertainty due to initial Th. This strategy allows us to produce precise U-Th dates from lacustrine carbonates. The principal consideration in dating such carbonates is the composition and quantity of initial Th incorporated into the carbonate, and additional uncertainty is introduced because this initial Th may have two sources in lacustrine deposits. Isochron plots, measured (230Th/ 232Th), and X-ray diffraction and trace element chemistry of silicic residues all favor regional soil and dust as the sole source of initial Th in carbonates from the Bolivian Altiplano, a situation that simplifies single-sample dating of Altiplano carbonates. Copyright 2006 by the American Geophysical Union.
• Placzek, C., Quade, J., & Patchett, P. J. (2006). Geochronology and stratigraphy of late Pleistocene lake cycles on the southern Bolivian Altiplano: Implications for causes of tropical climate change. Bulletin of the Geological Society of America, 118(5-6), 515-532.
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  Abstract: Large paleolakes (∼33,000-60,000 km2) that once occupied the high-altitude Poopo, Coipasa, and Uyuni Basins in southern Bolivia (18-22°S) provide evidence of major changes in low-latitude moisture. In these now-dry or oligosaline basins, extensive natural exposure reveals evidence for two deep-lake and several minor-lake cycles over the past 120 k.y. Fifty-three new U-Th and 87 new 14C dates provide a chronologic framework for changes in lake level. Deposits from the "Ouki" deep-lake cycle are extensively exposed in the Poopo Basin, but no deep lakes are apparent in the record between 98 and 18.1 ka. The Ouki lake cycle was ∼80 m deep, and nineteen U-Th dates place this deep-lake cycle between 120 and 98 ka. Shallow lakes were present in the terminal Uyuni Basin between 95 and 80 ka (Salinas lake cycle), at ca. 46 (Inca Huasi lake cycle), and between 24 and 20.5 ka (Sajsi lake cycle). The Tauca deep-lake cycle occurred between 18.1 and 14.1 ka, resulting in the deepest (∼140 m) and largest lake in the basin over the past 120 ka. Multiple 14C and U-Th dates constrain the highest stand of Lake Tauca along a topographically conspicuous shoreline between 16.4 and 14.1 ka. A probable post-Tauca lake cycle (the Coipasa) produced a ≤55-m-deep lake that is tentatively dated between 13 and 11 ka. We suggest that paleolakes on the Bolivian Altiplano expanded in response to increased moisture in the Amazon and enhanced transport of that moisture onto the Altiplano by strengthened trade winds or southward displacement of the Intertropical Convergence Zone (ITCZ). Pole-to-equator sea-surface temperature (SST) and atmospheric gradients may have influenced the position of the ITCZ, affecting moisture balance over the Altiplano and at other locations in the Amazon Basin. Links between the position of the ITCZ and the ca. 23 ka precessional solar cycle have been postulated. March insolation over the Altiplano is a relatively good fit to our lake record, but no single season or latitude of solar cycling has yet to emerge as the primary driver of climate over the entire Amazon Basin. Temperature may influence Altiplano lake levels indirectly, as potentially dry glacial periods in the Amazon Basin are linked to dry conditions on the Altiplano. Intensification of the trade winds associated with La Niña - like conditions currently brings increased precipitation on the Altiplano, and deep-lake development during the Tauca lake cycle coincided with apparently intense and persistent La Niña - like conditions in the central Pacific. This suggests that SST gradients in the Pacific are also a major influence on deep-lake development on the Altiplano. © 2006 Geological Society of America.
• Reynolds, A. C., Betancourt, J. L., Quade, J., Patchett, P. J., Dean, J. S., & Stein, J. (2005). ⁸⁷Sr/⁸⁶Sr sourcing of ponderosa pine used in Anasazi great house construction at Chaco Canyon, New Mexico. Journal of Archaeological Science, 32(7), 1061-1075.
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  Abstract: Previous analysis of 87Sr/86Sr ratios shows that 10th through 12th century Chaco Canyon was provisioned with plant materials that came from more than 75 km away. This includes (1) corn (Zea mays) grown on the eastern flanks of the Chuska Mountains and floodplain of the San Juan River to the west and north, and (2) spruce (Picea sp.) and fir (Abies sp.) beams from the crest of the Chuska and San Mateo Mountains to the west and south. Here, we extend 87Sr/86Sr analysis to ponderosa pine (Pinus ponderosa) prevalent in the architectural timber at three of the Chacoan great houses (Pueblo Bonito, Chetro Ketl, Pueblo del Arroyo). Like the architectural spruce and fir, much of the ponderosa matches the 87Sr/86Sr ratios of living trees in the Chuska Mountains. Many of the architectural ponderosa, however, have similar ratios to living trees in the La Plata and San Juan Mountains to the north and Lobo Mesa/Hosta Butte to the south. There are no systematic patterns in spruce/fir or ponderosa provenance by great house or time, suggesting the use of stockpiles from a few preferred sources. The multiple and distant sources for food and timber, now based on hundreds of isotopic values from modern and archeological samples, confirm conventional wisdom about the geographic scope of the larger Chacoan system. The complexity of this procurement warns against simple generalizations based on just one species, a single class of botanical artifact, or a few isotopic values. © 2005 Elsevier Ltd. All rights reserved.
• Semaw, S., Simpson, S. W., Quade, J., Renne, P. R., Butter, R. F., McIntosh, W. C., Levin, H., Domingues-Rodrigo, M., & Rodgers, M. J. (2005). Early Pliocene hominids from Gona, Ethiopa. Nature, 433(7023), 301-305.
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  PMID: 15662421;Abstract: Comparative biomolecular studies suggest that the last common ancestor of humans and chimpanzees, our closest living relatives, lived during the Late Miocene-Early Pliocene1,2. Fossil evidence of Late Miocene-Early Pliocene hominid evolution is rare and limited to a few sites in Ethiopia 3,4,5, Kenya6 and Chad7. Here we report new Early Pliocene hominid discoveries and their palaeoenvironmental context from the fossiliferous deposits of As Duma, Gona Western Margin (GWM), Afar, Ethiopia. The hominid dental anatomy (occlusal enamel thickness, absolute and relative size of the first and second lower molar crowns, and premolar crown and radicular anatomy) indicates attribution to Ardipithecus ramidus. The combined radioisotopic and palaeo-magnetic data suggest an age of between 4.51 and 4.32 million years for the hominid finds at As Duma. Diverse sources of data (sedimentology, faunal composition, ecomorphological variables and stable carbon isotopic evidence from the palaeosols and fossil tooth enamel) indicate that the Early Pliocene As Duma sediments sample a moderate rainfall woodland and woodland/grassland.
• Shanahan, T. M., Pigati, J. S., Dettman, D. L., & Quade, J. (2005). Isotopic variability in the aragonite shells of freshwater gastropods living in springs with nearly constant temperature and isotopic composition. Geochimica et Cosmochimica Acta, 69(16), 3949-3966.
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  Abstract: We conducted a year-long, intensive monitoring program of live aquatic gastropods (Helisoma duryi, Melanoides tuberculata, Physa virgata, Pyrgulopsis sp., and Tyronia sp.) and their host springs in the Ash Meadows National Wildlife Refuge of southern Nevada. Our purpose was to constrain the degree of natural variation in the isotopic values of shell aragonite for gastropods living in near-constant conditions. Inter- and intraspecies variations, as well as within-shell variations, of δ18O and δ13C values for all taxa were larger than predicted based on variations in environmental conditions alone. This result suggests that different organisms growing in identical or nearly identical environmental conditions may not produce shells with equilibrium isotopic compositions and that these offsets from equilibrium may differ by small, but statistically significant amounts. For the gill-breathing, fully aquatic gastropods M. tuberculata, Pyrgulopsis sp., and Tyronia sp., the deviation of measured isotopic values compared to predicted values based on average environmental conditions were consistent with differences between taxa in the seasonal timing of shell growth. Measured values for the lung-breathing gastropods H. duryi and P. virgata were higher for δ18O and lower for δ13C than predicted at isotopic equilibrium, even when accounting for seasonality effects. We suggest that explaining the differences between the shell isotopic composition of lung- and gill-breathing snails requires a combination of both behavioral and physiologic factors. Our results illustrate the potential complexities of interpreting stable isotopic data from fossil gastropod shells even when environmental conditions are nearly constant, and place limitations on the paleoenvironmental deductions that can be made from the isotopic measurements on fossil gastropods. Copyright © 2005 Elsevier Ltd.
• Stout, D., Quade, J., Semaw, S., Rogers, M. J., & Levin, N. E. (2005). Raw material selectivity of the earliest stone toolmakers at Gona, Afar, Ethiopia. Journal of Human Evolution, 48(4), 365-380.
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  PMID: 15788183;Abstract: Published evidence of Oldowan stone exploitation generally supports the conclusion that patterns of raw material use were determined by local availability. This is contradicted by the results of systematic studies of raw material availability and use among the earliest known archaeological sites from Gona, Afar, Ethiopia. Artifact assemblages from six Pliocene archaeological sites were compared with six random cobble samples taken from associated conglomerates that record pene-contemporaneous raw material availability. Artifacts and cobbles were evaluated according to four variables intended to capture major elements of material quality: rock type, phenocryst percentage, average phenocryst size, and groundmass texture. Analyses of these variables provide evidence of hominid selectivity for raw material quality. These results demonstrate that raw material selectivity was a potential component of Oldowan technological organization from its earliest appearance and document a level of technological sophistication that is not always attributed to Pliocene hominids. © 2004 Elsevier Ltd. All rights reserved.
• Biedenbender, S. H., McClaran, M. P., Quade, J., & Weltz, M. A. (2004). Landscape patterns of vegetation change indicated by soil carbon isotope composition. Geoderma, 119(1-2), 69-83.
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  Abstract: Vegetation change, particularly from the grass to shrub life form, is a critical issue on the world's semiarid rangelands. Stable carbon isotope (δ13C) values and associated radiocarbon ages from soil organic matter (SOM) were used to evaluate vegetation change across five landscape positions at a small enclosed basin in southeastern Arizona. Light and dense SOM fractions were separated to distinguish recent vegetation changes. The direction and timing of vegetation change differed with landscape position along a gentle elevation gradient from the basin outlet to a nearby volcanic ridge top. C4 perennial grasses have dominated the basin outlet, center, and toe slope landscape positions since at least 5000-6000 years BP, except for the dominance of C3 plants at the bottom of the outlet excavation at 5000 years BP. This isotopic change is associated with rounded cobbles that may have been a stream channel, suggesting the presence of C 3 herbaceous or woody riparian vegetation. On mid-slope and ridge top landscape positions, where semidesert shrubs now dominate, the proportion of plants with C4 metabolism calculated from mass balance mixing formulas decreased from approximately 60% as recently as 400 years BP to only 1.5% observed today. The light SOM fraction from mid-slope and ridge top surface soil horizons was approximately 30% C4 and had a post-bomb date, suggesting that the conversion from grass to shrub occurred over the last several decades. © 2003 Elsevier B.V. All rights reserved.
• Hart, W. S., Quade, J., Madsen, D. B., Kaufman, D. S., & Oviatt, C. G. (2004). The ⁸⁷Sr/⁸⁶Sr ratios of lacustrine carbonates and lake-level history of the Bonneville paleolake system. Bulletin of the Geological Society of America, 116(9-10), 1107-1119.
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  Abstract: Lakes in the Bonneville basin have fluctuated dramatically in response to changes in rainfall, temperature, and drainage diversion during the Quaternary. We analyzed tufas and shells from shorelines of known ages in order to develop a relation between 87Sr/86Sr ratio of carbonates and lake level, which then can be used as a basis for constraining lake level from similar analyses on carbonates in cores. Carbonates from the late Quaternary shorelines yield the following average 87Sr/86Sr ratios: 0.71173 for the Stansbury shoreline (22-20 14C ka; 1350 m), 0.71153 for the Bonneville shoreline (15.5-14.5 14C ka; 1550 m), 0.71175 for the Provo shoreline (14.4-14.0 14C ka; 1450 m), 0.71244 for the Gilbert shoreline (∼10.3-10.9 14C ka; 1300 m), and 0.71469 for the modern Great Salt Lake (1280 m). These analyses show that the 87Sr/86Sr ratio of lacustrine carbonates changes substantially at low- to mid-lake levels but is invariant at mid- to high-lake levels. Sr-isotope mixing models of Great Salt Lake and the Bonneville paleolake system were constructed to explain these variations in 87Sr/86Sr ratios with change in lake level. Our model of the Bonneville system produced a 87Sr/86Sr ratio of 0.71193, very close to the observed ratios from high-shoreline tufa and shell. The model verifies that the integration of the southern Sevier and Beaver rivers with the Bear and others rivers in the north is responsible for the lower 87Sr/86Sr ratios in Lake Bonneville compared to the modern Great Salt Lake. We also modeled the 87Sr/86Sr ratio of Lake Bonneville with the upper Bear River diverted into the Snake River basin and obtained an 87Sr/86Sr ratio of 0.71414. Coincidentally, this ratio is close to the observed ratio for Great Salt Lake of 0.71469. This means that 87Sr/86Sr ratios of >0.714 for carbonate can be produced by climatically induced low-lake conditions or by diversion of the upper Bear River out of the Bonneville basin. This model result also demonstrates that the upper Bear River had to be flowing into the Bonneville basin during highstands of other late Quaternary lake cycles: carbonates from the Little Valley (130-160 ka) and Cutler Dam (59 ± 5 ka) lake cycles returned 87Sr/86Sr ratios of 0.71166 and 0.71207, respectively, and are too low to be produced by a lake without the upper Bear River input. © 2004 Geological Society of America.
• Levin, N. E., Quade, J., Simpson, S. W., Semaw, S., & Rogers, M. (2004). Isotopic evidence for Plio-Pleistocene environmental change at Gona, Ethiopia. Earth and Planetary Science Letters, 219(1-2), 93-110.
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  Abstract: A 4.5 Ma record of fluvial and lacustrine deposits is well exposed at Gona, in the Afar Depression of Ethiopia. We use isotopic values of pedogenic carbonate and fossil teeth to reconstruct Plio-Pleistocene environmental change at Gona. An increase in δ13C values of pedogenic carbonates since 4.5 Ma points to a shift from woodlands to grassy woodlands in the early Pliocene, -10.4 to -3.9‰ (VPDB), to more open but still mixed environments in the late Pleistocene, -3.0 to -1.4‰ (VPDB). This pattern is also seen in isotopic records elsewhere in East Africa. However, at 1.5 Ma the higher proportion of C4 grasses at Gona is largely a result of a local facies shift to more water-limited environments. The wide range of δ13C values of pedogenic carbonate within single stratigraphic levels indicates a mosaic of vegetation for all time intervals at Gona that depends on depositional environment. Elements of this mosaic are reflected in δ13C values of both modern plants and soil organic matter and Plio-Pleistocene soil carbonate, indicating higher amounts of C4 grasses with greater distance from a river channel in both the modern and ancient Awash River systems. δ18O values of pedogenic carbonates increase up-section from -11.9‰ in the early Pliocene to -6.4‰ (VPDB) in the late Pleistocene. The wide range of δ18O values in paleovertisol carbonates from all stratigraphic levels probably reflects short-term climate changes and periods of strong evaporation throughout the record. Based on the comparison between δ18O values of Plio-Pleistocene pedogenic carbonates and modern waters, we estimate that there has been a 6.5‰ increase in mean annual δ18O values of meteoric water since 4.5 Ma. δ18O values of pedogenic carbonate from other East African records indicate a similar shift. Increasing aridity and fluctuations in the timing and source of rainfall are likely responsible for the changes in δ18O values of East African pedogenic carbonates through the Plio-Pleistocene. © 2004 Elsevier B.V. All rights reserved.
