渤海湾盆地沧东凹陷孔二段细粒混合沉积岩特征及控制因素

摘要

Mixed clastic-carbonate deposits are widely distributed in the fine-grained sedimentary rocks from the 2nd Mem-ber of the Kongdian Formation in Cangdong Sag.The mixing styles of the fine-grained sedimentary rocks can be divided into componential mixtures( CM) and structural mixtures( SM) .The componential mixtures are characterized by mixing of different minerals within one lamina.The structural mixtures feature in vertical overlying of different single-mineral lami-nae and componential mixture laminae.Through detailed core description,thin section observation and X-ray diffraction analysis,it was considered that there develop two types of componential mixtures in the 2nd Member of Kongdian Forma-tion in Cangdong Sag, namely clay-carbonate ( CM1 ) and felsic-carbonate-clay ( CM2 ) componential mixtures.And there also develop four types of structural mixtures, namely felsic/clay-carbonate ( SM1 ) , felsic/clay/carbonate ( SM2 ) , clay/carbonate(SM3)and clay-carbonate/clay-organism(SM4)structural mixtures.There are two kinds of vertical combina-tions both with a bottom-up order change from massive structure to bedded structure and lamina structure.The vertical combination dominated by dolomitic( limy) fine-grained mixed sedimentary rocks is formed due to climate changes.And the vertical combination dominated by felsic fine-grained mixed sedimentary rocks is due to the changes in supply intensi-ty of terrigenous materials.%渤海湾盆地沧东凹陷孔店组二段(孔二段)深水细粒沉积岩中普遍发育陆源碎屑与碳酸盐矿物的混合沉积.细粒沉积岩中的混合沉积样式可划分为组分混合和组构混合两种类型,组分混合表现为不同矿物在层内的混合沉积;组构混合表现为单一矿物纹层或组分混合纹层在垂向上的相互叠置.通过岩心精细描述、薄片镜下鉴定和全岩X-射线衍射分析等手段,认为沧东凹陷孔二段细粒沉积岩中发育两种组分混合类型:粘土-碳酸盐型组分混合(CM1)、长英质-碳酸盐-粘土型组分混合(CM2);以及4种组构混合类型:长英质/粘土-碳酸盐型组构混合(SM1)、长英质/粘土/碳酸盐型组构混合(SM2)、粘土/碳酸盐型组构混合(SM3)和粘土-碳酸盐/粘土-有机质型组构混合(SM4)等.混合沉积样式在垂向上主要呈两种组合形式,分别以云(灰)质细粒混合沉积岩和长英质细粒混合沉积岩为主导,自下而上均表现为块状、层状和纹层状的有序变化.气候变化形成云(灰)质细粒混合沉积岩为主导的垂向组合,而陆源碎屑供应强度变化则形成以长英质细粒混合沉积岩为主导的垂向组合.