Stable carbon isotopes of sedimentary kerogens and carbonaceous macrofossils from the Ediacaran Miaohe Member in South China: Implications for stratigraphic correlation and sources of sedimentary organic carbon

Ediacaran stratigraphic correlation depends on the integration of paleontological and delta C-13(carb) data. However, these data often come from different lithologies (e.g., shales vs. carbonates), making it difficult to directly link biostratigraphic and chemostratigraphic markers. Ediacaran successions in South China consist of mixed carbonates and shales, offering an opportunity for integrated biostratigraphic and chemostratigraphic investigations. Black shales of the Ediacaran Miaohe Member in the Yangtze Gorges area contain macroalgae and Ediacara-type macrofossils, both preserved as carbonaceous compressions. The Miaohe Member has been traditionally regarded as an equivalent to Member IV of the uppermost Doushantuo Formation that records part of the Shuram negative delta C-13(carb) excursion in South China. Thus, the Miaohe Member may have the potential to clarify the stratigraphic relationship between Ediacara-type fossils and the Shuram excursion. Recently, however, the Miaohe Member has been partially correlated with the Shibantan Member of the Dengying Formation (the A correlation) or partially with Member IV (the Z correlation). These correlations have different implications for the relationship between the Miaohe Member and the Shuram excursion. Here we test these two correlations using delta C-13 data of sedimentary kerogen or total organic carbon (delta C-13(org)TOC), taking advantage of the distinct delta C-13(org)TOC values between the Shibantan Member and Member IV. Our data show that delta C-13(org)TOC of the Miaohe Member is more similar to that of Member IV than to Shibantan Member, providing tentative support for the Z correlation. In addition, we also analyzed delta C-13(org) of individual carbonaceous compression fossils (delta C-13(org)taxon), which have lower carbon isotope values than TOC. The data suggest that oxygenic photo synthesizers (e.g., macroalgae, cyanobacteria, and eukaryotic phytoplankton) were not the only contributors to sedimentary TOC. Methylotrophs, photoautotrophs, and chemoautotrophs living in anoxic waters or at the oxycline may have fixed recycled CO2 derived from organic carbon remineralization, thus contributing a significant amount of C-13-depleted organic carbon to sedimentary kerogen in the Miaohe Member.