Ryan T. Tucker, J. Crowley, M. T. Mohr, Ray K. Renaut, P. Makovicky, Lindsay E. Zanno
Understanding the effects of climatic upheavals during the Early to Late Cretaceous transition is essential for characterizing the tempo of tectonically driven landscape modification and biological interchange; yet, current chronostratigraphic frameworks are too imprecise, even on regional scales, to address many outstanding questions. This includes the Mussentuchit Member of the uppermost Cedar Mountain Formation, central Utah (southwestern United States), which could provide crucial insights into these impacts within the Western Interior Basin of North America yet remains imprecisely constrained. Here, we present high-precision U-Pb zircon dates from four primary ash beds distributed across ∼50 km in central Utah that better constrain the timing of deposition of the Mussentuchit Member and the age of entombed fossils. Ages for ash beds are interpreted through a combination of Bayesian depositional age estimation and stratigraphic age modeling, resulting in posterior ages from 99.490 +0.057/−0.050 to 98.905 +0.158/−0.183 Ma. The age model predicts probabilistic ages for fossil localities between the ashes, including new ages for Moros intrepidus, Siats meekerorum, and several undescribed ornithischian dinosaur species of key interest for understanding the timing of faunal turnover in western North America. This new geochronology for the Mussentuchit Member offers unprecedented temporal insights into a volatile interval in Earth’s history.
{"title":"Exceptional age constraint on a fossiliferous sedimentary succession preceding the Cretaceous Thermal Maximum","authors":"Ryan T. Tucker, J. Crowley, M. T. Mohr, Ray K. Renaut, P. Makovicky, Lindsay E. Zanno","doi":"10.1130/g51278.1","DOIUrl":"https://doi.org/10.1130/g51278.1","url":null,"abstract":"Understanding the effects of climatic upheavals during the Early to Late Cretaceous transition is essential for characterizing the tempo of tectonically driven landscape modification and biological interchange; yet, current chronostratigraphic frameworks are too imprecise, even on regional scales, to address many outstanding questions. This includes the Mussentuchit Member of the uppermost Cedar Mountain Formation, central Utah (southwestern United States), which could provide crucial insights into these impacts within the Western Interior Basin of North America yet remains imprecisely constrained. Here, we present high-precision U-Pb zircon dates from four primary ash beds distributed across ∼50 km in central Utah that better constrain the timing of deposition of the Mussentuchit Member and the age of entombed fossils. Ages for ash beds are interpreted through a combination of Bayesian depositional age estimation and stratigraphic age modeling, resulting in posterior ages from 99.490 +0.057/−0.050 to 98.905 +0.158/−0.183 Ma. The age model predicts probabilistic ages for fossil localities between the ashes, including new ages for Moros intrepidus, Siats meekerorum, and several undescribed ornithischian dinosaur species of key interest for understanding the timing of faunal turnover in western North America. This new geochronology for the Mussentuchit Member offers unprecedented temporal insights into a volatile interval in Earth’s history.","PeriodicalId":12642,"journal":{"name":"Geology","volume":" ","pages":""},"PeriodicalIF":5.8,"publicationDate":"2023-08-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"44878788","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
L. Melim, Sebastien R. Mure-Ravaud, T. Hegna, Brian J. Bellott, R. Lerosey‐Aubril
{"title":"Silicification of trilobites and biofilm from the Cambrian Weeks Formation, Utah: Evidence for microbial mediation of silicification: REPLY","authors":"L. Melim, Sebastien R. Mure-Ravaud, T. Hegna, Brian J. Bellott, R. Lerosey‐Aubril","doi":"10.1130/g51561y.1","DOIUrl":"https://doi.org/10.1130/g51561y.1","url":null,"abstract":"","PeriodicalId":12642,"journal":{"name":"Geology","volume":" ","pages":""},"PeriodicalIF":5.8,"publicationDate":"2023-08-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"44521999","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
P. Kapp, G. Jepson, B. Carrapa, A. Schaen, John He, Jordan W. Wang
