Paleogene sedimentation changes in Lenghu Area, Qaidam Basin in response to the India–Eurasia collision

摘要

The Cenozoic India-Eurasia collision is evidently recorded in the Qaidam Basin, which is located in the north margin of the Tibetan Plateau. The present study describes a dextrorotary phenomenon at the end of the Eocene in Lenghu Area in the northern Qaidam Basin, discovered in sedimentary and tectonic records. This phenomenon is interpreted to have been a result of the levorotatory movement along the Altyn Tagh Fault (ATF) based on the following evidence. First, provenance, as analyzed by heavy mineral assemblages, was slightly deflected from southwestward to the westward by about 45 degrees. Second, paleocurrent inferred from dip logging and seismic reflection changed clockwise by approximately 25 degrees. Third, there is evidence of increases in fault activity in the area, especially in northwest-southeast-trending branches relative to older west-east-trending branches. Increases in faulting coincide with abrupt increases in sediment supply in the Oligocene, after earlier decreases based on total sand content during the Eocene. Our results demonstrate that the northern margin of the Tibetan Plateau synchronously responded to the initiation and termination of the India-Eurasia collision. The levorotatory strike slip of the ATF was immediately triggered by the complete collision at the end of Eocene, and the strike-slip movement caused the dextrorotary phenomenon in the Lenghu Area.