Origin of organic matter and depositional characteristics of early Cambrian Niutitang Formation from South China: New insights using molecular fossils

Abstract

The early Cambrian Niutitang Formation is broadly developed in South China, especially in the Yangtze region. This research explains the nature of hydrocarbons through bitumen fractions of the early Cambrian sediments of the Niutitang Formation. For this purpose, source rock samples from two diverse outcrop sections are utilized for total organic carbon content (TOC), solvent extraction, and gas chromatography–mass spectrometry (GC–MS). Results show a lower quantity of extractable organic matter in these older sediments because of higher maturation history. The presence of monomethyl alkanes suggests the contribution of prokaryotic organisms, whereas the presence of hopanoids and C27–C29 steranes shows the occurrence of eukaryotic algal sources in organic matter. Likewise, C30‐4‐methyl sterane, dinosteranes, and ß‐carotene also suggested incorporating prokaryotic and eukaryotic sources during the early Cambrian period. Various hopanoid parameters, alkylated aromatic isomers, triaromatic steroids, and vitrinite reflectance via methyl‐phenanthrene index reveal mature to higher thermal evolution levels of these lower Palaeozoic sediments. Similarly, a higher abundance of polyaromatic pyrene and fluoranthene indicates mature organic matter, and their presence could be due to hydrothermal action. The higher gammacerane index, lower pristine/phytane, and the presence of C30 dimethyl steranes indicate the anoxic saline sedimentary condition throughout the deposition of these lower Palaeozoic Niutitang Formation. The early Cambrian Niutitang Formation is deposited in an oxygen‐deficient environment and contains an adequate amount of mature‐high mature organic matter that could have the potential to produce gaseous hydrocarbons.

Investigation on the thermal maturity, organic matter sources and depositional environment of lacustrine source rocks in the Dongying Formation of the Bozhong Sag, Bohai Bay Basin, China

“…Recent studies have highlighted that the geochemical characteristics and the hydrocarbon potential of source rocks within a single continental lacustrine basin may exhibit significant vertical heterogeneity (Gao et al, 2016; Hu et al, 2022; Hu et al, 2023; Jiang & Pang, 2011; Justwan & Dahl, 2005; Pan et al, 2021). In general, the heterogeneity characteristics of source rocks largely depend on the origin, quality, depositional environment and maturity of the organic matter (Awan et al, 2023; Ding et al, 2023; Gao et al, 2017; Peters, 1986; Tissot, 1984). The quality difference of the source rocks can be determined by employing detailed geochemical analysis, e.g., TOC, vitrinite reflectance ( R o ), kerogen elemental, extractable organic matter (EOM), carbon isotope and biomarkers analysis (Hakimi et al, 2023; Peters, 1986; Stahl, 1978; Wang, Hao, et al, 2015).…”