• Maier, R. M., Drees, K. P., Neilson, J. W., Henderson, D. A., Quade, J., Betancourt, J. L., Navarro-González, R., Rainey, F. A., & McKay, C. P. (2004). Microbial life in the Atacama Desert [2] (multiple letters). Science, 306(5700), 1289-1290.
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  PMID: 15556928;
• Pigati, J. S., Quade, J., Shahanan, T. M., & Haynes Jr., C. V. (2004). Radiocarbon dating of minute gastropods and new constraints on the timing of late Quaternary spring-discharge deposits in southern Arizona, USA. Palaeogeography, Palaeoclimatology, Palaeoecology, 204(1-2), 33-45.
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  Abstract: Gastropod shells are commonly preserved in Quaternary sediments, but are often avoided for radiocarbon dating because some taxa incorporate 14C-deficient carbon during shell formation. Recently, Brennan and Quade [(1997) Quat. Res. 47, 329-336] found that some minute taxa (Vallonia, Pupilla, and Succineidae) appear to yield reliable 14C ages for late Pleistocene samples. A more rigorous evaluation of the 14C inventory of minute gastropods is presented here, which involved measuring the 14C activity of specimens collected live in two geologic settings that maximize the potential for ingestion of 'old' carbon: (1) alluvium dominated by Paleozoic carbonate rocks, and (2) adjacent to extant springs with highly 14C-deficient water present at the surface. We found that several minute taxa, including Vallonia, incorporate significant and variable amounts of old carbon (∼2 to >30%) during shell formation. The 14C activities of the land snails Pupilla blandi and Euconulus fulvus, however, are indistinguishable from the 14C activity of live plants. The 14C activity of the semi-aquatic gastropod Catinella sp. (Family: Succineidae) deviates from modern values in the presence of 14C-deficient water by an amount equivalent to ∼10% of the local carbon-reservoir effect. These results imply that at least some minute gastropods can provide reliable 14C ages even when 14C-deficient carbon is readily available. To demonstrate an application of our findings, we 14C-dated shells from P. muscorum, E. fulvus, and Succinea sp. (Family: Succineidae) recovered from the Coro Marl, a late Pleistocene spring-fed marsh deposit exposed at the Murray Springs Paleoindian site in the San Pedro Valley of southern Arizona, USA. Radiocarbon ages obtained from the minute gastropods show that the unit was deposited between ∼25 000 and 13 000 14C years ago. The marl is situated >15 m above the modern water table at Murray Springs, and is similarly positioned in discontinuous outcrops along a ∼150-km stretch of the San Pedro Valley. Thus, the 14C ages of minute gastropods presented here may be used to infer the timing of high water-table levels throughout the valley. © 2003 Elsevier B.V. All rights reserved.
• Quade, J., Levin, N., Semaw, S., Stout, D., Renne, P., Rogers, M., & Simpson, S. (2004). Paleoenvironments of the earliest stone toolmakers, Gona, Ethiopia. Bulletin of the Geological Society of America, 116(11-12), 1529-1544.
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  Abstract: Fluvio-lacustrine sediments of the Hadar and Busidima Formations along the northern Awash River (Ethiopia) archive almost three million years (3.4 to
• Latorre, C., Betancourt, J. L., Rylander, K. A., Quade, J., & Matthei, O. (2003). A vegetation history from the arid prepuna of northern Chile (22-23°S) over the last 13 500 years. Palaeogeography, Palaeoclimatology, Palaeoecology, 194(1-3), 223-246.
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  Abstract: The Quaternary paleoclimate of the central Andes is poorly understood due to numerous discrepancies among the diverse proxy records that span this geographically and climatically complex region. The exact timing, duration and magnitude of wet and dry phases are seldom duplicated from one proxy type to another, and there have been few opportunities to compare climatic records from the same proxy along environmental gradients. Vegetation histories from fossil rodent middens provide one such opportunity on the Pacific slope of the Andes. We previously reported a vegetation history from the upper margin (2400-3000 m) of the absolute desert in the central Atacama Desert of northern Chile. That record identified a distinct wet phase that peaked between 11.8 and 10.5 ka, when steppe grasses and other upland elements expanded as much as 1000 m downslope, and a secondary wet period during the middle to late Holocene (7.1-3.5 ka). The latter wet phase remains controversial and is not as readily apparent in our low-elevation midden record. We thus sought to replicate both phases in a midden record from the mid-elevations (3100-3300 m) of the arid prepuna, where slight precipitation increases would be amplified. Midden records from these elevations identify conditions wetter than today at 13.5-9.6, 7.6-6.3, 4.4-3.2 and possibly 1.8-1.2 ka. Dry phases occurred at 9.4-8.4 ka and possibly at ca. 5.1 ka. Present floras and modern hyperarid conditions were established after 3.2 ka. The records from the two elevational bands generally match with some important differences. These differences could reflect both the discontinuous aspect of the midden record and the episodic nature of precipitation and plant establishment in this hyperarid desert. © 2003 Elsevier Science B.V. All rights reserved.
• Quade, J. (2003). Isotopic records from ground-water and cave speleothem calcite in North America. Developments in Quaternary Science, 1(C), 205-220.
• Quade, J., English, N., & DeCelles, P. G. (2003). Silicate versus carbonate weathering in the Himalaya: A comparison of the Arun and Seti River watersheds. Chemical Geology, 202(3-4), 275-296.
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  Abstract: We studied the water chemistry of two large and geologically differing Himalayan watersheds in order to maximize the contrast between silicate versus carbonate weathering effects on river chemistry. Our previous research involved the Seti River of westernmost Nepal, geologically typical of many rivers in Nepal in draining mixed carbonate/silicate lithologies, including abundant carbonate rocks of the Lesser Himalayan Sequence. For comparison, the Arun River was chosen for study because south of the Himalayan front it drains almost exclusively Greater and Lesser Himalayan silicate rocks. Despite this dominance of silicate rocks, carbonate weathering - probably of metamorphic calcite in Great Himalayan paragneisses - is clearly in evidence in many Arun watersheds. Weathering of silicate rocks exposed all along the Arun south of the range front has a small impact on mainstem river chemistry. The mainstems of both the Seti and Arun systems are dominated by weathering of carbonate rocks, although the contribution of silicate weathering is more visible in Arun mainstem chemistry. The carbonate weathering source to the Arun mainstem is probably both limestone in the Tethyan Sequence widely exposed in northern headwaters of the system, and metamorphic calcite within the Greater Himalayan Sequence. A number of small watersheds along the Arun and Seti appear to be carbonate-free. They probably provide the best constraints to date on the Ca/Na and Mg/Na ratios of waters draining Himalayan silicate rocks, two critical parameters for calculation of CO2 consumption by silicate weathering in the Himalaya. The observed Ca/Na and Mg/Na ratios would produce slightly higher estimates of silicate weathering fluxes than previous studies. The geologic contrasts between the Seti and the Arun produce large differences in the 87Sr/86Sr ratio of each mainstem, unlike the major element chemistry. The Seti mainstem displays much higher 87Sr/86Sr ratios than the Arun mainstem, the opposite of the expected relationship since radiogenic silicate rocks of the Greater and Lesser Himalaya are so widely exposed along the Arun. 87Sr/86Sr ratios of the Arun mainstem never exceed 0.734 and show little downstream change as the mainstem passes through silicate rocks of the Greater and Lesser Himalaya. 87Sr/86Sr ratios of the Seti mainstem increase sharply from 0.725 to 0.785 when the river enters the belt of metacarbonate rocks of the northern Lesser Himalayan Sequence, a pattern also displayed by other Himalayan rivers such as the Kali Gandaki and Bhotse Khola. Metacarbonate rocks, including those of the Lesser Himalaya, are a major source of radiogenic Sr in modern Himalayan Rivers and probably have been key players in elevating marine 87Sr/86Sr ratios since the Early Miocene. © 2003 Elsevier B.V. All rights reserved.
• Quade, J., Forester, R. M., & Whelan, J. F. (2003). Late Quaternary paleohydrologic and paleotemperature change in southern Nevada. Special Paper of the Geological Society of America, 368, 165-188.
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  Abstract: Paleo-spring discharge activity in the southern Great Basin responded to changes in recharge, hence climate changes, in high mountain areas during the late Quaternary. In our study, we examined four stratigraphic sections in southern Nevada in order to reconstruct paleohydrologic change spanning the last two major discharge cycles. The largest discharge event in those sections is expressed as extensive wetland deposits (Unit B) that fall beyond the range of radiocarbon dating (>41 ka). We tentatively correlate this event with marine isotope stage 6, which is so conspicuously represented in cores from Death Valley and Owens Lake. Major wetlands were also present during last glacial maximum (Unit D) deposited between 16.4 and 400 ostracode shells vary by ∼5‰, and there is no consistent, section-wide, difference in isotopic values between standing water and spring taxa. This pattern strongly suggests short residence times for water in local basins, due to loss of water from basins by outflow as groundwater or overflow, rather than by evaporation. We used the δ18O value of fossil ostracodes to place constraints on paleotemperature in the valley bottoms during glacial periods. This analysis entails at least three key assumptions: no vital or evaporation effects during valve formation of the ostracode Cypridopsis vidua, short transit imes in the aquifer, and the basic relationship between modern air and spring water temperature holds for the past. If these and other assumptions are satisfied, we estimate that mean annual air temperature during the penultimate wet period (Unit B2) in the valley bottom was at least 10.8 °C colder than today, and at least 5.6 °C colder during the last glacial maximum (Unit D). If a vital effect of 0.8-1‰ is assumed using δ18O values from groundwater candonids, then the above estimates of maximum valley-bottom temperatures during Unit D time increase by ∼2-3 °C. © 2003 Geological Society of America.
• Rech, J. A., Pigati, J. S., Quade, J., & Betancourt, J. L. (2003). Re-evaluation of mid-Holocene deposits at Quebrada Puripica, northern Chile. Palaeogeography, Palaeoclimatology, Palaeoecology, 194(1-3), 207-222.
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  Abstract: During the middle Holocene (8-3 ka), wetland deposits accumulated in areas with emergent water tables in the central Atacama Desert (22-24°S), producing a stratigraphic unit (Unit C) that can be mapped and correlated across different basins and geomorphic settings. Wherever mapped, Unit C is located between 6 and 30 m above modern wetlands, and includes thick sequences of diatomite and organic mats. The origin, depositional environment, and paleoclimatic significance of Unit C is controversial and currently under debate. Grosjean [Science 292 (2001) 2391a] suggests the unit developed under a regime of falling lake and ground-water levels, whereas evidence presented here suggests that Unit C formed during a period of rising ground-water levels and increased vegetation cover. The debate is embedded in broader discussions about geomorphic processes in ground-water-fed streams, as well as the history and forcing of climate variability in the central Andes. The central Atacama and Andes are remote, with few opportunities for different researchers to examine the same site. One exception is a sequence of mid-Holocene deposits at the confluence of Quebrada Seca and Rio Puripica in northern Chile (23°S). Grosjean et al. [Quat. Res. 48 (1997) 239-246] initially suggested the deposits accumulated in temporary lake basins, which formed when recurring debris flows from a side canyon (Quebrada Seca) dammed the main channel (Río Puripica) during a period of drought and reduced stream flow. Upon our visit to the site, we found evidence that clearly demonstrates the deposits were not formed in temporary lakes, but rather were deposited in a wetland environment. Disagreement remains about the climatic interpretation of wetland deposits. Grosjean [Science 292 (2001) 2391a] now suggests that local ground-water levels rise and wetland deposits aggrade in deep canyon systems, such as Río Puripica, when stream power and channel erosion is reduced during prolonged dry spells. However, sedimentological evidence and the presence of Unit C in many depositional environments, not just deep canyons, indicate that it formed during a period of higher regional ground-water levels that were sustained by enhanced precipitation and recharge in the High Andes. © 2003 Elsevier Science B.V. All rights reserved.
• Rech, J. A., Quade, J., & Hart, W. S. (2003). Isotopic evidence for the source of Ca and S in soil gypsum, anhydrite and calcite in the Atacama Desert, Chile. Geochimica et Cosmochimica Acta, 67(4), 575-586.
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  Abstract: The origin of pedogenic salts in the Atacama Desert has long been debated. Possible salt sources include in situ weathering at the soil site, local sources such as aerosols from the adjacent Pacific Ocean or salt-encrusted playas (salars), and extra-local atmospheric dust. To identify the origin of Ca and S in Atacama soil salts, we determined δ34S and 87Sr/86Sr values of soil gypsum/anhydrite and 87Sr/86Sr values of soil calcite along three east-west trending transects. Our results demonstrate the strong influence of marine aerosols on soil gypsum/anhydrite development in areas where marine fog penetrates inland. Results from an east-west transect located along a breach in the Coastal Cordillera show that most soils within 90 km of the coast, and below 1300 m in elevation, are influenced by marine aerosols and that soils within 50 km, and below 800 m in elevation, receive >50% of Ca and S from marine aerosols (δ34S values > 14‰ and 87Sr/86Sr values >0.7083). In areas where the Coastal Cordillera is > 1200 m in elevation, however, coastal fog cannot penetrate inland and the contribution of marine aerosols to soils is greatly reduced. Most pedogenic salts from inland soils have δ34S values between +5.0 to +8.0‰ and 87Sr/86Sr ratios between 0.7070 and 0.7076. These values are similar to average δ34S and 87Sr/86Sr values of salts from local streams, lakes, and salars (+5.4 ±2‰ δ34S and 0.70749 ± 0.00045 87Sr/86Sr) in the Andes and Atacama, suggesting extensive eolian reworking of salar salts onto the surrounding landscape. Ultimately, salar salts are precipitated from evaporated ground water, which has acquired its dissolved solutes from water-rock interactions (both high and low-temperature) along flowpaths from recharge areas in the Andes. Therefore, the main source for Ca and S in gypsum/anhydrite in non-coastal soils is indirect and involves bedrock alteration, not surficially on the hyperarid landscape, but in the subsurface by ground water, followed by eolian redistribution of ground-water derived salar salts to soils. The spatial distribution of high-grade nitrate deposits appears to correspond with areas that receive the lowest fluxes of local marine and salar salt, supporting arguments for tropospheric nitrogen as the main source for soil nitrate. © 2003 Elsevier Science Ltd.
• Semaw, S., Rogers, M. J., Quade, J., Renne, P. R., Butler, R. F., Dominguez-Rodrigo, M., Stout, D., Hart, W. S., Pickering, T., & Simpson, S. W. (2003). 2.6-Million-year-old stone tools and associated bones from OGS-6 and OGS-7, Gona, Afar, Ethiopia. Journal of Human Evolution, 45(2), 169-177.
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  PMID: 14529651;
• Biggs, T. H., Quade, J., & Webb, R. H. (2002). δ¹³C values of soil organic matter in semiarid grassland with mesquite (Prosopis) encroachment in southeastem Arizona. Geoderma, 110(1-2), 109-130.
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  Abstract: Over the past century, C3 woody plants and trees have increased in abundance in many semiarid ecosystems, displacing native C4 grasses. Livestock grazing, climatic fluctuations, and fire suppression are several reasons proposed for this shift. Soil carbon isotopic signatures are an ideal technique to evaluate carbon turnover rates in such ecosystems. On the gunnery ranges of Fort Huachuca in southeastern Arizona, study sites were established on homogeneous granitic alluvium to investigate the effects of fire frequency on δ13C values in surface soil organic matter (SOM). These ranges have had no livestock grazing for 50 years and a well-documented history of fires. Prosopis velutina Woot. (mesquite) trees have altered SOM δ13C pools by the concentration of plant nutrients and the addition of isotopically light litter. These soil carbon changes do not extend beyond canopy margins. Elevated total organic carbon (TOC), plant nutrient (N and P) concentrations, and depleted SOM δ13C values are associated with C3 Prosopis on an unburned plot, which enables recognition of former Prosopis-occupied sites on plots with recent fire histories. Elevated nutrient concentrations associated with former Prosopis are retained in SOM for many decades. Surface SOM δ13C values indicate the estimated minimum turnover time of C4-derived carbon beneath large mature Prosopis is about 100-300 years. In contrast, complete turnover of original C3 carbon to C4 carbon under grasslands is estimated to take a minimum of 150-500 years. Our study confirms that C4 grass cover has declined over the past 100 years, although isolated C3 trees or shrubs were not uncommon on the historic C4-dominated grasslands. We find evidence in surface soil layers for a modern C3 plant expansion reflected in the substantial shift of SOM δ13C values from C4 grasses to C3 shrublands. © 2002 Elsevier Science B.V. All rights reserved.
