塔里木盆地库车坳陷中、新生代沉降特征探讨

应用回剥分析方法(Backstripping analalysis)选取有代表性的四条剖面地层,计算了库车盆地中、新生代地层的沉降速率和沉积速率,其中构造沉降在早三叠世、早白垩世、上新世分别达到32.45 m/Ma、37.35 m/Ma和59.82 m/Ma的高峰,沉积速率曲线也清楚的揭示了库车盆地在演化过程中沉降速率起伏变化的特点.结合地震剖面上的构造证据以及岩相古地理、古生物化石证据,分析了库车盆地在中生代以来的构造演化过程,认为库车盆地自中生代以来的构造活动经历了挤压,应力松弛,构造伸展,挤压,应力松弛,再挤压等六个构造活动阶段,说明了盆地演化过程中构造活动的阶段性.由盆地的沉降特点、构造的活动性质,分析认为库车盆地是由三叠纪早期的前陆盆地经历了中生代应力松弛、盆地伸展以及晚白垩世的挤压隆升和剥蚀,经过早第三世的海侵,在新生代再次复活,是再生的前陆盆地.

The Meso-Cenozoic Subsidence Features of Kuqa Depression, Tarim Basin

In this paper, backstripping analysis technique is applied to the quantitative research of Meso-Cenozoic subsidence history of Kuqa basin. The curves of the total subsidence and tectonic subsidence in 4 different test sites ( Well YN2, Kuqa river cross section, Kelasu river cross section and Awate river cross section), as well as the curves of sedimentation velocities and tectonic subsidence velocities through time, were established. We thus inferred that Kuqa basin experienced 6 various subsident stages, of which 3 stages (230-190 Ma, 190-135 Ma, 65-25 Ma) being concave, implying the extensional tectonic settings, and the other 3 (250-230 Ma, 135-114 Ma, 25-1.67 Ma) being convex, indicating the compressional tectonic settings. In combination with the evidence of the sedimentary facies, fossils, paleogeomorphy and seismic profiles, we believe that Kuqa basin in early Triassic (250-230 Ma) was at the end of a foreland basin stage and that the extensive stages (230- 190 Ma and 190 - 135 Ma) may result from the sequential stress relaxation after the foreland thrusting. Moreover, we infer that the hiatus and deformation of early Cretaceous (135- 114 Ma) to late Cretaceous may result from the remote tectonic effect by the formation of the Bangong Lake-Nujiang River suture and the subsequential stress relaxationstage in Paleocene (65 -25 Ma). During the last stage of Miocene-Pleistocene (25 - 1. 67 Ma), as a result of long distance propagation of stress of the collision between India-Eurasia continental collision, the tectonic subsidence accelerated drastically with more than several thousand meters of accumulation of clastic sediments, showing typical features of rejuvenation foreland basin.