Geochemical and petrographic characteristics of Wufeng-Longmaxi shales, Jiaoshiba area, southwest China: Implications for organic matter differential accumulation

Lithofacies Types, Assemblage Characteristics, and Sedimentary Evolution Model of Lacustrine Shale in Dongyuemiao Formation of Fuxing Area

“…On the contrary, in a reducing water environment, these elements are easily deposited and enriched due to their low solubility under anoxic conditions. When the V/Cr ratio > 4.25, it indicates an anoxic water environment; when it is between 2-4.25, it indicates a dysoxic sedimentary environment; and when it is < 2, it indicates an oxygen-rich sedimentary environment (Algeo and Maynard, 2004;Tribovillard et al, 2006;Wang et al, 2018;Lu et al, 2019). The V/Cr index of the shale samples from the Dongyuemiao Formation shows that the ratio is greater than 4.25 on the whole, which indicates that it was deposited in an anoxic sedimentary environment.…”

“…As redox-sensitive elements, vanadium (V) and chromium (Cr) are widely used to indicate the redox environment during the deposition of paleowater (Algeo and Maynard, 2004;Algeo and Tribovillard, 2009;Liu et al, 2017;Lu et al, 2019;Ross and Bustin., 2009;Wang et al, 2018). The V/Cr ratio in the Dong-1 Member is higher than that in the Dong-2 Member and the Dong-3 Member; the V/Cr ratio in the Dong-1 Member is generally higher than 4.25, while in the Dong-2 Member and Dong-3 Member, the ratio is basically between 2-4.25, indicating that the sedimentary environment intensely changed upward from anoxic conditions to oxic conditions.…”

“…Beginning in 2010, this research group began to study the potential for the exploration and development of shale oil and gas in China's geological terrain by drawing lessons from the successful shale revolution in the United States. In recent years, research on shale oil has become extremely important (Jia et al, 2013a;Sun et al, 2013;Xu et al, 2015;He et al, 2017;Wang et al, 2018;Li W. et al, 2020). At present, shale oil research in the United States is mainly focused on the Permian, Bakken, Eagle Ford, Niobrara, and other zones, and most of them are marine deposits.…”

Influence of Organic Matter on Gas-Bearing Properties and Analysis of Sedimentary Mechanism of Organic Matter Enrichment: A Case Study on the Yangtze Region of Southern China during the Early Cambrian

“…Exploring the enrichment pattern of sedimentary organic matter is becoming increasingly significant as the total organic carbon (TOC) content in shale is influenced by thermal evolution degrees and abundance of this matter. Many studies using different approaches have been conducted to analyze the mechanism [5][6][7][8][9]. Xia et al utilized trace and rare Earth elements to prove that ascending currents facilitated organic matter enrichment.…”

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“…Due to the differences in geological characteristics between the lacustrine shale in China and the marine shale in North America, such as complex structure, deep burial, and strong heterogeneity, it is hard to copy the successful experience and models of North America (Cui et al, 2015;Zhou et al, 2015;Jin et al, 2016). At present, the research of lacustrine shale has already made certain understanding and essential progress in mineral composition and genesis (Aplin and Macquaker, 2011;Slatt and Rodriguez, 2012;Chermak and Schreiber, 2014;Liu et al, 2020a), shale sedimentary environment (Wang et al, 2019;Liu et al, 2020b;Ji et al, 2020;Liu et al, 2021;Wang et al, 2021), and pore types and characteristics (Loucks et al, 2012;Milliken et al, 2013;Ji et al, 2019). The lithofacies of shale contain information including mineral components, rock types, sedimentary structures, and organic matter abundance (Loucks and Ruppel, 2007;Ross and Bustin, 2009;Xu et al, 2018;Xu et al, 2019;Xu et al, 2020), which makes the division and distribution of lithofacies become a fundamental geology issue (Newport et al, 2016;Tang et al, 2016;Wang et al, 2018).…”