SHALLOW SEISMIC STRATIGRAPHY AND SEDIMENTARY CHARACTER IN THE WESTERN SOUTH YELLOW SEA

The character of Quaternary continental shelf in the South Yellow Sea is transgressive-regressive cycles and alternating continental-marine strata,the sediment facies and distribution are controlled mainly by sea-level changes,paleo-channel and its delta.Based on the 5 600 km shallow seismic profile acquired in western South Yellow Sea recently,we distinguished and interpreted the stratigraphic sequences,and following conclusions are made:(1)The strata of South Yellow Sea since early Pleistocene are divided into fourteen seismic units,and composed of six seismic sequences,representing six transgressive-regressive cycles,and the strata developed during oxygen-isotope stage 5 widespread mostly.(2)The study area can be divided into six deposit zones by Holocene strata thickness:eastern weak depositional zone,mid-north depositional zone,depositional zone out of Haizhou Bay,abandoned Yellow River mouth depositional zone,erosional zone out of Sheyang River, and Subei shoal depositional zone.(3)During oxygen-isotope stage 6 to 2,three paleo-channel stages are found in the area:the upper layer was developed during oxygen-isotope stage 2,the paleo-Yangtze and paleo-Yellow River systems flowed into southern and northern paleo-Yellow Sea;the middle layer was developed during oxygen-isotope stage 4,and found in the coastal area;the lower layer was developed during oxygen-isotope stage 6,distributed west of 123°E.The southern paleo-channel on broad scale should belong to the paleo-Yangtze River,and the northern paleo-channel is distributed in limited range on small scale.(4)Paleo-Yangtze River flowed into paleo-Yellow Sea in early Quaternary,and paleo-Yellow River flowed into paleo-Yellow Sea in mid-late late Quaternary.To some extent,their paleo-channel distributions were inherited,and the scale of late stage more widespread.(5)The early delta developed during high sea-level warm climate was large,and late delta developed when sea-level lowered was small.During oxygen-isotope stages 3 to 5,several stages of paleo-deltas were developed in southern South Yellow Sea by paleo-Yangtze River,and two stages of paleo-deltas were developed in northern South Yellow Sea by paleo-Yellow River.(6)During transgression between late Pleistocene and early Holocene,paleo river-mouth sandbars and buried tidal creeks were developed.