松辽盆地西斜坡上白垩统青山口组二段及三段底部四级层序格架下沉积微相分布

摘要

Based on seismic,logging and core data,the 4th-order sequence stratigraphic framework of the Member 2 and lower Member 3 of Upper Cretaceous Qingshankou Formation in the west slope of the Songliao Basin was established and the spatial distribution of the sedimentary microfacies under the frame-work of the 4th-order sequence was reconstructed.The Qingshankou Formation was divided into two 4th-or-der sequences (Cg4、Cg3),each of the 4th-order sequence was divided into lake expanding system tract and lake shrinking system tract,respectively named Eg4、Sg4,Eg3、Sg3 upwardly.Shore-shallow lacus-trine sedimentary bodies (shore-shallow lacustrine sandy bars, mud bank and mixed bank ) and delta front (mouth bars and distal bars)characterised the deposition pattern of the Member 2 and lower Member 3 of Qingshankou Formation in west slope.Delta front sedimentary bodies from the west and north were de-veloped in the Eg4,shore-shallow lacustrine mixed beaches were developed among the sedimentary bodies of delta front.The early delta expanded and a new northwest delta was developed in Sg4.Delta from the west and north extended to the east and delta front sedimentary bodies from the southwest shrinked in Eg3. Delta front sedimentary bodies were dominant and overlapped each other,while shore-shallow lacustrine sediments reduced in Sg3.The depositional zones continued to expand,and delta front sedimentary bodies expanded in the Member 2 and lower Member 3 of Qingshankou Formation upwardly.%综合利用地震、录井、测井、岩心资料，建立了松辽盆地西斜坡上白垩统青山口组二段及三段底部四级层序地层格架，查明了四级层序格架内沉积微相的空间分布。青山口组二段划分为2个四级层序（Cg4、Cg3），每个四级层序均可划分为湖泊扩张体系域和湖泊收缩体系域，分别命名为 Eg4、Sg4，Eg3、Sg3。西斜坡青山口组二段及三段底部的沉积格局为滨浅湖沉积体（砂坝、泥滩、混合滩）和三角洲前缘沉积体（河口坝、远砂坝）共存。Eg4沉积时期发育了物源来自西部与北部的4个三角洲前缘沉积体，沉积体之间发育滨浅湖混合滩；Sg4沉积时期三角洲沉积体规模较前期扩大，并且发育了物源来自西北方向的三角洲。Eg3沉积时期物源来自西部及北部的三角洲向东推进，东北部三角洲前缘沉积体萎缩；Sg3沉积时期以三角洲前缘沉积占优势，三角洲前缘沉积体错叠连片，滨浅湖沉积大量减少。青山口组二段及三段底部自下而上，沉积区范围和三角洲前缘沉积体的规模逐渐扩大。