Over the past decade, Oklahoma became the most seismically active region of the mid-Continental U... more Over the past decade, Oklahoma became the most seismically active region of the mid-Continental USA as a result of industry operations. However, seism ic net work li mitations and
The oxygen isotopic composition of lacustrine carbonate deposits has been frequently used to reco... more The oxygen isotopic composition of lacustrine carbonate deposits has been frequently used to reconstruct paleoaltimetry of orogenic belts. However, the primary oxygen isotopic composition of lacustrine carbonate can be partially or wholly altered by post-depositional diagenetic processes, such as deep burial recrystallization and the interaction with geologically younger meteoric waters. To better understand how ancient lacustrine carbonates are diagenetically modified by meteoric waters, we present detailed mineralogy, petrography, stable carbon and oxygen isotopic compositions, and major and minor element geochemistry of lacustrine carbonates from the Miocene Wudaoliang Group, which underwent only shallow burial (b300 m) in the Hoh Xil Basin, northern Tibetan Plateau. Our observations indicate that the primary mineralogy in the Wudaoliang carbonate muds consists of a mixture of both low-Mg and high-Mg calcite. During or shortly after deposition, the carbonate muds experienced stabilization and associated carbonate cementation in a closed phreatic meteoric diagenetic system. Interaction with 18 O-depleted meteoric waters during diagenesis slightly reduced 18 O c values, but overall the Wudaoliang carbonates largely retained primary oxygen isotope compositions. Our data support previous interpretations that δ 18 O c values of the Wudaoliang Group lacustrine carbonates are indicative of the primary δ 18 O composition of Miocene meteoric water and can be used for paleoelevation estimate of the Miocene Hoh Xil Basin, northern Tibetan Plateau. By demonstrating the oxygen isotopic fidelity of the Wudaoliang carbonates, we are able to rule out open-system meteoric diagenesis from younger meteoric waters and subsequent isotopic alteration. This study highlights that integration of scanning-electron-microscope and cathodoluminescence petrography with stable isotopic and mineralogical data enables the determination of the extent of meteoric diagenetic alteration in lacustrine carbonates, particularly whether the diagenetic systems were open or closed with respect to the oxygen isotope.
Increased rates of seismicity in tectonically quiescent regions like the midcontinent region of t... more Increased rates of seismicity in tectonically quiescent regions like the midcontinent region of the United States have been hypothesized to be related to human activities such as oil and gas production and wastewater injection. It can be difficult to establish how human activities relate to earthquakes, particularly when local seismic networks are not available to provide a high-quality characterization of the seismic sequence in question. Here, we use a multistation waveform crosscorrelation approach to evaluate the relationships between earthquakes associated with the 2011–2012 Youngstown, Ohio, seismic sequence and the injection history of a local wastewater disposal well. By using data recorded by four regional seismic stations 50–200 km (31–124 mi) away from Youngstown, we demonstrate that high-resolution results can be achieved without using costly and scientifically focused local seismic deployments. Compared to the number of events recorded using standard detection methodologies, we realize a 25-fold increase in detected seismicity (282 detected events) during the sequence, and allow us with confidence to interpret a direct link between seismicity and well injection volumes. Using a combination of absolute and relative location techniques, we demonstrate that seismicity migrated from below the injection well toward the west, along a line consistent with a nodal plane of the largest earthquake in the sequence. We are able to separate the seismic sequence into three distinct phases, consistent with changes in injection rates and maximum injection pressures. In addition, using daily injection volume records, we can identify two families of similar earthquakes. The first family occurred early in the sequence and close to the injection well and was followed by a recurrence pattern that lagged injection activity by 1 day. The second family. which occurred later in the sequence and farther from the well, displayed a 4-day lag. We interpret these relationships to be related to pore-pressure diffusion rates within the fault network responsible for the seismicity. Collectively, our technique shows the high quality of results possible when only a few regional seismic stations are available for monitoring.
The origin of Australopithecus, the genus widely interpreted as ancestral to Homo, is a central p... more The origin of Australopithecus, the genus widely interpreted as ancestral to Homo, is a central problem in humanevolutionary studies. Australopithecus species differ markedly from extant African apes and candidate ancestral hominidssuch as Ardipithecus, Orrorin and Sahelanthropus. The earliest described Australopithecus species is Au. anamensis, theprobable chronospecies ancestor of Au. afarensis. Here we describe newly discovered fossils from the Middle Awashstudy area that extend the known Au. anamensis range into northeastern Ethiopia. The new fossils are fromchronometrically controlled stratigraphic sequences and date to about 4.1–4.2million years ago. They include diagnosticcraniodental remains, the largest hominid canine yet recovered, and the earliest Australopithecus femur. These newfossils are sampled from a woodland context. Temporal and anatomical intermediacy between Ar. ramidus andAu. afarensis suggest a relatively rapid shift from Ardipithecus to Australopithecus in this region of Africa, involving eitherreplacement or accelerated phyletic evolution.
