The Paleocene-Eocene Thermal Maximum(PETM) event was a dramatic global warming w55.93 Ma ago that resulted in biological extinction events, lithological changes, and major deviations in σ13 C and σ18 O.The southwest...The Paleocene-Eocene Thermal Maximum(PETM) event was a dramatic global warming w55.93 Ma ago that resulted in biological extinction events, lithological changes, and major deviations in σ13 C and σ18 O.The southwestern Tarim Basin of China exposes successive Paleogene strata as a result of Tethys evolution and is considered an ideal region for PETM research.Based on calcareous nannoplankton biostratigraphy, we also used stable isotopes and XRD to analyse the Paleocene-Eocene transition in the Tarim Basin. At the Bashibulake Section, the PETM interval is characterized by(1) an abrupt negative shifts in σ13 C_(org), σ13 C_(carb) and σ18 O(-3%, -4.5% and -3%respectively);(2) an obvious negative correlation between the K-mode(Discoaster, Fasciculithus, Ericsonia, Sphenolithus and Rhomboaster) and r-mode(Biscutum, Chiasmolithus, Toweius) nannofossil taxa coincident with a robust Rhomboaster-Discoaster assemblage; and(3) a significant increase in the percentage of detrital input along with an increase in gypsum content. In the upper part of the Qimugen Formation Micrantholithus and Braarudosphaera are commonly found right up to the top where most of the nannofloras suffer a sharp decrease. In the overlying Gaijitage Formation, calcareous nannofossils disappear completely. These events indicate that the southwestern Tarim Basin was a warm shallow continental shelf during the deposition of the Qimugen Formation. From the early Eocene, the environment changed conspicuously. Evaporation increased and sea level fell, which led to an acid climate.This climate mode continued within the youngest unit studied, the Gaijitage Formation, characterized by the deposition of thick evaporates. Consequently, most of the marine plankton, i.e. calcareous nannoplankton, became disappear, because of the significant climate shift.展开更多
The Eocene Kuldana Formation(KF)in the Yadgar area of Pakistan,comprises a diverse range of sedimentary facies,including variegated red beds of shales,mudstones,and sandstones,as well as interbedded limestone and marl...The Eocene Kuldana Formation(KF)in the Yadgar area of Pakistan,comprises a diverse range of sedimentary facies,including variegated red beds of shales,mudstones,and sandstones,as well as interbedded limestone and marl.In this study,we conducted an integrated micropaleontological,sedimentological,mineralogical,and geochemical investigation to determine the depositional setting,biochronology,provenance,and paleoclimate of the KF.The study identified six lithofacies and six microfacies,which indicate a variety of environments ranging from floodplains and channels to the margins and shallow marine settings.The nannofossil biostratigraphy places the KF in the Early Eocene,more precisely the NP10 zone(Ypresian),and the fossil zone of benthic foraminifera classifies the study section as the Shallow Benthic Zone SBZ-8(Middle Ilerdian 2).In terms of petrography,the KF sandstone was classified as litharenite and feldspathic litharenite,while the QtFL diagram suggests a recycled orogen.Geochemical proxies indicate an oxidizing environment,a high-to-low regular sedimentation rate,moderate-to-intense chemical weathering in the source region,and a warm-humid to dry climate during the deposition of KF.Overall,the findings suggest that the deposition of KF marks the end of Neo-Tethys due to the Early Eocene Indian–Kohistan collision and that the uplifting of the Himalayas provided the source for the deposition of KF in the foreland basin.The study provides new insights into the depositional environment,biochronology,provenance,and paleoclimate of KF,and highlights the potential for red beds as reliable indicators of oxygenation levels in proximity to mineral deposits.展开更多
基金financially supported in part by funds from the State Key Laboratory of Palaeobiology and Stratigraphy (Nanjing Institute of Geology and Palaeontology, CAS) (GBL215010)National Basic Research Program of China (973 Program, No. 2012CB822002)+3 种基金the National Natural Science Foundation of China (Nos. 41302008, 41172037)the Fundamental Research Funds for the Central Universities (53200859490)Science and Technology Innovation Fund of the China University of Geoscience (Beijing)the Beijing Higher Education Young Elite Teacher Project (YETP0665)
文摘The Paleocene-Eocene Thermal Maximum(PETM) event was a dramatic global warming w55.93 Ma ago that resulted in biological extinction events, lithological changes, and major deviations in σ13 C and σ18 O.The southwestern Tarim Basin of China exposes successive Paleogene strata as a result of Tethys evolution and is considered an ideal region for PETM research.Based on calcareous nannoplankton biostratigraphy, we also used stable isotopes and XRD to analyse the Paleocene-Eocene transition in the Tarim Basin. At the Bashibulake Section, the PETM interval is characterized by(1) an abrupt negative shifts in σ13 C_(org), σ13 C_(carb) and σ18 O(-3%, -4.5% and -3%respectively);(2) an obvious negative correlation between the K-mode(Discoaster, Fasciculithus, Ericsonia, Sphenolithus and Rhomboaster) and r-mode(Biscutum, Chiasmolithus, Toweius) nannofossil taxa coincident with a robust Rhomboaster-Discoaster assemblage; and(3) a significant increase in the percentage of detrital input along with an increase in gypsum content. In the upper part of the Qimugen Formation Micrantholithus and Braarudosphaera are commonly found right up to the top where most of the nannofloras suffer a sharp decrease. In the overlying Gaijitage Formation, calcareous nannofossils disappear completely. These events indicate that the southwestern Tarim Basin was a warm shallow continental shelf during the deposition of the Qimugen Formation. From the early Eocene, the environment changed conspicuously. Evaporation increased and sea level fell, which led to an acid climate.This climate mode continued within the youngest unit studied, the Gaijitage Formation, characterized by the deposition of thick evaporates. Consequently, most of the marine plankton, i.e. calcareous nannoplankton, became disappear, because of the significant climate shift.
文摘The Eocene Kuldana Formation(KF)in the Yadgar area of Pakistan,comprises a diverse range of sedimentary facies,including variegated red beds of shales,mudstones,and sandstones,as well as interbedded limestone and marl.In this study,we conducted an integrated micropaleontological,sedimentological,mineralogical,and geochemical investigation to determine the depositional setting,biochronology,provenance,and paleoclimate of the KF.The study identified six lithofacies and six microfacies,which indicate a variety of environments ranging from floodplains and channels to the margins and shallow marine settings.The nannofossil biostratigraphy places the KF in the Early Eocene,more precisely the NP10 zone(Ypresian),and the fossil zone of benthic foraminifera classifies the study section as the Shallow Benthic Zone SBZ-8(Middle Ilerdian 2).In terms of petrography,the KF sandstone was classified as litharenite and feldspathic litharenite,while the QtFL diagram suggests a recycled orogen.Geochemical proxies indicate an oxidizing environment,a high-to-low regular sedimentation rate,moderate-to-intense chemical weathering in the source region,and a warm-humid to dry climate during the deposition of KF.Overall,the findings suggest that the deposition of KF marks the end of Neo-Tethys due to the Early Eocene Indian–Kohistan collision and that the uplifting of the Himalayas provided the source for the deposition of KF in the foreland basin.The study provides new insights into the depositional environment,biochronology,provenance,and paleoclimate of KF,and highlights the potential for red beds as reliable indicators of oxygenation levels in proximity to mineral deposits.
