Characteristics of sedimentary system evolution and sequence stratigraphy boundary of Denglouku group in Xujiaweizi fault depression, Songliao Basin

Abstract

In the previous studies on this area, the sequence division is relatively rough. This study has improved the precision, and the Denglouku formation is divided into 10 fourth-order sequences, with the thickness of each small layer of about 70-80m. The characteristics of each small sequence boundary are described, and three third-order, four fourth-order sequence flooding surfaces are found. The stratigraphic framework is established. From bottom to top, the base level of all strata shows decline-rise-decline, which means regression-transformation-regression.The Denglouku 1st mainly includes lacustrine and fan delta, the sources of sediments from northeast, northwest, southwest and Southeast directions. In Denglouku 2nd and Denglouku 3rd, braided fluvial delta and intermittent lacustrine are dominant, which were controlled by the sedimentary systems from east, south, north, northeast, southwest, and the northwest. In Denglouku 4th, there is mainly braided fluvial, rarely are lacustrine and braided fluvial delta plain, the main source was from the northeast, and a small amount of source is from the west.