The northwest-trending transition zone (TZ) in Arizona (southwestern United States) is an ∼100-km-wide physiographic province that separates the relatively undeformed southwestern margin of the Colorado Plateau from the hyperextended Basin and Range province to the southwest. The TZ is widely depicted to have been a Late Cretaceous−Paleogene northeast-dipping erosional slope along which Proterozoic rocks were denuded but not significantly deformed. Our multi-method thermochronological study (biotite 40Ar/39Ar, zircon and apatite [U-Th-Sm]/He, and apatite fission track) of Proterozoic rocks in the Bradshaw Mountains of the west-central Arizona TZ reveals relatively rapid cooling (∼10 °C/m.y.) from temperatures of >180 °C to <60 °C between ca. 70 and ca. 50 Ma. Given minimal ca. 70−50 Ma upper-crustal shortening in the TZ, we attribute cooling to exhumation driven by northeastward bulldozing of continental lower crust and mantle lithosphere beneath it by the Farallon flat slab. Bulldozing is consistent with contemporaneous (ca. 70−50 Ma) underplating and initial exhumation of Orocopia Schist to the southwest in western Arizona and Mesozoic garnet-clinopyroxenite xenoliths of possible Mojave batholith keel affinity in ca. 25 Ma TZ volcanic rocks.
{"title":"Laramide bulldozing of lithosphere beneath the Arizona transition zone, southwestern United States","authors":"P. Kapp, G. Jepson, B. Carrapa, A. Schaen, John He, Jordan W. Wang","doi":"10.1130/g51194.1","DOIUrl":"https://doi.org/10.1130/g51194.1","url":null,"abstract":"The northwest-trending transition zone (TZ) in Arizona (southwestern United States) is an ∼100-km-wide physiographic province that separates the relatively undeformed southwestern margin of the Colorado Plateau from the hyperextended Basin and Range province to the southwest. The TZ is widely depicted to have been a Late Cretaceous−Paleogene northeast-dipping erosional slope along which Proterozoic rocks were denuded but not significantly deformed. Our multi-method thermochronological study (biotite 40Ar/39Ar, zircon and apatite [U-Th-Sm]/He, and apatite fission track) of Proterozoic rocks in the Bradshaw Mountains of the west-central Arizona TZ reveals relatively rapid cooling (∼10 °C/m.y.) from temperatures of >180 °C to <60 °C between ca. 70 and ca. 50 Ma. Given minimal ca. 70−50 Ma upper-crustal shortening in the TZ, we attribute cooling to exhumation driven by northeastward bulldozing of continental lower crust and mantle lithosphere beneath it by the Farallon flat slab. Bulldozing is consistent with contemporaneous (ca. 70−50 Ma) underplating and initial exhumation of Orocopia Schist to the southwest in western Arizona and Mesozoic garnet-clinopyroxenite xenoliths of possible Mojave batholith keel affinity in ca. 25 Ma TZ volcanic rocks.","PeriodicalId":12642,"journal":{"name":"Geology","volume":" ","pages":""},"PeriodicalIF":5.8,"publicationDate":"2023-08-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"43132323","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Yeong-Hee Oh, Y. Choe, J. S. Peel, Y. Zhen, Patrick Smith, T. Park
{"title":"Silicification of trilobites and biofilm from the Cambrian Weeks Formation, Utah: Evidence for microbial mediation of silicification: COMMENT","authors":"Yeong-Hee Oh, Y. Choe, J. S. Peel, Y. Zhen, Patrick Smith, T. Park","doi":"10.1130/g51428c.1","DOIUrl":"https://doi.org/10.1130/g51428c.1","url":null,"abstract":"","PeriodicalId":12642,"journal":{"name":"Geology","volume":" ","pages":""},"PeriodicalIF":5.8,"publicationDate":"2023-08-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"44045168","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
M. Marvin, M. Lapôtre, Andrew W Gunn, M. Day, Alejandro Soto
Windblown dunes are common features in our solar system, forming on planetary surfaces that span wide ranges in gravity and both atmospheric and sediment properties. The patterns formed by their crests, which are readily visible from orbital images, can record information about recent changes in boundary conditions, such as shifts in wind regime or varying sediment availability. Here, we demonstrate that the density of dune interactions (where neighboring crestlines are close to each other) within a dune field is an indicator of such changes. Using orbiter-based images of 46 dune fields on Earth and Mars, we compiled a database of pattern parameters including dune spacing, crestline orientation, and interaction density. Combined with sediment