塔里木盆地库车坳陷古近系库姆格列木群底砂岩段沉积古地理和物源体系

库车坳陷古近系库姆格列木群底砂岩段沉积可划分为北缘砂砾岩带冲积扇粗碎屑沉积-下切辫状水道充填-河流-三角洲沉积、温宿凸起边缘近端冲积扇-扇三角洲沉积和塔北凸起西南缘的下切谷充填-河流三角洲-滨浅湖滩坝3个相带,中部为干旱盐湖-泻湖-海湾沉积.物源体系分析表明,西部的温宿凸起、北边的南天山造山带和塔北隆起上的大陆蚀源区为坳陷提供物源.库车坳陷碎屑物基本上来自于南天山和温宿凸起再循环造山带,坳陷北缘的逆冲造山和隆升作用形成了长期的物源供给区,沿坳陷东北缘发育了巨厚的冲积扇.西部的温宿凸起早期存在物源,沿凸起边缘发育有小型的边缘扇或扇-辫状河三角洲.塔北隆起在古近纪早期提供一定的物源,克拉201井附近结晶基底的剥蚀是南部大陆蚀源区的主要物质来源.却勒1井、羊塔5井等地的碎屑物极可能来自3个物源区.研究区物源体系的分析与总体的古构造、古地理格局相一致,库车坳陷古近系基底东高西低,有大量陆源碎屑由东向西推进,东、西两侧的低凸起带和北缘的前陆前渊带构成的古构造特征决定着物源和岩相分布的总体格局.

Depositional paleogeography and source rock analysis of the lower sandstone part of Eogene Kumugeliemu Group in Kuqa depression

The lower sandstone part of Eogene Kumugeliemu Group in Kuqa depression can be divided into three depositional belts, namely the fluvial fan coarse de posit-incised channel filling-fluvial-delta system of South Tianshan Mountain marginal grit belt, the near fluvial fan-fan delta deposit of Wensu uplift margin belt, and the incised valley filling-fluvial-delta shallow lake shoal bar of Tabei uplift belt. There are dry salt lake-lagoon-sea gulf sediments in the middle of the depression. A source rock analysis shows that the western Wensu uplift, northern south Tianshan Mountain and continent eroded source rocks of Tabei uplift comprised the major source rocks of Eogene Kumugeliemu Group sediments. The clastic materials mainly came from South Tianshan Mountain and Wensu uplift recycle orogenic belts. The thrust orogenesis and the uplift of the northern margin of the depression formed a prolonged source rock supply area. Along the northeastern margin of the depression, there was developed a fluvial fan of great thickness. The western Wensu uplift provided source rock in the early period, and there was developed a small marginal fan or a fan-braided fluvial delta along the uplift margin. The Tabei uplift also provided some source meterials in the early Eogene, and the erosion of the crystalline basement near Kela 201 well was the major material source of southern continent eroded area. The substance of Quele 1 and Yangta 5 well came probably from the above three source rock belts forming a mixed source area. The result of the source system analysis is consistent to the global paleo-structure and paleogeographic framework. The eastern basement was much higher than western Eogene Kuqa depression, and hence there existed the migration of large amounts of terrigenous detrital materials from east to west. The paleo-structure framework combined with the eastern and western uplift belts and t he northern marginal foreland frontal deep belt determined the source system and the paleolithologic distribution.