Chemostratigraphy And Biostratigraphy Of Ediacaran Doushantuo Formation In The Yangtze Goreges,South China

The section of the Ediacaran in the Yangtze Gorges, which contains abundant fossils with a long reserch history, is one of the most important Edidacaran sections in the world. We combine new and previously publishid δ13C data to construct a composite δ13C profile for Doushantuo Formation of Eidacaran systerm. Using the fossil date, we confirm that two different acritarchs assemblage zone can be recognized in the second and third members of Doushantuo Formation. In addition, the research objective for this study is to ueing chemo-and biostratigarphic markers to develop a framework of Ediacaran systerm from the East Yangtze Gorges.Carbonates of the Doushantuo Formation in the East Yangtze Gorges record three remarkable negative and two positive carbon isotope anomaly,1) a negative 8 C excursion (EN1) values vary from-0.9‰ to-41.166%o in the Doushantuo cap carbonate (member I) which is characterized by tepee-like structures, stromatacties-like cavities, sheet cracks, cemented breccias and tube structures. It can be correlated with the other carbon isotope excursion, which appear in the Marinoan cap carbonates worldwide; 2) a positive δ13 C excursion (EP1) in the lower to middle part of the member II of Doushantuo Formation, which values range from 0 to+6%o; 3) a negative δ13C excursion (EN2) in the uppermost of the member II of the Doushantuo Formation range from 0 to-2.1‰; 4) a positive 8’C excursion (EP2) occurs in the lower member III; 5) a negative δ13C excursion (EN3) occurs in the uppermost member III to the member IV with a nadir of-8.7%o, which is considered to be the largest carbon isotope trend in the geological record and it can be correlated with negative δ13C excursion in Australia, Oman, Namibia, California, Siberian and Scotland.Two different acritarchs assemblage zone can be recognized in the second and third members of Doushantuo Formation. The frist assemblage zone is characterized by Tianzhushania and a diverse suite of large acanthomorphic acritarchs, e.g. Knollisphaeridium maximum, Meghystrichosphaeridium perfectum, Ericiasphaera spjeldnaesii, Papillomembrana compta. The second assemblage zone is characterized by the appearance of Ceratosphaeridium glaberosum, Tanarium anozos, T. conoideitm, tubular microfossils are found in this assemblage zone. Furthermore, two acritarchs assemblage zones are separated by EN2 and the second assemblage zone disappeared before EN3, both EN2 and EN3 are related to the oxidation events, which probably cause the eukaryote diversity in the Ediacaran oceans.In Weng’an area, the Doushantuo Formation comprises just a lower and upper part which contains Weng’an biota separated by a mid-Doushantuo erosional surface. Previous work on the biostratigraphic correlation indicates that the Weng’an biota can be correlated with the second acritarchs assemblage zone. Our biostratigraphic study in the Yangtze Gorges and Weng’an indicate the Weng’an biota which are found above the erosional surface in Weng’an area should be correlated with the first acritarchs assemblage zone in East Yangtze Gorges.The Ediacaran systerm of East Yangtze Gorges may be subdivided into two series and five stages. The negative δ13C excursion in the uppermost part of the Doushantuo Formation is suggested as the Lower and Upper series boundy of the Ediacaran systerm, the first appearance of acirtarchs and tubular ainimals may be suggested as the stages boundy.