Palaeogeographic reconstructions of the Eocene-Oligocene Tarim Basin (NW China): Sedimentary response to late Eocene sea retreat

The Paleogene sedimentary successions of the Tarim Basin of western China document a major regression of the proto-Paratethys Sea, significantly changing the land-sea distribution and thereby the palaeoclimatic conditions in Central Asia. However, a comprehensive reconstruction of the palaeogeographic evolution of the basin is lacking because only few exposures are known from the central part of the basin that is mostly covered by the Taklamakan Desert. Here, we reconstruct the main palaeoenvironmental changes following Eocene sea retreat by determining the sedimentological facies of 69 wells that are internally correlated by using seismic profiles and externally to published sections of the exposed southwestern and northern margins of the Tarim Basin. Two major depocentres existed in the Southwest Foredeep and the Kuqa Depression, separated from each other by the Bachu Uplift that was most likely not a particularly high terrain during the Paleogene. We confirm that a major transition from marine to continental-lacustrine sedimentation took place during the Eocene-Oligocene transition in the central parts of the Tarim Basin. We provide new palaeogeographic maps with Eocene and Oligocene facies distributions in the Tarim Basin, which will facilitate a better understanding of the sedimentary response to Paleogene sea-level change and tectonic events of the neighboring mountain ranges. Our reconstruction confirms that both tectonic and eustatic forcing played an active role in controlling the late Paleogene transgression-regression in the Tarim Basin. Provenance and palaeocurrent analyses, combined with sediment distribution patterns, indicate gradual growth and continuous uplift of the Tibetan Plateau following India–Asia collision in the early Paleogene. The demise of the Tarim Sea at ~41 Ma correlates with palaeoclimatic and environmental changes observed in several basin of central Asia. After sea retreat, the Tarim region progressively transformed into a large and shallow lake system that potentially persisted up to the (early) Oligocene.