Study On The Sedimentary System Of The First Member Of Paleogene Funing Formation In Subei Basin

Subei Basin is the overland part of Subei-Southern Yellow Sea Basin,with an area of about 35000 km~2.Subei Basin has undergone more than 40 years of exploration practices.It has been fully studied in terms of chronostratigraphic,tectonic evolution,palaeogeographic evolution,and hydrocarbon accumulation and migration.However,the study on the sedimentary system of the first member of Funing Formation are confined to a certain sag,and the study of the entire basin is still weak.Based on the theory of sedimentology,using regional geology,core,logging,and seismic data,the paper established the sequence stratigraphic framework of the Funing Formation in the study area.Based on this,it classified the type of sedimentary system and discussed the distribution characteristics,the control factors,and established the deposition patterns.The main results include:(1)Through sequence stratigraphy analysis,the sequence stratigraphic framework of the Funing Formation in the entire basin was established.The Funing Formation in Subei Basin was divided into two third-order sequences.Each of the third-order sequences contained LST,TST and HST.The first member of Funing Formation of the Dongtai Depression in the southern part of the basin includes the LST and part of the TST of the SQ1.And in the Yanfu Depression in the northern part of the basin,it mainly contained the LST of the SQ1.(2)In the sequence stratigraphic framework,the identification of core,logging,and biologically sedimentary facies indicates that the study area mainly developed sheet-flow-flooded-lake system,wave-dominated delta-beach bar system and storm deposits facies in the first member of Funing Formation.The sheet-flow-flooded-lake sedimentary system is developed under the conditions of a dry climate and a flat terrestrial lake basin.Periodically,the sediments are exposed.According to the corresponding features of sedimentary tectonics and logging,they can be divided into several sedimentary microfacies such as sheet-flow deposits,sand flats,mixed sand/mud flats,mud flats,and flooded-lake bar deposits.The wave-dominated delta-beach bar system can be divided into beach and bar under normal wave conditions(3)where the wave action is strong.The beach bar is mainly developed in the shore-shallow lake and is controlled by wave conditions.The strom deposits are developed in semi-deep lake.(4)During the LST,Dongtai Depression developed an intermittently exposed sheet-flow-flooded-lake system.The source mainly came from the western part of the Jianhu Uplift,the Zhangbaling Uplift,and the western and middle parts of the Sunan Uplift,and was supplied with sheet-flow deposits of alluvial fans.Sand flats were mainly developed in Jinhu Sag and Gaoyou Sag,and there are mixed flats and mud flat deposits in relatively low areas.Mixed flats and mud flat deposits were developed successively to the northeast of the depression.In the northern part of the basin,a wave-dominated delta-beach bar system was developed.The Binhai Uplift and the Southern Yellow Sea were supplied to the depression,and two delta deposits were developed.Beach bar were deposited in the middle of the depression.In the south of the depression,there was a deep depression with storm deposits developed.The TST sediments mainly occurred on the top of the first member of Funing Formation in Dongtai Depression.It developed a wave-dominated delta-beach bar system.The wave-dominated delta mainly developed in the Zhangbaling Uplift,the western part of Jianhu Uplift and the middle part of the Sunan Uplift.Beach bar was mainly distributed in the western and southeastern parts of the Jinhu Sag,and in the central part of the Gaoyou Sag.They were distributed in strips with storm deposits on the sand bodies.(5)The depositional patterns of the sheet-flow-flooded-lake system and the wave-dominated delta-beach bar system of the first member of Funing Formation in Subei Basin were studied and established.The development and distribution of the sedimentary system were controlled by various factors,among which the most significant was the paleoclimate conditions,palaeogeomorphology conditions,paleowind conditions,andf ancient water depth conditions.