Proceedings of the National Academy of Sciences, 2018
Significance Recent studies have focused on how wastewater disposal wells have caused dramatic in... more Significance Recent studies have focused on how wastewater disposal wells have caused dramatic increases in eastern US earthquakes. We focused instead on less common cases where hydraulic fracturing alone has caused earthquakes and found seismicity separated into two depth zones: a shallow zone on younger faults, with more small-magnitude earthquakes than expected, and a deeper zone on older faults, with larger magnitude earthquakes and seismicity continuing after fracturing stops. Hence, inducing deeper seismicity creates more hazard. Our observations are consistent with prior geologic, laboratory, and theoretical work indicating that age and maturity of faults causes the different seismicity patterns. We utilize data from well operators to demonstrate that both fluid pressure changes and rock stress transfer are needed to explain our observations.
Abstract The Lower-Upper Cretaceous Cedar Mountain and Dakota formations are easy to distinguish ... more Abstract The Lower-Upper Cretaceous Cedar Mountain and Dakota formations are easy to distinguish in outcrop due to lithological and color variations but they are difficult to correlate in the subsurface. Cedar Mountain and Dakota (CMD) sandstones are important gas reservoirs in the southern Uinta Basin, yet their subsurface distribution is poorly constrained due to difficulties in distinguishing the two units in the subsurface, as well as differentiating the interval from the underlying Upper Jurassic Morrison Formation. The first step in understanding the distribution of these intervals and the respective contributions of these sandstones to gas production is to develop a correlation model for them. Outcrop gamma-ray logs through the CMD were obtained at six locations on the southern rim of the Uinta Basin. An additional outcrop gamma-ray log was acquired from the east flank on the San Rafael Swell to characterize the log signature of the Buckhorn Conglomerate, the lowermost member of the Cedar Mountain Formation. The outcrop logs showed consistent signatures at the stratigraphic contacts between the Morrison, Cedar Mountain and Dakota formations, and the overlying Upper Cretaceous Mancos Shale. There were no identifiable patterns to partition these intervals further. These gamma-ray profiles were used to construct a correlation envelope for the CMD interval in the southeastern Uinta Basin.
Special Paper 416: Paleoenvironmental Record and Applications of Calcretes and Palustrine Carbonates, 2006
The thicknesses of stratigraphic sections of the Late Triassic (Carnian) Ischigualasto Formation ... more The thicknesses of stratigraphic sections of the Late Triassic (Carnian) Ischigualasto Formation change significantly, from ~300 to 700 m, along a 15 km transect in the Ischigualasto Provincial Park, San Juan, NW Argentina. Channel sandstone deposits dominate the thickest section, whereas pedogenically altered layers dominate the thinnest stratigraphic section. Eight paleosol types have been recognized in the study area, and they are unevenly distributed across the basin. In particular, paleosol B horizons are thinner and redoximorphic soil morphologies dominate in the thickest, whereas B horizons are thickest and argillic and calcic morphologies dominate in the thinnest stratigraphic section. These observations suggest that the geomorphic evolution of the Ischigualasto basin exerted the primary control on sediment distribution, depositional rate, soil drainage, and depth of the groundwater table through most of Late Triassic time in the Ischigualasto basin. In addition, δ 18 O values of paleosol calcite nodules are similar to modern soil calcites that form in frigid to cool climates between ~0 °C and 10 °C. Considering both lateral and stratigraphic distribution of paleosol morphological variability, there appears to be three different general modes of climate recorded throughout deposition of the Ischigualasto Formation: (1) Humid conditions recorded by Argillisols, Gleysols, and Vertisols in the lower quarter of the formation; (2) relatively dry conditions recorded by Calcisols, calcic Argillisols, and calcic Vertisols in the middle half of the formation; and (3) generally more humid conditions in the upper quarter of the formation recorded by Argillisols, Gleysols, and Vertisols.
