Research On The Lithofacies Paleogeography Of The Triassic In The Southwestern Margin Of Ordos Basin

Based on the pilot project of the five-stage loess-covered area in the northwest of China,it uses the method of field investigation and indoor research to study the rock strata in this area,Rock form and type,contact relationship,rock stratigraphic overlay characteristics,sedimentary structure and paleontological fossils and other characteristics,and collect the data and compare the previous studies systematically,and we have made the following conclusions:1.By the work of the field and the geological mapping,the spatial distribution of the Triassic in the project area,the contact relationship between the strata,the sedimentary sequence,the sedimentary facies and the combination of the rocks are identified.2.Based on the collection of a large number of drilling,outcrop and core data,the sedimentary system types of the Triassic Ermaying Formation and Yanchang Formation in the southwestern margin of the Ordos Basin are studied in detail.The sedimentary systems are river,braided river delta,delta,lake and deep lake Turbidite.The sedimentary system is mainly controlled by the source of the northeastern and western parts of the Yangtze River,and the sand body extends far more than that of the northeastern and western parts.The sedimentary system is mainly composed of alluvial fan,braided river,meandering river,lake(shallow water)delta and shore shallow lake.,The southwest water system is limited and the southern provenance is weak,which has little effect on the basin sedimentary pattern.The lacustrine basin of the Yanchang Formation is the northwest-south east,northeast terrain,the development of meandering river delta,and the southwest of China is slightly steep to form braided river delta.The delta front is dominated by gravity and forms turbidites3.Based on the analysis of sedimentary facies and lithofacies palaeogeography in this area,the Triassic of the southwestern margin of Ordos Basin is an important oil-producing layer.The overall oil-bearing area is wide,the oil storage sand layer is large,the lateral change is big,the reservoir permeability is low,and it has a favorable prospect for oil and gas development.