OVERBANK AND CHANNELFILL DEPOSITS OF THE MODERN YELLOW-RIVER DELTA

The Huanghe is noted for its high transport rate of silt and clay, whi ch may reach depth-averaged values of 200 kg m-3 during peak discharge . The sediment load transported through the river on entering the delt a plain, amounts to 10(12) kg per year. In contrast to most other larg e deltas only one distributary channel is active at any one time. The high sediment load causes the rivermouth to prograde at a yearly rate of 1-4 km into the shallow (less than 20 m deep) Bohai gulf. The verti cal aggradation of the channel belt and mouth bar complex is also rapi d (decimetres per year on average), so that after a normal average of twelve years increasing channel instability and avulsion create the st art of a new delta lobe. A series of satellite images covering the las t fifteen years has provided insight in the evolution of the river pat tern as well as the progradation of the delta front. A newly developed distributary passes from a multichannel to a single, straight channel system, and ends with the formation of meanders. The protruding matur e delta lobe shows a radiating pattern of crevasse channels. Overbank/ crevasse deposits are made of vertically stacked dm-scale waning flow sequences, structurally characterized by (from bottom to top) small sc our-and-fills, even (parallel) lamination, and climbing-ripple crossla mination. Accumulation rates on crevasse splays can be predicted on th e basis of estimated river sediment discharge. It can be concluded tha t each sequence has been deposited within a few hours, and that tidal waterlevel fluctuations may have played a role in the generation of a single sequence.