The Mesozoic palaeorelief of the northern Tian Shan (China)

The Tian Shan range offers a natural laboratory to study orogenic processes. Most of the previous studies focused on either the Paleozoic evolution of the range or its Cenozoic intracontinental evolution linked with the India-Asia collision. In this study, detailed field investigations on the relationship between sedimentary cover and basement constrain the Mesozoic evolution of the northern Tian Shan. Sedimentological observations argue for limited transport distance for Lower and Uppermost Jurassic deposits. Geological sections presented in this paper show that, in preserved locations, Triassic to Jurassic sedimentary series present a continuous onlap type sedimentary unconformity on the top of the basement. At different scales, observations clearly evidence the existence of a major palaeorelief during Mesozoic. According to the present study, the current Tian Shan range topography and the associated movements along its northern front structures cannot be considered as the consequence of Cenozoic reactivation alone.