Late Cenozoic evolution in the Pamir-Tian Shan convergence: New chronological constraints from the magnetostratigraphic record of the southwestern Tianshan foreland basin (Ulugqat area)

The northeastern Pamir-Tian Shan convergence zone is a key region for understanding ongoing intracontinental mountain building. A detailed magnetostratigraphic study combined with color reflectance variations of continental sediments from the 1120 m-thick Sankeshu Section in the south west sector of the Tianshan Foreland Basin of western China yields important insights into the tectonic evolution of this zone. Correlation with the geomagnetic polarity time scale identifies deposition lasting from 16.7 to 2.6 Ma with a marked increase in sedimentation rate at ~ 7 Ma. A further rapid increase occurred after 2.6 Ma with influx of the conglomeratic Xiyu Formation. Observed height-dependent changes of rock magnetic parameters (shape parameter T and AMS ellipsoid parameters) show that these sediments were influenced by weak deformation, with the sediments accumulated before ~ 11 Ma recording a signature of compressive deformation from northward indentation by the Pamir. The succession of sedimentary events in the foreland basin is comparable to previous investigations of magnetostratigraphic and sedimentological analyses, and with thermochronology collectively showing that deformation in the Tian Shan region has been concentrated in Miocene and later times. The regional correlations resulting from these analyses show that sedimentary events correlate with the episodic nature of regional uplift with the latter inducing climatic changes that are in turn recorded in the sediment record.