SEDIMENT ACCUMULATION IN A MODERN EPICONTINENTAL-SHELF SETTING - THE YELLOW SEA

Sediment accumulation in the Yellow Sea epicontinental-shelf environment is investigated on 100-yr and 1000-yr time scales using Pb-210 and C-14 geochronologies. The distribution of modern (Pb-210) accumulation rates in the Yellow Sea reveals that the loci of modern Huanghe sediment accumulation are the topset (1-2 mm/yr), foreset (4-9 mm/yr), and proximal bottomset deposits (2-4 mm/yr) of the Shandong subaqueous delta (which extends south from the Shandong Peninsula). Pb-210 rates in the distal bottomset deposits of the subaqueous delta (in the central and southern Yellow Sea) are generally low (0.3-0.9 mm/yr). A sediment budget demonstrates that between 9-15% of the annual Huanghe discharge is accumulating in the Yellow Sea. About two-thirds of this sediment is accumulating in the topset, foreset and proximal bottomset deposits of the Shandong subaqueous delta, with the remaining third accumulating as widespread distal bottomset deposits. C-14 age dates of subaqueous delta sediments indicate that the thick (approximately 40 m) clinoform structure formed predominantly between 6200 and 4060 yrs B.P. (at rates approaching 20 mm/yr). Observations in the Yellow Sea, as well as on the Amazon and Ganges-Brahmaputra shelves demonstrate that subaqueous-deltaic stratigraphy is the general rule where major rivers enter energetic shelves, whether epicontinental or pericontinental. The development of extensive bottomset deposits may be restricted to epicontinental-shelf environments and may be diagnostic of sedimentation in this type of setting.