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

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Origin of organic matter and depositional characteristics of early Cambrian Niutitang Formation from South China: New insights using molecular fossils
Geological Journal ( IF 1.4 ) Pub Date : 2022-09-21 , DOI: 10.1002/gj.4593
Rizwan Sarwar Awan _{1,

2,

3} , Chenglin Liu _{2,

3} , Feng Dehao _{2,

3} , Qibiao Zang _{2,

3} , Yuping Wu _{2,

3} , Sajjad Ali _{2,

3}

Affiliation

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.

中文翻译：

华南早寒武世牛蹄塘组有机质来源与沉积特征：分子化石新认识

早寒武世牛蹄塘组广泛发育于华南地区，尤其是长江地区。这项研究通过牛蹄塘组早寒武世沉积物的沥青组分解释了碳氢化合物的性质。为此，来自两个不同露头部分的烃源岩样品用于总有机碳含量 (TOC)、溶剂萃取和气相色谱-质谱 (GC-MS)。结果表明，由于成熟历史较长，这些较古老的沉积物中可提取的有机质含量较低。单甲基烷烃的存在表明原核生物的贡献，而类槐烷和 C ₂₇ -C ₂₉甾烷的存在表明有机物中存在真核藻类来源。同样，C₃₀ -4-甲基甾烷、恐龙甾烷和 ß-胡萝卜素也建议在寒武纪早期结合原核和真核来源。各种 hopanoid 参数、烷基化芳烃异构体、三芳烃类固醇和通过甲基菲指数的镜质体反射表明这些下古生代沉积物成熟到更高的热演化水平。同样，较高丰度的多芳烃芘和荧蒽表明成熟有机质，它们的存在可能是由于热液作用。较高的 gammacerane 指数、较低的原始/植烷和 C _30的存在二甲基甾烷表明了这些下古生界牛蹄塘组沉积过程中的缺氧盐水沉积条件。早寒武世牛蹄塘组沉积于缺氧环境，含有充足的成熟-高成熟有机质，具有形成气态烃的潜力。

更新日期：2022-09-21

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