• J., S., & Quade, J. (2002). Tracing spatial and temporal variations in the sources of calcium in pedogenic carbonates in a semiarid environment. Geoderma, 108(3-4), 259-276.
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  Abstract: In arid environments, significant amounts of calcium (Ca) are stored in pedogenic carbonates that develop in soils. There are two sources for Ca in pedogenic carbonates in soils: local parent material and dust deposited on the surface. In this study, the strontium (Sr) isotopes (87Sr/86Sr ratios) were used as a tracer for Ca from these sources. We studied spatial and temporal variations in the sources of Ca in pedogenic carbonates in soils developed in six Quaternary basalt flows and a cinder deposit in the Zuni-Bandera volcanic field near Grants, NM. Young basalt is an excellent rock type on which to study soil development because it provides a chemically and isotopically uniform substrate. Age dating of the flows provides control for the beginning of soil development. Other rock types (with varying 87Sr/86Sr ratios) cropping out around the basalt provide an opportunity to evaluate spatial variations in sources of Ca and Sr. The 87Sr/86Sr ratio of pedogenic carbonates (average 0.7078) is similar to the average ratio of marine limestone cropping out in the region, and is distinctly different from that of basalt bedrock (average 0.7053), indicating that chemical alteration of dust is the principle source of Ca. There is a strong correlation between the 87Sr/86Sr ratio of pedogenic carbonate and the labile fraction of dust and A soil horizon samples. There is little correlation between the 87Sr/86Sr ratio of pedogenic carbonate and that of the residual (silicate) fraction of dust or A horizon samples. This indicates that the major source of Ca cycling through these soils is chemical weathering of carbonate minerals in dust and that only a minor component is from chemical weathering of silicate minerals, either in dust or the underlying basalt. Mixing calculations using Sr isotopes as a tracer for Ca support the qualitative observations. Some variability in the 87Sr/86Sr ratio of pedogenic carbonates was found on a local scale (several hundred meters to several kilometers), and can be attributed to changes in dust composition due to contributions from local bedrock. There was no correlation found between the age of a basalt flow and the 87Sr/86Sr ratio of the pedogenic carbonate developed on them, indicating that the composition of dust has not changed significantly over the last 0.7 Ma. © 2002 Elsevier Science B.V. All rights reserved.
• Latorre, C., Betancourt, J. L., Rylander, K. A., & Quade, J. (2002). Vegetation invasions into absolute desert: A 45 000 yr rodent midden record from the Calama-Salar de Atacama basins, northern Chile (lat 22°-24°S). Bulletin of the Geological Society of America, 114(3), 349-366.
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  Abstract: Plant macrofossils, percentage abundance of grass taxa, fecal-pellet δ13C, and plant-cuticle contents from 49 fossil rodent middens dated by 14C record changes in local vegetation and precipitation since 45 ka (calibrated or measured to thousands of calendar years before present) in the central Atacama Desert (lat 22°-24°S) of northern Chile. The midden sites are along the hyperarid upper margin (2400-3100 m) of the "absolute desert," in an extreme environment sparsely vegetated by annual herbs and halophytic shrubs. Conditions between 40 and 22 ka may have been at least intermittently dry, and possibly cooler, as implied by four middens with low species richness. We infer a large increase in summer rainfall between 16.2 and 10.5 ka on the basis of the lowering of steppe grasses by as much as 1000 m, prominence of C4 grasses and summer annuals, high species richness, and displacement of northern species at least 50 km south of their modern ranges. The precipitation increase was greatest for a cluster of middens between 11.8 and 10.5 ka. Abrupt drying, evident in a dramatic decrease in grass abundance, occurred after 10.5 ka at all four midden localities. Increased percentages of grass, higher species richness, and extralocal taxa record slightly wetter conditions between 7.1 and 3.5 ka. The present hyperarid conditions were established after 3 ka. Present-day variability of summer precipitation in the central Atacama Desert and adjacent Altiplano is related to the intensity and position of upper air circulation anomalies, which in turn respond to Pacific sea-surface temperature anomalies. Summer insolation over the central Andes (lat 20°S) was at its minimum during the latest glacial to early Holocene transition, so regional insolation forcing cannot account for intensified pluvial conditions in the central Atacama. Summer precipitation collapsed abruptly between 10.5 and 10 ka, indicating either nonlinear relationships with seasonal insolation or a change in intensity of upper air circulation over the Altiplano, effectively blocking moisture transport to the Atacama Desert. Here, we suggest that precipitation variations on millennial time scales in the central Atacama are the result of extraregional forcing of the South American Summer Monsoon through intensified Walker Circulation (stronger easterlies) and La Niña-like conditions operating through insolation anomalies (i.e., departures in insolation values) directly over central Asia and the equatorial Pacific.
• Libarkin, J. C., Quade, J., Chase, C. G., Poths, J., & McIntosh, W. (2002). Measurement of ancient cosmogenic ²¹Ne in quartz from the 28 Ma Fish Canyon Tuff, Colorado. Chemical Geology, 186(3-4), 199-213.
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  Abstract: Measurement of 21Ne in quartz from the 28 Ma buried Fish Canyon Tuff of Colorado yielded a maximum of 2.75 ± 0.57 x 10621Ne atoms (g SiO2) -1 above nucleogenic and modern concentrations. This quantity represents cosmogenic 21Ne produced on the Fish Canyon Tuff surface prior to the deposition of the overlying Carpenter Ridge Tuff. Ancient 21Ne was isolated through the analysis and identification of (1) background 21Ne produced from α-particle interactions or inherited; and (2) cosmogenic 21Ne produced from modern radiation. Multiple samples of Fish Canyon Tuff shielded during both exposure periods, 28 Ma ago and in modern time, yielded the background that was then subtracted from all samples. Likewise, samples of Fish Canyon exposed today, but well below the Fish Canyon-Carpenter Ridge contact and therefore shielded 28 Ma ago, yielded a modern component that was also removed from all sample concentrations. The presence of an ancient cosmogenic isotope in a buried surface has several potential applications, including the quantification of paleoelevation, paleolatitude, and pre-Quaternary erosion rates. © 2002 Elsevier Science B.V. All rights reserved.
• Quade, J. (2002). Desert pavements and associated rock varnish in the Mojave Desert: How old can they be?. Geology, 29(9), 855-858.
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  Abstract: Desert pavements are common features of arid landscapes and have been widely used as a relative age indicator of the geomorphic surfaces upon which they are developed. In this study I examined the patterns of pavement development as a function of elevation in the Mojave Desert as well as the causes for the gradual disappearance of pavement at high elevations. Pavement density, as measured by percentage of pebble coverage, decreases systematically with elevation gain by ∼3% per 100 m, from 95% coverage below 500 m to less than 60% at 1700 m. Plants appear to be the main agent of pavement disruption; plant density decreases as pavement density increases. Burrowing by rodents and crusting by cryptobiota also disrupt pavement development at higher elevation. During the last glacial maximum, plant communities were displaced 1000-1400 m downward in the Mojave Desert. Pavements today generally do not survive above the blackbush (Coleogyne ramossisma)-sagebrush (Artemisia tridentata) zone. Evidence from packrat middens shows that these and other plants typical of high elevations today grew as low as 300-400 m during the last glacial maximum. I suggest that during the last glacial maximum, desert pavements were confined to the lowest alluvial fans of Death Valley and adjoining low valleys. No alluvial desert pavements above ∼400 m in the region are older than the latest Pleistocene. By the same reasoning, desert varnish on desert pavements above 400 m may all be Holocene in age, except where developed on stable boulders.
• Rech, J. A., Quade, J., & Betancourt, J. L. (2002). Late Quaternary paleohydrology of the central Atacama Desert (lat 22°-24°S), Chile. Bulletin of the Geological Society of America, 114(3), 334-348.
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  Abstract: In northern Chile, precipitation in the High Andes (>3500 m) recharges groundwater systems that flow down the Pacific slope and feed large aquifers in the hyperarid Atacama Desert. Wetlands, which are often found along the base of the Andes, mark locations where the water table intersects the land surface. At these locations, paleo-wetland deposits, which are present as terraces between 3 and 20 m above modern wetlands, record past water-table heights along the Andean front and are used to reconstruct changes in groundwater discharge. Paleo-wetland deposits in the central Atacama Desert (lat 22°-24°S) record an episode (>15.4-9 ka) of high water tables followed by an episode (8-3 ka) of moderately high water tables. Elevated water tables result from increased groundwater discharge and ultimately from enhanced recharge in the Andes. The concordance of results from three separate hydrologic systems suggests that changes in groundwater discharge and recharge are regional and reflect climatic fluctuations. This interpretation is supported by close agreement with other paleoclimatic records in the region. The periods of greater groundwater discharge were separated by episodes (9-8 and 3-0 ka) of significant groundwater lowering and stream incision, implying greatly diminished discharge. The central Atacama and Andes (lat 22°-24°S) receive precipitation mainly from moist air masses transported from the Amazon Basin by the South American Summer Monsoon (SASM). Increases in groundwater recharge are therefore thought to reflect an increase in the frequency and/or moisture content of SASM air masses crossing the Andes. Fluctuations in SASM precipitation have previously been linked to summer insolation in the Southern Hemisphere. The wettest period in the central Atacama (>15.4-9 ka), however, coincides with a minimum in austral-summer insolation at 10 ka, suggesting that regional summer insolation is not a dominant influence on the SASM. Instead, intensification of the SASM may be linked to extraregional forcings such as the Walker Circulation.
• Wasson, R. J., Caitcheon, G., Murray, A. S., McCulloch, M., & Quade, J. (2002). Sourcing sediment using multiple tracers in the catchment of Lake Argyle, Northwestern Australia. Environmental Management, 29(5), 634-646.
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  PMID: 12180178;Abstract: Control of sedimentation in large reservoirs requires soil conservation at the catchment scale. In large, heterogeneous catchments, soil conservation planning needs to be based on sound information, and set within the framework of a sediment budget to ensure that all of the potentially significant sources and sinks are considered. The major sources of sediment reaching the reservoir, Lake Argyle, in tropical northwestern Australia, have been determined by combining measured sediment fluxes in rivers with spatial tracer-based estimates of proportional contributions from tributaries of the main stream entering the lake, the Ord River. The spatial tracers used are mineral particle magnetics, the strontium isotopic ratio, and the neodymium isotopic ratio. Fallout of 137Cs has been used to estimate the proportion of the sediment in Lake Argyle eroded from surface soils by sheet and rill erosion, and, by difference, the proportion eroded from subsurface soils by gully and channel erosion. About 96% of the sediment in the reservoir has come from less than 10% of the catchment, in the area of highly erodible soils formed on Cambrian-age sedimentary rocks. About 80% of the sediment in the reservoir has come from gully and channel erosion. A major catchment revegetation program, designed to slow sedimentation in the reservoir, appears to have had little effect because it did not target gullies, the major source of sediment. Had knowledge of the sediment budget been available before the revegetation program was designed, an entirely different approach would have been taken.
• Decelles, P. G., Robinson, D. M., Quade, J., Ojha, T. P., Garzione, C. N., Copeland, P., & Upreti, B. N. (2001). Stratigraphy, structure, and tectonic evolution of the Himalayan fold-thrust belt in Western Nepal. Tectonics, 20(4), 487-509.
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  Abstract: Regional mapping, stratigraphic study, and 40Ar/39Ar geochronology provide the basis for an incremental restoration of the Himalayan fold-thrust belt in western Nepal. Tectonostratigraphic zonation developed in other regions of the Himalaya is applicable, with minor modifications, in western Nepal. From south to north the major structural features are (1) the Main Frontal thrust system, comprising the Main Frontal thrust and two to three thrust sheets of Neogene foreland basin deposits; (2) the Main Boundary thrust sheet, which consists of Proterozoic to early Miocene, Lesser Himalayan metasedimentary rocks; (3) the Ramgarth thrust sheet, composed of Palcoproterozoic low-grade metasedimentary rocks; (4) the Dadeldhura thrust sheet, which consists of medium-grade metamorphic rocks, Cambrian-Ordovician granite and granitic mylonite, and early Paleozoic Tethyan rocks; (5) the Lesser Himalayan duplex, which is a large composite antiformal stack and hinterland dipping duplex; and (6) the Main Central thrust zone, a broad ductile shear zone. The major structures formed in a general southward progression beginning with the Main Central thrust in late early Miocene time. Eocene-Oligocene thrusting in the Tibetan Himalaya, north of the study area, is inferred from the detrital unroofing record. On the basis of 40Ar/39Ar cooling ages and provenance data from synorogenic sediments, emplacement of the Dadeldhura thrust sheet took place in early Miocene time. The Ramgarh thrust sheet was emplaced between ~ 15 and ~ 10 Ma. The Lesser Himalayan duplex began to grow by ~ 10 Ma, simultaneously folding the north limb of the Dadeldhura synform. The Main Boundary thrust became active in latest Miocene-Pliocene time; transport of its hanging wall rocks over an ~ 8-km-high footwall ramp folded the south limb of the Dadeldhura synform. Thrusts in the Subhimalayan zone became active in Pliocene time. The minimum total shortening in this portion of the Himalayan fold-thrust belt since early Miocene time (excluding the Tibetan zone) is ~ 418-493 km, the variation depending on the actual amounts of shortening accommodated by the Main Central and Dadeldhura thrusts. The rate of shortening ranges between 19 and 22 mm/yr for this period of time. When previous estimates of shortening in the Tibetan Himalaya are included, the minimum total amount of shortening in the fold-thrust belt amounts to 628-667 km. This estimate neglects shortening accommodated by small-scale structures and internal strain and is therefore likely to fall significantly below the actual amount of total shortening.
• Dettman, D. L., Kohn, M. J., Quade, J., Ryerson, F. J., Ojha, T. P., & Hamidullah, S. (2001). Seasonal stable isotope evidence for a strong Asian monsoon throughout the past 10.7 m.y.. Geology, 29(1), 31-34.
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  Abstract: Stable isotope profiles of fossil freshwater bivalve shells and mammal teeth provide a record of the seasonal δ18O variation in surface waters of the Himalayan foreland over the past 11 m.y. Between 3.1 and 10.7 Ma the δ18O of surface waters approached or exceeded 0‰ standard mean ocean water (SMOW) in the dry season. Since 9.5 Ma the magnitude of seasonal variability in δ18O has remained essentially unchanged. Both observations imply that the Tibetan Plateau had attained sufficient elevation and area prior to 10.7 Ma to support a strong Asian monsoon. These data also imply that the δ18O of wet-season rainfall was significantly more negative (-9.5‰ SMOW) prior to 7.5 Ma than after (-6.5‰ SMOW). If this change is attributable to a lessening of the amount effect in rainfall, this agrees with floral and soil geochemical data that indicate increasing aridity beginning at 7.5 Ma.
• Dettman, D. L., Kohn, M. J., Quade, J., Ryerson, F. J., Ojha, T. P., & Hamidullah, S. (2001). Seasonale stable isotope evidence for a strong Asian monsoon throughout the past 10.7 m.y. Geology, 29(1), 31-34.
