Sub-lacustrine debrite system: Facies architecture and sediment distribution pattern

Abstract

The deep-water systems in different types of sedimentary basins exhibit significant variability. Current knowledge of deep-water deposition is mainly derived from deep-marine turbidite systems. However, the characteristics and differences of sub-lacustrine gravity flow deposition systems have been a research focus in the fields of sedimentology and petroleum geology. This study investigates the facies architecture, depositional processes, and sediment distribution patterns of a sub-lacustrine debrite system in the Eocene Dongying Rift of the Bohai Bay Basin, China, through the analysis of integrated core data, 3-D seismic data, and well-log data. Nine facies have been identified within the debrite system, representing various depositional processes such as sandy debris flow, muddy debris flow, turbidity currents, sandy slide, sandy slide/slump, and mud flow. Our research indicates that the sub-lacustrine system is primarily influenced by debris flow rather than turbidity currents, as supported by facies quantification, interpretation, and flow rheology analysis. Additionally, we have identified five basic facies building blocks in debrite systems, including slide masses, slump masses, debrite channels, debrite lobes, and turbidite sheets. We have also elucidated and proposed detailed sedimentary processes, flow transport, and transformation within the sub-lacustrine system through analysis of flow origins, facies sequences, and distribution characteristics. Our findings highlight the evolutionary progression from delta-front collapse to sandy slide/slump, sandy debris flow, and finally muddy debris flow. The efficient generation of turbidity currents from parental landslides on sand-prone slopes is deemed unlikely due to rift-basin morphology and transport distances. The formation of the five basic facies building blocks is closely linked to depositional processes and dominant flow types. Consequently, we present a deep-water depositional model for sub-lacustrine debrite systems, focusing on flow dynamics, sediment distribution patterns, and basin morphology within deep lacustrine rifts. This model offers valuable insights into the variability of deep-water deposition in diverse basin settings and aids in predicting lithologic reservoirs during deep-water hydrocarbon exploration.