塔里木西部古生代层序地层特征

塔里木西部在古生代地质演化过程中,由于构造活动、海平面升降变化、沉积物供应速率等因素变化,造成了不同形式和不同级别的沉积间断,其产物---不整合面是建立该区层序地层格架的关键。研究区古生代大体经历了(寒武-奥陶纪)海进→(志留-泥盆纪)海退)→(石炭纪)海进→(二叠纪)海退的沉积旋回,形成了特征各异的层序序列。研究表明,其中Ⅰ级不整合面(层序面)有前震旦系顶界面、奥陶系顶界面和古生界顶界面。根据地面剖面、钻井和地震资料以及不整合面的特征和级别,首次在古生界识别出2个Ⅰ级层序、6个Ⅱ级层序和12个Ⅲ级层序。Ⅰ级层序是在不同的构造背景和沉积条件下形成的。Ⅱ级层序尽管特征各异,但一般均有四种基本叠置方式组成,即退积、进积、加积和上超。Ⅲ级层序一般由层序界面、海侵面和最大海泛面所限定的体系域组成,均发育TST和HST,有时出现SMST和LST。不同的体系域和沉积相控制着烃类生储盖层的分布,TST与生油层和储集层的形成有关,而HST多与盖层和储集层的形成有关。

Sequence Stratigraphy of the Paleozoic in West Tarim Basin

As a result of tectonic activites,sea level changes and sediment supply rate etc., West Tarim has formed many depositional hiatuses with different forms and orders during its Paleozoic geological evolution,and its product uncomformites becomes the key element to establish the sequence stratigraphic framework in the study area.It is believed that the Paleozoic has undergone such a depositional cycles as transgrssion( O)→retrogression(S D)→transgression(C)→retrogression(P),which formed a variety of sequences with different features. The research shows that I order unconformities (sequence boundary) involve the Presinian top boundary, Ordovician top boundary and Paleozoic top bundary. According to the data of section,well and seism,as well as the characterisics and orders of different boundaries or uncomformities, two Ⅰ order sequences,six Ⅱ order sequences and twelve Ⅲ order sequences have been recognizaed for the first time.Ⅰ order sequence is formed under different tectonic settings and depositonal conditions,and Ⅱ order sequence are generally composed of four kinds of basic superimposing forms,i.e.,regression,progradation,aggradation and onlap.Ⅲ order sequence consists usually of system tracts limited by sequence boundary,transgression surface and MFS,in which TST and HST are frequently present, SMST and LST occasionally observed.In the study area,the transgressire system tracts(TST)are formed as the sea water become deeper step by step.As the sediments deposit towards the basin and,at the same time,the coast line retreats gradually,it is a sedimentary background that the highstand system tracts(HST)are formed.Different system tracts and sedimentary facies have controlled the distribution of source,reservoire and cap rocks.TST has a close relationship to the formation of source rock and reservoir and HST is generally related to the cap rock as well as reservoirs.