Depositional Characteristics And Distribution Of Sand-conglomerate Bodies Of Eocene Sha4(Es4) Interval In Yongan Area

Yongan-Yong 1 block is located in the northeast of the Dongying depression and is adjacent to the Chenjiazhuang Salient on the north,the Qingtuozi Salient on the east and the old uplift from Chenjiazhuang Salient on the west.The study area is a depression surrounded by three salient.By the comprehensive utilization of the region's seismic data,drilling core data,logging data and a variety of analysis and test data,and based on the the sedimentology theoretical,a systematic research of provenance system,sedimentary periods and sedimentary system of the lower Es4 member in Yongan-Yong 1 block was carried on.The provenance of glutenite of lower Es4 in Yongan-Yong 1 block is confirmed to be Chenjiazhuang uplift in northwest by aggregate analysis of palaeo-geomorphology,sand body distribution,seismic reflection characteristics and petrographic composition,from macro and micro aspect.There are many northwest-southeast trending channels which connect Chenjiazhuang uplift and Yong 1 block in study area.And the glutenite fans,moving and magritting from northwest to southeast,obviously distribute along the channels.The glutenite fans have a characteristic of coarser lithology,more matrix as well as discordant seismic reflection in aeras near Chenjiazhuang uplift,and are characterized by finer lithology,obvious stratification as well as continuous parallel seismic reflection in the southeast areas far away from Chenjiazhuang uplift.In the study of sedimentary periods of sand-conglomerate bodies.In this paper,the sand-conglomerate bodies of lower Es4 member in Yongan-Yong 1 block was studied as the research object.Under the guidance of sedimentary periods division and correlation method of sand-conglomerate bodies,that is “the sedimentary cycles can be divided by the stable mudstone in the longitudinal profile,and architectures of sand-conglomerate bodies can be dissected with the rule of superposing with compensating migration”,the constraint of seismic interpretation,and combined use of well-log and seismic data,sedimentary units of sand-conglomerate bodies are divided finely.There are 3 relatively high-grade sedimentary periods and 10 secondary sedimentary periods recognized in Yongan-Yong 1 block.The shape of single sedimentary unit is like a lobe,and it has typical feature of migration and swinging.From root fan to fan edge,lithofacies change from conglomerate into gravelly sandstone-pebbled sandstone,sandstone,and finally it is thin sand existing in thick mud.On the section,along vertical source direction the shape of single sedimentary unit is lenticular,and sedimentary units deposit with compensating migration.Along source direction,the shape of single sedimentary unit is wedge,and sedimentary units sustaining deposit toward source direction,and multiple sedimentary cycles superpose positively.Based on the establishment of the provenance system and the fine division of the sedimentary period,this paper studied the geological phase mark in lithologic character,petrological characteristics,color feature,structure characteristics of grain size and sedimentary structural characteristics.Based on this,16 kinds of lithofacies and 25 kinds of lithofacies assemblages were divided.Combined with seismic facies and single well sedimentary analysis,ultimately determine the type of sedimentary facies in research area is nearshore subaqueous fans facies.With aggregate analysis of seismic reflection characteristics and distribution of sand-conglomerate body of each sedimentary period,the areal distribution of sedimentary facies are plotted on the basis of sedimentary facies marks study and the recognition of sedimentary facies types.The distribution characteristics of sand-conglomerate body in research area is studied with the combination of tectonic evolution study,provenance system analysis and division of the sedimentary period.It shows that the lithology of of lower Es4 member become fine gradually from northwest to southeast and nowday's uplift topography of Yong 1 sand-conglomerate body was formed in Es3-Es2 period because of the deformation caused by magmatic intrusion.