fluxes derived from ERA5-Land data and a martian global circulation model, we also compiled dune turnover time scales (the time it takes for a dune to migrate one dune length) for each investigated dune field. First, we show that dune fields undergoing changes in boundary conditions display higher than expected dimensionless interaction indices. Second, dune fields with longer turnover times display a wider range in interaction indices on both Earth and Mars because they are more likely to be observed while still adjusting to recent changes in boundary conditions. Thus, a dune field’s interaction index offers a novel tool to detect and possibly quantify recent environmental change on planetary surfaces.
{"title":"Dune interactions record changes in boundary conditions","authors":"M. Marvin, M. Lapôtre, Andrew W Gunn, M. Day, Alejandro Soto","doi":"10.1130/g51264.1","DOIUrl":"https://doi.org/10.1130/g51264.1","url":null,"abstract":"Windblown dunes are common features in our solar system, forming on planetary surfaces that span wide ranges in gravity and both atmospheric and sediment properties. The patterns formed by their crests, which are readily visible from orbital images, can record information about recent changes in boundary conditions, such as shifts in wind regime or varying sediment availability. Here, we demonstrate that the density of dune interactions (where neighboring crestlines are close to each other) within a dune field is an indicator of such changes. Using orbiter-based images of 46 dune fields on Earth and Mars, we compiled a database of pattern parameters including dune spacing, crestline orientation, and interaction density. Combined with sediment fluxes derived from ERA5-Land data and a martian global circulation model, we also compiled dune turnover time scales (the time it takes for a dune to migrate one dune length) for each investigated dune field. First, we show that dune fields undergoing changes in boundary conditions display higher than expected dimensionless interaction indices. Second, dune fields with longer turnover times display a wider range in interaction indices on both Earth and Mars because they are more likely to be observed while still adjusting to recent changes in boundary conditions. Thus, a dune field’s interaction index offers a novel tool to detect and possibly quantify recent environmental change on planetary surfaces.","PeriodicalId":12642,"journal":{"name":"Geology","volume":" ","pages":""},"PeriodicalIF":5.8,"publicationDate":"2023-08-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"43945443","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Andrew I. Stearns, J. Wellner, Jerome J. Kendall, Shuhab D. Khan
Southeastern Texas (United States) recorded one of the largest flooding events in U.S. history during Hurricane Harvey (25−31 August 2017), mobilizing millions of cubic meters of sediment in Houston fluvial-estuarine systems. We conducted an integrated quantitative analysis to determine the net minimum volume of sediment transported during the storm using subaerial elevation change, satellite and ground-based images, and sediment dredging reports along major waterways. The 12 fluvial-estuarine streams and two controlled reservoir drainages in the Houston area transported a minimum of ∼2.723 × 107 m3 of sediment. This volume is ∼6−51 times larger than the average annual volume of sediment delivered to Galveston Bay in modern times (in the past 200 yr), and ∼30−118 times larger when compared to Holocene rates. Nearly ∼26% of the measured volume was deposited in Addicks and Barker reservoirs, decreasing holding capacities by ∼1.2% and ∼1.6%, respectively. In the stream drainages, sediment was mobilized from west-northwest of Houston and pulsed toward Galveston Bay, highlighting the extreme short-term variability in sediment delivery. Sediment flux through the Houston region during Harvey is an example of sediment storage followed by a pulsed delivery of high sediment volume rather than continuous delivery of sediment. Comparison of sediment volumes transported through natural and modified drainages through Houston demonstrates that channel modification resulted in significant bypass of sediment downstream. Urban watershed management is more effective when continual updates are implemented based on regional circumstances rather than based on historical fluxes.
