The Sedimentary Systerm Study In The Lower Fourth Member Of Shahejie Formation In The Bonan Subsag

Bonan depression of the fourth sedimentary formation is mainly composed by aset of red continental clastic sedimentary strata. Exploration results show that the redlayer shows a good sign of oil and gas.After this period it has happened many times ofsuperposition and transformation,the original pattern has changed a lot.Restoring theoriginal pattern of the basin and Study on the characteristics of depositional system todetermine its distribution of sand body reservoir and to expand the scale of reserves hasimportant theoretical and practical significance.This paper starts with the identification of developmental features and formationinterface of the strata, restoring the denudation thickness of the Bonan subsag Es4strata and its original formation thickness, itdetermine the tectonic evolution,according tothis, Comprehensive recover the prototype basin pattern of this period of the study area.It focuses on the classification and identification of the depositional types and features.It does more detailed analysis and research on the influence of ancient environmentdepositional system.There are many ways to respond to erosion thickness, In view of the area of foursand strata erosion thickness restoration,which method is more accurate, when it isspecific to different structural positions and different layers, that is an important aspectof this paper. Combination with the different erosion thickness recovery method’sapplicability conditions,different areas choose different methods. The seismic andgeological data shows that the study area has been generally denuded, it has threedifferent erosion belts: Internal uniform erosion belt; Tectonic zone of the southern faultsexist in the sag internal;The southern gentle slope zone which has been completelydenuded.According to this, it puts forward Multi-method-step-by-step method tocalculate the erosion amount: Internal uniform erosion belt, using acoustic time law of the mudstone and deposition rate method; Tectonic zone of the southern faults exist inthe sag internal, using structural cross section method; The southern gentle slope zonewhich has been completely denuded, using the stratigraphic distribution method. Itshould be emphasized that the amount of the internal erosion is the bases of the other twomethods. Integrated the original tectonic framework and denudation thickness calculation,The prototype basin of the Bonan sag Es4is mainly controlled by NW-trending faultsystem, presents the structural pattern of "basin and range phase”, The overallperformance is a fault south of the north faulted basins. The provenance system mainlycomes from two directions of eastern and Southern, The southern Chenjiazhuang uplift isthe main source of the sediment.Based on the restoration of the prototype basin and denudation thickness,Combined with the analysis of ancient tectonic pattern, the types of sedimentary systemsunder the Bonan sag Es4has been finely divided and systematically researched.At thesame time, affecting factors of the ancient climate and ancient salinity of sedimentarysystem has also been detailly analysised.the sub sedimentary period under Bonandepression of the four sedimentary formation, The whole Bohai Bay Basin is in the earlystage of the rifting basin,the climate is dry, Lake basin range is small,water is shallow,the sub sedimentary of the four sedimentary formation has the features that Gravity flowand traction flow coexist, Water deposition and underwater deposition coexist,Alternating wet and dry climate dominated by arid,that caused the fourth sudsedimentary formation has various genetic types and Complex distribution laws. Bonandepression of the fourth sub sedimentary formation mainly developed alluvial fan,floodplain, fluvial facies. Formation lithology portfolio is characterize by interbeddedsandstone and mudstone.