Distribution and erosion of the Paleozoic tectonic unconformities in the Tarim Basin, Northwest China: Significance for the evolution of paleo-uplifts and tectonic geography during deformation

The distribution and erosional features of the Paleozoic major tectonic unconformities in the Tarim Basin, and their genetic relation to the development of paleo-uplifts as well as the evolution of geodynamic settings, are documented in this paper based on the integral analysis of seismic, drilling, and outcrop data. During the Paleozoic, the Tarim Basin underwent three major tectonic deformation stages, which resulted in three angular unconformities and in significant changes in basin geomorphology and paleogeography. The tectonic deformation at the end of the Middle Ordovician was characterized by development of the southern central paleo-uplift, the northern depression, and the southeastern Tangguzibasi depression in the basin. The thickest denudation belts of the unconformity (Tg5-2) are distributed mainly along the thrust structural highs. A stronger deformation event took place at the end of the Late Ordovician and formed a huge uplift along the southwestern and southeastern basin margins and the western part of the Tabei uplift along the northern basin margin, producing an extensive angular unconformity (T-g5) with maximum erosion thickness of 1500-2000 m. This tectonic event resulted in an abrupt change in overall geography of the basin, from a deepwater marine environment at the late stages of the Late Ordovician to a littoral and neritic basin in the Early Silurian. The deformation that occurred at the end of the Middle Devonian was the strongest in the Paleozoic. It generated the most widespread angular unconformity (T-g3) within the basin and led to extensive erosion, with maximum denudation thickness of 30005000 m in the northern and northeastern parts of the basin. The topography of the basin during the late Devonian was characterized by a high in the northeast and a low in the southwest, forming an embayment basin opening to the southwest during the Early Devonian to Carboniferous. The transgression in general from southwest to northeast deposited extensive coastal sandstones onlapping the erosion-leveled unconformity (T-g3). Comparative analysis of uplifting in the basin with the regional tectonic setting shows that deformation that took place during the three periods was related to the evolution of the paleo-oceanic plates and the orogenesis around the basin. The closure of the North Kunlun Ocean and subsequent collision is suggested to be the main cause for the development of the central paleo-uplift at the end of the Middle Ordovician and the strong uplift and erosion of the southwestern and southeastern basin margin at the end of the Late Ordovician. The large-scale uplift and denudation of the northern part of the basin, including the Tabei-Kongquehe uplift belt, as well as the folding and hinging of the Manjiaer depression, was coeval with, and more related to, the subduction and collision of the South Tianshan orogenic belt and the Altyn trench-arc-basin system at the end of the Middle Devonian. (C) 2011 Elsevier Ltd. All rights reserved.