柴达木盆地西部地区早—中侏罗世沉积体系与古气候环境探讨

柴达木盆地西部地区（简称“柴西地区”）发育下—中侏罗统烃源岩，油气勘探潜力较好。但目前对该地区下—中侏罗统的物质来源、古气候环境及沉积体系研究较为薄弱，这在一定程度上制约了油气勘探进程。通过露头、钻井、地震资料及元素地球化学分析，结合古水流、重矿物、砾石统计及碎屑组分分析，重建了柴西地区下—中侏罗统的物源、沉积体系及古气候环境。研究表明，柴西地区北段侏罗系沉积中心在盆地内部，古阿尔金山为其主要物源区；南段沉积中心位于现今阿尔金山前，接受来自古阿尔金山、昆仑山及盆地内部古隆起等多个源区的物源供给；下—中侏罗统主要发育冲积扇—辫状河—辫状河三角洲—湖泊沉积体系。柴西地区早—中侏罗世整体以温暖、潮湿的古气候为主。柴西地区早—中侏罗世沉积具有近源堆积、相变快、多沉积中心的特点。早侏罗世发育多个相互分隔的小型断陷湖盆；中侏罗世盆地沉积范围扩张，形成规模较大的多沉积中心坳陷湖盆。

Discussion on depositional system and paleo-climate during the Early-Middle Jurassic in the western Qaidam Basin

The Lower-Middle Jurassic source rocks are developed in the western Qaidam Basin （WQB）， which has good hydrocarbon exploration potential. However， the current research on the provenance， paleo-environment and depositional system of the Lower-Middle Jurassic in this area is relatively weak， which hinders the process of hydrocarbon exploration. Based on outcrop， drilling， seismic data and element geochemical analysis， combined with paleocurrent， heavy minerals， gravel statistics and clastic composition analysis， this study reconstructs the provenance， depositional system and paleo-climate environment of the Early-Middle Jurassic in the WQB. The result shows that the depocenter of the Jurassic in northern WQB was located in the inner basin， and the paleo-Altyn Tagh Mountain was the main provenance area. The depocenter of south part of the WQB was located in piedmont of the present Altyn Tagh Mountain， accepting detrital supply from multiple sources such as paleo-Altyn Tagh Mountain， Kunlun Mountain and paleo-uplift in the basin. The dominated depositional system in the Lower-Middle Jurassic comprises alluvial fan， braided river， braided river delta and lacustrine facies. The Early-Middle Jurassic in the WQB was dominated by a warm and humid paleo-climate. The Early-Middle Jurassic deposition in the WQB was characterized by near source accumulation， rapid facies transition and multiple depo-centers. In the Early Jurassic， several small-scale faulted lacustrine sags developed which separated from each other， whereas there was a large-scale multi-depocenter depression lacustrine basin which was developed in the Middle Jurassic.