论文摘要
The Cretaceous is recognized as a period of long-term climate stability with warm equable climates resulting from a higher atmospheric greenhouse gas content, punctuated by rapid climate and carbon cycle perturbations such as ocean anoxic events（OAEs）.The role of the Cretaceous terrestrial deposit corresponding to theses rapid climate events and further to the global carbon cycle perturbations, is still ambiguous.In this study, TOC-rich deposits from the Qingshankou Formation（K2qn1, ～91.0-91.9 Ma） of the Songliao Basin, one of the largest Cretaceous continental sedimentary basins developed post OAE2（～93.9 Ma）, were collected.Using molecular isotopic geochemistry methods, our objectives are to probe the mechanisms controlling the organic matter deposit dynamics and to evaluate the long-lasting impact of greenhouse climate in the post OAE2 Formation of the Songliao Basin.The molecular and stable carbon isotopic results suggest three distinct stages corresponding the organic matter accumulation and paleoenvironmental evolution.Stage Ⅲ（oldest） and Stage Ⅰ（youngest） are characterized by high Total Organic Carbon contents with relatively high Pr/Ph ratios and low Gammacerane Index values, implying that high primary productivity, rather than redox condition, accounted for organic matter accumulation.The high primary productivity in paleolake system was most likely induced by a large amount input of land-based nutrients due to strengthened weathering, and further resulted in the strong methane cycle at the water bottom（methanogens and methanotrophs）.The weak water stratification enabled a large amount of 12C-rich CO2 and CH4 to enter the upper water body, which was reutilized by the primary productivity.On the other hand, Stage Ⅱ is characterized by relatively low Total Organic Carbon contents, low Pr/Ph ratios and high Gammacerane Index values, indicating that good preservation condition and strong water stratification played a key role on organic matter accumulation.Water stratification could be induced by higher water level and salinity at this stage.Compared to Stages Ⅲ and Ⅰ, relatively weak methane cycle occurred at Stage Ⅱ as evidenced by 13C-enriched hopanes, also favored the organic matter accumulation at the water/sediment interface.Therefore, the long-lasting impact of greenhouse climate post OAE2 induced a large amount of carbon burial in the Songliao Basin, by accelerating surface erosion and thus the nutrient supply into terrestrial lake ecosystem.The terrestrial system could be one of the main factors accounting for atmospheric CO2 concentration in the Late Cretaceous, asking for further studies other Cretaceous terrestrial sedimentary basins to address this issue.
论文目录
文章来源
类型: 国际会议
作者: Yuxin HE,Changfeng ZHU,Yongge SUN,Tian XIA,Jianping CHEN
来源: 第一届亚洲古生物学大会—暨中国古生物学会成立90周年纪念 2019-11-17
年度: 2019
分类: 基础科学
专业: 地质学,地质学,地质学
单位: School of Earth Sciences, Zhejiang UniversityResearch Institute of Petroleum Exploration and Development
分类号: P534.53;P512.2;P532
页码: 122-123
总页数: 2
文件大小: 105k
下载量: 1