Sedimentary Facies And Environmental Evolution In The Huanghe(Yellow River) Delta Since The Late Pleistocene

The delta is a fairly sensitive area to study the global climate change and sealevel fluctuations due to its location in the intersection of the land and sea. Numerousstudies on Quaternary sedimentary indicate that sediment records preserve theinformation of regional changes of climate change and environment. Therefore, it ispossible to extract the regional climate change and sea-level fluctuation informationfrom the sediment records obtained from the Yellow River Delta. Discriminating thesedimentary facies and illustrating the environmental change are of importance tounderstanding the delta evolution. Further more, those works provide a scientificbasis for the rational use of resources and sustainable development of the delta.In2011a sediment core (QSG) was obtained in the present delta lobe of theYellow River, located in the intertidal zone between the presently active course andthe abandoned course before the bifurcation in1996. In-laboratory measurements areprocessed including the descripsion of lithology, analysis of granularity, volumesusceptibility and geochemical elements. Micropaleontology is processed togetherwith AMS14C dating. Based on the datasets sedimentary facies of bore QSG areidentified such as tidal flat and shore face, shallow sea face, modern Huanghedelaface. Combined with other core analysis in this region, a comprehensive study of thedepositional environment of the Yellow River Delta and relative sea-level variationsis performed.Since the late Pleistocene, the bore QSG can be divided into six sedimentaryfacies from the top to the bottom:1) The first sedimentary facies is delta plain faciesfrom1.8to3.3m;2) The second sedimentary facies is delta front facies from3.3to8.92m;3) The third sedimentary facies is prodelta facies from8.92to17.92m;4) Theforth sedimentary facies is shallow facies from17.92to20.49m;5) The fifthsedimentary facies is tidal flat and coastal marsh facies from20.49to24.22m;6) Thesixth sedimentary facies is lacustrine facies from24.22to32.10m.The environmental evolution can be divided into four stages:The first stage (24.22-32.10m): In the Last Glacial Maximum when the sea levelreached the lowest level, rivers and lakes mainly developed in this area. Subsequently,temperature increased together with rising sea level, the rivers and lakes were still dominant in the area as the environment became dry and oxidized.The second stage (20.49-24.22m): In the post glacial period, sea level continuedto rise, transgression began as the seawater invade into the coastal plain gradually,which favors the development of tidal marsh and shore sediments, and made theregional sedimentary environment more complex.The third stage (17.92m-20.49m): This stage was the period of high sea level.About7000a BP, with the sea level rising, this region was being submerged graduallyand developing shallow environment. About6000a BP, the sea level reached to thehighest and remained stable, the rate of sea level rise decreased. This area developedcontinental shelf (shallow) environment and the degree of reduction enhanced.The fourth stage (1.8-17.92m): This stage was stable stage during the stage ofthe high sea level. This modern Yellow River delta developed after1855. The YellowRiver has delivered a large volume of sediment that accumulated in the outer estuary,forming the subaqueous delta. This area developed prodelta sediments, delta-frontsediments and delta plain sediments. The environment was reduction-oxidation.Environmental evolution in the Yellow River delta closely responded to thesea-level variation. Combined with the previous core studies in this region, theconceptual model of the Yellow River Delta development could be built for betterunderstanding the delta evolution since the late Pleistocene, which would provide animportant reference to research of sea-level rise and climate change in this region.