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  Abstract: Stable isotope profiles of fossil freshwater bivalve shells and mammal teeth provide a record of the seasonal δ18O variation in surface waters of the Himalayan foreland over the past 11 m.y. Between 3.1 and 10.7 Ma the δ18O of surface waters approached or exceeded 0‰ standard mean ocean water (SMOW) in the dry season. Since 9.5 Ma the magnitude of seasonal variability in δ18O has remained essentially unchanged. Both observations imply that the Tibetan Plateau had attained sufficient elevation and area prior to 10.7 Ma to support a strong Asian monsoon. These data also imply that the δ18O of wet-season rainfall was significantly more negative (-9.5‰ SMOW) prior to 7.5 Ma than after (-6.5‰ SMOW). If this change is attributable to a lessening of the amount effect in rainfall, this agrees with floral and soil geochemical data that indicate increasing aridity beginning at 7.5 Ma.
• English, N. B., Betancourt, J. L., Dean, J. S., & Quade, J. (2001). Strontium isotopes reveal distant sources of architectural timber in Chaco Canyon, New Mexico. Proceedings of the National Academy of Sciences of the United States of America, 98(21), 11891-11896.
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  PMID: 11572943;PMCID: PMC59738;Abstract: Between A.D. 900 and 1150, more than 200,000 conifer trees were used to build the prehistoric great houses of Chaco Canyon, New Mexico, in what is now a treeless landscape. More than one-fifth of these timbers were spruce (Picea) or fir (Abies) that were hand-carried from isolated mountaintops 75-100 km away. Because strontium from local dust, water, and underlying bedrock is incorporated by trees, specific logging sites can be identified by comparing 87Sr/86Sr ratios in construction beams from different ruins and building periods to ratios in living trees from the surrounding mountains. 87Sr/86Sr ratios show that the beams came from both the Chuska and San Mateo (Mount Taylor) mountains, but not from the San Pedro Mountains, which are equally close. Incorporation of logs from two sources in the same room, great house, and year suggest stockpiling and intercommunity collaboration at Chaco Canyon. The use of trees from both the Chuska and San Mateo mountains, but not from the San Pedro Mountains, as early as A.D. 974 suggests that selection of timber sources was driven more by regional socioeconomic ties than by a simple model of resource depletion with distance and time.
• Holmgren, C. A., Betancourt, J. L., Rylander, K. A., Roque, J., Tovar, O., Zeballos, H., Linares, E., & Quade, J. (2001). Holocene vegetation history from fossil rodent middens near Arequipa, Peru. Quaternary Research, 56(2), 242-251.
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  Abstract: Rodent (Abrocoma, Lagidium, Phyllotis) middens collected from 2350 to 2750 m elevation near Arequipa, Peru (16°S), provide an ∼9600-yr vegetation history of the northern Atacama Desert, based on identification of >50 species of plant macrofossils. These midden floras show considerable stability throughout the Holocene, with slightly more mesophytic plant assemblages in the middle Holocene. Unlike the southwestern United States, rodent middens of mid-Holocene age are common. In the Arequipa area, the midden record does not reflect any effects of a mid-Holocene mega drought proposed from the extreme lowstand (100 m below modern levels, >6000 to 3500 yr B.P.) of Lake Titicaca, only 200 km east of Arequipa. This is perhaps not surprising, given other evidence for wetter summers on the Pacific slope of the Andes during the middle Holocene as well as the poor correlation of summer rainfall among modern weather stations in the central AndesAtacama Desert. The apparent difference in paleoclimatic reconstructions suggests that it is premature to relate changes observed during the Holocene to changes in El Niño Southern Oscillation modes. © 2001 University of Washington.
• Lifton, N. A., Jull, A., & Quade, J. (2001). A new extraction technique and production rate estimate for in situ cosmognic ¹⁴C in quartz. Geochimica et Cosmochimica Acta, 65(12), 1953-1969.
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  Abstract: The potential of in situ cosmogenic 14C (in situ 14C) for surficial process studies is widely recognized, yet a realible means of isolating it has proved difficult to develop. We present here a new method for extracting in situ 14C from quartz that overcomes difficulties encountered with earlier techniques, yielding more reliable production rate estimates. Comparison of 14C thermal release patterns from surficial and deeply shielded quartz samples (Lifton, 1997) demonstrated that contaminant 14C is relased at or below 500°C, and that 14C released between 500 and 1500°C is essentially all in situ-produced. The new technique builds on this key result, using resistance heating of samples in the presence of a lithium metaborate (LiBO2) flux, and collection of all evolved carbon as CO2 between 500°C and 1100 to 1200°C. Our improved method has four distinct advantages over other extraction methods: (1) we can identify and quantitatively eliminate atmospheric/organic 14C contamination; (2) we can identify the in situ 14C component unambiguously without assumptions of 14CO/14CO2 production proportions within the rock or equilibria on extraction; (3) in situ 14C is reliably extracted from quartz at lower temperatures and in less time than earlier methods and (4) blank 14C levels are consistently low ((2.3 ± 0.1) × 10514C atoms (1σ)). Our new extraction procedures should thus enable researchers to use in situ 14C in diverse applications without reservation. We developed our new procedures using samples of wave-cut quartzite benches from the well-dated Bonneville (17.4 ± 0.3 cal ky) and Provo (16.8 ± 0.3 cal ky) shorelines of Pleistocene Lake Bonneville, Utah, and from underlying deeply shielded locations. In situ 14C was extracted from quartz separated from 2 Bonneville shoreline samples (6 aliquots) and 1 Provo shoreline sample (2 aliquots). Results demonstrate that our new procedures can effectively isolate the in situ 14C fraction with replicate analytical precision bettern than 2% (1σ, n = 5), while remaining consistent with earlier results. This level of precision and accuracy is comparable to or exceeds those currently obtainable with in situ cosmogenic 10Be, 26Al, 3He, 21Ne, and 36Cl. Resulting weighted mean in situ 14C site production rates for the Bonneville and Provo shorelines are 52.9 ± 1.7 (14C atoms/g SiO2)/y and 48.7 ± 2.8 (14C atoms/g SiO2)/y (1σ), respectively-consistent with earlier production rate estimates. Current and previuosly published in situ 14C site production rate estimates were then scaled to sea level and high geomagnetic latitude using the latitude-altitude scaling models of Lal (1991) and Dunai (2000). Results indicate that both models yield sea level, high-latitude production rates consistent with independent estimates. Our new in situ 14C data yield integrated late Quaternary production rate estimates at sea level and high latitude of 15.1 ± 0.5 (14C atoms/g SiO2)/y using the Lal (1991) model, and 15.8 ± 0.5 (14C atoms/g SiO2)/y with that of Dunai (2000). Until significant uncertainties in these models are addressed, however, we prefer the value from the widely-used Lal (1991) model as our best estimate of the integrated late Quaternary production rate for in situ 14C. Copyright © 2001 Elsevier Science Ltd.
• Madsen, D. B., Rhode, D., Grayson, D. K., Broughton, J. M., Livingston, S. D., Hunt, J., Quade, J., Schmitt, D. N., & III, M. S. (2001). Late Quaternary environmental change in the Bonneville basin, western USA. Palaeogeography, Palaeoclimatology, Palaeoecology, 167(3-4), 243-271.
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  Abstract: Excavation and analyses of small animal remains from stratified raptor deposits spanning the last 11.5 ka, together with collection and analysis of over 60 dated fossil woodrat midden samples spanning the last 50 ka, provide a detailed record of changing climate in the eastern Great Basin during the late Pleistocene and Holocene. Sagebrush steppe dominated the northern Bonneville basin during the Full Glacial, suggesting that conditions were cold and relatively dry, in contrast to the southern basin, which was also cold but moister. Limber pine woodlands dominated ∼13-11.5 ka, indicating increased dryness and summer temperatures ∼6-7°C cooler than present. This drying trend accelerated after ∼11.5 ka causing Lake Bonneville to drop rapidly, eliminating 11 species of fish from the lake. From ∼11.5-8.2 ka xerophytic sagebrush and shadscale scrub replaced more mesophilic shrubs in a step-wise fashion. A variety of small mammals and plants indicate the early Holocene was ∼3°C cooler and moister than at present, not warmer as suggested by a number of climatic models. The diversity of plants and animals changed dramatically after 8.2 ka as many species disappeared from the record. Some of the upland species returned after ∼4 ka and Great Salt Lake became fresh enough at ∼3.4 and ∼1.2 ka to support populations of Utah chub. © 2001 Elsevier Science B.V.
• Ojha, T. P., Butler, R. F., Quade, J., Decellesi, P. G., & Upreti, B. N. (2001). Magnetic polarity stratigraphy of foreland basin sediments of Nepal Himalaya. Journal of Asian Earth Sciences, 19(3A), 48-49.
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  Abstract: The synorogenic sediments of Siwalik group and Dumri formation in sub-Himalayan region have been deposited within the flexural foredeep of the Himalayan foreland basin system since early Miocene, eroded from developing fold-thrust belt to the north (Tokuoka et al., 1986; Hisatomi, 1990; Critelli and Ingersoll, 1994; DeCelles et al., 1998a). The aim of our project is to date the Mio-Pliocene Siwalik group and late Oligocene to early Miocene Dumri formation across Nepal, in order to put all our other petrographic and isotopic work in a geochronologic context, to construct a sediment accumulation history, and compare it to the chronology of thrusting/unroofing of the Himalayan fold-thrust belt in Nepal. The Siwalik group and Dumri formation in Nepal contain only sparse fossils, hence it is practically impossible to use biostratigraphy for age calibration. Magnetostratigraphy has proved a most useful tool for determining the age of Siwalik group sediments through the northern Indian sub-continent. Efforts to date sediments in Nepal are relatively new and have been concentrated in the western half of the country (Appel et al., 1991; Harrison et al., 1993; Gautam and Appel, 1994; Ojha et al., 2000). From previously published work, it is obvious that there was no uniformity among paleomagnetists regarding preferred lithology for sampling. Previously sampled lithologies have included sandstone (Appel et al., 1991; Gautam and Appel, 1994), bedded siltstone (Harrison et al., 1993), and undifferentiated mudrocks (Opdyke et al., 1979). Given the diversity of sampling strategies, we decided to revisit previously sampled areas and rigorously test the paleomagnetic behavior of the different lithologies. We sampled Siwalik group sediments exposed at Tinau Khola, Surai Khola, Khutia Khola, and Muksar Khola as well as older (>15 Ma) foreland basin deposits belonging to the Dumri formation along the Tansen road and laterally equivalent Suntar formation in Swat Khola. We analyzed a pilot set of samples from those sections in different kind of lithologies. Our results show that wherever possible, bedded siltstone should be sampled for paleomagnetic analysis. Paleosols yield paleomagnetic results of highly variable quality, whereas sandstones generally display very erratic behavior during thermal demagnetization.
• Placzek, C., Quade, J., & Betancourt, J. L. (2001). Holocene lake-level fluctuations of Lake Aricota, Southern Peru. Quaternary Research, 56(2), 181-190.
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  Abstract: Lacustrine deposits exposed around Lake Aricota, Peru (17° 22′S), a 7.5-km2 lake dammed by debris flows, provide a middle to late Holocene record of lake-level fluctuations. Chronological context for shoreline deposits was obtained from radiocarbon dating of vascular plant remains and other datable material with minimal 14C reservoir effects (
• Quade, J., English, N. B., Betancourt, J. L., Dean, J. S., & Quade, J. -. (2001). Strontium isotopes reveal distant sources of architectural timber in Chaco Canyon, New Mexico. Proceedings of the National Academy of Sciences of the United States of America, 98(21).
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  Between A.D. 900 and 1150, more than 200,000 conifer trees were used to build the prehistoric great houses of Chaco Canyon, New Mexico, in what is now a treeless landscape. More than one-fifth of these timbers were spruce (Picea) or fir (Abies) that were hand-carried from isolated mountaintops 75-100 km away. Because strontium from local dust, water, and underlying bedrock is incorporated by trees, specific logging sites can be identified by comparing (87)Sr/(86)Sr ratios in construction beams from different ruins and building periods to ratios in living trees from the surrounding mountains. (87)Sr/(86)Sr ratios show that the beams came from both the Chuska and San Mateo (Mount Taylor) mountains, but not from the San Pedro Mountains, which are equally close. Incorporation of logs from two sources in the same room, great house, and year suggest stockpiling and intercommunity collaboration at Chaco Canyon. The use of trees from both the Chuska and San Mateo mountains, but not from the San Pedro Mountains, as early as A.D. 974 suggests that selection of timber sources was driven more by regional socioeconomic ties than by a simple model of resource depletion with distance and time.
• Betancourt, J. L., Latorre, C., Rech, J. A., Quade, J., & Rylander, K. A. (2000). A 22,000-year record of monsoonal precipitation from northern chile's atacama desert. Science, 289(5484), 1542-1546.
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  Abstract: Fossil rodent middens and wetland deposits from the central Atacama Desert (22°to 24°S) indicate increasing summer precipitation, grass cover, and groundwater levels from 16.2 to 10.5 calendar kiloyears before present (ky B.P.). Higher elevation shrubs and summer-flowering grasses expanded downslope across what is now the edge of Absolute Desert, a broad expanse now largely devoid of rainfall and vegetation. Paradoxically, this pluvial period coincided with the summer insolation minimum and reduced adiabatic heating over the central Andes. Summer precipitation over the central Andes and central Atacama may depend on remote teleconnections between seasonal insolation forcing in both hemispheres, the Asian monsoon, and Pacific sea surface temperature gradients. A less pronounced episode of higher groundwater levels in the central Atacama from 8 to 3 ky B.P. conflicts with an extreme lowstand of Lake Titicaca, indicating either different climatic forcing or different response times and sensitivities to climatic change.
• Broughton, J. M., Madsen, D. B., & Quade, J. (2000). Fish remains from Homestead Cave and lake levels of the past 13,000 years in the Bonneville basin. Quaternary Research, 53(3), 392-401.
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  Abstract: A late Quaternary ichthyofauna from Homestead Cave, Utah, provides a new source of information on lake history in the Bonneville basin. The fish, represented by 11 freshwater species, were accumulated between ~11,200 and ~1000 14C yr B.P. by scavenging owls. The 87Sr/86Sr ratio of Lake Bonneville varied with its elevation; 87Sr/86Sr values of fish from the lowest stratum of the cave suggest they grew in a lake near the terminal Pleistocene Gilbert shoreline. In the lowest deposits, a decrease in fish size and an increase in species tolerant of higher salinities or temperatures suggest multiple die-offs associated with declining lake levels. An initial, catastrophic, post-Provo die-off occurred at 11,300-11,200 14C yr B.P. and was followed by at least one rebound or recolonization of fish populations, but fish were gone from Lake Bonneville sometime before ~10,400 14C yr B.P. This evidence is inconsistent with previous inferences of a near desiccation of Lake Bonneville between 13,000 and 12,000 14C yr B.P. Peaks in Gila atraria frequencies in the upper strata suggest the Great Salt Lake had highstands at ~3400 and ~1000 14C yr B.P. (C) 2000 University of Washington.
• Chesley, J. T., Quade, J., & Ruiz, J. (2000). The Os and Sr isotopic record of Himalayan paleorivers: Himalayan tectonics and influence on ocean chemistry. Earth and Planetary Science Letters, 179(1), 115-124.
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  Abstract: Weathering products in Himalayan paleosols provide a unique archive of changes in 187Os/188Os and 87Sr/86Sr records of Himalayan rivers in the Neogene and can provide important constraints on the potential role of Himalayan weathering in controlling seawater isotopic compositions. Covariation in the Sr and Os isotopic records of the paleosols from the Indus and Ganges river systems indicates that these elements are derived from the same source terranes. The Os isotopic ratios from the Indus paleosols are less radiogenic than that of the paleo-oceans until ~ 5 Ma, whereas Os in the Ganges system paleosols is significantly more radiogenic than seawater ratios throughout the last ~ 20 Myr. Os isotopic ratios in the paleosols have increased by over 100% over the last 11 Myr in both the Indus and Ganges river systems. Variations in both the Os and Sr records of paleosols from the Ganges river system can be explained utilizing the tectonic history of the Central Himalayas. The paleosol record provides important new constraints on the potential role of Himalayan weathering in controlling seawater Sr and Os. If the Himalayan rivers systems are responsible for the observed changes in the marine Sr and Os records, then large changes in the fluxes of both these elements must be invoked to accommodate the paleosol record. Future models of marine isotopic variation need to account for potentially large and rapid changes in the riverine isotopic ratios over time. (C) 2000 Published by Elsevier Science B.V. All rights reserved.
