济阳坳陷细粒混积岩类型与湖盆演化的耦合关系

Types of Fine-Grained Mixed Sedimentary Rocks of Shahejie Formation and Evolution of Lake Basin in Jiyang Depression, Eastern China

综合钻井、岩心、薄片和地球化学等资料,详细研究了济阳坳陷沾化凹陷沙三段下亚段细粒混积岩的混积类型、不同类型细粒混积岩的成因、垂向分布以及古湖泊水文演化规律.结果表明,沾化凹陷沙三段下亚段细粒混积岩包括层状-纹层状组构混积型和块状矿物组分混积型等2种混积类型;自下而上主要由层状-纹层状组构混积型夹块状矿物组分混积型发育段,过渡为块状矿物组分混积型夹层状-纹层状组构混积型发育段;表明了由潮湿且受季节性气候影响明显的深水湖泊,演化为水体较浅、盐度均一且受季节性气候影响不明显的湖泊环境,并建立了高水位早期-高水位中-晚期-低水位期的湖泊演化模式.在湖泊高水位早期阶段的早-中期和高水位中-晚期,有机质富集的主控因素主要是氧化还原条件和古生产力;在湖泊高水位早期阶段的晚期,古生产力是有机质富集的主控因素;在湖泊低水位时期,有机质富集的主控因素是氧化还原条件.总体上,适量的陆源供给(粘土矿物和石英含量均小于22%)会促进有机质富集,而过量的陆源碎屑输入以及碳酸盐的快速沉淀都会导致有机质被稀释.

In this paper,it conducts detailed fine-grained mixed sedimentary rocks characterization of the lower submember of Es3 by combining detailed core descriptions,microscopic observation and geochemical data,and then study on characteristics of different types of fine-grained mixed sedimentary rocks of Shahejie Formation,depositional process and evolution of lake basin in the Zhanhua depression in details.It is identified two major fine-grained mixed sedimentary rocks associations in the lower submember of Es3,including the laminar interbedding mixed sedimentary rocks association and the massive component mixed sedimentary rocks association upward,which suggests that the lake changed from larger one with stratified water column to shallower and smaller one with homogenization salinity when the paleoclimate changed from warmer and humid to cooler and drier through time.It is inferred that the accumulation of organic matter within the early and middle stage of early lacustrine high stand and middle to late lacustrine high stand was controlled by the combination of redox conditions and primary productivity,while only by primary productivity accumulation in the late stage of the early lacustrine high stand and only by redox conditions in lacustrine low stand.On the whole,the appropriate amount of terrigenous supply(clay mineral and quartz content are less than 22%)could promote the enrichment of organic matter,while excessive terrigenous input and rapid precipitation of carbonate lead to the dilution of organic matter.