Triassic and Jurassic palaeoclimate development in the Junggar Basin, Xinjiang, Northwest China—a review and additional lithological data

Abstract

The Junggar Basin in the Xinjiang Uygur Autonomous Region (NW China) comprises an almost continuous sequence of continental Mesozoic sediments. The basin was positioned at a latitude of about 45°N from the Permian onwards and existed almost during the entire Mesozoic. As such, it is well suited for studies on palaeoclimatic and palaeoenvironmental changes during this period as tectonic movements of the basin between different climate zones can largely be excluded. Current knowledge about Triassic and Jurassic palaeoclimate development is complemented by new lithological data from the southern part of the basin, ranging from the Late Triassic (Norian) up to the latest Jurassic (Tithonan). Preliminary palynostratigraphical data demonstrate that the base of the Middle Jurassic probably does not coincide with lithostratigraphical formation boundaries (i.e., boundary between Sangonghe and Xishanyiao Formation), but lies within the lower part of the Sangonghe Formation. Humid climates dominated during the Triassic and the Early Jurassic, with only a few drier excursions, especially in upland regions. In the northeastern part of the Junggar Basin, the oldest evidence of seasonally dry climatic conditions is recognized during the latest Early Jurassic, and the first basin-wide evidence of seasonally dry conditions is recognized in the middle Middle Jurassic. A seasonally dry climate was permanently established in the basin from the beginning of the Late Jurassic onwards.