A detailed study of the mineral composition and microstructure of the black shales associated with OAE1 a （Eastern Russian Platform）, OAElb （Middle Caspian）, and the host rocks has been carried out using X-ray dif...A detailed study of the mineral composition and microstructure of the black shales associated with OAE1 a （Eastern Russian Platform）, OAElb （Middle Caspian）, and the host rocks has been carried out using X-ray diffraction, scanning electron microscopic, and microprobe analyses. The results provide important constraints for depositional environments in the sedimentary basins. Black shales with pyrite framboids imply euxinic （sulfidic） conditions with increased organic matter preservation. Disintegrating framboids suggest partial or complete dissolution of the organic matter inside the framboids due to increasing water oxygenation. OAEla on the Eastern Russian Platform is heterogeneous as it includes thin interbeds of concretionary coccolith limestones within the interval of bituminous shales, and correlates with the Lower Aptian Rhagodiscus angustus nannofossil zone. The coccolith limestones indicate short intermittent episodes of interrupted stagnation, rapid oxygenation, and restoration of normal marine conditions. The presence of montmorillonite, albite, microcline, and diopside in the bituminous siltstones and in the host siltstones of OAEla on the Eastern Russian Platform, as well as a high content of titanium in the black siltstones correlated with OAEIb in the Middle Caspian allow proposing significant input of pyroclastic material into the extant sea.展开更多
The palaeo-atmospheric CO_(2)concentration(pCOz)variation in the Yumen,Gansu Province during the middle Cretaceous has been reconstructed using the newly established plant photosynthetic gas exchange mechanistic model...The palaeo-atmospheric CO_(2)concentration(pCOz)variation in the Yumen,Gansu Province during the middle Cretaceous has been reconstructed using the newly established plant photosynthetic gas exchange mechanistic model,and the results show that the pCO_(2)values are in the range of about 550-808 ppmv.The present pCO_(2)values are higher than the pCO_(2)results(531-641 ppmv)of the previous study according to the Recent standardization of the stomatal ratio method,and much lower than the pCO_(2)results(882-1060 ppmv)according to the Carboniferous standardization of the stomatal ratio method.The present pCOz variation is not only within the error range of GEOCARB II and GEOCARB Ill but also is similar to the reconstructed results based on the biochemistry and carbon isotope models.Besides,the present Brachyphyllum specimens were collected from four consecutive horizons of the upper Zhonggou Formation of the Hanxia Section,and the reconstructed pCO_(2)exhibits the reconstructed pCO_(2)exhibits a decline trend during the late Aptian to early Albian.This decline variation is probably associated with the Oceanic Anoxic Events(OAElb)and the Cold snap event.With the combination of pCO_(2)during the Albian to Cenomanian recovered by the plant photosynthetic gas exchange mechanistic model,the pCO_(2)showed a prominent increase during the late Aptian to early Cenominian,which indicates a response to the greenhouse warming during the middle Cretaceous.Therefore,the mechanical model of the plant photosynthetic gas exchange shows a relatively strong accuracy in the reconstruction of thepCO_(2)and can reflect a strong relation between the atmospheric CO_(2)concentrations and climatic events.展开更多
基金a contribution to UNESCO-IUGS International Geoscience Programme (IGCP) Project 609 "Climate-environmental deteriorations during greenhouse phases:Causes and consequences of short-term Cretaceous sea-level changes"(SZ)
文摘A detailed study of the mineral composition and microstructure of the black shales associated with OAE1 a （Eastern Russian Platform）, OAElb （Middle Caspian）, and the host rocks has been carried out using X-ray diffraction, scanning electron microscopic, and microprobe analyses. The results provide important constraints for depositional environments in the sedimentary basins. Black shales with pyrite framboids imply euxinic （sulfidic） conditions with increased organic matter preservation. Disintegrating framboids suggest partial or complete dissolution of the organic matter inside the framboids due to increasing water oxygenation. OAEla on the Eastern Russian Platform is heterogeneous as it includes thin interbeds of concretionary coccolith limestones within the interval of bituminous shales, and correlates with the Lower Aptian Rhagodiscus angustus nannofossil zone. The coccolith limestones indicate short intermittent episodes of interrupted stagnation, rapid oxygenation, and restoration of normal marine conditions. The presence of montmorillonite, albite, microcline, and diopside in the bituminous siltstones and in the host siltstones of OAEla on the Eastern Russian Platform, as well as a high content of titanium in the black siltstones correlated with OAEIb in the Middle Caspian allow proposing significant input of pyroclastic material into the extant sea.
基金the National Natural Science Foundation of China(No.41402007,41602023,40972025)the State Key Laboratory of Palaeobiology and Stratigraphy,Nanjing Institute of Geology and Palaeontology,CAS(No.153102)
文摘The palaeo-atmospheric CO_(2)concentration(pCOz)variation in the Yumen,Gansu Province during the middle Cretaceous has been reconstructed using the newly established plant photosynthetic gas exchange mechanistic model,and the results show that the pCO_(2)values are in the range of about 550-808 ppmv.The present pCO_(2)values are higher than the pCO_(2)results(531-641 ppmv)of the previous study according to the Recent standardization of the stomatal ratio method,and much lower than the pCO_(2)results(882-1060 ppmv)according to the Carboniferous standardization of the stomatal ratio method.The present pCOz variation is not only within the error range of GEOCARB II and GEOCARB Ill but also is similar to the reconstructed results based on the biochemistry and carbon isotope models.Besides,the present Brachyphyllum specimens were collected from four consecutive horizons of the upper Zhonggou Formation of the Hanxia Section,and the reconstructed pCO_(2)exhibits the reconstructed pCO_(2)exhibits a decline trend during the late Aptian to early Albian.This decline variation is probably associated with the Oceanic Anoxic Events(OAElb)and the Cold snap event.With the combination of pCO_(2)during the Albian to Cenomanian recovered by the plant photosynthetic gas exchange mechanistic model,the pCO_(2)showed a prominent increase during the late Aptian to early Cenominian,which indicates a response to the greenhouse warming during the middle Cretaceous.Therefore,the mechanical model of the plant photosynthetic gas exchange shows a relatively strong accuracy in the reconstruction of thepCO_(2)and can reflect a strong relation between the atmospheric CO_(2)concentrations and climatic events.
