Abstract: Based on accurate 3-D seismic interpretation,comprehensive analysis of the drilling and geological data,it is indicated that the fault systems of the Yubei region in Tarim Basin are dominated by thrust faults.These thrust faults occur in two horizons.One is the basement where the thrusts consist basement fault zone(or basement weak zones).The other is the Cambrian-Ordovician carbonates where a thrust zone occurs.The Yubei fault system consists of a series of NEE-trending thrust zones including Yubei No.7,Yubei No.1,Yudong No.1,Yu-dong No.2,Yudong No.3 and Yudong No.4.Each single thrust belt is often composed of one main thrust and a set of associated secondary thrust faults.The fault plane of the main fault dips steeply at the upper part and flattens towards the deeper part,and detaches in the Mid-Lower Cambrian salt la-yers.The main thrust and its associated secondary back-thrusts commonly form pop-up fault assemblage showing "fault-horse" geometry on profile.These fault zones in the Cambrian-Ordovician carbonate rocks were mainly formed in the mid-Caledonian,experiencing movement of the early-epoch(the Early Ordovician Penglaiba stage),Ⅰ-epoch(the Mid-Early-Ordovician Yingshan stage),and Ⅲ-epoch(the Late-Ordovician)of the mid-Caledonian.The fault movement was very weak in the Hercynian.The fault zones are characterized by significant segmented deformation.The fault system and major unconformities jointly control the vertical structural layering.

Key words: thrusting, detachment, fault system, Yubei area, Tarim Basin