DISTRIBUTION OF FORAMINIFERA AND OSTRACODA IN THE SURFACE SEDIMENTS OF WESTERN COAST OF BOHAI GULF AND ITS ENVIRONMENTAL SIGNIFICANCE

39 surface sediment samples taken from the western coast of Bohai Gulf are analyzed by the authors for foraminifera and ostracoda. A total of 41 benthic foraminifera species of 20 genera and 32 marine ostracoda species of 26 genera, were recognized. The distribution of benthic foraminifera is mainly depending upon the distance to the coast, freshwater injection, tidal current and corresponding water depth, salinity and sedimentation rate. There are three foraminifera assemblages. The southern part of the water is dominated by Assemblage Ⅰ with Quinqueloculina akneriana rotunda and Ammonia beccarii vars. as leading species, representing an estuarine depositional environment under the affect of fresh water injection. The Assemblage Ⅱ is mainly observed in the northwest dominated by Ammonia beccarii vars., Protelphidium tuberculatum and Quinqueloculina akneriana rotunda, representing a coastal shallow water depositional environment. The Assemblage Ⅲ dominated by Protelphidium tuberculatum, however, mainly occur in the water deeper than 10 m, more or less similar to the normal marine environment. The distribution of marine ostracoda species are mainly affected by salinity, water depth, the bottom sediment types and migration law. There are two assemblages approximately separated by the 10 m isobath. The shallow Assemblage Ⅰ is absolutely dominated by the species of Neomonoceratina chenae, representing the coastal and shallow estuarine environment with wide temperature and salinity, while the Assemblage Ⅱ, which is dominated by Bicornucythere bisanensis, indicates an offshore environment less affected by fresh water.