{"title":"Sediment routing in an incised valley during Hurricane Harvey (2017) in Houston, Texas, USA: Implications for modern sedimentation","authors":"Andrew I. Stearns, J. Wellner, Jerome J. Kendall, Shuhab D. Khan","doi":"10.1130/g51312.1","DOIUrl":"https://doi.org/10.1130/g51312.1","url":null,"abstract":"Southeastern Texas (United States) recorded one of the largest flooding events in U.S. history during Hurricane Harvey (25−31 August 2017), mobilizing millions of cubic meters of sediment in Houston fluvial-estuarine systems. We conducted an integrated quantitative analysis to determine the net minimum volume of sediment transported during the storm using subaerial elevation change, satellite and ground-based images, and sediment dredging reports along major waterways. The 12 fluvial-estuarine streams and two controlled reservoir drainages in the Houston area transported a minimum of ∼2.723 × 107 m3 of sediment. This volume is ∼6−51 times larger than the average annual volume of sediment delivered to Galveston Bay in modern times (in the past 200 yr), and ∼30−118 times larger when compared to Holocene rates. Nearly ∼26% of the measured volume was deposited in Addicks and Barker reservoirs, decreasing holding capacities by ∼1.2% and ∼1.6%, respectively. In the stream drainages, sediment was mobilized from west-northwest of Houston and pulsed toward Galveston Bay, highlighting the extreme short-term variability in sediment delivery. Sediment flux through the Houston region during Harvey is an example of sediment storage followed by a pulsed delivery of high sediment volume rather than continuous delivery of sediment. Comparison of sediment volumes transported through natural and modified drainages through Houston demonstrates that channel modification resulted in significant bypass of sediment downstream. Urban watershed management is more effective when continual updates are implemented based on regional circumstances rather than based on historical fluxes.","PeriodicalId":12642,"journal":{"name":"Geology","volume":" ","pages":""},"PeriodicalIF":5.8,"publicationDate":"2023-07-31","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"47608997","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
G. Sun, Xiumian Hu, E. Garzanti, M. BouDagher-Fadel, Yiwei Xu, Jingxin Jiang, E. Wolfgring, Yasu Wang, Shijun Jiang
The timing of continental collision between Arabia and Eurasia is a highly controversial issue, on which new constraints are here provided from the Amiran Basin (Zagros Mountains, Iran). Upper Cretaceous carbonate ramps grown along the Arabian northern margin are overlain by the siliciclastic deep-water Amiran and shallow-water Kashkan Formations, dated biostratigraphically as 64−60 Ma (Paleocene) and 56−52 Ma (earliest Eocene), respectively. Abundant ophioliticlastics, detrital Cr-spinel geochemistry, and detrital zircons with positive εHf(t) values dated as 110−80 Ma, 180−160 Ma, and 260−200 Ma indicate that the Amiran Formation was derived from the obducted Kermanshah ophiolite and Sanandaj-Sirjan zone. Besides sharing similar composition and zircon-age spectra, the overlying Kashkan Formation contains recycled detritus and one new zircon-age component with negative εHf(t) values dated as 250−200 Ma, suggesting supply from additional sources in Central Iran. The Amiran Formation thus indicates that the Kermanshah ophiolite, obducted in the Late Cretaceous, was subaerially exposed to erosion in the Paleocene. The Kashkan Formation testifies to the establishment of a new fluvial system, sourced from Central Iran and flowing across the Zagros suture zone. This implies that continental collision between Arabia and Eurasia took place before the beginning of the Eocene (56 Ma) in the Lorestan region (Iran).
