The Sedimentary Facies Study Of Baiyanghe Formation Of Paleogene In Jiuxi Depression,Jiuquan Basin

In this study,the paper based on the previous researeh results,guided by the sequence-straigraphic and sedimentologic theories and methods,through the analyses of outcrops,cores,drilling and logging date,to research the sequence-straigraphic feature and sedimentary system distributions feature in Baiyanghe Formation of Jiuxi depression,Jiuquan Basin.According to the result of sequence interface recognition and sequence stratigraphic contrast between Wells,shows that the formation of Baiyanghe can be described as a complete three-order sequence,which can be divided into 7 quasi-sequence sets,the Ps3 and Ps7 are basically distributed in all the region,while Psl and Ps2 are not developed in the east of depression,Baiyanghe.According to the researeh results of facies marks.single well facies and comparison of connecting-well sections,combined with the condition of provenancers and palaeogeomorphology,the paper totally points out 4 types of facies in the study area,including alluvial fans,braided rivers,braided river deltas and lake depostis.The formation of Baiyanghe in Jiuxi depression represents a complete process of lake transgression and regression,intially,the water level of the lake is low,main developed alluvial fans and braided rivers depostis in the study area;with the rise of the lake,braided rivers and braided river deltas depostis gradually ocuppy the dominent position;when the water reached the highest level,the whole region was submerged by the lake,only the lake depostis developed;with the retreat of the lake,braided rivers and braided river deltas have begun to develop again in the study area;horizontally,the facies presents itself as a near northwest-southeast sedimentary system.Throughout the process,the change of the lake level,climate and palaeogeomorphology controll the distribution of sedimentary system.