蒙古国塔木察格盆地塔南凹陷下白垩统铜钵庙组沉积特征和构造-古地理意义

铜钵庙组是蒙古国塔木察格盆地早白垩世发生初始裂陷的记录。铜钵庙组沉积早期,受强烈起伏的基底地貌和同生正断层活动的双重控制,塔南凹陷主要发育扇三角洲相;铜钵庙组沉积晚期,断裂活动趋于平息,研究区发育扇三角洲相和湖相。笔者系统总结了塔南凹陷铜钵庙组的扇三角洲相和湖相沉积特征,分析了沉积相带的平面展布特征。铜钵庙组沉积时期塔南凹陷出现雏形,沉积中心多且相对孤立,至南屯组沉积时期因同生正断层的进一步活动而连接成北东向条带状延伸的沉降带,盆地向西扩大。

Sedimentary features and its tectono-palaeogeographic significance of the Lower Cretaceous Tongbomiao Formation in Tanan sag,Tamtsag Basin,Mongolia

The Tongbomiao Formation is a record of initial rifting stage of the Tamtsag Basin in Mongolia during the Early Cretaceous. Constrained by both the violently rolling topography of the Upper Jurassic basement and the contemporaneous normal faulting,the sediments with fan delta facies were developed during early depositional period of the Tongbomiao Formation in Tanan sag. The normal faulting is tending towards calm during the late depositional period of the Tongbomiao Formation,and the fan delta and lacustrine sandstone and mudstone occurred in study area. Based on granulometric analysis,well logging sedimentary facies analysis and facies changes along the section lines,the sedimentary features of fan delta facies and lacustrine facies are concluded in this paper,and the planar distribution of the sedimentary facies belts of Tongbomiao Formation in Tanan sag is drawn. Only an embryonic form of Tanan sag occurred during the depositional period of Tongbomiao Formation. Correspondingly,there were multiple and relatively isolated depositing centers,which were connected together and became linear subsidence belts with NE-orientated elongation by further activities of the contemporaneous normal faults during the depositional period of Nantun Formation,when the sag expanded westwards.