Stratigraphy and paleogeography of the Ediacaran Doushantuo Formation (ca. 635–551 Ma) in South China

Abstract

The Ediacaran Doushantuo Formation (ca. 635–551 Ma) in South China contains exceptionally well-preserved fossils of multicellular eukaryotes including early animals, and it is one of the most intensively investigated Ediacaran units in the world. Various stratigraphic methods including litho-, chemo-, bio-, and sequence-stratigraphy have been applied to establish a stratigraphic framework for the Doushantuo Formation, but so far regional correlation across the basin relies heavily on two distinctive marker beds, the cap carbonate at the base and the organic-rich black shale at the top of the Doushantuo Formation. The majority of the Doushantuo Formation in the Yangtze platform was deposited on a rimmed carbonate shelf, with a shelf margin shoal complex that restricted the shelf lagoon from the open ocean. Large facies variations are observed in the shallow margins of the shelf lagoon and in the shelf margin-to-slope transition, where depositional environments were near the chemocline of the stratified, anoxic/euxinic shelf lagoon and of the broader Nanhua basin, respectively. Chemocline instability in the shelf lagoon and in the Nanhua basin caused local geochemical cycling, resulting in significant variations in carbon and sulfur isotopes and in redox-sensitive elemental concentrations. Most benthic eukaryotic fossils (including animal fossils) of the Doushantuo Formation have been found from the shallow margins of the shelf lagoon and from the shelf margin–slope transition, but rarely from deep-water environments that may have been below the chemocline for most of the Doushantuo time, implying the sensitivity of eukaryotes to paleogeographically controlled chemocline fluctuations.