Paleosols in the Morrison Formation (Upper Jurassic) from the Western Interior and Colorado Plate... more Paleosols in the Morrison Formation (Upper Jurassic) from the Western Interior and Colorado Plateau regions occur in fluvial/overbank and marginal-lacustrine depositional facies associated with aggradational settings, and at sequence-bounding unconformities that mark divisions between major aggradational and degradational successions. Pedogenic features within these horizons preserve important contextual information about the local and regional paleoclimate and paleoenvironment in which the soils formed. Floodplain and lake-margin paleosols show evidence that most of the Morrison basin was characterized by a semi-arid to tropical wet-dry paleoclimate with fluctuating groundwater conditions, a low precipitation to evaporation ratio, and weak to moderately seasonal precipitation. Paleosol ichnofauna show evidence of a diverse and opportunistic flora and fauna that exploited changing conditions and existing nutrient and moisture regimes. Changes in paleosol type and degree of development over the basin indicate the overall regional paleoclimate was drier in the western and southern portions of the basin. Vertical trends indicate paleoclimatic conditions over the basin became steadily more humid through time. Laterally continuous, well-developed, deeply weathered paleosols formed during times of little or no deposition and mark regional unconformities. The paleosols at these sequence-bounding unconformities serve as useful regional stratigraphic markers to trace genetic packages across the Morrison depositional basin and to determine regional accommodation trends.
y las facies observadas en la Formación Ischigualasto parecen corresponder a variaciones en el es... more y las facies observadas en la Formación Ischigualasto parecen corresponder a variaciones en el espacio de acomodamiento de fallas ubicadas dentro de la cuenca durante su depositación.
Argentina, has been constrained by fi eld studies coupled with mineralogic, whole-rock, and fi ne... more Argentina, has been constrained by fi eld studies coupled with mineralogic, whole-rock, and fi ne-fraction chemical and stable isotope analysis of a Triassic (Carnian) basalt-hosted fossil soil. Field evidence, such as wedgeshaped aggregate structure and slickensides, indicate this was likely a paleo-Vertisol. Whole-rock analysis defi nes down-profi le trends in clay mineralogy and chemical composition that are consistent with modern soils developed upon basalt parent material. X-ray diffraction analysis indicates that the basaltic parent material is dominated by plagioclase with trace amounts of weathered 2:1 phyllosilicate. Overlying weathered horizons show a progressive loss of plagioclase and an increase in phyllosilicates with minor amounts of kandite clays and detrital quartz. X-ray diffraction analysis of the <2 µm fraction shows that the weathered layers are dominated by dioctahedral smectite (montmorillonite) with a minor fraction of kaolinite in the upper layers of the profi le. There is a progressive loss of basic cations in conjunction with an increase in concentration, on a wt% basis, of conservative elements from the basalt upward through the weathering profi le. The combined data indicate that this soil likely formed on a stable landscape in a cool and humid climate. In addition, the presence of quartz in the paleosol profi le suggests an eolian contribution of sediment during pedogenesis. Despite these apparent morphologic and bulk chemical trends indicative of a pedogenic origin, none of the authigenic minerals formed in isotopic equilibrium. However, based on measured oxygen and hydrogen isotope compositions, these minerals apparently formed from meteoric waters with a narrow range of δ 18 O and δD compositions at different temperatures. If this is correct, then amygdaloidal calcites formed at ~60-100 °C, followed by precipitation of montmorillonites at 49-57 °C during late-stage hydrothermal alteration. Finally, goethite formed at low temperatures of 6 ± 3 °C in a pedogenic environment. This complex history of hydrothermal alteration and pedogenic overprinting brings to light the need for cautious interpretation of bulk chemical trends in paleosols as a means for paleoclimate reconstruction. Comparison of the calculated Triassic oxygen isotopic compositions of meteoric water and soil temperature with modern environments suggests that this soil formed in a seasonal, humid, and cool climate.
Figure 1. A: Location map of Tibetan basins from which paleoelevation estimates have been derived... more Figure 1. A: Location map of Tibetan basins from which paleoelevation estimates have been derived. B: Location map of Oiyug Basin samples described in text. Only streams and rivers mentioned in text are highlighted. Large black stars are carbonate nodule localities. Northern black star also corresponds with Miocene floral locality described by Spicer et al. (2003). Gray stars are sample localities for modern surface waters, including tufa spring west of Wangbadui. Abbreviations: IYS-Indus-Yarlung suture; STD-South Tibetan detachment; MBT-Main Boundary thrust; MCT-Main Central thrust.
