Research On Mesozoic Early Cretaceous Sedimentary System In Luanping Basin

Previous studies have generally believed that the Luanping Basin is dominated by shallow water deposits and does not develop deep water deposits,so it does not have oil and gas exploration potential.There are two main problems solved in this study.First,what are the types of sediments in the Luanping Basin,especially whether deep-water sediments exist,and secondly,the distribution,evolution,and deposition patterns of the sedimentary systems in the Luanping Basin.The main strata in this study are the Late Jurassic-Early Cretaceous strata in the Luanping Basin,which were conducted through literature survey,geological survey and core observation.Through a large amount of literature research to grasp the previous research results;using high-definition digital cameras,drones,gamma instruments,ground penetrating radar and other advanced survey equipment and traditional geological three-piece set,geological survey of the steep slope belt of the basin,preferably 12 A geological profile;observe the core of Luantan 1 well,and count and analyze its deposition type.Through these studies,the following achievements and understandings have been achieved:1.By sorting out the previous stratigraphic division plan,combined with geological survey and zircon dating data,the stratigraphic division plan of Tian Shugang et al.is selected and modified to remove the Jiufotang Formation and above strata.In addition,combined with previous literature and geological investigations,the scope of the basin and the direction of the two major provenances were determined.2.Through geological survey and core observation,it is determined that there are three sedimentary facies in Luanping Basin,shallow water facies,deep water facies and volcanic eruption facies.The shallow water facies include alluvial fans,fan deltas and shallow lakes;the deep water facies include deep lakes,near-shore underwater fans and various types of lake bottom fans;the volcanic eruption facies are mainly andesite,rhyolite,tuff and other volcanic rocks.3.Analyze the sedimentary evolution and distribution of the basin by analyzingthe changing rules of lithologic lithofacies in various layers and profile comparison and sand-to-land ratio analysis of key horizons.According to analysis,during the Dabeigou Formation period,the lake basin was a continuous expansion process.During the Dadizi Formation,the Lake Basin experienced a process of small expansion in the early stage-small uplift in the middle stage-large expansion in the late stage.During the watermelon orchard formation,the lake basin experienced three stages: initial rift-deep expansion-uplift and contraction,and deep-water deposition was most developed in the middle and late periods.According to the profile comparison and sand-to-land ratio analysis of the Watermelon Formation,the shallow water deposition was predominant in the early stage of the Watermelon Formation and the deep water deposition was in the middle and late stages.The shallow water deposition system was distributed along two faults in the basin,and the deep water deposition was widely distributed in the basin Central and South China.4.Use the database method to quantitatively count the types of deep-water deposits in the core of Luantan 1 well and the types of deep-water deposits in the outcrop of the field,and combine the nature of the basin to draw a map of the sedimentary model of the steep slope zone in Luanping Basin.Then,according to the deposition model,several control factors of the basin were determined,namely tectonic function,basin nature,paleoclimate and paleowater depth.