Latest Jurassic–earliest Cretaceous (Tithonian–Berriasian) dinoflagellate cysts from the Yanshiping Group of the northern Qinghai-Xizang Plateau (Tibet), western China

Abstract

Dinoflagellate cysts from the Xiali, Suowa and Xueshan formations (Yanshiping Group) of the Tanggula Mountains, Qinghai-Xizang Plateau, western China were studied. The palynofloras are sparse and poorly-preserved due to high levels of thermal maturation relating to intense tectonic activity. These formations are interpreted as being of Tithonian to Berriasian (latest Jurassic to earliest Cretaceous) age based on key markers such as Amphorula delicata, Amphorula metaelliptica, ? Batioladinium sp., ? Glossodinium dimorphum, Gochteodinia sp., Gonyaulacysta sp. cf. G. dualis, ? Muderongia sp. and ? Scriniodinium crystallinum. The Jurassic–Cretaceous transition probably lies within the upper Suowa Formation. This sparse and low diversity assemblage cannot be easily compared with other floras of the same age. However Amphorula is relatively common, and this indicates a connection with the western Tethyan Realm. No endemic Austral or high latitude taxa were encountered. The sizes of the dinoflagellate cysts are markedly smaller than their respective type material. This phenomenon is interpreted as being a result of the loss of volatile components during intense thermal maturation. The dinoflagellate cyst biostratigraphy herein indicates that the narrowing and the closure of the meso-Tethys in western China occurred during the Tithonian and Berriasian.