Holocene development of the Yellow River's subaqueous delta, North Yellow Sea

Abstract

High-resolution seismic profiles from the North Yellow Sea reveal a 20–40-m-thick subaqueous clinoform delta that wraps around the eastern end of the Shandong Peninsula, extending into the South Yellow Sea. This complex sigmoidal-oblique clinoform, containing an estimated 400 km 3 of sediment, overlies prominent relict transgressive surfaces. The nearshore topset of the clinoform, <30-m water depth, has a ≪1:1000 gradient, with high sedimentation rates ( 210Pb) ∼6–12 mm/year. Foreset beds (30–50 m) dip seaward at a steeper gradient (2:1000) and have sedimentation rates ∼3 mm/year. Bottomset strata, in water depths >50 m, contain less than 1 m of Holocene sediment, with low sedimentation rates, <1 mm/year. In contrast to other clinoforms, the Shandong clinoform appears to be a compound subaqueous deltaic system, with what we interpret to be proximal and distal phases of clinoform development. The underlying proximal sequence formed proximally between ∼11 and 9.2 ka in response to a temporary pause in the rapid postglacial sea-level rise after the meltwater pulse 1B (MWP-1B) and increased discharge from the Yellow River to the North Yellow Sea due to intensification of the summer monsoon. A flooding surface appears to separate the proximal and distal phases, corresponding to the next rapid sea-level rise 9.5–9.2 ka BP (MWP-1C). Since 9.2 ka BP, an overlying distal sedimentary sequence has accumulated, reflecting the back-stepping and shifting river mouth westward to the Gulf of Bohai. Some inputs from coastal erosion and nearby small streams may be locally important. Along-shore transport, cross-shelf advection, and upwelling in the North Yellow Sea have reworked post-LGM sediment and have helped maintain the morphology of the clinoform in the Shandong mud wedge.