The Sedimentary Sequence and Palaeogeographic Changes of the South Yellow Sea Since the Olauvai Subchron1

Abstract According to the alternation of terrestrial beds and transgressive beds, the sedimentary sequence of the South Yellow Sea since the Olduvai subchron can be divided into 15 strdatigraphical intervals. According to the facies analysis, there are 7 transgressive beds an one bed with transgression marks, and classical transgressive‐regressive facies sequence also appears in the major transgressive beds.Palaeogeographic evolution in the shelf area involved 4 periods: (1) 1.70‐0.5 Ma B. P. was the stage for the development of the Palaeo‐Yangtze River alluvial plain and delta. Tide influenced‐river channel sediments formed during the Olduvai have been found in borehole QC2. The river mouth was located near 124° E and during the transgressive stage from 0.97‐0.73 Ma B.P. to the east of 122.2° E, a large‐scale undersea delta was formed. In the regressive stage, the shelf area became an alluvial plain. (2) 0.50‐0.75 Ma B.P. was a multi‐transgressive fluctuation stage during which 3 transgressive beds (HVI, HV, HIV)developed, being dated as 0.50‐0.30 Ma B.P., 0.27‐0.20 Ma B.P. and 127‐75 Ka B.P. respectively, with the extent of transgression increasing gradually. Influenced by southeast monsoons, the eastern China continent began to have a larger moisture source. (3) 75–14 Ka B.P. was the lower sea‐level stage during the last glacial period. The downcuttihg depth of rivers was up to ‐133 m. The palaeo‐Yangtze River system flowed northeastwards into the Sea of Japan through the Sea of Japan through the Tsushima and Korean Straits. The interfluvial area became an eroded, weathered high land. In the cores, two short‐lived, relatively high sea‐level stages were recorded, corresponding to two interstades in the last glacial period. (4) The period since 14 Ka B.P. is the stage for “Holocene transgression” and the development of the Yellow River‐Huaihe River delta. Before 14 Ka the sea level rose to ‐68 m, and before 11 Ka to ‐50 m, and the sea‐level was once at a standstill or slightly got down, which is coincident with the Younger Dryas event. The Yellow River‐Huaihe River delta developed on transgressive bed HI and consists of the superimpositions of 6 deltaic complexes.