ABSTRACT: Jurassic through Paleogene Tectonics and Paleogeography of the Southwest Tarim Basin, Northwest China

SOBEL, EDWARD R., Stanford University, Stanford, CA

Vertical profiles, backstripping, facies analysis, and paleocurrent data collected in the piedmonts of the south Tian Shan (Heavenly Mountains) west of Kashgar and the west Kunlun Mountains strongly suggest that the Jurassic through Paleogene southwest Tarim basin was a north-south-trending elongate basin partially congruent with the nonmarine Neogene foreland basin. Independent paleomagnetic and stratigraphic data indicate that the reactivated Neogene Kunlun Mountains and Pamir Plateau, currently overthrusting the southwest Tarim foreland basin, are now located at least 500 km north of their position in the Paleogene.

Lower to Middle Jurassic fluvial, alluvial, and lacustrine sediments of the southwest Tarim basin overlie a Late Permian to Late Triassic unconformity. These sediments thicken to over 2000 m northward and extend into the Fergana Mountains, U.S.S.R. A Late Jurassic unconformity is overlain by a basal Cretaceous conglomerate. This unconformity is approximately contemporaneous with the collision of the Lhasa Block with the southern continental margin of Asia. Isopach configurations of Lower Cretaceous fluvial and alluvial red beds are similar to those of the underlying Jurassic strata.

During the Late Cretaceous, the southwest Tarim basin was infilled with shallow marine to lagoonal sediments in an epicontinental sea connected to the Tethys Seaway through the Tadjik basin, U.S.S.R. The transgression/regression curve for Upper Cretaceous strata in the southwest Tarim basin strongly mimics the global sea level curve, suggesting that global eustasy was the primary depositional influence.

In contrast, Paleocene and Eocene strata define a transgression/regression curve that is markedly different from the global eustasy curve, suggesting local tectonic influences to be the primary control on sediment deposition. This tectonism was most likely provided by the Late Cretaceous-Paleogene accretion of the Kohistan-Dras arc complex onto the south Asian continental margin.

AAPG Search and Discovery Article #91012©1992 AAPG Annual Meeting, Calgary, Alberta, Canada, June 22-25, 1992 (2009)