渤海湾西北岸HG01孔晚更新世以来的微体化石特征及沉积演化过程

MICROFOSSIL ASSEMBLAGES CHARACTERISTICS AND SEDIMENTARY EVOLUTION OF HG01 BOREHOLE IN THE NORTHWEST COAST OF BOHAI BAY SINCE LATE PLEISTOCENE

气候变暖、海平面上升背景下，全新世海湾型海侵以海洋动力为主，记录的海平面变化信息更为全面。本文对渤海湾西北岸HG01孔（20.0m以浅）进行了微体古生物化石、AMS ^14C测年和沉积特征等分析，共划分了7个沉积环境：埋深19.4-17.0m，时代为MIS 3阶段，微体化石仅见有孔虫，且丰度、分异度较低，为河口沙咀；埋深17.0-10.0m，时代为末次冰消期初期（18.0-11.4cal.ka B.P.），其中，17.0-12.9m未见微体化石，为泛滥平原，12.9-10.0m仅见陆相介形类，为淡水沼泽；埋深10.0-8.2m，时代为早全新世（11.4-8.0cal.ka B.P.），微体化石数量极少，陆相介形类与海相介形类、有孔虫共生，为滨海湖沼；埋深8.2-1.3m，时代为中全新世（8.0-6.0cal.ka B.P.），其中，8.2-3.5m微体化石的丰度、分异度较大，自下而上整体呈上升趋势，为潟湖；3.5-1.3m微体化石的丰度和分异度达到最大，为滨岸沙坝；埋深1.3-0.5m，时代为中晚全新世（6.0cal.ka B.P.至今），自下而上，微体化石的丰度和分异度呈降低趋势，上部见有少量陆相介形类，为潮上带。

Under the background of the climate warming and sea-level rising, the bay transgression in the Holocene is dominated by marine dynamic, and the information which recorded the sea-level changes may be more abundant. Studying the type and extent of transgressions in the Holocene can provide the basis for predicting the transgression of the gulf. The HG01 borehole is located in the northwest coast of Bohai Bay（39°28＇21.16＂N, 118°01＇16.50＂E）, about 28km from the modern coastline. 85 samples were collected from the depth of about 20-0m at 20-40cm intervals. The results of AMS^14C dating show that the formation we study covers the time period since the Late Pleistocene. All samples were analyzed and identified for quantitative statistic of foraminifera and ostracod microfossils. The abundance and diversity of microfossils were calculated later and 65 species of 24 genera of foraminifera and 39 species of 27 genera of ostracodes were found. According to the vertical distribution characteristics of micropaleontology and their indicators of the sedimentary environments of the northwest coast of Bohai Bay, combined with sedimentary characteristics, HG01 borehole（20m to shallow）is divided into 6microfossil assemblages and a fossil spacer, indicating the different sedimentary environments, from the bottom to top as follows：The depth of 19.4-17.0m（MIS 3） is the river mouth identified by the lower abundance and diversity of foraminifer fossils and the olive yellow fine sand including the fragments of oyster. The depth of 17.0-10.0m, aged the early period of the Last Deglaciation（18.0-11.4cal.ka B.P.）. The lower part（17.0-12.9m）is the floodplain identified by the lack of microfossil and sedimentary characteristics. The upper part（12.9-10.0m）is the freshwater swamp identified by freshwater ostracodes. The depth of 10.0-8.2m dated the Early Holocene（11.4-8.0cal.ka B.P.）. In this period, foraminifera and terrestrial ostracoda are coexisting, but the number of microfossils is few. This period is the coastal lacustrine. The depth of 8.2-1.3m dated the Middle Holocene（8.0-6.0cal.ka B.P.）. In the lower part（8.2-3.5m）, abundance and diversity of microfossils are relatively large, and the overall upward trend is from bottom to top. This period is the lagoon. In the upper part（3.5-1.3m）, the abundance and diversity of microfossils reached the maximum and this period is the coastal sand bar. The depth of 1.3-0.5m aged the Middle-Late Holocene（6.0cal.ka B.P. to present）. In this period, the abundance and divergence of the microfossils showed a decreasing tendency from bottom to the top, and there were a few terrestrial ostracodes in the upper part. This period is the supralittoral zone.