Over the past decade, Oklahoma became the most seismically active region of the mid-Continental U... more Over the past decade, Oklahoma became the most seismically active region of the mid-Continental USA as a result of industry operations. However, seism ic net work li mitations and
The oxygen isotopic composition of lacustrine carbonate deposits has been frequently used to reco... more The oxygen isotopic composition of lacustrine carbonate deposits has been frequently used to reconstruct paleoaltimetry of orogenic belts. However, the primary oxygen isotopic composition of lacustrine carbonate can be partially or wholly altered by post-depositional diagenetic processes, such as deep burial recrystallization and the interaction with geologically younger meteoric waters. To better understand how ancient lacustrine carbonates are diagenetically modified by meteoric waters, we present detailed mineralogy, petrography, stable carbon and oxygen isotopic compositions, and major and minor element geochemistry of lacustrine carbonates from the Miocene Wudaoliang Group, which underwent only shallow burial (b300 m) in the Hoh Xil Basin, northern Tibetan Plateau. Our observations indicate that the primary mineralogy in the Wudaoliang carbonate muds consists of a mixture of both low-Mg and high-Mg calcite. During or shortly after deposition, the carbonate muds experienced stabilization and associated carbonate cementation in a closed phreatic meteoric diagenetic system. Interaction with 18 O-depleted meteoric waters during diagenesis slightly reduced 18 O c values, but overall the Wudaoliang carbonates largely retained primary oxygen isotope compositions. Our data support previous interpretations that δ 18 O c values of the Wudaoliang Group lacustrine carbonates are indicative of the primary δ 18 O composition of Miocene meteoric water and can be used for paleoelevation estimate of the Miocene Hoh Xil Basin, northern Tibetan Plateau. By demonstrating the oxygen isotopic fidelity of the Wudaoliang carbonates, we are able to rule out open-system meteoric diagenesis from younger meteoric waters and subsequent isotopic alteration. This study highlights that integration of scanning-electron-microscope and cathodoluminescence petrography with stable isotopic and mineralogical data enables the determination of the extent of meteoric diagenetic alteration in lacustrine carbonates, particularly whether the diagenetic systems were open or closed with respect to the oxygen isotope.
Increased rates of seismicity in tectonically quiescent regions like the midcontinent region of t... more Increased rates of seismicity in tectonically quiescent regions like the midcontinent region of the United States have been hypothesized to be related to human activities such as oil and gas production and wastewater injection. It can be difficult to establish how human activities relate to earthquakes, particularly when local seismic networks are not available to provide a high-quality characterization of the seismic sequence in question. Here, we use a multistation waveform crosscorrelation approach to evaluate the relationships between earthquakes associated with the 2011–2012 Youngstown, Ohio, seismic sequence and the injection history of a local wastewater disposal well. By using data recorded by four regional seismic stations 50–200 km (31–124 mi) away from Youngstown, we demonstrate that high-resolution results can be achieved without using costly and scientifically focused local seismic deployments. Compared to the number of events recorded using standard detection methodologies, we realize a 25-fold increase in detected seismicity (282 detected events) during the sequence, and allow us with confidence to interpret a direct link between seismicity and well injection volumes. Using a combination of absolute and relative location techniques, we demonstrate that seismicity migrated from below the injection well toward the west, along a line consistent with a nodal plane of the largest earthquake in the sequence. We are able to separate the seismic sequence into three distinct phases, consistent with changes in injection rates and maximum injection pressures. In addition, using daily injection volume records, we can identify two families of similar earthquakes. The first family occurred early in the sequence and close to the injection well and was followed by a recurrence pattern that lagged injection activity by 1 day. The second family. which occurred later in the sequence and farther from the well, displayed a 4-day lag. We interpret these relationships to be related to pore-pressure diffusion rates within the fault network responsible for the seismicity. Collectively, our technique shows the high quality of results possible when only a few regional seismic stations are available for monitoring.
The origin of Australopithecus, the genus widely interpreted as ancestral to Homo, is a central p... more The origin of Australopithecus, the genus widely interpreted as ancestral to Homo, is a central problem in humanevolutionary studies. Australopithecus species differ markedly from extant African apes and candidate ancestral hominidssuch as Ardipithecus, Orrorin and Sahelanthropus. The earliest described Australopithecus species is Au. anamensis, theprobable chronospecies ancestor of Au. afarensis. Here we describe newly discovered fossils from the Middle Awashstudy area that extend the known Au. anamensis range into northeastern Ethiopia. The new fossils are fromchronometrically controlled stratigraphic sequences and date to about 4.1–4.2million years ago. They include diagnosticcraniodental remains, the largest hominid canine yet recovered, and the earliest Australopithecus femur. These newfossils are sampled from a woodland context. Temporal and anatomical intermediacy between Ar. ramidus andAu. afarensis suggest a relatively rapid shift from Ardipithecus to Australopithecus in this region of Africa, involving eitherreplacement or accelerated phyletic evolution.
