Development and evolution of a euxinic wedge on the ferruginous outer shelf of the early Cambrian Yangtze sea

Redox fluctuations and organic accumulation on the outer shelf of the Early Cambrian (Ages 2–3) Yangtze sea: Geochemical records on a seaward submarine sill

“…Laterally, in terms of the lithology and TOC variation trend, both the EHST and LHST successions can be generally correlated well with those deposited in backsill lower slope-basin (Bahuang) and further updip mid-upper slope (Daotuo) settings (Figure 5). The enhanced carbonate flux reflected by the occurrences of intercalated limestones from EHST to LHST successions at Daotuo further confirmed the interpretation of HST of these deposits (Yeasmin et al, 2017;Huang et al, 2019).…”

“…Note the palaeogeographic setting of Guantang section (on the submarine sill). Data sources: 1 -Jinsha (Jin et al, 2016); 2 -Daotuo and 4 -Bahuang (Huang et al, 2019;Yeasmin et al, 2017); 3 -Songtao (Canfield et al, 2008); 5 -Yangtou (27 41 0 59 00 N, 109 25 0 51 00 E), 6 -Daqiao (27 40 0 34 00 N, 109 41 0 10 00 E), 7 -Guantang (27 38 0 27 00 N, 109 44 0 10 00 E), 8 -Huaqiao (27 40 0 18 00 N, 110 11 0 38 00 E), 9 -Dalongtan (27 29 0 18 00 N, 110 14 0 53 00 E; this study); and 10 -Longbizui (Feng et al, 2014; supercontinent from ca. 880-860 Ma (Charvet, 2013;Li et al, 2009;Li, Li, Li, & Lou, 2008;Wang et al, 2007).…”

“…Stratigraphic correlation is generally ambiguous for the deep water E-C boundary sections due to the sparse availability of ageconstrained biostratigraphic markers. Based on previous works (Chen et al, 2015;Huang et al, 2019;Yeasmin et al, 2017), the stratigraphic successions of the Niutitang black shales/mudstones can be subdivided into depositional systems tracts (Catuneanu, 2006) and correlated with equivalents in terms of vertical TOC content and lithological variations.…”

“…The vertical dashed lines in each box represent key threshold values of Fe speciation and redox-sensitive trace element proxies documented in the text. See Figures 1 and 5 for lithology and abbreviation information [Colour figure can be viewed at wileyonlinelibrary.com] of the Niutitang Formation (528 Ma) to the end of the Tommotian (521 Ma) ages (Chen et al, 2015;Huang et al, 2019;, yielding a time span of 7 Ma. These data thus yield average sedimentation rates of 0.41 cm/kyr, 0.17 cm/kyr, and 0.16 cm/kyr for the low part of the Niutitang black shales at Daotuo, Bahuang, and Guantang, respectively.…”

“…However, the predominance of ferruginous, anoxic waters in the landward intrashelf sub-basins of the inner shelf, notably in the Upper Yangtze Block (Goldberg, Strauss, Guo, & Liu, 2007;Och et al, 2013; did not reconcile such a hypothesis. In contrast, some recent studies demonstrated that the euxinic wedge predominated and fluctuated on the outer shelf-basin transect off the principal shelf margin zone where the riverine input was relatively low (e.g., Huang et al, 2019;Yeasmin et al, 2017). In this case, alternative driving forces, including enhanced oceanic upwelling (or circulation), specific palaeogeographic, and palaeoclimatic conditions, may have collectively caused the development and fluctuations of the euxinic wedge and organic enrichment on the outer shelf slope to basin settings.…”