The Neogene extension of the Tianshui basin: Evidence from sedimentary and structural records

Tianshui basin is located at the transition from the compressive high in northeastern Tibet to the extensional zone around Ordos, where Neotectonic deformation is strongly developed. However, the tectonics of Tianshui basin remains elusive. In this study, the authors performed detailed analysis of sedimentation, tectonic subsidence and structural deformation, with some conclusions reached①Tianshui basin is filled with aeolian loess, pluvial fan, fluvial and lacustrine deposits, and lacustrine deposits which represent depocenter occur along the major faults, like West Qinling northern fault, Xihe fault and Lixian-Luojiabao fault; ②the basin experienced a three-phase subsidence, which happened at 16~14Ma, 9.2~7.4Ma and 3.6~2.6Ma respectively; ③the controlling faults are normal faults formed during the synsedimentary phase. The lacustrine occurrence, increasing subsidence and growth of normal faults indicate that Tianshui basin was controlled by extensional tectonics in at least Late Miocene and recorded the extrusion process of northeastern Tibet in the Late Cenozoic.