Study On Sedimentary Environments Of Early Faulted Stage And Their Controling On Sedimentation In Dongying Sag

In the early Paleogene,Dongying Sag was located in the East Asian monsoon climate area,and the climate was relatively arid and occasionally humid.The restoration of the paleoenvironment is not only conducive to deepen the understanding of deep-time paleoclimate,but also good for the comprehensive study of sedimentary systems and hydrocarbon accumulation factors.Strontium（Sr）,copper（Cu）,magnesium（Mg）,vanadium（V）,chromium（Cr）,manganese（Mn）,δ¹³C,δ¹⁸O and other indicators which are sensitive to paleoenvironmental changes are selected in this paper,supplemented by sporopollen and micro paleontological data,to analyze the corresponding relationship between the element content and ratio of the target strata,sporopollen climate parameters and the sedimentary environment,and finally clarify the paleoenvironmental characteristics of the Kongdian Formation（Ek）and the lower 4th Member of Shahejie Formation（Es₄^x）in Dongying Sag based on the experimental results of major elements,trace elements and carbon-oxygen isotopes of carbonate rocks of the Ek and the Es₄^x in Donying Sag,Bohai Bay Basin.The results show that the evolution of the climate of Ek and Es₄^x in Dongying sag has experienced three stages:from the humid and hot climate stage of the 2nd Member of Kongdian Formation（Ek₂）to the arid and hot climate stage of the 1st Member of Kongdian Formation（Ek₁）,and finally to the warm and semi-humid climate stage of the Es₄^x.There were high-frequency alternation of drought and humidity,and high-frequency alternation of warm and hot within the arid and hot stage,which made the water bodies the shallowest of the Ek₁ interval,with high salinity and oxidation degree,and the whole target strata was in an oxidation environment with weak stratification.There was a good correlation among the indicators used for paleoenvironment reconstruction.The results of paleoenvironment restoration indicate that the climate in the early Paleogene in Dongying Sag was largely affected and controlled by the global climate change.Meanwhile,the sedimentary types and the evolution characteristics of the target strata in the study area are systematically defined by integrated analyses of seismic,logging and core data.Alluvial fan,river,delta and salt lake are mainly developed of the Ek and the Es₄^x in Dongying Sag,and the sedimentary distribution is controlled by climate change.Alluvial fan-river-floodplain-arid salt lake sedimentary system is developed in the arid climate stage of the Ek₁ interval,while shallow water delta and fan delta depositional systems are developed in the humid climate stage of the Ek₂ and the Es₄^x interval.