准噶尔盆地西北缘三叠纪沉积体系与环境

Sedimentary system and environment research on the Triassic strata in northwest Junggar Basin

准噶尔盆地西北缘三叠系沉积体系划分与沉积环境演化是新疆地区值得探讨的2个问题,其中沉积微相的研究对恢复古环境及油气有利相带的预测有着重要的意义。综合运用露头、岩心、测井、地震资料,认为准噶尔盆地西北缘三叠系为冲积扇-扇三角洲,河流-三角洲和湖泊三类体系的组合,冲积扇-扇三角洲体系主要发育辫状河道、砂(砾)质漫滩等微相,河流-三角洲体系包含砂质和砂砾质辫状河,该体系进一步划分为分流河道、心滩、河漫滩、河漫湖、河漫沼泽等微相,湖泊体系以滨浅湖泥为主。此外,孢粉及C、O同位素分析显示,克拉玛依组上段所属时代为中三叠世,且盆地西北缘在三叠纪处于陆相环境。早—晚三叠世,盆地由干旱炎热的亚热带气候逐渐转为潮湿温暖适宜植被生长的温带气候。

Sedimentary microfacies research has great significance in reconstructing the palaeoenvironment and predicting the beneficial facies belt. Combining outcrop, core, logging and seismic data together, it is considered that the northwest Junggar Basin developed the combination of alluvial fan-fan delta, fluid-delta and lacustrine systems in Triassic period. The alluvial fan-fan delta system developed the braided stream channel and the sand(glutenite) floodplain microfacies and some other geological bodies, the fluid-delta system, containing sand and glutenite braided rivers, consisted of such geological bodies as the channel, the bar, the floodplain and the flood lucastrine microfacies, and the lacustrine system mainly developed the shore-shallow lacustrine mud microfacies. Furthermore, according to the analysis of pollen and δ^(13)C, δ^(18)O, it is suggested that the Upper Karamay belongs to the Middle Triassic period. Northwest Junggar Basin was in continental crust environment, and its climate gradually changed from the dry hot subtropical zone into wet warm temperate zone which was suitable for plants growth from Early to Late Triassic.