Paleogene flooded lake sediments in the southern part of the Jiyang depression

Abstract：The Paleogene sedimentary characteristics from the 1st Member of the Kongdian Formation to the 4th Member of the Shahejie Formation in the southern Jiyang depression have been studied by core observation, thin section identification，grain size analysis, fossil identification and log interpretation. Results indicate the following：the Jiyang depression was in the initial stage of lake downfaulting from the 1st Member of the Kongdian Formation to the early stage of the 4th Member of the Shahejie Formation and the sedimentation was significantly controlled by inflow of ephemeral flood; a flooded lacustrine sedimentary system formed in the Dongying and Huimin subbasins. The main lithologic characteristic is that the rock types are dominated by light-colored clastic rocks reflecting the oxidation environment with a low maturity. The grain size distribution and sedimentary structure show that the rocks have the sedimentary characters of both gravity currents and tractional currents. Plant fragments are lacking and bioturbation structures are abundant and cyclic. Sandbodies are distributed in a ring shape. The sedimentary system may be divided into the side-edge distal and near-shore distal facies sequences and five microfacies, namely, flood channel terminus, mud flat, sand flat, mixed mud/sand flat and flooded lake tempestite.