Abstract
We examined in detail the lithostratigraphy and lithofacies of Middle-Upper Permian shallow-marine limestone (150 m thick) at Chaotian in northern Sichuan, South China, to clarify temporal changes in the sedimentary environment. The main part of the upper Middle Permian Maokou Fm and the lowermost Upper Permian Wujiaping Fm consist of bioclastic (fusuline, algae, and coral) limestone that was probably deposited in the euphotic zone on a continental shelf. In contrast, the uppermost Maokou Fm (11 m thick) is composed of thinly interbedded black shale/chert with abundant radiolarians, which was probably deposited in the dysphotic zone on a continental slope/basin. This change in stratigraphic lithofacies at Chaotian indicates that sea level rose during the latest Guadalupian, but then fell rapidly across the Guadalupian-Lopingian (G-L) boundary. The redox condition of the sedimentary environment also shows a marked change in tandem with sea-level fluctuations. The transgression was probably caused by a local tectonic event that involved basin subsidence in western South China, while the following regression reflects a global sea-level fall across the G-L boundary.
