Ediacaran stratigraphy and paleogeography in the north Yangtze Block, South China

Abstract

The Ediacaran gas exploration of the Sichuan Basin in the northwest Yangtze Block, South China, indicates that the paleogeography and lithofacies are of great significance for understanding sedimentary environments and further exploration. There are several contrarian views, however, regarding the Ediacaran paleogeographic configuration and lithofacies distribution in the north Yangtze Block. In this study, we systematically analyzed the Ediacaran stratigraphic, paleogeographic, and facies distributions by integrating outcrop observation, well correlation and seismic interpretation. The Ediacaran in the Micangshan-Hannan terrane is dominated by progressive onlap successions from west to east. We suggest that during the Ediacaran an overall paleogeographic configuration evolved from a shallow-water platform to deeper slope-basin and finally into an open ocean (i.e., the Proto-Tethys ocean) in the north Yangtze Block. The platform margin is roughly distributed along the north margin of the Micangshan-Hannan terrane and the present-day Chengkou fault. During the Doushantuo time, the paleogeographic configuration was characterized by a distally steepened ramp passing seaward into slope-basin facies. During the Dengying time, a rimmed carbonate platform developed on the Doushantuo Formation ramp. The platform margin facies predominantly contained microbially laminated dolomites and stromatolite reef complex. The slope-basin facies were dominated by thin-bedded and slump dolomites. The Ediacaran of the north Yangtze Block experienced a sedimentary evolution from a mixed carbonate-siliciclastic ramp of the Doushantuo Formation to a rimmed carbonate platform of the Dengying Formation, primarily controlled by tectonic subsidence differences and sea level changes.