摘要： 为阐明塔里木盆地阿瓦提凹陷三叠系的沉积特征、层序格架及沉积古地理,根据陆相层序地层学和湖盆沉积学研究思路,利用钻井、岩心、地震等基础资料,提出了井震结合层序划分、物源与沉积特征、沉积古地理分布与演化等研究新认识。将阿瓦提凹陷三叠系俄霍布拉克组和克拉玛依组划分了7个三级层序,俄霍布拉克组分为5个层序(SQ1—SQ5),克拉玛依组分为2个层序(SQ6—SQ7)。各层序自下而上由低位体系域(LST)、湖侵体系域(TST)和高位体系域(HST)组成。研究认为阿瓦提凹陷三叠系发育多物源控制下的扇三角洲相、辫状河三角洲相和滨浅湖亚相等沉积。凹陷周边存在4大物源,主要来自西南部巴楚隆起和西部柯坪断隆,其次是北部塔北隆起和东南部塔中隆起。辫状河三角洲平原亚相主要分布在凹陷的南部—西南部边缘,以辫状分流河道微相的粗粒砂岩和砂砾岩体为主。湖盆主体位于凹陷东部地区,向凹陷内为辫状河三角洲前缘亚相和湖泊相,以水下分流河道、滩坝砂体为主。三叠纪湖盆经历了从初始形成、发育鼎盛、到充填消亡的过程。早三叠世早期(SQ1—SQ2),即俄霍布拉克组下段时期,是三叠纪阿瓦提湖盆的初始形成期。物源主要来自南部的巴楚隆起和西部的柯坪断隆地区,沉积相带从南向北呈不对称带状分布,发育辫状河三角洲平原—辫状河三角洲前缘—滨浅湖亚相等,湖盆呈南浅北深、西浅东深。早三叠世中—晚期(SQ3—SQ5),即俄霍布拉克组上段时期,是湖盆扩张发育鼎盛期。伴随着西南部和西部物源不断向盆地进积,形成扇三角洲相沉积。同时,湖盆向北部和北东部扩展,形成自南向北不断进积的辫状河三角洲平原和前缘亚相,北东部为滨浅湖—半深湖亚相。中三叠世早—中期(SQ6—SQ7),即克拉玛依组沉积时期,是湖盆充填消亡期。沉降中心向北东方向迁移,物源不断进积造成湖盆迅速萎缩,直至消亡。

关键词: 塔里木盆地, 阿瓦提凹陷, 三叠系, 层序, 沉积古地理演化

Abstract: In order to clarify the sedimentary-palaeogeography characteristics and sequence framework of the Triassic in Awati sag,Tarim Basin,based on the research ideas of terrigenous sequence stratigraphy and lake-basin sedimentology,and using basic data consisting of drilling core and seismic data,this paper puts forward new understanding on sequence division,sediment provenance,and sedimentary-palaeogeography distribution and evolution. In this study,the Ohobluk Formation and Karamay Formation of the Triassic in Awati sag are divided into seven third-order sequences,among which the Lower Triassic Ohobluk Formation is divided into five(SQ1-SQ5)and the Middle Triassic Karamay Formation is divided into two sequences(SQ6-SQ7). Each sequence is composed of the lowstand system tract(LST),transgressive system tract(TST),and highstand system tract(HST). It is suggested that the Triassic in Awati sag is characterized by fan deltas,braided river deltas,and shore-shallow lacustrine facies controlled by multiple sources. There are four major sources around the sag and the sediment supply is mainly from the southwestern Bachu Uplift and the western Keping Fault Uplift,then from the northern Tabei Uplift and the southeastern Tazhong Uplift. The braided river delta plain subfacies are mainly distributed at the southern and southwestern edge of the sag,mainly composed of coarse grained sandstone and sandy gravel sandbodies of braided distributary channel microfacies. The center of the lake basin is located in the eastern part of the sag. Within the sag,there are braided delta front subfacies and lacustrine facies,mainly composed of underwater braided distributary channels and beach bar sandbodies. During the Triassic,the lake basin experienced stages of early initiation,intermediate growth and peak,and finally filling and extinction. The early stage of the Lower Triassic(SQ1-SQ2 period),corresponding to the development of the lower part of the Ohobluk Formation,is the initiation stage of the Awati lake basin in the Triassic. Sediments mainly came from the Bachu Uplift in the south and the Keping Fault Uplift in the west. The sedimentary facies were distributed in an asymmetric belt from south to north,with the development of braided delta plain and front subfacies and shore-shallow lacustrine subfacies. Moreover,during that stages,the lake basin is shallow in the south and deep in the north,shallow in the west and deep in the east. The middle to late stage of the Lower Triassic(SQ3-SQ5 period),corresponding to the development of the upper member of the Ohobluk Formation,is the growth and peak period of lake basin. With the continuous progradation of sources from the southwest and west towards the basin,fan delta facies were formed. At the same time,the lake basin expanded to the north and northeast,forming a braided delta plain and front subfacies that continuously migrated from south to north,while the northeast is a shore-shallow to semi-deep lacustrine subfacies. The early-middle period of the Middle Triassic(SQ6-SQ7 period),corresponding to the development of the Karamay Formation,is the filling and extinction period of the lake basin. The migration of the subsidence center to the northeast region resulted in the continuous progradation of the sources,causing the lake basin to rapidly shrink and eventually died out.

Key words: Tarim Basin, Awati sag, Triassic, sequence, sedimentary palaeogeography evolution

中图分类号: 

• P531