• DeCelles, P. G., Gehrels, G. E., Quade, J., LaReau, B., & Spurlin, M. (2000). Tectonic implications of U-Pb zircon ages of the Himalayan orogenic belt in Nepal. Science, 288(5465), 497-499.
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  Abstract: Metasedimentary rocks of the Greater Himalaya are traditionally viewed as Indian shield basement that has been thrust southward onto Lesser Himalayan sedimentary rocks during the Cenozoic collision of India and Eurasia. Ages determined from radioactive decay of uranium to lead in zircon grains from Nepal suggest that Greater Himalayan protoliths were shed from the northern end of the East African orogen during the late Proterozoic pan- African orogenic event. These rocks were accreted onto northern Gondwana and intruded by crustal melts during Cambrian-Ordovician time. Our data suggest that the Main Central thrust may have a large amount of pre-Tertiary displacement, that structural restorations placing Greater Himalayan rocks below Lesser Himalayan rocks at the onset of Cenozoic orogenesis are flawed, and that some metamorphism of Greater Himalayan rocks may have occurred during early Paleozoic time.
• English, N. B., Quade, J., DeCelles, P. G., & Garzione, C. N. (2000). Geologic control of Sr and major element chemistry in Himalayan Rivers, Nepal. Geochimica et Cosmochimica Acta, 64(15), 2549-2566.
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  Abstract: Our study of the Seti River in far western Nepal shows that the solute chemistry of the river and its tributaries is strongly controlled by geology. The Seti flows through four distinct terranes, starting with the Tethyan sedimentary series (TSS) and Greater Himalayan series (GHS). TSS/GHS waters display 87Sr/86Sr ratios of 70% of total dissolved solids to the Seti River. Sr/Ca ratios of river waters provide a minimum estimate of the %-carbonate weathering contribution to Sr, due to partitioning of Sr and Ca during incongruent dissolution and reprecipitation of calcite. Overall, we attribute high 87Sr/86Sr ratios in the Seti River and its tributaries to the weathering of metacarbonates (especially dolostones in the upper Nawakhot Group) which have exchanged Sr with silicates during metamorphism. Our modeling of Sr fluxes in the Seti River indicates that the TSS/GHS accounts for 36-39% of the Sr, the LHS for 40-53%, and 8-23% for the DTS. Prior to exposure of LHS rocks at ~ 12 Ma, TSS and GHS carbonates with low 87Sr/86Sr ratios dominated Himalayan rivers. We attribute the elevated 87Sr/86Sr ratios of Himalayan paleorivers during the late Miocene and Pliocene to exposure and weathering of LHS metacarbonates. Copyright (C) 2000 Elsevier Science Ltd.
• Garzione, C. N., Dettman, D. L., Quade, J., Celles, P. D., & Butler, R. F. (2000). High times on the Tibetan Plateau: Paleoelevation of the Thakkhola graben, Nepal. Geology, 28(4), 339-342.
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  Abstract: East-west extension in the Tibetan Plateau is generally assumed to have resulted from gravitational collapse following thickening and uplift. On the basis of this assumption, several studies have dated east-west extensional structures to determine when the plateau attained its current high elevation. However, independent estimates of elevation are needed to determine whether extension occurred before, during, or after the plateau achieved its current elevation. Because the isotopic composition of meteoric water decreases with increasing elevation, significant change in local elevation throughout the Thakkhola graben depositional history should be recorded by change in δ18O values of fluvial and lacustrine carbonates. The δ18O values of -16‰ to -23‰ of Thakkhola graben carbonates reflect meteoric water values similar to modern values and suggest that the southern Tibetan Plateau attained its current elevation prior to east-west extension. Initiation of Thakkhola graben extension is constrained between 10 and 11 Ma, based on magnetostratigraphy of the older Tetang Formation. The δ13C values of soil carbonates suggest an age younger than 8 Ma for the base of the Thakkhola Formation.
• Garzione, C. N., Quade, J., DeCelles, P. G., & English, N. B. (2000). Predicting paleoelevation of Tibet and the Himalaya from δ¹⁸O vs. altitude gradients in meteoric water across the Nepal Himalaya. Earth and Planetary Science Letters, 183(1-2), 215-229.
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  Abstract: The δ18O value of meteoric water varies with elevation, providing a means to reconstruct paleoelevation if the δ18O values of paleowater are known. In this study, we determined the δ18O values of water (δ18O(mw)) from small tributaries along the Seti River and Kali Gandaki in the Nepal Himalaya. We found that δ18O(mw) values decrease with increasing altitude for both transects. δ18O(mw) vs. altitude along the Kali Gandaki in west-central Nepal fit a second order polynomial curve, consistent with increasing depletion of 18O with increasing elevation, as predicted by a Rayleigh-type fractionation process. This modern δ18O(mw) vs. altitude relationship can be used to constrain paleoelevation from the δ18O values of Miocene-Pliocene carbonate (δ18O(c)) deposited in the Thakkhola graben in the southern Tibetan Plateau. Paleoelevations of 3800±480 m to 5900±350 are predicted for the older Tetang Formation and 4500±430 m to 6300±330 m for the younger Thakkhola Formation. These paleoelevation estimates suggest that by ~ 11 Ma the southern Tibetan Plateau was at a similar elevation to modern. (C) 2000 Elsevier Science B.V. All rights reserved.
• Hoorn, C., Ohja, T., & Quade, J. (2000). Palynological evidence for vegetation development and climatic change in the Sub-Himalayan Zone (Neogene, Central Nepal). Palaeogeography, Palaeoclimatology, Palaeoecology, 163(3-4), 133-161.
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  Abstract: A palynological study on Miocene-Pleistocene sediments exposed at Surai Khola in central Nepal yields new information on vegetation and climate change over the last ~11.5 Ma. Our results show that during the late Middle Miocene to early Late Miocene (~11.5- ~8 Ma, Lower Siwalik) the Himalayan foothills and the Gangetic floodplain of Nepal were mainly forested with subtropical to temperate broad-leafed (b.l.) taxa (e.g. Quercus, Lithocarpus/Castanopsis, Alnus), and tropical forest taxa respectively. Grasses were present at the time but were not abundant. Between the early to late Late Miocene (~8-~6.5 Ma; lower Middle Siwalik) grassland replaced subtropical and temperate b.l. forest. This change may be related to disturbance of the vegetation on the slopes due to uplift, perhaps enhanced by intensification of the monsoon. Between late Late Miocene to Pliocene/Early Pleistocene? (~6.5< 2 Ma; Middle-Upper Siwalik) the grassland vegetation became well established and the influence of the subtropical climax vegetation is minor, with some occasional revivals. An increase in peak discharge in the fluvial system (also related to monsoonal intensification?) is recognized by an increase of the aquatic taxon Potamogeton and better preservation of all specimens. Enhanced seasonal flooding in the system during the Pliocene (~5.5-~3.5 Ma; top Middle Siwalik) may have produced local lacustrine conditions on the overbanks, evidenced by an abundance of algae (Spirogyra) and pteridophytes in the pollen assemblages. Evidence of climatic cooling between ~6.5-~5 Ma ago is indicated by the onset of steppe taxa, decrease of tropical forest taxa and disappearance of certain Dipterocarpaceae. Pollen assemblages from the Surai Khola section suggest complex vegetation changes, of which the shift to C4 grass dominance was only one. Global climatic cooling, the intensification of the monsoon, and the Late Miocene uplift may all have contributed to the phytogeography in the Sub-Himalayan Zone. (C) 2000 Elsevier Science B.V.
• Naiman, Z., Quade, J., & Patchett, P. (2000). Isotopic evidence for eolian recycling of pedogenic carbonate and variations in carbonate dust sources throughout the southwest United States. Geochimica et Cosmochimica Acta, 64(18), 3099-3109.
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  Abstract: Using isotopic ratios of Sr, C and O, we trace calcium carbonate through surface systems across a wide region of semi-arid terrain in Arizona, southwestern USA, in order to evaluate the contribution of cations from silicate weathering to soil carbonate. We present 87Sr/86Sr ratios of soil carbonate, parent rock, dry river course silts, floodplain, playa, dust and rain samples, as well as δ18O and δ13C values of selected samples. Results show that both parent rock and dust are important sources of cations for soil carbonate in this inland setting where bedrock is dominated by silicate lithologies. Dust in southeast Arizona has higher 87Sr/86Sr ratios (0.7100-0.7123) than Phanerozoic sea water (0.7070-0.7096). These high ratios derive ultimately from silicate rocks. Our δ18O and δ13C data show clearly that the dominant source of carbonate dust is eroded older soil carbonate, not bedrock limestone. Because dust contributes significantly to newly-forming soil carbonate, some products of silicate weathering may reside in soil carbonate two or more times before being removed from the region, and this recycling retards the rate at which the products of silicate weathering enter the sedimentary system. Comparison of the 87Sr/86Sr ratios of carbonate dust from southeast Arizona with those from surrounding regions shows that dust 87Sr/86Sr ratios, and by inference carbonate dust sources, vary on a scale of 200-300 km in the southwest United States. Copyright (C) 2000 Elsevier Science Ltd.
• Ojha, T. P., Butler, R. F., Quade, J., DeCelles, P. G., Richards, D., & Upreti, B. N. (2000). Magnetic polarity stratigraphy of the Neogene Siwalik Group at Khutia Khola, far western Nepal. Bulletin of the Geological Society of America, 112(3), 424-434.
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  Abstract: The middle Miocene-Pliocene Siwalik Group was deposited in the Himalayan foreland basin in response to uplift and erosion in the Himalayan fold-thrust belt. Results of thermal demagnetization experiments on samples from the Siwalik Group in central and western Nepal demonstrate that laminated siltstones yield paleomagnetic data useful for tectonic and magnetostratigraphic studies. Sandstones and paleosols of the Siwalik Group, however, generally display highly erratic paleomagnetic behavior during thermal demagnetization. On the basis of these observations, siltstones from a well-exposed, 2423-m-thick section of the Siwalik Group in Khutia Khola, far western Nepal, were sampled for magnetic polarity stratigraphy. The Siwalik Group is composed of informal lower, middle, and upper members. Correlation of the resulting polarity stratigraphy with the geomagnetic polarity timescale indicates that the exposed section spans 13.30 to 7.65 Ma. The lower-middle Siwalik boundary occurs at 11.05 Ma, near the beginning of chron C5n. The rate of sediment accumulation increases upsection, similar to rate changes previously observed in the Pakistan Siwalik Group, and probably in response to increasing proximity of the Himalayan thrust belt. In the Khutia Khola section, a discordant declination indicates that this region has rotated about a vertical axis 16.6° counterclockwise with respect to the Indian subcontinent. Measurements of δ13C in paleosol carbonate indicate the predominance of C3 plants until 7.65 Ma, and the clear presence of C4 plants higher in the undated portion of the section.
• Quade, J. A., & Roe, L. J. (1999). The stable-isotope composition of early ground-water cements from sandstone in paleoecological reconstruction. Journal of Sedimentary Research, 69(3), 667-674.
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  Abstract: The carbon-isotope composition of soil carbonates in paleosols records the global expansion of C 4 biomass in the late Miocene. However, soil carbonate is not present in many geological sections, or if present, is often difficult to distinguish from other carbonate cements. Here we report on the δ 13C values of sparry, early groundwater cements in sandstones from the Siwalik Group in Pakistan that record, like the soil carbonates from the same sections, the dramatic late Miocene expansion of C 4 vegetation. The early cements are confined to densely cemented nodules in the sandstones, but can also be found reworked as nodules into adjacent paleo-channels, demonstrating their formation shortly after burial. The early cements are isotopically distinct from later, higher-temperature calcite cements. Our results demonstrate that some early ground-water cements can be used in a manner similar to soil carbonates to reconstruct vegetation and perhaps pC0 2 changes in the past. Copyright ©1999, SEPM (Society for Sedimentary Geology).
• Bouchard, D. P., Kaufman, D. S., Hochberg, A., & Quade, J. (1998). Quaternary history of the Thatcher Basin, Idaho, reconstructed from the ⁸⁷Sr/⁸⁶Sr and amino acid composition of lacustrine fossils: Implications for the diversion of the Bear River into the Bonneville Basin. Palaeogeography, Palaeoclimatology, Palaeoecology, 141(1-2), 95-114.
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  Abstract: The Bear River, the largest river in the Great Basin, was diverted from its former course to the Pacific Ocean into the Bonneville Basin by Quaternary basalt flows that form the northern rim of Thatcher Basin, Idaho. Reconstructing the history of the river's diversion is important to understanding the aquatic biogeography of the Bonneville Basin and the climatological implications of its lake-level fluctuations. This study employs strontium (Sr) isotopes in lacustrine mollusc fossils as a tracer of Bear River water that entered Lake Thatcher, a small lake into which the redirected river flowed en route to the Bonneville Basin. The 87Sr/86Sr composition and Sr concentration of modem rivers were measured to construct a mixing model for Lake Thatcher water. The low 87Sr/86Sr ratio of the Bear River and its large discharge assures that the presence or absence of its flow into Lake Thatcher is readily detectable. Temporal control is provided by amino acid geochronology on lacustrine molluscs and calibrated using tephrochronology and 14C dating. 87Sr/86Sr ratios of six fossil molluscs from the oldest exposed Quaternary deposits in Thatcher Basin (lower Main Canyon Formation, MCF) indicate that, during the early Quaternary (>620 ka), the basin was occupied by shallow, locally fed lakes. A single shell from the base of the upper MCF, together with sedimentological evidence, suggests that the Bear River may have been diverted into Thatcher Basin by ~140 ka. 87Sr/86Sr ratios in eight younger shells from the upper MCF indicate that the Bear River was not present in the basin between ~140 and ~80 ka. By 50 ± 10 ka, however, it was tributary to Lake Thatcher. A simple hydrologic model shows that, if not for drainage through Oneida Narrows, Thatcher Basin would fill to its highest shoreline under present climate, even without the input of the Bear River. It is not clear when the lava flows that form the northern divide had been built high enough to allow Lake Thatcher to spill over its former southern divide into the Bonneville Basin, but it was probably by ~100 ka. At that time, headward incision of Oneida Narrows was underway. By ~20 ka, the incision of the narrows was complete and Lake Bonneville had backed up into Thatcher Basin.
• Cerling, T. E., Harris, J. M., MacFadden, B. J., Quade, J., Leakey, M. G., Eisenmann, V., & Ehleringer, J. R. (1998). Miocene/pliocene shift: One step or several? [2]. Nature, 393(6681), 126-127.
• Connin, S. L., Betancourt, J., & Quade, J. (1998). Late Pleistocene C₄ plant dominance and summer rainfall in the southwestern United States from isotopic study of herbivore teeth. Quaternary Research, 50(2), 179-193.
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  Abstract: Patterns of climate and C4 plant abundance in the southwestern United States during the last glaciation were evaluated from isotopic study of herbivore tooth enamel. Enamel δ13C values revealed a substantial eastward increase in C4 plant consumption for Mammuthus spp., Bison spp., Equus spp., and Camelops spp. The δ13C values were greatest in Bison spp. (-6.9 to + 1.7‰) and Mammuthus spp. (-9.0 to +0.3‰), and in some locales indicated C4-dominated grazing. The δ13C values of Antilocaprids were lowest among taxa (-12.5 to -7.9‰) and indicated C3 feeding at all sites. On the basis of modern correlations between climate and C4 grass abundance, the enamel data imply significant summer rain in parts of southern Arizona and New Mexico throughout the last glaciation. Enamel δ18O values range from +19.0 to +31.0‰ and generally increase to the east. This pattern could point to a tropical or subtropical source of summer rainfall. At a synoptic scale, the isotope data indicate that interactions of seasonal moisture, temperature, and lowered atmospheric pCO2 determined glacial-age C4 abundance patterns.
