Tectono-sedimentary evolution of piggy-back basin: Example from Kuqa fold and thrust belt, northern Tarim basin, northwest China

Abstract

The Baicheng (拜城) piggy-back basin was part of the intracontinental foreland basin system of southern Tianshan (天山) Mountains. It was formed on a thrust-and-fold belt induced by Mio-Pliocene collision between southern Tianshan Mountains and Tarim craton that controlled the thick synorogenic basin fills. Sedimentological analysis and a restored cross-section based on seismic data and field studies revealed three tectono-depositional sequences of synorogenic basin fills. (1) The Lower Miocene sequence (Jidike (吉迪克) Formation) was formed under alluvial-braided river-lacustrine environments, in response to geodynamic changes of the Kuqa (库车) fold and thrust belt from the embryonic foreland to a foredeep in the course of orogenic loading period. (2) The Upper Miocene sequence (Kangcun (康村) Formation) was developed in fluvial-delta and lacustrine environments, within a foredeep due to orogenic thrust. (3) The Pliocene sequence (Kuqa Formation) was formed in the Baicheng piggy-back basin that became a wedge-top depozone, thrusting in the Qiulitagh (秋里塔格) thrust belt that propagated progressively southward to the Yaken (牙肯) thrust belt.