Tectonostratigraphic history of the southern Tian Shan, western China, from seismic reflection profiling

Abstract

The modern Tian Shan formed due to the India-Eurasia collision. Uplift of the Tian Shan is recorded notably by the sedimentary sequences and subsidence history of the coupling foreland basins. We analyzed a 353-km-long seismic profile and logging data of four wells in the southern Tian Shan foreland area to decipher its tectonic, stratigraphic, and subsidence history. The sedimentary sequences comprise the Cambrian-Silurian, Devonian-Permian, Triassic, Jurassic-Cretaceous, and Paleogene tectonostratigraphic units, overlain by the late Oligocene-Quaternary foreland basin unit. The Jidike Formation is the oldest sedimentary sequence of the foreland succession, deposited at ∼26 Ma based on magnetostratigraphic constraints, indicating that uplift of the southern Tian Shan was initiated by at least ∼26 Ma. In addition, the tectonic subsidence rate of the southern Tian Shan foreland basin increased significantly since ∼26 Ma due to lithospheric flexure caused by building of the topography of the southern Tian Shan. The envelope line of the forelandward onlaping points within the foreland unit indicates that the forebulge of the southern Tian Shan foreland basin migrated southwards at 1.6 ± 0.1 mm/yr between ∼26 Ma and ∼12 Ma and at 14.6 ± 0.1 mm/yr after ∼12 Ma. The increase of migration rate at ∼12 Ma suggests an accelerated convergence between the Tarim Basin and the Tian Shan.