一幕完整的前陆盆地构造演化的地层记录:库车坳陷下白垩统

位于库车坳陷东部天山山前KZ露头的下白垩统为一套前渊带的充填沉积,包括卡普沙良群和巴什基奇克组两个粗-细-粗的沉积旋回,每个旋回底部的亚格列木组和巴什基奇克组底部均发育一套砾质粗碎屑沉积体.塔北隆起为前隆单元.从天山山前至塔北隆起,地层几何形态从卡普沙良群北厚南薄的强不对称楔型转变为巴什基奇克组北薄南厚的弱不对称楔型,且塔北隆起北斜坡带地震剖面显示卡普沙良群地层南部剥蚀强烈,而巴什基奇克组地层剥蚀位于北部,总体反映盆地由卡普沙良群时期北部沉降、南部抬升转变为巴什基奇克组时期北部抬升、南部沉降的构造反转现象,分别与前陆盆地逆冲构造活动期、宁静期的基底变形特征相一致.因此,卡普沙良群、巴什基奇克组两个的沉积旋回分别为逆冲构造活动期、宁静期的盆地充填记录,两个旋回底部的砾质粗碎屑沉积体分别为逆冲活动开始(岩石圈挠曲沉降)、逆冲活动停滞(岩石圈回弹隆升)的沉积响应.总之,库车坳陷下白垩统记录了一幕完整的前陆盆地构造演化过程.

Stratigraphic Record in a Whole Episode of Foreland Basin Tectonic Evolution:The Lower Cretaceous in Kuqa Depression

The Lower Cretaceous of outcrop KZ in the front of Tianshan Mountains,the eastern Kuqa Depression consists of foredeep-filling deposition.Two depositional cycles are identified to have developed respectively in Kapushaliang Group and Bashenjiqike Formation.At the bottom of each cycle,coarse gravelly sediments developed respectively in Yageliemu Formation and the bottom of Bashenjiqike Formation.The Tabei Uplift was the forebulge,from the front of Tianshan Mountains to the Tabei Uplift,Kapushaliang Group appears to be much asymmetric thinning toward south,In contrast,Bashenjiqike Formation is slightly asymmetric,thickening toward south.Moreover,in the seismic profile on the north slope of Tabei Uplift,southern Kapushaliang Group is more violently denuded,but northern Bashenjiqike Formation is denuded.This indicates the northern area subsided with the uplifting in the southern area in Kapushaliang Group,and the northern area reversely uplifted with the reverse subduction of the southern area in Bashenjiqike Formation.This tectonic reversal is accordant with lithosphere deformation from the thrust to the quiescence of foreland basin.Accordingly,the cycle at Kapushaliang Group developed during thrusting;the other at Bashenjiqike Formation during quiescence.The coarse gravelly sediment of Yageliemu Formation is a response to thrust renewing;the other at the bottom of Bashenjiqike Formation a resporse to lithosphere rebounding.In conclusion,the Lower Cretaceous in Kuqa Depression recorde a whole episode of foreland basin tectonic evolution.