Stratigraphic classification and sedimentary evolution of the late Neogene to Quaternary sequence on the Central Uplift of the South Yellow Sea

The Core of CSDP-2, which is more than 2800 m long, was retrieved from the Central Uplift of the South Yellow Sea, of which the Mesozoic-Paleozoic strata of the core have become a hot topic under research. However, research results of the uppermost sequence, 592 m in thickness made up of unconsolidated loose sediments, have not yet been reported so far. We have carried out paleomagnetic measurements, optically stimulated luminescence (OSL) dating, identification of benthic foraminifera and analyses of sedimentary facies for the sequence, in order to make its stratigraphic classification and reveal its history of sedimentary evolution. The results indicate that the 592 m- thick sequence came into being about 5.2 Ma, with its Quaternary bottom boundary at ~227.91 m of 2.59 Ma, the Lower and Middle Pleistocene boundary at ~65.23 m of 0.78 Ma, and the Middle - Upper Pleistocene boundary at 47.34 m of 128 ka, and covered by the Upper Pleistocene, which could be further subdivided into several sedimentary intervals formed during MIS 5, MIS 4, MIS 3 and MIS 1, while the MIS 2 deposits are missing. Also the results demonstrate that the denudation took place on the Central Uplift during Neogene and came to an end at ~5.2 Ma, followed by the deposition of fluvial deposits from ~5.2 to ~1.7 Ma, which was ceased as the first marine transgression took place in the region since Cenozoic presumably due to subsidence of the Zhe-Min Uplift. From ~1.7 to ~0.83 Ma, there was an alternation of tidal-flat and coastal deposits, and then from ~0.83 to the present the marine environments during high sea-level stands of the interglacial times were close to the marine environment of today in the region, due to the further subsidence of the Zhe-Min Uplift. On the western shelf of the South Yellow Sea, there was a cold water mass during MIS 5, which is broader than that of nowadays, and fluvial, deltaic, fluvial and coastal to inner-shelf environments prevailed successively during MIS 4, early MIS 3, late MIS 3 to MIS 2, and MIS 1. The sedimentary sequence was primarily controlled by tectonic subsidence and sea-level changes, and the sedimentation rates decreased evidently from the Holocene deposits to the Pleistocene and to the whole sequence, owing to the incompleteness of the older sediments comparing to the younger ones. Especially the pre-Late Pleistocene strata are marked by distinct erosion. The results of this study have provided new evidence for better understanding the evolution of sedimentary environments and the formation mechanism of strata in the western South Yellow Sea shelf since late Neogene.