HOLOCENE DEVELOPMENT OF THE YELLOW RIVER’S SUBAQUEOUS DELTA, AND CLINOFORM DEPOSITS IN THE NORTH AND SOUTH YELLOW SEA

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 km3 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/y. Foreset beds (30 - 50 m) dip seaward at a steeper gradient (2:1000) and have sedimentation rates ~ 3 mm/y. Bottomset strata, in water depths > 50 m, contain less than 1 m of Holocene sediment, with low sedimentation rates < 1 mm/y. 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 from 11-9.2 ka in response to a temporary pause in the rapid post-glacial sea-level rise 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 a 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 and upwelling in the North Yellow Sea presumably have reworked post-LGM sediment and help maintain the morphology of the clinoform in the Shandong mud wedge.