Stratigraphic charactertistic and tectonic control on the paleogene sedimentary evolution of the Baxian Half-graben, Bohai Bay Basin, east China

Abstract

The depositional and structural development of a deltaic dominated succession, interpreted from seismic data, cores, well curves and lab data, is discussed. The case is from a comprehensive analysis of stratigraphy and the depositional process of a deltaic to continental succession in the early to late Paleogene in the Baxian Half-graben, Bohai Bay Basin, East China. The evolution of three genetic successions with a total thickness of 1000–7000 m, comprising three facies associations, including fan delta, braided-river to shallow water delta and lacustrine deposit, records: a, initial rift stage, b, late rift stage, and c, post-rift stage. (1) The initial rift stage is made up of several fining-upward successions, mainly stacked in retrogradation style that pass from the fan delta plain, through the fan delta front to pro-delta in a deep lacustrine environment. This stage is characterized by high intensity rifting and the deposition was keeping up with subsidence. (2) The late rift stage is made up of several successions stacked in both progradation and retrogradation styles. The succession is defined by braided-river deltas, distributary channels, subaqueous channels, swamp, levees, and fluvial-dominated mouth bar, which are mainly identified using core data. This stage is characterized by a decrease in the intensity of rifting and finer-grained deposits. (3) The post-rift stage is made up of several successions stacked mainly in an aggradation style. Shallow water delta developed in the early phase, and lacustrine deposits developed in the late phase. The transition from initial-rift to late-rift phase is represented by a seismically identifiable regional angular unconformity and an overall upward decrease in the quantity of syn-depositional faults. The late-rift to post-rift evolution is represented by an overall decrease in grain size, decrease in fluvial influence and increase in wave influence. The research process can be a reference for the study of stratigraphic architecture and sedimentary process in other lacustrine basins where tectonic movements are well developed. The achievements of this article can be an important basis for the further exploration in the half-graben.