Late Cenozoic Tectonic History of the Qilian Shan, Northeastern Tibetan Plateau, Revealed by the Sedimentary Records of Northeastern Qaidam Basin, NW China

Guangsheng Zhuang and Bradley D. Ritts
Department of Geological Sciences, Indiana University Bloomington, Bloomington, IN

The intermontane Qaidam Basin on the NE Tibetan Plateau has been accommodating sediments shed off its surrounding mountains since the Cenozoic and thus provides the opportunity to decipher the tectonic evolution of its marginal tectonic features through basin analysis. The well-exposed Huaitoutala section in the Keluke anticline of northeastern Qaidam Basin was measured to understand the tectonic history of the Qilian Shan since the mid-Miocene. We have integrated the analysis of sedimentary facies & environment, paleocurrent indicators, and clast composition with published magnetostratigraphic and biostratigraphic data for this 5560 m thick section. Coarse clastics and conglomeratic strata indicate significant Miocene and Pliocene activities. The Qilian Shan was activated during the middle Miocene characterized by the cessation of fine-grained deposits and subsequent deposition of pebble-cobble conglomerate. A long quiescent period spanning a period from 15.3 Ma-2.5 Ma is indicated by fine-grained fluvial and lacustrine deposits of sandstone, siltstone and mudstone. The return to pebble-cobble conglomerate deposition in the Late Pliocene suggests renewed shortening within the Qilian Shan. Clasts within the conglomeratic strata are dominated by the dark limestone. Paleocurrent indicators and clast composition indicate a northerly source. Provided that this section is near to the Qilian Shan, only thin strata of fine-grained pre-Mid Miocene deposits were observed. This interpretation of the sedimentary record is consistent with the two-stage model of Altyn Tagh Fault (ATF). Initially (Oligocene-mid Miocene), India-Eurasian convergence was accommodated by rigid block extrusion along the left-lateral strike-slip ATF. In middle Miocene, internal shortening within the plateau was accommodated by thrust-faulting in the Qilian Shan resulting in coarse clastic sedimentation.

AAPG Search and Discover Article #90078©2008 AAPG Annual Convention, San Antonio, Texas