Sedimentary Response To Carboniferous Tectonic Evolution In The Eastern Margin Of The Pre-Caspian Basin

The Carboniferous strata in the eastern margin of Pre-Caspian Basin has great potential for oil and gas exploration,of which the breakthrough is very important for deployments of Chinese petroleum industry.This paper takes the Carboniferous strata as the main research object on base of the drilling and seismic data of the three blocks such as Central Block,KMK and so on.which was guided by theories including seismic stratigraphy,logging sedimentology and tectonics,sequence stratigraphy,paleogeography,and basin-mountain coupling theory,and some techniques were also utilized comprehensively inculuding sequence stratigraphic analysis techniques,sedimentary facies and sedimentary system identification techniques,sequence grid controlling phase analysis techniques,basin-mountain coupling analysis techniques,reservoir controlling factors analysis and prediction techniques.The paper focused on analysing the controlling process of Carboniferous regional tectonic evolution on the formation and evolution,and the sedimentary facies distribution of eastern margin of the Pre-Caspian Basin.The sedimentary palaeogeography of the eastern margin of the littoral basin has been restored.This paper have established a sequence division scheme,sedimntary facies identification criterias and a sedimentary facies model based on the Carboniferous strata in the Central Block of the eastern margin.The planar distribution characteristics,spatial evolution law of the sedimentary facies and the mechanism that sedimentation responded to tectonism in different sequence systems were studied.It revealed the east-west differentiation in the north-south zoning,and the differential sediments of sedimentary facies in the eastern margin of the Pre-Caspian Basin,and the kinetic reasons for sedimentary datum changes constrained by the regional tectonic movements.The regularities of SRCA(source reservoir caprock assemblage)in different lithologic sedimentary combinations controlled by the sequence system were explored too.The Pre-Caspian Basin belongs to a superimposed basin on the southeastern edge of the Eastern European Craton that formed after late Proterozoic.Its tectonic evolution is controlled by the evolution of the ancient Ural Ocean in the eastern margin,whose closure process in the Late Paleozoic was a scissor closure process from north to south.The sedimentation in the Carboniferous-Lower Permian is different in the north-south direction,which is well coupled with the closure and orogenic processes of the Ural Ocean.The Carboniferous strata in the Central Block can be divided into five secondary structural sequences(SS1,SS2,SS3,SS4,SS5)and 11 third-order sequences(S1,S2,S3,S4,S5,S6,S7,S8,S9,S10,S11).There is a close relationship between the sedimentary datum change of the Carboniferous research area and the global sea level change,but the regional tectonic effect makes the reaserach area have its own characteristics.There are four types of facies in the research area,such as evaporation platform,restricted platform,open platform and shelf phase;11 sub-phases such as Tainean Beach,Taineihai,Chaoping and so on,and 24 microfacies includes granulated beach,raw shoal,gray mud ping and so on.The vertical evolution sequence from the bottom to the top is the shelf-open platform-shelf-open platform-restricted platform-evaporation platform.In the horizontal direction,the phase belt distributes form north to south and is different form east to west.Specialty.two SRCA types are developed in the Carboniferous strata of the Central Block,respectively carbonate rocks-evaporite sequence stratigraphic framework and carbonate rocks – evaporate-clastic rock mixed sequence stratigraphic framework.