Marine redox variations and nitrogen cycle of the early Cambrian southern margin of the Yangtze Platform, South China: Evidence from nitrogen and organic carbon isotopes

Marine redox stratification during the early Cambrian (ca. 529‐509 Ma) and its control on the development of organic‐rich shales in Yangtze Platform

“…Early Cambrian ocean in Yangtze Platform in South China has been well studied on sedimentary environment reconstruction [ Zhu et al ., ; Dong et al ., ; Wang et al ., a], ocean redox [ Goldberg et al ., ; Guo et al ., ; Lehmann et al ., ; Wang et al ., ; Xu et al ., ; Och et al ., ; Pi et al ., ; Wang et al ., b], and hydrothermal activities [ Lott et al ., ; Steiner et al ., ; Jiang et al ., ; Chen et al ., ; Pašava et al ., ; Li et al ., ]. Overall, the sea level rose rapidly during Stage 2, and kept in high level during early Stage 3, then fell slowly during late Stage 3‐Stage 4 [ Peng et al ., ; Babcock et al ., ].…”

“…LCOS with high TOC, widely distributed in Yangtze Platform across shelf to basin, are considered as shales deposited in anoxic‐euxinic conditions during early Cambrian global transgression [e.g., Guo et al ., ; Lehmann et al ., ; Wille et al ., ; Wang et al ., ; Och et al ., ; Pi et al ., ]. It is a comprehensive result for organic‐rich sediments from multiple factors e.g.,: (1) high primary productivity [ Yeasmin et al ., ], coincided with the great bioradiation of metazoans during early Cambrian [ Brasier , ; Marshall , ], (2) high sea level and low sedimentation rate [ Wang et al ., ] due to a rapid transgression at the beginning of Cambrian [ Fike et al ., ; Babcock et al ., ], (3) upwelling existed around slope [ Xia et al ., ; Yeasmin et al ., ], (4) hydrothermal activity in local areas [ Steiner et al ., ; Chen et al ., ; Li et al ., ], (5) anoxic (and restrictive) sedimentary environment [ Liang et al ., ; Han et al ., ; Tan et al ., ; Wang et al ., a].…”

Controls on the organic carbon content of the lower Cambrian black shale in the southeastern margin of Upper Yangtze

“…During the early Niutitang Stage, the Upper Yangtze became quiet and stratified, when the relative sea level reached its maximum flooding surface, and the chemocline migrated to the euphotic zone. Afterward to the end of the Niutitang Stage, the reducing conditions in the bottom water weakened due to the sea-level falling, while sulfuration appeared in the deep basin only (Xu et al 2012;Li et al 2015;Wang et al 2015b). At the end of the early Cambrian, black shale deposited only in SMUY when the main part of the Upper Yangtze changed to a carbonate platform.…”

“…The lower Cambrian black shale (LCBS) has generally been considered as depositing in an anoxic-euxinic environment in the early Cambrian global transgression (Guo et al 2007;Lehmann et al 2007;Liu et al 2016a, b;Zhang et al 2017a, b) and it is a high-quality source rock (Hu et al 2015;Song et al 2015;Wu et al 2016;Liu et al 2017a, b;Zhang et al 2018) similar to typical black shale in North America, characterized by wide distribution, large thickness (100-400 m), high TOC (2%-10%), which means LCBS has geological advantages for shale gas accumulation (Dong et al 2009;Liu et al 2009;Wang et al 2009a, b;Xiao et al 2015;Zhang et al 2015). The LCBS in Upper Yangtze has been well analyzed, focusing on sedimentary environment assessment (Zhu et al 2003(Zhu et al , 2006Wang et al 2015a), redox conditions (Guo et al 2007;Lehmann et al 2007;Jiang et al 2009;Wang et al 2012Wang et al , 2015bXu et al 2012;Och et al 2013) and hydrothermal activity (Lott et al 1999;Steiner et al 2001;Jiang et al 2006Jiang et al , 2007Chen et al 2009). However, the controlling factors of TOC in the LCBS are still unclear, especially the control from multiple conditions in the sedimentary process.…”

REE and trace element patterns from organic-rich rocks of the Ediacaran–Cambrian transitional interval

“…Numerous studies have centered on the fossil record, the sedimentology, and the geochemistry of this period (Richard, 1998;Wu et al, 1999a, b;Yang et al, 2003;Yang et al, 2004;Xiao et al, 2005;Tribovillard et al, 2006;Goldberg et al, 2007;Jiang et al, 2007;Lehmann et al, 2007;Schröder and Grotzinger, 2007;Zhu et al, 2007;Guo et al, 2007a, b;Ishikawa et al, 2008;Sawaki et al, 2008;Wille et al, 2008;Guo et al, 2013;Ishikawaa et al, 2013;Pi et al, 2013;Xu et al, 2013;Feng et al, 2014;Och et al, 2015;Wang et al, 2015). Anoxic to euxinic conditions have been proposed for the early Cambrian based on the widespread deposition of black shales, the enrichment of certain redox-sensitive trace metals such as Mo, Ni, and PGE (Pt-group elements), and the prominent negative shifts in the isotopic evolution of C (lower δ…”