Proceedings of the National Academy of Sciences, 2018
Significance Recent studies have focused on how wastewater disposal wells have caused dramatic in... more Significance Recent studies have focused on how wastewater disposal wells have caused dramatic increases in eastern US earthquakes. We focused instead on less common cases where hydraulic fracturing alone has caused earthquakes and found seismicity separated into two depth zones: a shallow zone on younger faults, with more small-magnitude earthquakes than expected, and a deeper zone on older faults, with larger magnitude earthquakes and seismicity continuing after fracturing stops. Hence, inducing deeper seismicity creates more hazard. Our observations are consistent with prior geologic, laboratory, and theoretical work indicating that age and maturity of faults causes the different seismicity patterns. We utilize data from well operators to demonstrate that both fluid pressure changes and rock stress transfer are needed to explain our observations.
Abstract The Lower-Upper Cretaceous Cedar Mountain and Dakota formations are easy to distinguish ... more Abstract The Lower-Upper Cretaceous Cedar Mountain and Dakota formations are easy to distinguish in outcrop due to lithological and color variations but they are difficult to correlate in the subsurface. Cedar Mountain and Dakota (CMD) sandstones are important gas reservoirs in the southern Uinta Basin, yet their subsurface distribution is poorly constrained due to difficulties in distinguishing the two units in the subsurface, as well as differentiating the interval from the underlying Upper Jurassic Morrison Formation. The first step in understanding the distribution of these intervals and the respective contributions of these sandstones to gas production is to develop a correlation model for them. Outcrop gamma-ray logs through the CMD were obtained at six locations on the southern rim of the Uinta Basin. An additional outcrop gamma-ray log was acquired from the east flank on the San Rafael Swell to characterize the log signature of the Buckhorn Conglomerate, the lowermost member of the Cedar Mountain Formation. The outcrop logs showed consistent signatures at the stratigraphic contacts between the Morrison, Cedar Mountain and Dakota formations, and the overlying Upper Cretaceous Mancos Shale. There were no identifiable patterns to partition these intervals further. These gamma-ray profiles were used to construct a correlation envelope for the CMD interval in the southeastern Uinta Basin.
Special Paper 416: Paleoenvironmental Record and Applications of Calcretes and Palustrine Carbonates, 2006
The thicknesses of stratigraphic sections of the Late Triassic (Carnian) Ischigualasto Formation ... more The thicknesses of stratigraphic sections of the Late Triassic (Carnian) Ischigualasto Formation change significantly, from ~300 to 700 m, along a 15 km transect in the Ischigualasto Provincial Park, San Juan, NW Argentina. Channel sandstone deposits dominate the thickest section, whereas pedogenically altered layers dominate the thinnest stratigraphic section. Eight paleosol types have been recognized in the study area, and they are unevenly distributed across the basin. In particular, paleosol B horizons are thinner and redoximorphic soil morphologies dominate in the thickest, whereas B horizons are thickest and argillic and calcic morphologies dominate in the thinnest stratigraphic section. These observations suggest that the geomorphic evolution of the Ischigualasto basin exerted the primary control on sediment distribution, depositional rate, soil drainage, and depth of the groundwater table through most of Late Triassic time in the Ischigualasto basin. In addition, δ 18 O values of paleosol calcite nodules are similar to modern soil calcites that form in frigid to cool climates between ~0 °C and 10 °C. Considering both lateral and stratigraphic distribution of paleosol morphological variability, there appears to be three different general modes of climate recorded throughout deposition of the Ischigualasto Formation: (1) Humid conditions recorded by Argillisols, Gleysols, and Vertisols in the lower quarter of the formation; (2) relatively dry conditions recorded by Calcisols, calcic Argillisols, and calcic Vertisols in the middle half of the formation; and (3) generally more humid conditions in the upper quarter of the formation recorded by Argillisols, Gleysols, and Vertisols.
