蒙古国塔木察格盆地南贝尔凹陷铜钵庙组–南屯组的主要沉积特征

Abstract

塔木察格盆地南贝尔凹陷早白垩世早期的铜钵庙组–南屯组是断陷阶段的沉积。综合钻孔岩心观察、室内研究、录井资料和地震相标志，本文论述了各沉积相的识别标志，总结各沉积相及其亚相微相的特征，分阶段探讨砂体及沉积相带展布，进而分析了控制沉积的环境和构造背景及其油气勘探意义。铜钵庙组是初始裂陷期的记录，主要发育扇三角洲相，次为滨浅湖相；铜钵庙组一段有洪(冲)积扇，二段在西部次凹有近岸水下扇。南屯组一段是持续断陷期的沉积，以近岸水下扇和深湖–半深湖为特征的沉积相。南屯组二段沉积期实际上是断陷阶段与剪切–坳陷阶段之间的过渡期，近岸水下扇停止发育，扇三角洲的分布范围大规模缩小，主要为大面积的滨浅湖相沉积，开始有三角洲发育；后者在大磨拐河组沉积期成为主要的沉积相。 The Tongbomiao-Nantun Formations, in age of Early Cretaceous, are deposits of fault-depressing stage of the South Buir Sag, Tamtsag Basin in Mongolia. To synthesize the core sample observations, laboratory works, logging data and seismic facies signs, the paper illustrates the distinguished marks of each sedimentary facies, summarizes the main characteristics of each facies, sub-facies and micro-facies, explores the spatial distribution of the sand bodies and sedimentary facies belts, then analyses the controlling factors of environments and tectonic settings, as well as oil-gas exploration significances. The Tongbomiao Formation is a sedimentary record of the initial rifting-depressing phase, which is mainly composed of fan deltaic facies, and subordinate lake-shore-shallow lacustrine facies. In addition, there develop the pluvial/fluvial fan facies in the No. 1 member and inshore underwater fan facies in the No. 2 member of the formation in the West Sub-Sag. The No. 1 Member of Nantun Formation records a phase of sustained rifting-depressing, which is characterized with inshore underwater fan facies and deep/median deep lacustrine facies. Furthermore, there exist sediments with fan deltaic facies and lakeshore-shallow lacustrine facies. The depositing period of the No. 2 Member of Nantun Formation might be, actually, a transitional phase from the fault-depressing stage to the shear-subsidence stage (sedimentary period of the Damoguaihe-Yimin Formations). During this time, the lakeshore-shallow lacustrine facies are widely occurred, and the distribution scope of fan deltaic facies is extensively reduced. Moreover, delta appears in the southern part of the sag, and becomes main sedimentary facies in depositional period of the Damoguaihe Formation.