Integrated chemostratigraphy of the Doushantuo Formation at the northern Xiaofenghe section (Yangtze Gorges, South China) and its implication for Ediacaran stratigraphic correlation and ocean redox models

摘要

The Ediacaran Doushantuo Formation in the Yangtze Gorges of South China plays an important role in our understanding of biological evolution, global correlation, and ocean redox conditions, because of the availability of high-resolution paleontological and geochemical data and numerous radiometric dates. However, integrated study has been focused on the Jiulongwan section that was largely deposited below wave base in a restricted shelf lagoon (Jiang et al., 2011; Zhu et al., 2011). Studies of shallower water successions are lacking, and this presents a challenge to test Ediacaran stratigraphic correlation and ocean redox models. To fill this knowledge gap, we conducted a high-resolution integrated study of the Doushantuo Formation at the northern Xiaofenghe (NXF) section approximately 35. km to the northeast and paleogeographically updip of the Jiulongwan section. With the exception of the basal 20. m, NXF sediments were deposited above normal wave base. Integrated biostratigraphic and chemostratigraphic data indicate that the 140. m thick NXF section correlates with the lower Doushantuo Formation (Member I and much of Member II; i.e., the lower ca. 70. m of the formation) at Jiulongwan. Geochemical data from NXF and other Doushantuo sections indicate that euxinic conditions may have been limited to a shelf lagoon (represented by the Jiulongwan section) that was restricted between the proximal inner shelf and a distal shelf margin shoal complex, at least during early Doushantuo time following the deposition of the Doushantuo cap dolostone. Further integrated studies are necessary to test whether euxinic conditions existed in open marine shelves in South China and elsewhere during the Ediacaran Period.