• DeCelles, P. G., Gehrels, G. E., Quade, J., & Ojha, T. P. (1998). Eocene-early Miocene foreland basin development and the history of Himalayan thrusting, western and central Nepal. Tectonics, 17(5), 741-765.
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  Abstract: Sedimentologic, petrographic, and U-Pb detrital zircon ages from middle Eocene through early Miocene sedimentary rocks in the Lesser Himalayan zone of western and central Nepal indicate that a peripheral foreland basin system had developed in the eastern Himalayan collision zone by middle Eocene time. The shallow-marine, Eocene Bhainskati Formation accumulated in a back-bulge depozone between a southward migrating forebulge and the Indian craton. Migration of the forebulge through this region during Eocene-Oligocene time produced a regional unconformity that spans ~15-20 Myr. By early Miocene time, the forebulge unconformity was onlapped by the distal fringes of the southward migrating foredeep depozone, represented by fluvial deposits of the Dumri Formation. Continued southward migration of the foredeep during the Neogene accommodated the fluvial Siwalik Group. Light mineral provenance data and U-Pb detrital zircon ages suggest that the Bhainskati was derived partly from Tethyan sedimentary rocks of the Tibetan Himalayan zone during initial growth of the Himalayan fold-thrust belt. The Dumri was derived from metasedimentary and crystalline rocks of the Greater Himalayan zone during emplacement of the Main Central thrust and contemporaneous tectonic unroofing by normal faulting along the South Tibetan detachment system. The Lesser Himalayan crystalline thrust sheets were emplaced soon after deposition of the Dumri Formation. ~15-10 Ma. Paleocurrent and lithofacies data from the Dumri Formation indicate deposition by west-southwestward flowing rivers that drained into the Indus portion of the Himalayan foreland basin system during the early Miocene. Thick channel sandstones in the lower Dumri may represent the early Miocene counterpart of the modern Ganges River. Eastward diversion of the Ganges drainage system to near its present location had occurred by ~15 Ma, as the high-standing Aravalli Range on the northern Indian shield approached the front of the fold-thrust belt. Assuming reasonable values for the flexural rigidity of Indian lithosphere, the time span of the forebulge unconformity yields a velocity of ~14-33 mm/yr for the southward migration of the fold-thrust belt relative to India. This range of values is consistent with Neogene and present-day estimates and suggests that only one third to one half of India-Eurasia convergence has been accommodated by shortening in the Himalayan fold-thrust belt since the onset of collision.
• DeCelles, P. G., Gehrels, G. E., Quade, J., Ojha, T. P., Kapp, P. A., & Upreti, B. N. (1998). Neogene foreland basin deposits, erosional unroofing, and the kinematic history of the Himalayan fold-thrust belt, western Nepal. Bulletin of the Geological Society of America, 110(1), 2-21.
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  Abstract: Sedimentological and provenance data from the lower Miocene-Pliocene Dumri Formation and Siwalik Group in western Nepal provide new information about the timing of thrust faulting and the links between erosional unroofing of the Himalaya and the Cenozoic 87Sr/86Sr record of the ocean. In western Nepal, the Dumri Formation is an ∼750-1300-m-thick fluvial sandstone and overbank mudstone unit. The Siwalik Group is >4200 m thick and consists of a lower member (>850 m) of 2-12-m-thick fluvial channel sandstones and oxidized calcareous paleosols, a middle member (>2400 m) of very thick (>20 m) channel sandstones and mainly organic-rich Histosols, and an upper member (>1000 m) composed of gravelly braided river deposits. Paleocurrent data indicate that middle Miocene-Pliocene rivers in western Nepal flowed southward, transverse to the thrust belt, throughout deposition of the Siwalik Group. No evidence was found for an axial fluvial trunk system (i.e., the paleo-Ganges River) in Siwalik Group sandstones. A major increase in fluvial channel size is recorded by the transition from lower to middle Siwalik members at ∼10.8 Ma, probably in response to an increase in seasonal discharge. Modal petrographic data from sandstones in the Dumri Formation and the Siwalik Group manifest an upsection enrichment in potassium feldspar, carbonate lithic fragments, and high-grade metamorphic minerals. Modal petrographic analyses of modern river sands provide some control on potential source terranes for the Miocene-Pliocene sandstones. The Dumri Formation was most likely derived from erosion of sedimentary and low-grade metasedimentary rocks in the Tibetan (Tethyan) Himalayan zone during early Miocene emplacement of the Main Central thrust. The presence in Dumri sandstones of plagioclase grains suggests exposure of crystalline rocks of the Greater Himalayan zone, perhaps in response to tectonic unroofing by extensional detachment faults of the South Tibetan detachment system. During deposition of the lower Siwalik Group (∼15-11 Ma), emplacement of the Dadeldhura thrust sheet (one of the synformal crystalline thrust sheets of the southern Himalaya) on top of the Dumri Formation supplied abundant metasedimentary lithic fragments to the foreland basin. A steady supply of plagioclase grains and high-grade minerals was maintained by deeper erosion into the Main Central thrust sheet. From ∼11 Ma to the present, K-feldspar sand increased steadily, suggesting that granitic source rocks became widely exposed during deposition of the upper part of the lower Siwalik Group. This provenance change was caused by erosion of passively uplifted granites and granitic orthogneisses in the Dadeldhura thrust sheet above a large duplex in the Lesser Himalayan rocks. Since the onset of deposition of the conglomeratic upper Siwalik Group (∼4-5 Ma), fault slip in this duplex has been fed updip and southward into the Main Boundary and Main Frontal thrust systems. We obtained 113 U-Pb ages on detrital zircons from modern rivers and Siwalik Group sandstones that cluster at 460-530 Ma, -850-1200 Ma, ∼1.8-2.0 Ga, and ∼2.5 Ga. An abundance of Cambrian-Ordovician grains in the Siwalik Group suggests sources of Siwalik detritus in the granites of the Dadeldhura thrust sheet and possibly the Greater Himalayan orthogneisses. The older ages are consistent with sources in the Greater and Lesser Himalayan zones. An overall upsection increase in zircons older than 1.7 Ga suggests increasing aerial exposure of Lesser Himalayan rocks. None of the detrital zircons (even in the modern river samples) yielded a Cenozoic age that might suggest derivation from the Cenozoic Greater Himalayan leucogranites, but this may be attributable to the inheritance problems that characterize the U-Pb geochronology of the leucogranites. When compared with recent studies of the 87Sr/86Sr composition of paleosol carbonate nodules and detrital carbonate in paleosols from the Siwalik Group, the provenance data suggest that erosion and weathering of metamorphosed carbonate rocks in the Lesser Himalayan zone and Cambrian-Ordovician granitic rocks of the crystalline thrust sheets in central and eastern Nepal may have played a significant role in elevating the 87Sr/86Sr ratio of middle Miocene synorogenic sediments in the Indo-Gangetic foreland basin and the Bengal fan, as well as global seawater.
• McFadden, L. D., McDonald, E. V., Wells, S. G., Anderson, K., Quade, J., & Forman, S. L. (1998). The vesicular layer and carbonate collars of desert soils and pavements: formation, age and relation to climate change. Geomorphology, 24(2-3), 101-145.
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  Abstract: The vesicular, fine-grained A horizon (Av) is the widespread, ubiquitous surficial horizon of desert soils in diverse landforms and parent materials of varying ages. Now known to form mostly through accumulation of eolian dust, recent studies show that dust accumulation and concomitant soil development are genetically linked to stone pavement formation. Changes in the magnitude of eolian activity and effective leaching related to Quaternary climatic changes are also hypothesized to have influenced the evolution of the Av horizon. Numerical modeling, geochronologic, and field/laboratory studies elucidate the nature of pedogenic processes controlling compositional evolution of Av, how the changing Av horizon increasingly influences soil infiltration and carbonate translocation and accumulation, and the control that clasts of the evolving pavement exert on pedogenic processes. Results of a model that determines soil bulk chemical composition based on mixing of estimated proportions of externally derived (eolian) material and parent materials imply that the evolution of the soil bulk composition is strongly influenced by Av horizon formation. The early development of a weakly to moderately developed Av horizon directly over gravelly parent material in late and middle Holocene soils moderately influences soil infiltration, but significant leaching of very soluble materials and some carbonate in dust are permitted. In older, Pleistocene soils, however, the texturally more mature Av and underlying, cumulic nongravelly horizons more strongly limit the rate and depth of leaching, and soil bulk composition therefore more closely approximates a simple mixture of dust and parent material. Other aspects of Av horizon development and its relations to the pavement are evaluated through studies of pavement clasts with coatings of soil carbonate, referred to as carbonate collars. Development of a numberical model that integrates soil hydrology, a CO2 production-diffusion model, calcite kinetics and thermodynamic considerations, composition and thermal characteristics of pavement clasts and the textural and structural properties of the surface horizon provides the basis for testing a hypothesis of collar formation. Model results, combined with results of δ13C and δ18O analyses of collar carbonate, demonstrate how precipitation of calcite on pavement clasts and within the Av is favored at a depth much shallower than that indicated by the classic carbonate depth-climate relationship of previous workers.
• Quade, J., Forester, R. M., Pratt, W. L., & Carter, C. (1998). Black Mats, Spring-Fed Streams, and Late-Glacial-Age Recharge in the Southern Great Basin. Quaternary Research, 49(2), 129-148.
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  Abstract: Black mats are prominent features of the late Pleistocene and Holocene stratigraphic record in the southern Great Basin. Faunal, geochemical, and sedimentological evidence shows that the black mats formed in several microenvironments related to spring discharge, ranging from wet meadows to shallow ponds. Small land snails such as Gastrocopta tappaniana and Vertigo berryi are the most common mollusk taxa present. Semiaquatic and aquatic taxa are less abundant and include Catinellids, Fossaria parva, Gyraulus parvus, and others living today in and around perennial seeps and ponds. The ostracodes Cypridopsis okeechobi and Scottia tumida, typical of seeps and low-discharge springs today, as well as other taxa typical of springs and wetlands, are common in the black mats. Several new species that lived in the saturated subsurface also are present, but lacustrine ostracodes are absent. The δ13C values of organic matter in the black mats range from -12 to -26‰, reflecting contributions of tissue from both C3 (sedges, most shrubs and trees) and C4 (saltbush, saltgrass) plants. Carbon-14 dates on the humate fraction of 55 black mats fall between 11,800 to 6300 and 2300 14C yr B.P. to modern. The total absence of mats in our sample between 6300 and 2300 14C yr B.P. likely reflects increased aridity associated with the mid-Holocene Altithermal. The oldest black mats date to 11,800-11,600 14C yr B.P., and the peak in the 14C black mat distribution falls at ∼10,000 14C yr B.P. As the formation of black mats is spring related, their abundance reflects refilling of valley aquifers starting no later than 11,800 and peaking after 11,000 14C yrB.P. Reactivation of spring-fed channels shortly before 11,200 14C yr B.P. is also apparent in the stratigraphic records from the Las Vegas and Pahrump Valleys. This age distribution suggests that black mats and related spring-fed channels in part may have formed in response to Younger Dryas (YD)-age recharge in the region. However, the inception of black mat formation precedes that of the YD by at least 400 14C yr, and hydrological change is gradual, not rapid. © 1998 University of Washington.
• Stiner, M. C., Achyuthan, H., Arsebük, G., Howell, F. C., Josephson, S. C., Juell, K. E., Pigati, J., & Quade, J. (1998). Reconstructing cave bear paleoecology from skeletons: A cross-disciplinary study of middle Pleistocene bears from Yarimburgaz Cave, Turkey. Paleobiology, 24(1), 74-98.
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  Abstract: Cave bears, an extinct subgenus (Spelearctos) of Ursus, were versatile enough to inhabit large areas of the northern hemisphere during the middle and late Pleistocene, yet they had evolved a specialized dentition that emphasized grinding functions, implying a heavy dietary reliance on tough, fibrous foods (i.e., plants). Isotope studies have yielded conflicting results on cave bear diet, however, often without consideration of the provenance of the samples or the possible contradictions that taphonomic and morphologic evidence might pose to dietary interpretations. It is likely that cave bear habits varied somewhat in response to environmental circumstance, and the limits on their abilities to do so remain unknown. If the larger goal of paleontological inquiry is to reconstruct the adaptations of cave bear species, then variation and commonalities among populations must be tracked closely, and the disparate lines of evidence currently available examined together on a case by case basis. Clearly, no single analytical technique can achieve this. By way of example we present the results of a cross-disciplinary collaboration that combines osteometric, isotopic, and taphonomic approaches to studying the paleoecology of a bear assemblage from Yarimburgaz Cave in northwest Turkey. Reference information on the linkages between diet, hibernation, and population structure in modern bears provides test implications for the investigation. Osteometric techniques demonstrate the presence of two coextant middle Pleistocene bear species in the sample - Ursus (Spelearctos) deningeri, a form of cave bear, and U. arctos or brown bear - the former abundant in the sample, the latter rare. An attritional mortality pattern for the bears and the condition of their bones show that most or all of the animals died in the cave from nonviolent causes in the context of hibernation. The study also elucidates several characteristics of the cave bear population in this region. Osteometric techniques show that the adult sex ratio of the cave bears is only slightly skewed toward females. This pattern lies near one extreme of the full range of possible outcomes in modern bear species and can only reflect a strong dietary dependence on seasonally available plants and invertebrates, showing that hibernation was a crucial overwintering strategy for both sexes; the results specifically contradict the possibility of regular, heavy emphasis on large game (hunted or scavenged) as a winter food source. The nature of wear and breakage to the adult cave bear teeth indicates that food frequently was obtained from cryptic sources, requiring digging and prying, and that extensive mastication was necessary, leading to complete obliteration of some cheek tooth crowns in old individuals. The patterns of tooth damage during life corroborate the dietary implications of the adult sex ratio and also argue for a diet rich in tough, abrasive materials such as nuts, tubers, and associated grit. The carbon and oxygen isotopic compositions of cave and brown bear tooth enamel from the site are virtually identical, and there is no evidence of a strong marine signal in either species, despite the cave's proximity to a modern estuary of the Sea of Marmara; nitrogen isotope ratios could not be examined because of poor protein preservation. The isotope results suggest that both bear species were highly omnivorous in the region during the middle Pleistocene and obtained nearly all of their food from terrestrial and fresh-water habitats. Bone pathologies, usually originating from trauma, occur in some of the adult bears, testifying to long lifespans of some individuals in this fossil population. The Yarimburgaz cave bears also exhibit great size dimorphism between the sexes, based on weight-bearing carpal bone dimensions, with adult males attaining roughly twice the body mass of adult females.
• Brennan, R., & Quade, J. (1997). Reliable Late-Pleistocene Stratigraphic Ages and Shorter Groundwater Travel Times from ¹⁴C in Fossil Snails from the Southern Great Basin. Quaternary Research, 47(3), 329-336.
