松辽盆地晚白垩世青山口组缺氧事件层的地质地球化学特征

Geological and Geochemical Characteristics of Anoxic Event Bed in the Qingshankou Formation of Late Cretaceous in Songliao Basin

松辽盆地白垩系青山口组下部广泛分布一套富含有机碳的黑色泥岩、页岩沉积,是全盆地地层划分对比的一级标志。茂206井是中国白垩纪大陆科学钻探工程井,全井获取了青山口组497.02 m的岩心资料。茂206井青山口组具有相对高的有机碳、干酪根碳同位素正偏、重排甾烷含量低以及普遍存在伽马蜡烷生物标志化合物等有机地球化学特征,表征为白垩纪温室效应时间窗内古湖泊缺氧事件的产物。结合生物地层研究成果,认为青山口期缺氧事件层大体可与白垩纪古海洋Cenomanian—Turonian界线事件层进行对比,进一步证实了青山口组的地质时代属晚白垩世晚Ceno-manian—Turonian期的观点。

The core from the drillinghole of Mao 206 in the Songliao Basin was obtained by the China Cretaceous Continental Scientific Drilling Project.The interval of the Qingshankou Formation is 497.02 meters long and is the material of present study.The formation is a group of dark mudstone and shale sediments rich in organic carbon.The organic carbon-rich sediments are the marker beds of stratigraphic division and correlation in the basin.The organic geochemical characteristics identified from drillinghole Mao 206 are high organic carbon contents,positive excursion of kerogen isotopes and low diasteranes contents,and the biomarkers of gammacerane are ubiquitous.They are possibly the evidences of lacustrine anoxic records in the mid-Cretaceous extreme greenhouse climate period.According to the biostratigraphic constrain,the present authors suggest that the anoxic event might be happened in the Songliao Basin and corresponds to the marine oceanic anoxic event occurred at the Cenomanian-Turonian boundary.Based on both biostratigraphy and chemostratigraphy,the age of the Qing-shankou Formation should be Late Cenomanian to Turonian.