Paleosalinity and Its Association with Organic Matter:A Case Study from the Eocene Shahejie Formation,Laizhou Bay Sag,Bohai Bay Basin (China)

• 作者: LIANG Haoran XU Guosheng YU Qing XU Fanghao WANG Deying CHEN Zhiyuan
• 来源期刊: 中国海洋大学学报（自然科学英文版）
• 年，卷（期）: 2021,（4）
• 所属期刊栏目: Energy and Mineral Sedimentology in the East China Sea
• 页码范围: 741-754
• 页数: 14页
• 语种: 英文

摘要

Paleosalinity is vital for the paleoenvironmental reconstruction and affects the formation of source rock.The lower-middle sections of the third member of Eocene Shahejie formation (Es3M-L) constitute the most important source rock layer in Laizhou Bay Sag.However,the paleosalinity of the depositional water in which Es3M-L submembers are deposited remains unclear.A series of integrated experiments,including major and trace elements,X-ray diffraction,total organic carbon,and Rock-Eval,was performed to reveal the paleosalinity and its relationship with organic matter (OM).Various inorganic proxies (Sr/Ba,Rb/K,B/Ga,Walker's paleosalimeter,Adam's paleosalimeter,and Couch's paleosalimeter) were employed to determine the paleosalinity of sam-ples.Prominent differences existed in the proxies.Couch's paleosalimeter is the most reliable and qualitative approach for Laizhou Bay Sag.Samples from the lake center (depocenter) and margin showed paleosalinities from 4.92 wt‰ to 9.73 wt‰,suggesting a ubi-quitous brackish (oligohaline-mesohaline) water body in the paleolake.Molybdenum enrichment in samples indicates an oxygen-depleted (suboxic or anoxic) condition.The increase in salinity has a certain but non-significant positive correlation with oxygen reduction.This condition may be attributed to the weak stratification of the water column in brackish water bodies.Moreover,pa-leosalinity has a weak and indirect relationship with OM accumulation during the deposition of Es3M-L submembers in Laizhou Bay Sag.