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  Abstract: Both aquatic and land snails are common in the geologic record, but their utility in dating is greatly restricted by their well-documented tendency to yield 14C dates inconsistent with true 14C ages. In this study, we examine the use of 14C ages from (1) small, previously unstudied, terrestrial snails to date hosting spring deposits and from (2) cooccuring aquatic snails to constrain ground-water travel times during the last glacial period. Our study area in the southern Great Basin encompasses Yucca Mountain, site of the proposed high-level nuclear waste repository, where information on the age and extent of past high water tables and on ground-water flow times is crucial to several licensing issues. Our results show that shells of small terrestrial snails belonging to Vallonia sp. yield 14C dates consistent with 14C ages of associated carbonized wood. These results imply that these taxa can provide reliable 14C age control on the broadly distributed deposits in which they have been described. In contrast, cooccurring aquatic snails from fossil spring deposits yield 14C ages generally greater than the control age. This is because the aquatic shells often formed in spring waters that had an initial 14C deficiency. However, the magnitude of the deficiency is much less than that observed in nearby modern springs, arguing for much higher average 14C contents in late Pleistocene groundwaters in these basins. If representative, this implies shorter groundwater travel times through aquifers in southern Nevada during late-glacial time. © 1997 University of Washington.
• Cerling, T. E., Harris, J. M., MacFadden, B. J., Leakey, M. G., Quade, J., Eisenmann, V., & Ehieringer, J. R. (1997). Global vegetation change through the Miocene/Pliocene boundary. Nature, 389(6647), 153-158.
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  Abstract: Between 8 and 6 million years ago, there was a global increase in the biomass of plants using C4 photosynthesis as indicated by changes in the carbon isotope ratios of fossil tooth enamel in Asia, Africa, North America and South America. This abrupt and widespread increase in C4 biomass may be related to a decrease in atmospheric CO2 concentrations below a threshold that favoured C3-photosynthesizing plants. The change occurred earlier at lower latitudes, as the threshold for C3 photosynthesis is higher at warmer temperatures.
• Latorre, C., Quade, J., & McIntosh, W. C. (1997). The expansion of C₄ grasses and global change in the late Miocene: Stable isotope evidence from the Americas. Earth and Planetary Science Letters, 146(1-2), 83-96.
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  Abstract: δ13C values in paleosols and fossil teeth have been used to document the expansion of C4 plants in South Asia, Africa, and North America during the late Miocene. However, the exact timing and rate of expansion of C4 vegetation is unclear outside the Old World because of a lack of high-resolution records. We present a high-resolution record from northwest Argentina in which the δ13C values of soil carbonate rise above a threshold of -8‰, suggesting the presence of C4 plants, starting at 7.3-6.7 Ma. δ13C values of fossil teeth from well dated sections in South and North America display a concomitant increase of C4 plants in the diets of large herbivores. These results show that the late Miocene expansion of C4 plants was global, but occurred at different rates in each region. While it is has been suggested that declining pCO2 levels during the late Neogene caused C4 plant expansion, climate change, such as an increase in summer-dominated rainfall regimes globally, is an alternative explanation. The δ18O soil carbonate records from South Asia, East Africa and now also northwest Argentina all show an increase of at least 3-4‰ in the late Neogene, either the result of climate change or of greater evaporation in average grassland soils.
• Quade, J., Roe, L., DeCelles, P. G., & Ojha, T. P. (1997). The late neogene ⁸⁷Sr/⁸⁶Sr record of lowland himalayan rivers. Science, 276(5320), 1828-1831.
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  Abstract: Fossil shells and paleosol carbonate from ancestral Himalayan river deposits provide a 87Sr/86Sr record of lowland Himalayan river water during the late Neogene. Reconstructed 87Sr/86Sr river values increased sharply in the late Miocene, probably marking the beginning of exhumation of high-87Sr/86Sr metalimestones, more in the central than in the western Himalayas. These results imply that the marine 87Sr/86Sr record may not be a proxy for silicate weathering or consumption of atmospheric CO2 resulting from that weathering.
• McCarthy, L., Head, L., & Quade, J. (1996). Holocene palaeoecology of the northern Flinders Ranges, South Australia, based on stick-nest rat (Leporillus spp.) middens: A preliminary overview. Palaeogeography, Palaeoclimatology, Palaeoecology, 123(1-4), 205-218.
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  Abstract: Eight stick-nest rat (Leporillus spp.) middens from three locations in the northern Flinders Ranges, South Australia provide a discontinuous palaeoecological record spanning the Holocene. Evidence from radiocarbon dates, pollen, plant macrofossils and animal macrofossils is presented. Both pollen and plant macrofossils show that in the early to mid- Holocene (c. 8.8-5.3 ka), woodlands with grassy understoreys were more widespread than present. This accords with other studies suggesting wetter conditions at this time. Samples dating to the Pleistocene Holocene transition (10.9-9 ka) are dominated by halophytes. It is not yet clear whether this is due to the continuation of Pleistocene aridity, changes in rainfall seasonality, or local influences on vegetation.
• Behrensmeyer, A. K., Willis, B. J., & Quade, J. (1995). Floodplains and paleosols of Pakistan Neogene and Wyoming Paleogene deposits: a comparative study. Palaeogeography, Palaeoclimatology, Palaeoecology, 115(1-4), 37-60.
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  Abstract: Comparative study of fossil-bearing fluvi' deposits in the Eocene Willwood Formation of northern Wyoming and the Miocene Chinji Formation of northern Pakistan indicate how tectonic and climatic processes operating at different scales controlled physical and chemical features of floodplain environments and affected preservation of the paleontological record. The architecture of Willwood Fm. floodplain deposits represents a combination of avulsion-belt sediment packages and overbank sediments that formed alluvial ridges. The architecture of the Chinji Fm. floodplain deposits was controlled by widely distributed crevasse-splay deposition and floodplain topography. Similarities in individual paleosol-bounded overbank sequences from the two formations indicates that the internal structure of such deposits can be independent of channel belt proximity to areas of aggradation. Chinji Fm. paleosols have little vertical zonation and show no consistent pattern of lateral change in relation to major channels, while overbank paleosols in the Willwood Fm, exhibit considerable soil horizon development and a pattern of increasing maturity from alluvial ridge to distal floodplain. The "pedofacies model" of Bown and Kraus (1987) based on such lateral trends in the Willwood paleosols is not applicable to the Chinji Fm. Plant and animal fossils are abundant in the Willwood overbank deposits, with vertebrate remains concentrated in paleosol A horizons. Plant remains are rare in the Chinji Fm. and vertebrate fossils occur primarily in channel fills rather than in paleosols. These differences relate to contrasting patterns of floodplain deposition and to levels of oxidation that controlled penecontemporaneous recycling of organic material, particularly in paleosols. Different large-scale climatic and tectonic controls on temperature and rainfall, water table fluctuations, and soil biota are proposed to account for the differences in organic preservation. Large and small-scale environmental processes also affected spatial and temporal resolution of the organic record, resulting in important differences in the paleoecological and evolutionary information that can be reconstructed from the two sequences. © 1995.
• Brennan, R., & Quade, J. (1995). Radiocarbon dating of fossil mollusk shells in the Yucca Mountain Region. High Level Radioactive Waste Management - Proceedings of the Annual International Conference, 182-184.
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  Abstract: Fossil mollusk shells from late Quaternary deposits in Southern Nevada were radiocarbon dated to determine the age of paleogroundwater discharge events and to establish minimum 14C ages of paleogroundwater. Shells of the terrestrial taxa Vallonia sp. and Succineidae returned 14C dates consistent with those on organic material in the same stratigraphic position. The aquatic taxa Gyraulus parvus and Gyraulus circumstratus returned the oldest dates within each unit sampled. These results show that 1) fossil Vallonia and Succineidae are useful in dating deposits in which no other radiocarbon-datable material is available, and 2) Gyraulus sp. select micro habitats with the most 14C deficient water, providing minimum ages of groundwater in the area during the last glacial period.
• Quade, J., & Cerling, T. E. (1995). Expansion of C₄ grasses in the Late Miocene of Northern Pakistan: evidence from stable isotopes in paleosols. Palaeogeography, Palaeoclimatology, Palaeoecology, 115(1-4), 91-116.
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  Abstract: Stable-isotopic, clay-mineralogic, and bulk-chemical analyses were conducted on paleosols of the Neogene Siwalik sections in northern Pakistan in order to reconstruct floodplain environments over the past ∼ 17 Ma. The stable carbon isotopic composition of soil carbonate (mean δ13C (PDB) = -10.2%) and associated organic matter (mean δ13C (PDB) = -24.1%) in paleosols representing 17- ∼ 7.3 Ma reveal that floodplain vegetation was dominated by C3 plants. At 7.3 Ma, a shift toward more positive carbon isotopic values began, signaling the gradual expansion of C4 grasses onto the floodplain. From 6 Ma to present, carbon isotopic values for paleosol carbonate (mean δ13C (PDB) = +0.6%) and organic matter (mean δ13C (PDB) = -14.4%) are uniformly enriched in 13C, indicating the presence of nearly pure C4 grassland. The scarcity of kaolinite and abundance of smectite and pedogenic carbonate in most paleosols suggest that rainfall in the region remained 1.0-1.25 m/yr or less for the entire 17 Ma of record. Paleosols in the lower portion of the section lack organic A horizons but have reddish B horizons often containing secondary iron-oxide nodules. Leaching depths of soil carbonate in these older paleosols are typically greater than those in the Plio-Pleistocene part of the section, where organic A horizons are common, and B horizons are markedly more yellow. The combined evidence suggests that the mature paleosols in the pre-7.3 Ma part of the record are dominantly calcareous Alfisols or Mollisols that once underlay nearly pure C3 vegetation, perhaps trees and shrubs, while calcareous Mollisols underlying C4 grassland dominate the upper part of the record. The carbon- and oxygen-isotopic trends in the paleosol record in Pakistan are also evident in the diet of fossil mammals, and in paleosols from Nepal, thus demonstrating that these paleoenvironmental changes in floodplain vegetation may be continent-wide. Local effects, such as the development or intensification of the Asian Monsoon driven by uplift of the Tibetan Plateau, may have led to the expansion of C4 grasses. If, however, the expansion of C4 grasses proves globally synchronous, then a larger scale cause, such as a marked decrease in ρ{variant}CO2, may be the driving mechanism. © 1995.
• Quade, J., Cater, J. M., Ojha, T. P., Adam, J., & Harrison, T. M. (1995). Late Miocene environmental change in Nepal and the northern Indian subcontinent: stable isotopic evidence from paleosols. Geological Society of America Bulletin, 107(12), 1381-1397.
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  Abstract: Carbon and oxygen isotopic analyses of Siwalik paleosols from four long Siwalik sections record major ecological changes over the past ~11 m.y. The carbon isotopic composition of both soil carbonate and organic matter shifts dramatically starting ca. 7.0 Ma, marking the displacement of largely C3 vegetation by C4 grasslands. By the beginning of the Pliocene, all the flood plains of major rivers in this region were dominated by monsoonal grasslands. A similar carbon isotopic shift has been documented in the paleosol and fossil tooth record of Pakistan, and in terrigenous organic matter from the Bengal Fan, showing that the floral shift was probably continent wide. Himalayan uplift, driving both monsoonal intensification and consumption of CO2 through weathering, may be the common cause behind major late Miocene environmental change globally. -from Authors
• Quade, J., Cerling, T. E., Andrews, P., & Alpagut, B. (1995). Paleodietary reconstruction of Miocene faunas from Paşalar, Turkey using stable carbon and oxygen isotopes of fossil tooth enamel. Journal of Human Evolution, 28(4), 373-384.
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  Abstract: Miocene-age (\ 15 Ma) deposits at Paşalar in northwest Turkey contain abundant and well-preserved dental remains from a variety of herbivores. We used the carbon and oxygen isotopic compositions of inorganic carbonate in enamel from these teeth to reconstruct the paleodiet and sources of body water, respectively, of Miocene mammals. The δ13C (PDB) values of carbonate in the enamel fall between - 13.5 and -9.0%, indicating a diet dominated by C3 plants for all mammals. Some species are distinctly different isotopically from others, likely reflecting on variation in the δ13C values of the plants being consumed. Giraffokeryx and Caprotragoides display the most depleted δ13C values, probably indicating they were feeding upon C3 plants experiencing low water stress and/or CO2 recycling, such as in a forest. Hypsodontus and Conohyus, on the other hand, consistently display the most enriched δ13C values. They were therefore consuming isotopically enriched C3 plants or a small quantity of C4 grasses. In either case, a more open habitat is indicated. The other species we measured, including Griphopithecus, yielded intermediate values. The δ18O (PDB) values of the carbonate in fossil enamel also differ substantially between some taxa, and probably show that mammals such as Giraffokeryx, like East African giraffes today, were drawing their water from sources enriched in 18O, such as from the top of a forest canopy. Copyright © 1995 Academic Press. All rights reserved.
• Quade, J., Chivas, A. R., & McCulloch, M. T. (1995). Strontium and carbon isotope tracers and the origins of soil carbonate in South Australia and Victoria. Palaeogeography, Palaeoclimatology, Palaeoecology, 113(1), 103-117.
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  Abstract: Calcium carbonate occurs in soils in association with a variety of rock types in coastal and inland South Australia and Victoria. The 87Sr 86Sr ratios of the coastal soil carbonates fall between 0.7094 and 0.7098, showing that the ocean is the principal source of calcium to nearly all soils near the coast, and that contributions from bedrock are generally small. An exception is the soil formed on the young volcano at Mt. Gambier in which the average ratio for carbonate is about 0.7070 compared to 0.7041 for the volcanic ash. The basaltic ash of the volcano is readily weathered and rich in calcium: roughly 40% of strontium and 10 to 20% of the calcium in the soil carbonate derives from the ash, and the balance from marine sources. The 87Sr 86Sr ratios from soil carbonate gradually increase inland, reaching values of 0.7152. These higher ratios reflect, at least in part, the increasing 87Sr 86Sr ratio of inland dust. In contrast, the ocean does not contribute significantly to the carbon pool of the soils we studied. The δ13C (PDB) values of soil carbonates on Kangaroo Island and the higher rainfall areas of eastern Victoria fall between -11.0 and -8.7‰, indicating that the carbonate formed in equilibrium with the C3-dominated vegetation typical of the region. In the warmer inland areas to the north such as the Eyre Peninsula, the δ13C value of soil carbonate averages -5.3‰, reflecting the higher proportion of C4 plants in the local biomass. Mixing with marine sources of carbonate cannot account for the observed carbon isotopic patterns. The flux of carbon into soils from the ocean therefore must be small compared to that derived from plant respiration and decay. © 1995.
• Quade, J., Mifflin, M. D., Pratt, W. L., McCoy, W., & Burckle, L. (1995). Fossil spring deposits in the southern great basin and their implications for changes in water-table levels near Yucca Mountain, Nevada, during quaternary time. Bulletin of the Geological Society of America, 107(2), 213-230.
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  Abstract: Fossil spring deposits are common in the southern Great Basin, and their distribution provides important constraints on the hydrologic response of the regional water table to climate change. This information is crucial, because the proposed high-level nuclear waste repository at Yucca Mountain will be located nearly 200-400 m above the modern water table. Water tables will rise in response to a future return to glacial climates, but the magnitude of the change-and the consequences for radionuclide travel times and overall repository integrity-are key uncertainties. Increased recharge during past pluvial periods in the Spring Mountains and Sheep Range caused water tables to rise and ground water to discharge over broad expanses of the Las Vegas Valley system, and in nearby Pahrump, Sandy, and Coyote Springs Valleys. In contrast, other valleys in the region contain only small from local damming of ground water by faults that cut valley alluvium. The change in water-table levels since the last full glacial period varies between and within valleys, from as little as 10 m in several areas to 95 m in the Coyote Springs Valley. At Yucca Mountain, the water table has probably changed by ≤115 m in response to climate change. The spring deposits and the mollusk faunas found with them, often misinterpreted as lacustrine in origin, share many essential features with active spring systems in northeast Nevada. Deposits associated with discharge mainly consist of pale brown silt and sand that is entrapped by dense stands of phreatophytes covering valley bottoms when water tables are high. The record in subbasins of the Las Vegas Valley system is dominated by late Wisconsin-age sediments, although pond sediments and alluvium belonging to at least one older (pre-Wisconsin?) pluvial period are also locally exposed.
