Provenance, structure, and formation of the mud wedge along inner continental shelf of the East China Sea: A synthesis of the Yangtze dispersal system

Surficial grain-size and down-core clay mineralogical data show that sediment along the inner-most part of the continental shelf in East China Sea is mainly derived from the Yangtze River (Changjiang), spanning from the Yangtze mouth (33 degrees N) similar to 1000 km southward to the southwestern corner of the Taiwan Strait (24 degrees N). High-resolution CHIRP seismic profiles reveal an elongated mud wedge extending along the inner shelf, with a northern depocenter on the modern Yangtze delta and a southern depocenter at 27.5 degrees N. Four distinct acoustic units are delineated within the mud wedge (from bottom up): unit I (late-Pleistocene, mainly valley fills), unit II (formed by transgressions, thin strata), unit III (11-2 kyr BP, downlapping strata) and unit IV (2-0 kyr BP, flat and opaque strata). Incised valleys, up to 15-m deep, are filled by flat-lying or inclined strata in unit I. The thin (<3 m) and acoustically transparent unit II is only seen between 30 and 26 degrees N in water depths between 40 and 90 m. Separated by acoustically opaque strata or unconformities, units III and IV are widely distributed. During the past 11 kyr Yangtze sediment accumulation has been unsteady, showing two high and one low accumulation-rate periods. The high-accumulation period at 5-8 kyr BP may be related to maximum East Asian summer monsoon precipitation in the Yangtze basin; the other high-accumulation period, 0-2 kyr BP, probably reflects intensive human activities in the river's watershed. The low-accumulation-rate period at 2-5 kyr BP, which is seen in both northern and southern Yangtze depocenters, is probably related to low river discharge and/or intensified Taiwan Warm Current and China Coastal Current. (C) 2011 Elsevier B.V. All rights reserved.