Subaqueous delta sedimentation shaped by interaction of sediment gravity flows and contour currents: Insights from the modern Huanghe (Yellow River) Delta

Abstract Downslope sediment gravity flows (SGFs) and longitudinal (along-slope) transport regimes play critical roles in shaping subaqueous clinoforms globally, yet their combined impacts on sedimentation in subaqueous deltas, particularly in shallow marine subaqueous deltas, remain less understood compared to those on lower continental slopes. Here, we address this gap by examining the sedimentary and morphological patterns of SGF accumulations at the toe of the modern Huanghe subaqueous delta, using dense, high-resolution seismic data and sediment cores, along with historical bathymetric data. Building on prior research that identified a widespread SGF wedge superimposed on a conventional Gilbert-type clinoform, our seismic data confirm that this wedge exhibits shore-parallel elongated geometry that thickens from northwest to southeast, and aligns with the prevailing southeastward, tidal-driven contour currents. Near the abandoned Diaokou Lobe (upcurrent area), the wedge experiences significant erosion, as evidenced by truncation at its top, which is attributed to postdepositional erosion by contour currents. Downdrift, the wedge transitions from extensive erosion near the Diaokou Lobe to accumulation toward the active Qingshuigou Lobe, which involves the reworking and redistribution of eroded sediments from upcurrent locations to downcurrent areas through longitudinal transport regimes. Sediment cores that fully or partially penetrate the SGF wedge reveal intervals characterized by accumulations reworked by tidal or residual currents (e.g., sand-mud interbedding and/or bioturbation), interspersed with SGF-dominated layers. These findings highlight the important role of interactions between SGFs and contour currents in shaping the subaqueous deltas of both active and abandoned lobes. Variability in the intensity of contour currents and lobe switching events led to two distinct interaction patterns: (1) SGF-dominated sediments reworked by longitudinal transport, which is the predominant interaction pattern, and (2) slower SGF fine-grained plumes directly driven by longitudinal transport. These patterns share similarities with deep-water accumulations shaped by the interplay of SGFs and contour currents in terms of morphology and sedimentary features. These insights could have broader implications for predicting sedimentary and geomorphological evolution in other river deltas experiencing similar long-term SGF and longitudinal transport interactions.