Study Of Ostracod Characteristics And Evolution Of Transgression Of The Late Quaternary In The Laizhou Lay, Bohai Sea

Events of the coastline changes have experienced for nine times since the Late Pleistocene in the Bohai Bay region and three sets of marine strata had been formed. The first of marine strata in the Bohai Bay region came into being during Holocene. The second and the third marine strata formed in the late Pleistocene.As one of the three major bays in the Bohai Sea, the study of marine strata in the late Quaternary mainly concentrated in the Huanghe Delta and the east and the south of the Laizhou Lay. However,There are relatively few studies on the marine strata in the southwestern coast of Laizhou Lay. In this topic, we distinguish marine strata formed during Late Quaternary in the southwest bank of the Laizhou Lay and determine the time of the events of the coastline changes by isotopic-dating method and conclude sphere of influence in the highest period of transgression.In this study, collected and processed the 448 samples from the drills of GK138, GK111, GK95, GK89, GK79, GK74, GK59 in the southwest bank of Laizhou Lay by Hot acid method. Each sample was screened under a microscope. A total of 227 fossil were found, including 22 genera and 31 species. Marine ostracods include Cathatocytheretta apta, Legumi-nocythreis reticulata, Bicornucythere bisanensis, Loxoconcha ocellata,Sinocytheridea impreessa and so on. These categories have an absolute advantage in terms of quantity and distribution. Candoniella albicans,Ilyocypris bradyi and llyocypris salebrosa belong to types of continental facies. These spices are relatively less and the distribution is more concentrated.Three sets of marine strata, which are M1, M2, M3 were identified from the 7 drills in the study area by researching the species of ostracod and community characteristic in this study area. The 3sets of the marine strata correspond with MIS1 stage, MIS5 stage and MIS7 stage in which Global Sea Level changes by AMS 14C and OSL dating method.Temperatures around the world rise in MIS7 stage of Late Pleistocene.Melting ice caps lead to raising sea levels. Sea level is about 10m under modern sea level. The area of Lai-zhou Bay was influenced least during this time. Only somewhere near Hou Town of Weifang was influenced. The global temperature rose in MIS5 stage of last glaciation. The sea invaded Laizhou Lay against. Global sea levels are slightly higher than modern sea levels. At this stage, the intensity of transgression was large and the sediments were thicker. The coastline reached Guangrao county during the supreme period of transgression. Glacial period of Holocene transgression was finished, The temperature and sea level rose which formed marine strata of MIS.The coastline reached Longchi county nearby during the supreme period of transgression and extended to the direction of Chunhua County. Transgressive layer of MIS3 found in Bohai Bay was mainly transition sedimentary environment in this study area.