南堡凹陷东营组三段页岩特征及其对古环境和有机质富集的启示OA北大核心

To evaluate the shale oil exploration potential of the member 3 of the Paleogene Dongying Formation(Ed3)in the Nanpu sag,this study investigates paleoclimate and paleoenvironmental varia-tions and their impacts on organic matter accumulation through mineralogical and geochemical analyses of 21 shale samples.Results reveal strong heterogeneity in the Ed3 shale,with TOC ranging from 0.30％to 2.66％,S1+S2 from 0.44 to 11.41mg/g,and HI from 57 to 466 mg/g TOC,predominantly charac-terized by Type Ⅱ kerogen at low to mature thermal maturity stages.Multiple geochemical proxies indicate that a semi-humid to semi-arid paleoclimate during the Ed3 deposition influenced palaeoenvironmental fluctuations.From bottom to top,paleowater depth transitioned from shallow to deep and back to shallow,paleosalinity shifted from brackish to fresh and back to brackish,and redox conditions evolved from weakly oxidizing to weakly reducing and back to weakly oxidizing.These environmental fluctuations controlled differential organic matter accumulation.Under humid climates,high paleoproductivity and anoxic condi-tions in deeper waters promoted efficient organic matter burial and enrichment.Conversely,under arid climates,moderate paleoproductivity and oxic conditions in shallower waters resulted in lower organic matter burial and enrichment.The established model of organic-rich mudstone development provides a foundation for selecting favorable lacustrine shale oil exploration intervals.