Sedimentary architecture of hyperpycnal flow deposits: Cretaceous Sangyuan outcrop, from the Luanping Basin, North East China

Abstract

Due to their importance in hydrocarbon exploration field, hyperpycnal flow deposits have attracted widespread attention. However, compared to the river, delta, and hemi-deep lake deposits, relatively limited studies have been conducted on the hyperpycnal flow sediments. The well-exposed Sangyuan outcrop in the north-west of Luanping Basin in the Bohai Bay area, as a major hyperpycnal flow sedimentation sequence, is selected in this research to study its sedimentary architecture and stratigraphy in depth and propose a depositional model. Based on the sedimentary architecture and lithology, the Sangyuan outcrop can be divided into nine lithofacies and four facies associations. The four facie lithofacies represent process of strong erosion by the bedload dominated hyperpycnal flows, as well as the process of transitional deposition, controlled by both the bedload and suspended-load dominated hyperpycnal flows, and finally process of deposition by the suspended-load dominated hyperpycnal flows. Moreover, a larger amounts of the sediments are deposited near the source by the hyperpycnal flows. Unlike the coarse sediments, the fine-grain sediments, deposited on the less steep slope of the shelf, are not considered as the main product of deposition by the hyperpycnal flow. Furthermore, based on the sequence stratigraphy concept, we divide the Sangyuan outcrop into 15 parasequences and 3 parasequence sets. Through a detailed study of stratigraphic patterns and sand body thicknesses in the Sangyuan outcrop, a cycle of lake level rise-fall-rise is identified. The lake level fluctuation has controlled the distribution and characteristics of sediments. The results indicate that the thick and coarse sediments are easy to form, during the lake level falling period, by the hyperpycnal flows. All of the findings propose a new guideline for the exploration of new hydrocarbon reservoirs, deposited by the hyperpycnal flow.