EVOLUTION OF THE EDIACARAN-EARLY CAMBRIAN YANGTZE PLATFORM

The Ediacaran-early Cambrian strata in south China host a few exceptionally well-preserved biota that provide a rare window for understanding the evolution and diversification of early animals. Most of the biota are preserved in the proximal side of restricted shelf lagoons or shallow-water highlands where wave and tidal activities prevented permanent anoxic/euxinic conditions. Stratigraphic patterns and facies analyses indicate that the differentiation of a flat-topped Ediacaran shelf started after the Doushantuo cap carbonate deposition. Syndepositional faults along the platform margin, possibly induced by deglacial isostatic rebound, resulted in shallowing of the shelf margin and the deepening of restricted shelf-lagoons. For the majority of the Ediacaran Period (ca. 632-551 Ma), shelf lagoons and the open ocean basin had sediment starvation, implying that south China may have been an isolated continental block surrounded by oceanic basins. The differentiated Ediacaran Yangtze platform was filled by fast carbonate deposition during the latest Ediacaran (ca. 551-542 Ma) and a flat-topped carbonate platform was formed by the end of the Ediacaran. Karstification and erosion associated with the unconformity at the Ediacaran-Cambrian transition created local topographic differentiation that extended to the early Cambrian. Geochemical data including carbon, sulfur, and redox-sensitive elements obtained from the Ediacaran-early Cambrian Yangtze platform show large variations in response to chemocline changes across the facies zones and a more comprehensive geochemical study in open-ocean sections is required to understand the paleoceanography recorded in the Yangtze platform.