Sedimentary characteristics and models of beach-bar sandbodies in the upper part of the fourth member of Paleogene in the south slope of Dongying depression

Key words:  beach-bar  sedimentary characteristics  sedimentary model  Dongying depression

Abstract:

During the period of the upper part of the fourth member of Shahejie formation ( Es4 ) of Paleogene, the south slope of Dongying depression developed abundant beach-bar sandbodies. Based on the description and its associated test and analysis of the cores combined with the analysis of logging data and paleotopography, the sedimentary characteristics and models of beach-bar sandbodies in shore-shallow lacustrine were systematically summarized. The lithology of beach-bar sandbodies is mainly fine sandstone and siltstone. The quartz content in beach-bar sandstones is middle level，and the feldspar content and the lithic content are relatively high. The grain size probability curves are mainly two-segment of contents bouncing population and suspension population. Sedimentary structures are characterized by wave-cross bedding t wave-generated ripple and bio-turbation, and the sedimentary facies sequences are characterized by reverse grading and composite grading. According to the sedimentary and distribution characteristics, beach-bar sandbodies can be divided into bar subfacies and beach subfacies. And the former includes main body of bar microfacies and margin of bar microfacies, while the latter includes beach ridge microfacies and beach mat microfacies.