Late Permian tectono-sedimentary setting and basin evolution in the Upper Yangtze region, South China: Implications for the formation mechanism of intra-platform depressions

Abstract

Abstract The Upper Yangtze region in the northwestern part of the South China Block was situated in a relatively active tectonic zone during the Late Permian. The expansion of the South Qinling and Jinshajiang–Ailaoshan oceans to the north and south, active mantle plumes, and related magma upwelling in the plate margins have significantly influenced the evolution of this area. The sediments of the Upper Permian Wujiaping Formation and Changxing Formation developed in the Upper Yangtze region are typical intracratonic basin sequences, which records the sedimentological and structural development during this period. To reconstruct the tectonic and paleogeographic framework of the Upper Yangtze region and to better understand the formation mechanism of intra-plate depressions, this study integrates drill core, well log, cross-sections and outcrop data to examine the lithological associations, stratigraphic thicknesses, and sedimentary facies, and further reconstruct the paleogeographic framework of the Late Permian sedimentary successions. Moreover, we integrate this data with 2D and 3D seismic data to describe the tectono-sedimentary framework of the intra-platform depressions. Based on the results, three primary tectono-sedimentary stages are delineated: (1) the Wujiaping Formation documents a rapid basalt eruption event on the southwestern edge of the Upper Yangtze region at the beginning of the Wuchiapingian stage, followed by a marine transgression which occurred from the northeast to the southwest with initial intra-platform depressions formed on the northern basin; (2) during the early Changsingian stage, the Upper Yangtze region comprised a variety of environments, including tidal flat-coast, mixed-platform, open-platform, slope, deep-water shelf, and platform margin reef and shoal, with a rapid sea-level rise and (3) the sea level reached its peak and then slowly dropped. The reefs developed along the intra-platform depressions during the late Changsingian stage. We suggest that the formation and evolution of the Late Permian basin sequences in the Upper Yangtze region were controlled by the plutonic magmatic activities and regional crustal extension. The proposed model has important implications for interpreting the rapid transformation of intra-platform depressions from uplift to depression, as well as the tectono-sedimentary differentiation framework in intracratonic basins.