Neoproterozoic to Early Cambrian small shelly fossil assemblages and a revised biostratigraphic correlation of the Yangtze Platform (China)

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

“…Diagenetic alteration under oxic conditions usually increases the ␦ 15 N composition of organic matter (Gaye et al, 2009;Lehmann et al, 2002;Möbius et al, 2011;Nakanishi and Minagawa, 2003). This is Jiang et al, 2012;Steiner et al, 2007;Zhu et al, 2007) and stratigraphic columns of Sancha and Yuanjia sections (after Li et al, 2012b andGuo et al, 2013). because amino acids are much more easily degraded and therefore release more 14 N under oxic than anoxic conditions (Nguyen and Harvey, 1997). However, NH 4 + generated beneath the seafloor can be captured by clay minerals, in which case ␦ 15 N bulk values may show little or no change (Freudenthal et al, 2001).…”

“…Paleogeographic reconstruction shows that the late Ediacaran-early Cambrian succession overlying the Yangtze block of South China was deposited in various paleoenvironmental settings from large platformal areas with a transitional zone interpreted as outer shelf, into slope and then deeper more basinal areas Steiner et al, 2007;Zhu et al, 2007). The shelf regions of the Yangtze block were subaerially exposed and partially eroded during the earliest Cambrian, but a transgression during Cambrian Stage 2 (∼early Tommotian) submerged the shelf margins and led to homogeneous deposition of fine-grained, frequently organic-rich sediments across the entire Yangtze block Steiner et al, 2007;Zhu et al, 2003).…”

“…The shelf regions of the Yangtze block were subaerially exposed and partially eroded during the earliest Cambrian, but a transgression during Cambrian Stage 2 (∼early Tommotian) submerged the shelf margins and led to homogeneous deposition of fine-grained, frequently organic-rich sediments across the entire Yangtze block Steiner et al, 2007;Zhu et al, 2003). These 'black shales' are suggested to have been deposited under widespread anoxic, or even euxinic conditions based on numerous lines of geochemical evidence (Canfield et al, 2008;Goldberg et al, 2005Goldberg et al, , 2007Guo et al, 2007a;Kimura and Watanabe, 2001;Lehmann et al, 2007;Och et al, 2013;Wang et al, 2012a;Wille et al, 2008;Xu et al, 2012).…”

“…These 'black shales' are suggested to have been deposited under widespread anoxic, or even euxinic conditions based on numerous lines of geochemical evidence (Canfield et al, 2008;Goldberg et al, 2005Goldberg et al, , 2007Guo et al, 2007a;Kimura and Watanabe, 2001;Lehmann et al, 2007;Och et al, 2013;Wang et al, 2012a;Wille et al, 2008;Xu et al, 2012). Presumably, because of the rapidity of this sea level rise, lower Cambrian units across much of South China are condensed with only a few centimeters thickness in the deeper water realms (Goldberg et al, 2007;Schütter, 1998;Steiner et al, 2001Steiner et al, , 2007. Related to this condensation, a polymetallic enrichment layer occurs sporadically in the lower portion of this transgressive black shale along a NE-striking 1600 km belt, which can be used as a correlation marker Och et al, 2013;Zhu et al, 2003), but mineable ore layer is usually less than half meters in thickness and exposed only within Guizhou and Hunan provinces (Jiang et al, 2006(Jiang et al, , 2007.…”

The Precambrian-Cambrian biosphere (r)evolution: Insights from the Chinese Yangtze Platform

“…Other types of exceptional basal Cambrian fossil Lagerstätten yielded phosphatized Orsten-type organisms (arthropods, eggs, embryos, cnidarians, algae, etc., from several other localities), exceptional trilobite assemblages (Dai & Zhang 2012), and the rich small shelly fossil assemblages, widely distributed in the basal Cambrian of the entire Yangtze Platform (ca 540-520 Ma: e.g. Steiner et al 2007, Li et al 2012. Rencently, Sundberg et al (2011) proposed the Wuliu-Zengjiayan section situated in the Guizhou Province as the GSSP for Cambrian Stage 5.…”