Lateral Variations of Tectonic Shortening in Kuqa Fold-and-Thrust Belt, NW China: Implication for Sub-Salt Hydrocarbon Explorations

Abstract

The Cenozoic Kuqa fold-and-thrust belt (KFTB), south to the Chinese Tianshan Mountains, is characterized by evaporative salt and related structures. Sub-salt sequences in the Kelasu structural belt have been targeted as main fields for hydrocarbon exploration. However, along-strike variations of structural geometry and tectonic shortening remain unclear due to the relatively poor quality of early acquired seismic data. In this study, the deformation features and mechanics of the structural transition zones are investigated on the basis of newly acquired seismic data. We measured the surface and basement detachment angles of imbricate thrust wedges in the Kelasu structural belt, and divided them into four sectors: the Keshen, Dabei, Bozi and Awate sectors from east to west. Interpretations of seismic images demonstrate that the thrust faults commonly exhibit curved or spoon-shaped geometries, and oblique ramps characterize the transition zones.

More evidence also indicates that the development of multi-sectors of the Kelasu structural belt is related to the Mesozoic basal detachment. Specifically, the inconsistent depositional centers of Triassic and Jurassic coal layers would cause differences in the Mesozoic decollement competence. As a consequence, when shortening started in Pliocene, the thrust faults would propagate further with better detachment (depositional centers of coal layers), generating the lateral differential shortening in map view. The ramps oblique to the shortening direction would then form as the linkage between thrust faults.

Displacement of the hanging walls over these ramps often creates brachyanticlines where hydrocarbon traps are formed, which has been confirmed by recent well drillings.

AAPG Datapages/Search and Discovery Article #90323 ©2018 AAPG Annual Convention and Exhibition, Salt Lake City, Utah, May 20-23, 2018