Characteristics Of The Foraminifera And Evolution Of Sedimentary Environment Since Late Quaternary In The Laizhou Bay,Bohai Sea

The Laizhou Bay of Bohai is a transitional region for interactions between ocean and the land, which is sensitive to global climate change and regional geological processes. The deposition rate of sediments is rapid, and the abundant environmental changes for the interactions between ocean and the land and climate change are recorded. Samples from the boreholes in coast of Laizhou Bay, such as GK138, GK111,GK95, GK59, GK74, GK79 and GK89, were selected as the research object in this paper. Then the composition and vertical distribution of foraminifera in each borehole were analyzed and the distribution,symbiotic assemblage characteristics and environmental significance of foraminifera species were discussed. Finally the division of sedimentary units and analysis of the sedimentary environment were analysed and further discussed the sedimentary environmental evolution since the late quaternary after combined with dating data and clustering results.16 genera and 35 species of foraminiferal fossils were identified and mainly dominated by native benthic foraminifera from seven boreholes in study area, the dominant species were Ammonia beccarii, Ammonia annectens, Ammonia takanabensis, Ammonia convexus, Ammonia sobrina,Elphidium limpidum, Elphidium advenum, Elphidium excavatum,Astrononion italicum et al. The different stages of transgression,and the vary degrees of elevation and thickness of the marine strata in each transgression were revealed through the analysis of the sedimentary units.Three sets of marine strata were revealed in GK138, GK111, GK95, GK59 and GK79 boreholes, two sets of marine strata were revealed in GK74 borehole,while one in GK89. Three marine stratas mainly existed in the late Mid-Pleistocene, Late Pleistocene and Holocene period through the stratigraphic comparison, which were developed in the MIS7, MIS5 and MIS1 by comparing with the global sea level. Compared with the study of boreholes in the Bohai Sea, it is revealed that the marine stratas were widely distributed and had good contrast. The diversities between the elevation and the thickness of different marine strata showed that varied stages and intensity of tectonic activities occurred in the study area.