二连盆地乌里雅斯太凹陷下白垩统湖底扇沉积特征及成因分析

Depositional Characteristics and Genesis of Lower Cretaceous Sublacustrine Fan in Wuliyast Sag,Erlian Basin

二连盆地乌里雅斯太凹陷下白垩统发育一套典型的湖底扇沉积,其由补给水道、内扇、中扇和外扇4个部分组成,主要发育有补给水道,内扇主沟道和沟堤,中扇辫状沟道、沟道间和外扇席状浊积砂等微相类型。湖底扇单个扇体规模不大,但往往多期次发育、成群分布,垂向上相互叠置、横向上叠加连片,规模可观。足够的可容纳空间和持续的物源补给是形成厚层湖底扇的2个重要条件,同沉积断裂的下降盘和坡折带是湖底扇发育的有利部位。湖底扇砂砾岩体具有毗临生油洼槽、易于形成岩性圈闭、易于油气聚集等优越条件,对岩性油气勘探具有重要意义。

A set of typical sedimentation of sublacustrine fans in lower Cretaceous in Wuliyasitai sag of Erlian basin is composed of feeder channel,inner fan,middle fan,and outer fan.The main micro-facies include feeder channel and main channel in inner fan,furrow dam and braided channel in middle fan,inter-channel and sheet turbidite sand in outer fan.Although a single sub-lacustrine fan is not large in scale,the sedimentation is characterized as multi-stage development,group distribution,vertical superposition,and superimposed horizontal lace.Thus,the depositional scale is large.The big open ended space and continuous supply of deposits are two key factors for forming the thick sub-lacustrine fan.Meanwhile,the place of downthrown block of growth fault or the slope-break zones is the favorable area for the sub-lacustrine fan development.The conglomerate body in sub-lacustrine fan is close to hydrocarbon-generated sag and prone to lithologic trap formation and hydrocarbon accumulation;thus it is important for oil and gas exploration.