Paleontologic, Paleogeographic and Sedimentologic Controls On the Spatial-Temporal Distribution Of Permian Sponge Reefs In South China

Abstract

The Permian sponge reefs belong to different types, taxonomic composition and distribution varies. Their development and success depend both on intrinsic and extrinsic control mechanisms. Well-documented outcrops in South China, encompassing Permian sponge reefs have been sampled and investigated in aspects of palaeontology, stratigraphy, sedimentology and palaeogeography. Two important reef-forming periods, namely the Kuhfengian to Lengwuan and the late Wuchiapingian to Changhsingian, are mainly recorded in the Maokou and Changxing Formations.The reefs of these formations are morphologically subdivided into three types: fringing reef, patch reef and barrier reef. In the Kuhfengian to Lengwuan, fringing reef developed nearby a littoral clastic shelf and barrier reefs were mainly present at the isolated carbonate platform-margin within the Dian-Qian-Gui Basin. The reefs were dominated by hypercalcified sponges including sphinctozoans Amblysiphonella, Tebagathalamia, Rhabdactinia, Intrasporeocoelia and  Cystothalamia and inozoans Peronidella, Stellispongia, Guangxinella and Grossotubenella. In late Wuchiapingian to Changhsingian, patch reefs distributed on middle-upper Yangtze platform and on the isolated platform within the North Yangtze and Dian-Qian-Gui Basins. The barrier reefs located on the Yangtze platform-margin facing the North Yangtze and Jiangnan Basins and on the isolated platform-margins within the Dian-Qian-Gui Basin. Hypercalcified sponges were dominated by Amblysiphonella, Sollasia, Lichuanospongia, Intrasporeocoelia of sphinctozoa, and Peronidella of inozoa.High diversity and abundance of sphinctozoa and inozoa, massive microencrusters and binders need to be present for formation of sponge reefs. The favorable habitats for sponge reefs were subtidal high-energy shoals on stable platform-margin and interplatform environments. When all these conditions were not simultaneously satisfied, sponge reefs decreased and disappeared, as it happened during the latest Lengwuan to Wuchiapingian and the latest Changhsingian to early Triassic.

Keywords: Permian sponge reef, South China, Hypercalcified sponge, Time-spaced distribution, Geological controlled factors, Two important reef-forming periods