东营凹陷北带古近系沙四段砂砾岩体沉积特征及沉积模式

综合岩心观察、薄片鉴定、砂砾岩厚度及百分含量等资料,对东营凹陷北带沙四段砂砾岩的沉积特征、成因类型及沉积演化模式进行了系统研究。结果表明,东营凹陷北带沙四段砂砾岩储层中块状层理、粒序层理、平行层理、叠覆冲刷构造、交错层理发育,同时变形构造、泥岩撕裂屑、重荷模和火焰构造常见。碎屑颗粒表现为无分选-中等分选、棱角状-次棱角状到次圆状的近物源沉积特征。岩相类型以块状层理砾岩相、递变层理砾岩相、递变层理砂质砾岩相、交错层理砾质砂岩相、平行层理砾质砂岩相、块状层理砾质砂岩相、块状砂岩相、平行层理砂岩相、块状层理砂岩相、变形层理砂岩相、泥质撕裂变形砂岩相、薄层透镜状或压扁层理砂岩相为主。综合古地貌、砂砾岩沉积特征及沉积机制等,认为东营凹陷北带沙四段主要发育近岸水下扇、湖底扇和扇三角洲等成因类型的砂砾岩扇体。在沉积演化上,沙四下亚段沉积时期,胜坨地区和民丰地区发育近岸水下扇沉积,利津地区发育扇三角洲沉积,扇体规模较小,横向连续性较差;沙四上亚段沉积时期,胜坨地区和民丰地区广泛发育近岸水下扇-湖底扇沉积,利津西部地区发育扇三角洲沉积,扇体规模较大,横向连片发育。

Sedimentary characteristics and model for the sandstones and conglomerates in the 4th member of the Palaeogene Shahejie Formation, northern Dongying depression, Shandong

Sedimentary characteristics, genetic types and sedimentary model are treated in detail for the sandstones and conglomerates in the 4th member of the Palaeogene Shahejie Formation, northern Dongying depression. Sedimentary structures in the sandstones and conglomerates are common, including massive bedding, graded bedding, parallel bedding, superimposed scour structure, cross bedding, deformational structure, rip-up clasts, load cast and flame structure. The clastic grains are primarily derived from promixal sources, and non-sorted to moderately sorted and angular-subangular to sub-rounded. The lithofacies consist of the massive-bedded conglomerate facies, graded-bedded conglomerate facies, graded-bedded sandy conglomerate facies, cross-bedded gravelly sandstone facies, parallel-bedded gravelly sandstone facies, massive-bedded gravelly sandstone facies, massive sandstone facies, parallel-bedded sandstone facies, massive-bedded sandstone facies, deformationalbedded sandstone facies, rip-up deformational sandstone facies, and thin-bedded lenticular or flaser bedded sandstone facies. During the deposition of the 4th member of the Palaeogene Shahejie Formation, the nearshore submarine fan, sublacustrine fan and fan delta sandstones and conglomerates are accentuated in northern Dongying depression. The examination of the sedimentary characteristics and model for the 4th member of the Palaeogene Shahejie Formation, northern Dongying depression in this paper is important to the understanding of the sandstone distribution and future exploration of hydrocarbons in the study area.