Paleontologic, paleogeographic, and sedimentologic controls on the spatial-temporal distribution of Permian sponge reefs in South China

Abstract

The Permian sponge reefs belong to several distinct types, and their taxonomic composition and distribution vary. Their development and succession depend both on intrinsic and extrinsic control mechanisms. The well-documented outcrops in South China, encompassing Permian sponge reefs have been sampled and investigated in aspects of palaeontology, stratigraphy, sedimentology, and paleogeography. Two major reef-forming intervals, namely the Roadian to Capitanian and the late Wuchiapingian to Changhsingian, were recorded mainly in the Maokou and Changxing formations. The sponge reefs in these formations could be morphologically subdivided into three types: fringing reef, patch reef, and barrier reef. From the Roadian to Capitanian, fringing reefs developed near a littoral clastic shelf, and barrier reefs mainly presented on the margin of the isolated carbonate platforms within the Dian-Qian-Gui Basin. These reefs were dominated by frame-building hypercalcified sponges, including Amblysiphonella, Tebagathalamia, Rhabdactinia, Intrasporeocoelia, and Cystothalamia of sphinctozoa and Peronidella, Stellispongia, Guangxinella and Grossotubenella of inozoa. From late Wuchiapingian to Changhsingian, patch reefs distributed on the middle-upper Yangtze Platform and on the isolated platforms within the North Yangtze Basin and Dian-Qian-Gui Basin. The barrier reefs located on the margin of the Yangtze Platform facing the North Yangtze and Jiangnan basins and on the margin of the isolated platforms within the Dian-Qian-Gui Basin. Frame-building hypercalcified sponges were dominated by Amblysiphonella, Sollasia, Lichuanospongia, Intrasporeocoelia of sphinctozoa, and Peronidella of inozoa. The highly diversified and abundant hypercalcified sphinctozoans and inozoans, as well as massive microencrusters and binders made great contributions to the formation of sponge reefs. The subtidal high-energy shoal and the stable carbonate platform environment at the low-latitudes provided the favorable habitat for the growth of sponge reefs. Once these conditions could not be met simultaneously, sponge reefs would rapidly decrease and disappear, as it happened during the latest Capitanian and the latest Changhsingian.