Deposition in the Kuznetsk Basin, Siberia: Insights into the Permian–Triassic transition and the Mesozoic evolution of Central Asia

Abstract

This paper describes the Permian–Mesozoic stratigraphy of the Kuznetsk Basin, southern Siberia, which is adjacent to the vast and hydrocarbon-rich West Siberian Basin and on the edge of the Siberian flood basalts. The basin fill is Permian to Cretaceous in age, and is dominated by non-marine siliciclastics up to ∼ 7 km thick. Palaeocurrent indicators show dominant flow to the north/northeast during the Permian to Jurassic. Fourteen lithofacies are grouped in three facies associations: fluvial channel belt, overbank and floodplain/floodplain pond. Coal-bearing Permian siliciclastics are interpreted as meandering river deposits in a foreland basin, with subsidence generated by thrust-sheet loading from at least three basin margins. These sediments pass abruptly but conformably upwards into coal-barren sandstones and conglomerates and siltstones, interpreted as braided river deposits. Two basalt flows occur within the coal-barren succession. A recently-published, precise Ar-Ar age of 250.3 ± 0.7 Ma for the lower of these basalts, < 50 m above the sedimentary transition, suggests that the Permian–Triassic boundary occurs just above this flow. We relate the loss of coal-producing flora and the increase in mean sediment grain size to vegetation loss, in turn triggered by the eruption of the Siberian flood basalts to the north. End-Permian and Lower Triassic(?) strata are overlain by Lower Jurassic fluvial siliciclastics via a gentle angular unconformity. Conglomerates punctuate a sandstone-dominated succession that continues in to the Middle Jurassic. Both the basal unconformity and the rejuvenation in sedimentation may result from intracontinental thrusting at the basin margins and beyond; this thrusting was triggered by orogenies at the Eurasian margin. Lower and mid Cretaceous siliciclastics are poorly exposed and crop out only locally: field relations indicate an angular unconformity at their base. The end-Permian stratigraphy in the Kuznetsk Basin documents the environmental crisis at the time of the Siberian flood basalts, and reinforces the link between these eruptions and climatic and environmental deterioration. The Mesozoic sedimentary record highlights how episodic deformation influenced sediment supply to the West Siberian Basin, and is an example of the record of Eurasian assembly and deformation preserved within the continental interior.