塔里木盆地古近系层序地层研究

A basin-wide sequence stratigraphic analysis of the Paleogene in Tarim Basin

运用露头、钻井岩心及测井层序地层学的有关理论方法,对塔里木盆地周边露头及盆地内钻井剖面的古近系进行了详细的沉积学和层序地层学研究,共识别出6个三级层序界面,把塔里木盆地古近系划分为5个三级层序。其中,古新世—始新世早期(库姆格列木群沉积期)发育3个层序,从下到上为S1,S2和S3。S1大致相当于库姆格列木群底部的砾岩段、膏泥岩段到白云岩段,在塔西南地区相当于土依洛克组。S2和S3大致相当于库车坳陷库姆格列木群上部两套膏盐岩段以及塔西南坳陷阿尔塔什组-齐姆根组及卡拉塔尔组-乌拉根组的两套膏盐岩段。始新世晚期—渐新世(苏维依组沉积期)发育1～2个三级层序,即S4和S5。S4相当于库车坳陷的苏维依组和塔西南坳陷巴什布拉克组的主体,S5仅在部分钻井中见到,以苏维依组顶部局部发育的扇三角洲相砂砾岩为代表。在这些层序中,低位体系域往往以发育扇三角洲分流河道及辫状河道相砂砾岩以及咸化潟湖或蒸发台地相厚层膏盐岩为特征,而水进体系域多以滨浅湖相泥岩和粉砂岩为主,高位体系域则主要为碳酸盐岩及富泥质的沉积序列。

Principles and methods of sequence stratigraphy for outcrops, drilling cores and well logs have been used for reconstructing the Paleogene sequence stratigraphic framework in the Tarim Basin. Ex- tensive investigations of the outcrop, borehole and well log data revealed that a total of 6 third order sequence boundaries and 5 third-order sequences were developed in the Paleogene in the Tarim Basin. Three sequences, namely S1, S12 and S13, were developed from Paleocene to Early Eocene （the deposition period of Kumugeliemu Group and its equivalents）. On the whole, S1 is equivalent to the basal conglomerate member, gypsum and gypseous mudstone member to dolostone member of the Kumugeliemu Group in the Kuqa Depression, and is equivalent to the Tuyiluoke Formation in the southwestern Tarim area. S12 and S13 correspond to the two gypsum-containing members developed in the upper part of the Kumugeliemu Group in the Kuqa Depression, respectively. They are equivalent to the two gypsum intervals in the Aertashi Formation-the Qimugen Formation and the Kalataer Formation-the Wulagen Formation in the southwestern Tarim Depression. Two sequences, S14 and S15 were developed from Late Eocene to Oligocene （the deposition period of the Suweiyi Formation and its equivalents）. S14 is equivalent to the Suweiyi Formation in the Ku- qa Depression and the main part of the the Bashibulake Formation in the southwestern Tarim Depression, and S15 is only locally developed at the top of the Suweiyi Formation in a few boreholes and it is characterized by the fan delta sandy conglomerates. Within these sequences, the lowstand systems tracts are represented by the conglomerates and sandstones of fan delta distributary channel and braided channel as well as the thick-bedded gypsum and gypseous rocks of saline lagoon and evaporate platform. The transgressive systems tracts are dominated by coastal-shallow lacustrine mudstones and sihstones, and the highstand systems tracts are mainly composed of the carbonate rocks and mudstone-abundant successions.