Records Of Sulfur Burial And Paleolimnological Change In Unit 1 Of Qingshankou Formation, Cretacous Songliao Basin

Songliao Basin, located in northeastern China(E119°40′～128°24′,N42°25′～49°23′),is a large-scale Cretaceous sedimentary Basin in China, and one of the most big Cretaceous lake in Asia. The Cretaceous strata developed most completely and continuously here. Qingshankou period in Cretaceous is the time when the first large-scale lacustrine transgressional events happened in Songliao Basin. For a long time, Anoxic events and Marine transgressional events have been the research focuses in Songliao region, during that period.Based on the drill core description of the Qingshankou formation from SkⅠin Songliao Basin, we summarized the characters of core, such as sedimentary structure, mineral and palaeontology, having a comprehensive understanding for the Qingshankou Formation. Meanwhile, 15 lithofacies, 5 lithofacies assemblages and 6 boundaries have been identified systematically in the cores. Qingshankou Formation consists of mudstones intercalated with calcareous siltstones and bioclastic limestones. From the top to bottom, the lithology becomes more and more homogeneous and the color deepens.Having Studied the sulfur isotope composition of pyrite, the weight percent of pyrite sulfur, the TOC in unit 4 of Quantou formation and unit 1 of Qingshankou Formation, we got the depth profiles forδ34S of pyrite, pyrite sulphur(weight percentage) and TOC. Most pyrite mineral are enriched in 34S relative to CDT standard, changing from 14.4‰to 24.06‰and having the average value of 18.48‰. The abundance of pyrite sulphur (weight percent) varies from 0.03‰to 1.74‰and having the average value of 0.59‰, which is higher than many other environments.The value of TOC is also high, changing from 1.02‰to 8.63‰and having the average value of 3.25‰. The three curves share the same trend, and reach the peak around the bottom of unit 1 of Qingshankou Formation.Based on the evidences mentioned above, We studied the lacustrine anoxic events, the concentration of the sulphate in the Songliao palaeolake and the Marine transgressional events during the period when the unit 1 of Qingshankou Formation deposited. During that time, suffering one of the most large-scale lacustrine transgressional events, Songliao lake had a anoxic bottom water body, and the concentration of the sulphate probably originated from marine was relatively low.