{"title":"Pre-Eocene Arabia-Eurasia collision: New constraints from the Zagros Mountains (Amiran Basin, Iran)","authors":"G. Sun, Xiumian Hu, E. Garzanti, M. BouDagher-Fadel, Yiwei Xu, Jingxin Jiang, E. Wolfgring, Yasu Wang, Shijun Jiang","doi":"10.1130/g51321.1","DOIUrl":"https://doi.org/10.1130/g51321.1","url":null,"abstract":"The timing of continental collision between Arabia and Eurasia is a highly controversial issue, on which new constraints are here provided from the Amiran Basin (Zagros Mountains, Iran). Upper Cretaceous carbonate ramps grown along the Arabian northern margin are overlain by the siliciclastic deep-water Amiran and shallow-water Kashkan Formations, dated biostratigraphically as 64−60 Ma (Paleocene) and 56−52 Ma (earliest Eocene), respectively. Abundant ophioliticlastics, detrital Cr-spinel geochemistry, and detrital zircons with positive εHf(t) values dated as 110−80 Ma, 180−160 Ma, and 260−200 Ma indicate that the Amiran Formation was derived from the obducted Kermanshah ophiolite and Sanandaj-Sirjan zone. Besides sharing similar composition and zircon-age spectra, the overlying Kashkan Formation contains recycled detritus and one new zircon-age component with negative εHf(t) values dated as 250−200 Ma, suggesting supply from additional sources in Central Iran. The Amiran Formation thus indicates that the Kermanshah ophiolite, obducted in the Late Cretaceous, was subaerially exposed to erosion in the Paleocene. The Kashkan Formation testifies to the establishment of a new fluvial system, sourced from Central Iran and flowing across the Zagros suture zone. This implies that continental collision between Arabia and Eurasia took place before the beginning of the Eocene (56 Ma) in the Lorestan region (Iran).","PeriodicalId":12642,"journal":{"name":"Geology","volume":" ","pages":""},"PeriodicalIF":5.8,"publicationDate":"2023-07-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"45981919","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
M. Westoby, S. Dunning, J. Carrivick, T. Coulthard, K. Sain, Ajay Kumar, E. Berthier, U. Haritashya, D. Shean, M. Azam, Kavita Upadhyay, M. Koppes, Harley R. McCourt, D. Shugar
High-magnitude mass flows can have a pervasive geomorphological legacy, yet the short-term response of valley floors to such intense disturbances is poorly known and poses significant observational challenges in unstable landscapes. We combined satellite remote sensing, numerical modeling, and field observations to reconstruct the short-term geomorphological response of river channels directly affected by the 7 February 2021 ice-rock avalanche−debris flow in Chamoli district, Uttarakhand, India. The flow deposited 10.4 ± 1.6 Mm3 of sediment within the first 30 km and in places reset the channel floor to a zero-state condition, requiring complete fluvial re-establishment. In the 12 months post-event, 7.0 ± 1.5 Mm3 (67.2%) of the deposit volume was removed along a 30-km-long domain and the median erosion rate was 2.3 ± 1.1 m a−1. Most sediment was removed by pre-monsoon and monsoon river flows, which conveyed bedload waves traveling at 0.1−0.3 km day−1 and sustained order-of-magnitude increases in suspended sediment concentrations as far as 85 km from the event source. Our findings characterize a high-mountain fluvial cascade with a short relaxation time and high resilience to a high-magnitude geomorphological perturbation. This system response has wider implications, notably for water quality and downstream hydropower projects, which may be disrupted by elevated bedload and suspended sediment transport.
