Sedimentary Characteristics and Depositional Model of Lacustrine Gravity Flows: A Case Study of Paleogene Shahejie Formation in the Gubei Sag, Eastern China

Abstract

The genesis and sedimentary architecture of lacustrine gravity flow deposits include ongoing questions affecting the exploration and development of oil and gas, which require attention and investigation. Based on the core description, logging characteristics, and seismic facies in the third member of Paleogene Shahejie formation from the southern Bohai Bay Basin, this study provides some insights regarding lacustrine gravity flows by analyzing the characteristics, distribution patterns, and sedimentary processes of lacustrine gravity flow deposits. Twenty lithofacies are classified into eight bed types which are caused by cohesive flows, inflated flows, concentrated-density flows, or turbidity currents. The characteristics and distributions of different bed types in five sublacustrine fans with two provenance directions and in a slump olistolith reflect two sedimentary processes influenced by sediment supply, basin structure, and climate, including cohesive flow deposits covered by inflated sandflow deposits transforming into concentrated-density flow deposits into hybrid event beds and finally into turbidity current deposits from inner to outer fan, and cohesive flow deposits transforming into inflated sandflow deposits covered by turbidity current deposits into concentrated-density flow deposits into hybrid event beds finally into turbidity current deposits from proximal to distal lobe. Based on the results, a depositional model of lacustrine gravity flow deposits is established, which highlights the change from superimposed channels to anastomosing channels, the distributions and characteristics of hybrid event beds, and distinctive facies in different elements.