大港滩海区第三系湖相混积岩的成因与成岩作用特征

Sedimentary and Diagenetic Characteristics of Paleogene Lacustrine “Hunji” Rock in Beach District, Dagang

大港滩海第三系沙河街组一段下部分布的混积岩主要为陆源碎屑质—碳酸盐混积岩 ,其次为碳酸盐质—陆源碎屑混积岩和含碳酸盐—陆源碎屑混积岩。其中白水头地区的混积岩发育于辫状河—扇三角洲前缘水下分流河道沉积体系之中 ,为相缘渐变混合沉积的产物 ;而马东—马东东地区的混积岩发育于重力流沉积体系之中 ,为浊流沉积的产物。本区混积岩主要经历了压实作用、胶结作用和溶蚀溶解作用。孔隙流体的化学性质经历了由碱性到酸性 ,最后又回到碱性的变化历程。其中海绿石、微晶方解石、部分石英溶蚀和连生方解石为碱性流体条件下的共生组合 ;次生加大石英、油气侵位、溶蚀溶解、高岭石为酸性条件下的共生组合 ;伊利石、绿泥石、钠长石化、孔隙充填方解石和白云石为碱性流体条件下的共生组合。

“Hunji” rocks of the lower part of number 1 of Shahejie Formation,Beach district,Dagang, are dominantly terrigenous clastithic carbonate “Hunji” rock,subordinately carbonatic terrigenous clastic “Hunji” rock and carbonate bearing terrigenous clastic “Hunji” rock. “Hunji” rock of Baishuitou district lies in braided stream fan delta front subfluvial branching river deposits,which mixed by gradual facies change. While Madong Madongdong district is distributed in gravity flow deposit systems, mixed by turbidites. “Hunji” rocks of this area experienced compaction , cementation and dissolution /alteration process. Pore fluid experienced alkaline to acid and return to alkaline. The association of glauconite and micro calcite cement, calcite precipitation and a part of quartz dissolution is with alkaline pore fluid; The association of hydrocarbon emplacement, dissolution, quartz overgrowth and kaolinite precipitation is with acid pore fluid; And the association of illite, chlorite, albitization, pore filling calcite and dolomite is with alkaline pore fluid.