{"title":"Rapid fluvial remobilization of sediments deposited by the 2021 Chamoli disaster, Indian Himalaya","authors":"M. Westoby, S. Dunning, J. Carrivick, T. Coulthard, K. Sain, Ajay Kumar, E. Berthier, U. Haritashya, D. Shean, M. Azam, Kavita Upadhyay, M. Koppes, Harley R. McCourt, D. Shugar","doi":"10.1130/g51225.1","DOIUrl":"https://doi.org/10.1130/g51225.1","url":null,"abstract":"High-magnitude mass flows can have a pervasive geomorphological legacy, yet the short-term response of valley floors to such intense disturbances is poorly known and poses significant observational challenges in unstable landscapes. We combined satellite remote sensing, numerical modeling, and field observations to reconstruct the short-term geomorphological response of river channels directly affected by the 7 February 2021 ice-rock avalanche−debris flow in Chamoli district, Uttarakhand, India. The flow deposited 10.4 ± 1.6 Mm3 of sediment within the first 30 km and in places reset the channel floor to a zero-state condition, requiring complete fluvial re-establishment. In the 12 months post-event, 7.0 ± 1.5 Mm3 (67.2%) of the deposit volume was removed along a 30-km-long domain and the median erosion rate was 2.3 ± 1.1 m a−1. Most sediment was removed by pre-monsoon and monsoon river flows, which conveyed bedload waves traveling at 0.1−0.3 km day−1 and sustained order-of-magnitude increases in suspended sediment concentrations as far as 85 km from the event source. Our findings characterize a high-mountain fluvial cascade with a short relaxation time and high resilience to a high-magnitude geomorphological perturbation. This system response has wider implications, notably for water quality and downstream hydropower projects, which may be disrupted by elevated bedload and suspended sediment transport.","PeriodicalId":12642,"journal":{"name":"Geology","volume":" ","pages":""},"PeriodicalIF":5.8,"publicationDate":"2023-07-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"44416246","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
We documented the impact of Late Pleistocene−Holocene climate change on terrace deposits and preserved channels in the unglaciated drainage of the Colorado River in central Texas (south-central United States) using integrated channel morphology and provenance analysis. Detrital zircon (DZ) U-Pb ages (n = 1850) from fluvial terrace deposits and new quantitative analysis of fluvial channel morphology based on LiDAR data were used to reconstruct sediment provenance and shifts in paleohydraulic conditions during Late Pleistocene to Holocene aridification. These data reveal a reduction in fluvial channel size and discharge temporally coupled with a rapid shift in erosion locus and dominant sediment sourcing, from the Southern Rocky Mountains to the Llano area, during the glacial-interglacial transition. Geomorphic mapping and morphometric analysis show narrowing of river channels linked to diminishing Colorado River discharge. DZ data show an abrupt shift to erosion in the lower drainage basin and the remobilization of older terraces due to river incision and lateral channel migration. We attribute these systematic changes to upper-basin contraction caused by drainage reorganization and aridification during the Late Pleistocene, as well as the onset of enhanced convective precipitation sourced from the Gulf of Mexico, driving focused erosion along the topographic edge of the Llano uplift in central Texas since the early to mid-Holocene.