• Bird, M. I., Quade, J., Chivas, A. R., Fifield, L. K., Allan, G. L., & Head, M. J. (1994). The carbon isotope composition of organic matter occluded in iron nodules. Chemical Geology, 114(3-4), 269-279.
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  Abstract: This study presents δ13C and 14C results for soil organic carbon and carbon occluded by iron nodules from a Quaternary soil profile developed on basalt in western Victoria, Australia. The results suggest that the δ13C-value of organic matter in the iron nodules is directly inherited from the surrounding soil profile without isotopic fractionation, and that therefore the δ13C-value of organic matter occluded by the iron nodules can be related to the vegetation present during nodule formation. However, 14C results suggest that iron nodules are not closed systems with respect to organic carbon, and that even chemically resistant immobile particulate carbon (of probable microbial origin) has been added to the nodule carbon pool since formation. Nevertheless, the turnover time for chemically resistant particulate carbon in the iron nodules is at least three times that for the same fraction in the surrounding soil, making iron nodules useful repositories of palaeoenvironmental information, particularly where they have been removed from the active surface soil layer by burial. © 1994.
• Cerling, T. E., Quade, J., Wang, Y., Morgan, M. E., Kingston, J. D., & Marino, B. D. (1994). Expansion and emergence of C4 plants [10]. Nature, 371(6493), 112-113.
• Quade, J., Solounias, N., & Cerling, T. E. (1994). Stable isotopic evidence from paleosol carbonates and fossil teeth in Greece for forest or woodlands over the past 11 Ma. Palaeogeography, Palaeoclimatology, Palaeoecology, 108(1-2), 41-53.
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  Abstract: Mio-Pliocene fluvial rocks containing buried paleosols are common in Greece and Turkey. We used the carbon and oxygen isotopic composition of pedogenic carbonates associated with these paleosols to estimate the proportion of C3 (trees, shrubs, and cool growing season grasses) and C4 (warm growing season grasses) plants once present on the landscape. Evidence from the paleosols in well-known fossil-bearing formations in the lower Axios Valley in Macedonia, and from Samos, Pikermi near Athens, and Rhodes all show that Mio-Pliocene vegetation was dominated by C3 plants, as the entire region is today. In addition, nearly all paleosols contained carbonate, indicating that mean annual pitation has remained under about 1 m/yr during the last 11 Ma. The carbon isotopic evidence thus precludes the presence of Serengeti-type C4 grasslands favored by summer precipitation, but permits C3 forest or grasses fed by winter rains, or forest with mixed seasonal precipitation. However, there is no evidence in the published palynological records from the region for abundant grasses. Given these lines of evidence, we suggest that dry forest and woodland (largely C3) dominated the vegetation of the region. C3 grasslands, if present, were probably of very restricted extent. This reconstruction is supported by carbon isotopic evidence from fossil teeth from Samos and from Paşalar in NW Turkey, and by published evidence on masticatory morphology of Turolian-age ruminants from Samos and Pikermi. Our findings imply that the classic fossil-bearing localities on Samos and at Pikermi, and from the lower Axios Valley in Macedonia were not open savannas, as has been previously suggested, but rather, woodlands or forests. © 1994.
• lull, A. J., Lifton, N., Phillips, W. M., & Quade, J. (1994). Studies of the production rate of cosmic-ray produced ¹⁴C in rock surfaces. Nuclear Inst. and Methods in Physics Research, B, 92(1-4), 308-310.
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  Abstract: We have developed a method of extracting 14C in rock samples which is produced by the direct spallation of oxygen in the rock. The low levels of 14C produced in rocks, approximately 106 atoms/g of rock at an altitude of 2000 m, are detectable only by accelerator mass spectrometry (AMS). This radioisotope can be extracted from the rock by melting in an rf furnace in a flow of oxygen, and earlier work has discussed this in some detail. Several improvements have been made to this system, allowing for processing of up to 100 g of rock sample at one time, and reduction of the blank. Our measurements from Tabernacle Hill, Utah, an intermediate-altitude basalt with well-constrained conventional 14C ages, yield an estimated cosmogenic 14C production rate of about 50 14C atoms/g/yr. When corrected to sea level we obtain a value of 20 ± 2 14C/g/yr for high-latitude samples. © 1994.
• Cerling, T. E., Wang, Y., & Quade, J. (1993). Expansion of C4 ecosystems as an indicator of global ecological change in the late Miocene. Nature, 361(6410), 344-345.
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  Abstract: The most common and the most primitive pathway of the three different photosynthetic pathways used by plants is the C3 pathway, or Calvin cycle, which is characterized by an initial CO2 carboxylation to form phosphoglyceric acid, a 3-carbon acid. The carbon isotope composition (δ13C) of C3 plants varies from about -23 to -35‰1-3 and averages about -26‰. Virtually all trees, most shrubs, herbs and forbs, and cool-season grasses and sedges use the C3 pathway. In the C4 pathway (Hatch-Slack cycle), CO2 initially combines with phosphoenol pyruvate to form the 4-carbon acids malate or aspartic acid, which are translocated to bundle sheath cells where CO2 is released and used in Calvin cycle reactions1-4. The carbon isotope composition of C4 plants ranges from about -10 to -14‰, averaging about -13‰ for modern plants1-3. Warm-season grasses and sedges are the most abundant C4 plants, although C4 photosynthesis is found in about twenty families5. The third photosynthetic pathway, CAM, combines features of both C3 and C4 pathways. CAM plants, which include many succulents, have intermediate carbon isotope compositions and are also adapted to conditions of water and CO2 stress. The modern global ecosystem has a significant component of C4 plants, primarily in tropical savannas, temperate grasslands and semi-desert scrublands. Studies of palaeovegetation from palaeosols and palaeodiet from fossil tooth enamel indicate a rapid expansion of C4 biomass in both the Old World and the New World starting 7 to 5 million years ago. We propose that the global expansion of C4 biomass may be related to lower atmospheric carbon dioxide levels because C4 photosynthesis is favoured over C3 photosynthesis when there are low concentrations of carbon dioxide in the atmosphere.
• Cerling, T. E., Kappelman, J., Quade, J., Ambrose, S. H., Sikes, N. E., & Andrews, P. (1992). Reply to comment on the Paleoenvironment of Kenyapithecus at Fort Ternan. Journal of Human Evolution, 23(4), 371-377.
• Quade, J., Cerlinga, T. E., Barry, J. C., Morgan, M. E., Pilbeam, D. R., Chivas, A. R., Lee-Thorp, J. A., & J., N. (1992). A 16-Ma record of paleodiet using carbon and oxygen isotopes in fossil teeth from Pakistan. Chemical Geology: Isotope Geoscience Section, 94(3), 183-192.
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  Abstract: The Siwalik Sequence of northern Pakistan contains a 16-Ma record of paleosol carbonate and fossil teeth from which a record of paleovegetation can potentially be reconstructed and compared. The carbon isotopic composition of paleosol carbonate and organic matter from Siwalik strata reflects a major paleoecological change on the floodplains of major rivers beginning ∼ 7.3 Ma ago. By 6 Ma C3-dominated plant communities, probably composed of mostly trees and shrubs, were displaced by nearly continuous C4 grassland. We find that the carbon isotopic ratios in herbivore tooth enamel reflect this dramatic ecologic shift. Carbonate in enamel older than 7 Ma averages -11‰ in δ13CPDB, consistent with a largely C3 diet. Enamel from the Plio-Pleistocene averages +1.9‰ in δ13C, similar to the value displayed by modern C4 grazers. Analysis of post-burial carbonate cements, and the concordance with isotopic evidence from paleosols argues strongly against major isotopic alteration of the enamel, while coexisting bone may have been altered early in burial. This study confirms that enamel apatite is useful for paleodietary reconstruction much further back in the geologic record than was previously thought. © 1992.
• Cerling, T. E., Quade, J., Ambrose, S. H., & Sikes, N. E. (1991). Fossil soils, grasses, and carbon isotopes from Fort Ternan, Kenya: grassland or woodland?. Journal of Human Evolution, 21(4), 295-306.
• Cerling, T. E., Solomon, D., Quade, J., & Bowman, J. R. (1991). On the isotopic composition of carbon in soil carbon dioxide. Geochimica et Cosmochimica Acta, 55(11), 3403-3405.
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  Abstract: In this study it is shown that the isotopic composition of carbon in soil CO2 differs from the isotopic composition of carbon in soil-respired CO2. Soil CO2 collected from a montane soil has an endmember δ13C value of -23.3%. whereas soil-respired CO2 in this system has a δ 13C value of -27.5%. This difference is very close to the theoretical difference of 4.4%. which is predicted by the difference in the diffusion coefficients for 12CO2 and 13CO2. Because of the measured and the theoretical difference between the isotopic composition of carbon in soil CO2 and soil-respired CO2 it is suggested that, in the future, a distinction should be made between them. © 1991.
• Cerling, T. E., & Quade, J. (1990). Global ecologic and climatic change during the Neogene: Stable isotopic evidence from soils. Chemical Geology, 84(1-4), 164-165.
• Quade, J., & Cerling, T. E. (1990). Stable isotopic evidence for a pedogenic origin of carbonates in trench 14 near Yucca Mountain, Nevada. Science, 250(4987), 1549-1552.
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  PMID: 17818282;Abstract: Layered carbonate and silica encrust fault fractures exposed in Trench 14 near Yucca Mountain, site of the proposed high-level nuclear waste repository in southern Nevada. Comparison of the stable carbon and oxygen isotopic compositions of the fracture carbonates with those of modern soil carbonates in the area shows that the fracture carbonates are pedogenic in origin and that they likely formed in the presence of vegetation and rainfall typical of a glacial climate. Their isotopic composition differs markedly from that of carbonate associated with nearby springs. The regional water table therefore remained below the level of Trench 14 during the time that the carbonates and silica precipitated, a period probably covering parts of at least the last 300,000 years.
• Cerling, T. E., Quade, J., Wang, Y., & Bowman, J. R. (1989). Carbon isotopes in soils and palaeosols as ecology and palaeoecology indicators. Nature, 341(6238), 138-139.
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  Abstract: There are few quantitative techniques in use today for palaeoecological reconstruction in terrestrial depositional systems. One approach to such reconstructions is to estimate the proportion of C3 to C4 plants once present at a site using carbon isotopes from palaeosol carbonates1-3. Until now, this has been hampered by an inadequate understanding of the relationship between the carbon isotopic composition of modern soil carbonate and coexisting organic matter. Here we have found that the two systematically differ by 14-16% in undisturbed modern soils. This difference is compatible with isotopic equilibrium between gaseous CO2, and aqueous and solid carbonate species in a soil system controlled by diffusive mass transfer of soil CO2 derived from irreversible oxidation of soil organic matter. Organic matter and pedogenic carbonate from palaeosols of Pleistocene to late Miocene age in Pakistan also differ by 14-16%,. This indicates that diagenesis has not altered the original isotopic composition of either phase, thus confirming their use in palaeoecological reconstruction. © 1989 Nature Publishing Group.
• Quade, J., & Pratt, W. L. (1989). Late Wisconsin groundwater discharge environments of the southwestern Indian Springs Valley, southern Nevada. Quaternary Research, 31(3), 351-370.
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  Abstract: Badland exposures in the Indian Springs Valley, southern Nevada, contain evidence of formerly widespread spring and seep discharge. The stratigraphic position and appearance of most of these deposits suggests correlation with late Wisconsin (30,000 to ca. 10,000 yr B.P.) marsh sediments in nearby Las Vegas Valley. Previously, all these deposits have been loosely described as lacustrine because of the presence of extensive green mudstones associated with aquatic mollusks. However, this association also typifies modern groundwater discharge environments in many basins of northeast Nevada such as the Steptoe Valley, basins often without hydrographic closure. Such analogs best explain the origin of late Wisconsin fine-grained deposits in the unclosed southwestern arm of the Indian Springs Valley. Key features of these depositional systems are the lack of shoreline deposits, the presence of a broad belt of subaerially deposited plae-brown silts surrounding spring, "wet meadow," and marsh deposits, and the intermixture of terrestrial and aquatic mollusks in most horizons where mollusks occur. © 1989.
• Quade, J., Cerling, T. E., & Bowman, J. R. (1989). Development of Asian monsoon revealed by marked ecological shift during the latest Miocene in northern Pakistan. Nature, 342(6246), 163-166.
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  Abstract: CARBON isotopes from soil carbonate1-4 and soil organic matter5,6 yield palaeoecological information because the carbon in the soil carbonate forms in isotopic equilibrium with local soil CO2 (refs 1, 7), the isotopic composition of which is in turn determined by local plant cover. Siwalik Group sediments in northern Pakistan contain a well exposed palaeosol record spanning the past 18 Myr. Here we report on stable-carbon-isotope results from associated pedogenic carbonate which indicate a dramatic ecological shift from C3- to C4-dominated floodplain biomass beginning ∼7.4-7.0 Myr ago. The earlier C3 floodplain biomasses were probably mainly composed of trees and shrubs, whereas C4 grasslands dominated in the Plio-Pleistocene. Oxygen isotopes also exhibit a shift in the latest Miocene, probably corresponding to a major climate change which may have induced the forest-to-grassland transition. This dramatic ecological shift in the latest Miocene may mark the inception or a marked strengthening of the Asian monsoon system. © 1989 Nature Publishing Group.
• Quade, J., Cerling, T. E., & Bowman, J. R. (1989). Systematic variations in the carbon and oxygen isotopic composition of pedogenic carbonate along elevation transects in the southern Great Basin, United States. Geological Society of America Bulletin, 101(4), 464-475.
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  Abstract: The modeled best fit to observed isotopic profiles suggests that the profile differences in part result from differing soil-respiration rates at each site. Soil CO2 and soil-respiration rates increase systematically with elevation. Suggests that evaporative isotopic enrichment of soil waters may have occurred at all elevations prior to precipitation of carbonate, or that seasonal differences in the isotopic composition of meteoric waters coupled with differential infiltration may be taking place. -from Authors
• Mifflin, M., & Quade, J. (1986). ESTIMATING CLIMATE CHANGE FROM HYDROLOGIC RESPONSE.. Array, 51-58.
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  Abstract: In the eighty-one hydrographically closed basins within Nevada many large lakes developed during the pluvial climate of the Pleistocene. Pluvial lake area and tributary basin area have been established from the geomorphic evidence. A method is presented for estimating the climatic parameters of the lake forming pluvial climates using modern climatic relationships within the Great Basin and known hydrologic responses to varied climates. The quantitative approach could be used to estimate water supply change due to given climatic change.
• Quade, J. (1986). Late quaternary environmental changes in the upper Las Vegas valley, Nevada. Quaternary Research, 26(3), 340-357.
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  Abstract: Five stratigraphic units and five soils of late Pleistocene to Holocene age crop out in dissected badlands on Corn Creek Flat, 30 km northwest of Las Vegas, Nevada, and at Tule Springs, nearer to Las Vegas. The record is dominantly fluvial but contains evidence of several moister, marsh-forming periods: the oldest (Unit B) dates perhaps to the middle Wisconsin, and the more widespread Unit D falls between 30,000 and 15,000 yr B.P. Unit D therefore correlates with pluvial maximum lacustrine deposits elsewhere in the Great Basin. Standing water was not of sufficient depth or extent during either period to form lake strandlines. Between 14,000 and 7200 yr B.P. (Unit E), standing surface water gradually decreased, a trend also apparent in Great Basin pluvial lake chronologies during the same period. Groundwater carbonate cementation and burrowing by cicadas (Cicadae) accompany the moist-phase units. After 7200 yr B.P., increased wind action, decreased biotic activity, and at least 25 m of water-table lowering accompanied widespread erosion of older fine-grained deposits. Based on pack-rat midden and pollen evidence, this coincides with major vegetation changes in the valley, from sagebrush-dominated steppe to lower Mohave desertscrub. © 1986.