Paleosols in the Morrison Formation (Upper Jurassic) from the Western Interior and Colorado Plate... more Paleosols in the Morrison Formation (Upper Jurassic) from the Western Interior and Colorado Plateau regions occur in fluvial/overbank and marginal-lacustrine depositional facies associated with aggradational settings, and at sequence-bounding unconformities that mark divisions between major aggradational and degradational successions. Pedogenic features within these horizons preserve important contextual information about the local and regional paleoclimate and paleoenvironment in which the soils formed. Floodplain and lake-margin paleosols show evidence that most of the Morrison basin was characterized by a semi-arid to tropical wet-dry paleoclimate with fluctuating groundwater conditions, a low precipitation to evaporation ratio, and weak to moderately seasonal precipitation. Paleosol ichnofauna show evidence of a diverse and opportunistic flora and fauna that exploited changing conditions and existing nutrient and moisture regimes. Changes in paleosol type and degree of development over the basin indicate the overall regional paleoclimate was drier in the western and southern portions of the basin. Vertical trends indicate paleoclimatic conditions over the basin became steadily more humid through time. Laterally continuous, well-developed, deeply weathered paleosols formed during times of little or no deposition and mark regional unconformities. The paleosols at these sequence-bounding unconformities serve as useful regional stratigraphic markers to trace genetic packages across the Morrison depositional basin and to determine regional accommodation trends.
y las facies observadas en la Formación Ischigualasto parecen corresponder a variaciones en el es... more y las facies observadas en la Formación Ischigualasto parecen corresponder a variaciones en el espacio de acomodamiento de fallas ubicadas dentro de la cuenca durante su depositación.
Argentina, has been constrained by fi eld studies coupled with mineralogic, whole-rock, and fi ne... more Argentina, has been constrained by fi eld studies coupled with mineralogic, whole-rock, and fi ne-fraction chemical and stable isotope analysis of a Triassic (Carnian) basalt-hosted fossil soil. Field evidence, such as wedgeshaped aggregate structure and slickensides, indicate this was likely a paleo-Vertisol. Whole-rock analysis defi nes down-profi le trends in clay mineralogy and chemical composition that are consistent with modern soils developed upon basalt parent material. X-ray diffraction analysis indicates that the basaltic parent material is dominated by plagioclase with trace amounts of weathered 2:1 phyllosilicate. Overlying weathered horizons show a progressive loss of plagioclase and an increase in phyllosilicates with minor amounts of kandite clays and detrital quartz. X-ray diffraction analysis of the <2 µm fraction shows that the weathered layers are dominated by dioctahedral smectite (montmorillonite) with a minor fraction of kaolinite in the upper layers of the profi le. There is a progressive loss of basic cations in conjunction with an increase in concentration, on a wt% basis, of conservative elements from the basalt upward through the weathering profi le. The combined data indicate that this soil likely formed on a stable landscape in a cool and humid climate. In addition, the presence of quartz in the paleosol profi le suggests an eolian contribution of sediment during pedogenesis. Despite these apparent morphologic and bulk chemical trends indicative of a pedogenic origin, none of the authigenic minerals formed in isotopic equilibrium. However, based on measured oxygen and hydrogen isotope compositions, these minerals apparently formed from meteoric waters with a narrow range of δ 18 O and δD compositions at different temperatures. If this is correct, then amygdaloidal calcites formed at ~60-100 °C, followed by precipitation of montmorillonites at 49-57 °C during late-stage hydrothermal alteration. Finally, goethite formed at low temperatures of 6 ± 3 °C in a pedogenic environment. This complex history of hydrothermal alteration and pedogenic overprinting brings to light the need for cautious interpretation of bulk chemical trends in paleosols as a means for paleoclimate reconstruction. Comparison of the calculated Triassic oxygen isotopic compositions of meteoric water and soil temperature with modern environments suggests that this soil formed in a seasonal, humid, and cool climate.
Figure 1. A: Location map of Tibetan basins from which paleoelevation estimates have been derived... more Figure 1. A: Location map of Tibetan basins from which paleoelevation estimates have been derived. B: Location map of Oiyug Basin samples described in text. Only streams and rivers mentioned in text are highlighted. Large black stars are carbonate nodule localities. Northern black star also corresponds with Miocene floral locality described by Spicer et al. (2003). Gray stars are sample localities for modern surface waters, including tufa spring west of Wangbadui. Abbreviations: IYS-Indus-Yarlung suture; STD-South Tibetan detachment; MBT-Main Boundary thrust; MCT-Main Central thrust.
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