{"title":"Fluvial response to Late Pleistocene−Holocene climate change in the Colorado River drainage, central Texas, USA","authors":"E. Gutiérrez, D. Stockli","doi":"10.1130/g51239.1","DOIUrl":"https://doi.org/10.1130/g51239.1","url":null,"abstract":"We documented the impact of Late Pleistocene−Holocene climate change on terrace deposits and preserved channels in the unglaciated drainage of the Colorado River in central Texas (south-central United States) using integrated channel morphology and provenance analysis. Detrital zircon (DZ) U-Pb ages (n = 1850) from fluvial terrace deposits and new quantitative analysis of fluvial channel morphology based on LiDAR data were used to reconstruct sediment provenance and shifts in paleohydraulic conditions during Late Pleistocene to Holocene aridification. These data reveal a reduction in fluvial channel size and discharge temporally coupled with a rapid shift in erosion locus and dominant sediment sourcing, from the Southern Rocky Mountains to the Llano area, during the glacial-interglacial transition. Geomorphic mapping and morphometric analysis show narrowing of river channels linked to diminishing Colorado River discharge. DZ data show an abrupt shift to erosion in the lower drainage basin and the remobilization of older terraces due to river incision and lateral channel migration. We attribute these systematic changes to upper-basin contraction caused by drainage reorganization and aridification during the Late Pleistocene, as well as the onset of enhanced convective precipitation sourced from the Gulf of Mexico, driving focused erosion along the topographic edge of the Llano uplift in central Texas since the early to mid-Holocene.","PeriodicalId":12642,"journal":{"name":"Geology","volume":"7 1","pages":""},"PeriodicalIF":5.8,"publicationDate":"2023-07-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"41292846","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Liuwen Xia, Jian Cao, Wenxuan Hu, E. Stüeken, Xiaolin Wang, S. Yao, Dongming Zhi, Yong Tang, Baoli Xiang, Wenjun He
Methane (CH4) is an important greenhouse gas, but its behavior and influencing factors over geological time scales are not sufficiently clear. This study investigated the Late Paleozoic Ice Age (LPIA), which is thought to have experienced an interval of rapid warming at ca. 304 Ma, that may have been analogous to modern warming. To explore possible causes of this warming event, we investigated ancient alkaline lakes in the Junggar Basin, northwestern China. Results show that microbial CH4 cycling here was strong, as evidenced by carbonate δ13C (δ13Ccarb) values of >5‰, ∼+0.6‰ offsets between pristane δ13C (δ13CPr) and phytane δ13C (δ13CPh) values, a 3β-methylhopane index of 9.5% ± 3.0%, and highly negative δ13C values of hopanes (−44‰ to −61‰). Low sulfate concentrations in the alkaline lakes made methanogenic archaea more competitive than sulfate-reducing bacteria, and the elevated levels of dissolved inorganic carbon promoted methanogenesis. Biogenic CH4 emissions from alkaline lakes, in addition to CO2, may have contributed to rapid climate warming.
{"title":"Effects on global warming by microbial methanogenesis in alkaline lakes during the Late Paleozoic Ice Age (LPIA)","authors":"Liuwen Xia, Jian Cao, Wenxuan Hu, E. Stüeken, Xiaolin Wang, S. Yao, Dongming Zhi, Yong Tang, Baoli Xiang, Wenjun He","doi":"10.1130/g51286.1","DOIUrl":"https://doi.org/10.1130/g51286.1","url":null,"abstract":"Methane (CH4) is an important greenhouse gas, but its behavior and influencing factors over geological time scales are not sufficiently clear. This study investigated the Late Paleozoic Ice Age (LPIA), which is thought to have experienced an interval of rapid warming at ca. 304 Ma, that may have been analogous to modern warming. To explore possible causes of this warming event, we investigated ancient alkaline lakes in the Junggar Basin, northwestern China. Results show that microbial CH4 cycling here was strong, as evidenced by carbonate δ13C (δ13Ccarb) values of >5‰, ∼+0.6‰ offsets between pristane δ13C (δ13CPr) and phytane δ13C (δ13CPh) values, a 3β-methylhopane index of 9.5% ± 3.0%, and highly negative δ13C values of hopanes (−44‰ to −61‰). Low sulfate concentrations in the alkaline lakes made methanogenic archaea more competitive than sulfate-reducing bacteria, and the elevated levels of dissolved inorganic carbon promoted methanogenesis. Biogenic CH4 emissions from alkaline lakes, in addition to CO2, may have contributed to rapid climate warming.","PeriodicalId":12642,"journal":{"name":"Geology","volume":" ","pages":""},"PeriodicalIF":5.8,"publicationDate":"2023-07-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"47538576","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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