The Sedimentary Environmental Evolution Of The North Area Of The Modern Yellow River Delta Since The Late Pleistocene

The coastal zone is land-ocean interaction and a sensitive zone of the global sealevel change caused by the climate change and regional variations. A wealth ofinformation concerning land-ocean interaction, sea level change, river-input materialand climate change is concerned by the sediment.This thesis is mainly focused on two aspects as followes of the Modern RiverDelta in the south of Bohai sea.first of all, three marine beds are indentified within the60-m-thick strata, and the transgressive stages are determined. Sophisticatedsubdivision for the stratas and Comparing with other drilling results, we obtain thepalaeoenvironment in the study area since the late Pleistocene. Second, the analysis ofthe sediment grain size reveals the sedimentary characteristics in differentsedimentary environment.After analying the lithology, sediment compositions and structures, thedistribution of foramiferal combination and dating data (AMS14C and OSL) inYRD-1101, the results are as followed:1. Three marine beds are indentified in the60-m-thick strata, indicating that thestudy area has experienced three major transgressions since the latePleistocene. According to the dating results in drilling of the YRD-1101andcompared with the global sea level change curve, the three phase of themarine strata are corresponding with the high sea level during MIS5(the deepsea Oxygen Isotope Stage5, MIS5), MIS3and MIS1, suggesting the marinestratas recorded in the study area are consistent with the trend of the globalsea level change.2. The north area of the Modern Yellow River Delta experienced nearshore/shallow water, near shore, shallow sea, intertidal zone/supratidal, fluvial,intertidal zone/supratidal zone, shallow sea, prodelta to delta plain since thelate Pleistocene. Several erosion surfaces are identified in the YRD-1101,indicating there are several hiatus.3. The sedimentary characteristics show that the main sediment is silt,approximately63.85%on average; the clay and sand are18.70%and17.45%repectively, the mean grain size is5.81Φ.4. The analysis of lithology and grain size characteristics reveal the sediment isyellowish gray, the grain sorting is poor, which indicates the sediment aremainly coming from the Yellow River; by comparing with other drilling coresthe Yellow River has disembogued into the Bohai Sea since AD1855, thedelta’s thickness in study area is up to10.5meters with a high desositionalrate.