The Role of Evaporites, Foreland Basin Fill, and Inherited Crustal Weaknesses on Structural Styles in the Pamir and Tian Shan Forelands, Western Tarim Basin, NW China

Abstract

The structural styles that develop in foreland basins as the basin is incorporated into the fold and thrust belt are influenced by a number of factors, including inherited basement structures and the basin stratigraphy. The Pamir and Tian Shan orogens in Central Asia formed during the Neogene as a result of the Indo-Eurasian collision. In the far western Tarim Basin, the two orogens share a broader foreland basin that has been disrupted during the late Cenozoic as the deformation in the Tian Shan migrates southward and the Pamir migrates northward. Despite their proximity and broad similarities in basin stratigraphy and inherited structures, these two orogens exhibit different structural styles on their leading edges, resulting in spatial differences in the patterns of Neogene deformation. To better understand the factors controlling the differences in structural styles, we integrate interpretations of previously published seismic lines and structural cross-sections, stratigraphic sections and published well data, and geochronologic data. The results characterize the patterns of active and recent deformation on the NE Pamir margin and the SW Tian Shan front, as deformation incorporates the foreland basin fill. The Pamir foreland has a thick, localized section (50-200 m) of lower Tertiary evaporites that act as a regional decollement, localizing deformation along the Pamir Frontal Thrust at the leading edge of the orogen. On the Tian Shan margin, inherited structural weaknesses in the Paleozoic basement rocks as well as thin, distributed gypsiferous layers in the lower Miocene section and a thicker Cenozoic basin fill, control the patterns of thrust faults, fault propagation folds, and detachment folds in the Kashi-Atushi Fold and Thrust Belt. These differences in pre-existing structural weaknesses and the sedimentary basin fill, particularly the thicknesses and distribution of evaporites and the thickness and lithology of the Cenozoic basin fill, influence the structural styles and patterns of Neogene through Quaternary deformation within the basin. These differences in structural styles have resulted in different trapping mechanisms and trap formation timing for petroleum reservoirs in the Pamir and Tian Shan forelands of the western Tarim Basin.

AAPG Datapages/Search and Discovery Article #90291 ©2017 AAPG Annual Convention and Exhibition, Houston, Texas, April 2-5, 2017