Formation Mechanism of Subaqueous Distributary Channels in Lacustrine Deltas: Insights from Hyperpycnal Flow Depositional Models

Key words: 
• delta /
• subaqueous distributary channel /
• lacustrine basin /
• hyperpycnal flow /
• depositional model

Abstract: Abstract: [Significance] The genetic mechanism of river-dominated subaqueous distributary channels in lacustrine deltas has long been controversial, as traditional fluvial sediment dynamics fail to adequately explain their formation and distribution patterns. Based on recent advances in global research, this study systematically investigates the formation mechanism of subaqueous distributary channels in lacustrine deltas and explores new insights from hyperpycnal flow depositional theory regarding deltaic depositional processes and sandbody distribution patterns. [Progress] Hyperpycnal flows originate from the delta-front river mouth zone, transporting terrigenous sediments through the prodelta and shallow lake into deep-water depositional environments. While significant breakthroughs have been made in deep-water hyperpycnal flow deposition, descriptions and interpretations of hyperpycnal flow deposits in delta-shallow lake systems remain limited. The new concept of hyperpycnal deltas integrates river mouth deposition with gravity-driven processes, revealing that hyperpycnal channels serve as critical links between deltas and deep-water deposits. Modern and ancient hyperpycnal flow deposits demonstrate the development of hyperpycnal channels in delta-front to shallow lake or marine environments, suggesting that hyperpycnal flows could be the key dynamic force behind subaqueous distributary channel formation. The erosional mechanisms of these channels are closely associated with supercritical hyperpycnal flows (density Froude exceed the critical value). [Conclusions and Prospects] Subaqueous distributary channels are likely formed by episodic hyperpycnal flows rather than being mere underwater extensions of delta plain distributaries. The finding challenges classical delta theories and highlights flood-generated high-density hyperpycnal flows as a dominant geological force controlling deltaic depositional process. Revising existing models based on hyperpycnal flow dynamics provides a novel theoretical framework for studying delta-front depositional patterns. Future research should integrate quantitative sediment physical simulations with analyses of ancient delta-front deposits to advance hyperpycnal flow dynamics in deltaic systems, offering new theoretical foundations for lacustrine sedimentology.