The oil shale formation mechanism of the Songliao Basin Nenjiang Formation triggered by marine transgression and oceanic anoxic events 3

摘要

The influence of oceanic anoxic events 3 (OAE3) and transgression events during the Coniacian-Santonian boundary period on the sedimentary paleoenvironment of Nenjiang Formation strata and the oil shale formation mechanism is not clear yet. The high-precision determination of elements, stable isotopes and biomarkers of the Nenjiang Formation oil shale samples was tested in this study. The study showed that the source of organic matter (OM) of the Nenjiang Formation oil shale was a mixture of aquatic organisms (algae and bacteria) and higher plants. Some geochemical parameters also indicated that the OM in the formation might contain a certain amount of marine organic matter. Under OAE3, the pCO(2) and warm and humid paleoclimate caused an increase in the total organic carbon (TOC) and the organic carbon isotope (delta C-13(org)) negative deviation near the Santonian-Campanian (S-C) boundary. Seawater entered the Songliao Lake Basin, and the nutrient composition, water density stratification and sulfate content increased. The reducing environment of the bottom water was conducive to the accumulation and burial of organic matter. With increasing sulfate content, the total organic carbon/total sulfur (TOC/TS) in the formation decreased, and the sulfate delta S-34 produced a negative bias. Under the influence of OAE3 and transgression events, the paleoenvironment of oil shale formation in the Nenjiang Formation was divided into four stages.