Stratigraphic correlation of the Givetian (late Middle Devonian) deposits in Qujing, Yunnan, southwestern China and the paleogeographic implications

Detailed description of spatio-temporal framework of fossil-bearing strata is of fundamental significance for understanding the evolution of organisms and regional tectonics. The Qujing and Haikou formations are two lithological units exposed in eastern Yunnan, southwestern China, and both bear rich fossils indicative of a Middle Devonian age, while their relationship or lateral correlation remains unclear. Based on detailed observations of outcrops of these two formations in Qujing, eastern Yunnan, and as well as their typical rock characteristics and fossil contents, we propose that the two formations are basically contemporaneous heterotopic facies. From north to south of the Qujing area, the transition from the Haikou Formation to the Qujing Formation is gradual and shows an increase of carbonate component (in terms of the cumulative thickness of carbonate rocks) and as offset, a decrease of the siliciclastic component. The distribution of the Haikou/Qujing Formation indicates the development of a marine environment in the Qujing area during the Givetian, as a part of the South China Sea connected to the Paleo-Tethys Ocean, and supports that the transgression might have peaked in southwestern China during the late Middle Devonian. The available biostratigraphic evidence favors an expansion of the Paleo-Tethys Ocean prior to or during the Middle Devonian.