江苏弶港附近强潮环境有孔虫埋葬群特征及其地质意义

FORAMINIFERAL TAPHOCOENOSES FROM SOME STRONG TIDAL ENVIRONMENTS NEAR JIANGGANG OF JIANGSU PROVINCE AND THEIR GEOLOGICAL SIGNIFICANCE

江苏弶港附近若干近岸强潮环境,包括海滨沼泽、潮间带浅滩及潮流沙脊,其表层沉积物中的有孔虫埋葬群由41属98种组成,本区可划分出两个组合区,三个亚区。各亚区的平均复合分异度H(S)值变化于2.4—2.99之间,均远远高于黄、东海沿岸一般的海滨沼泽及潮间带浅滩。在所有取样点中,H(S)值最高为3.31,该点(534站)竟位于距陆地最近、滩面最高的海滨沼泽上;而H(S)值最低为1.68。该点(233站)却位于潮间下带的外缘。本区某些H(S)高值的异常分布及逆向梯度分布,可与环境的盐度、深度、温度因子无关,而与强潮、风暴潮以及不同方向的潮流汇合带等特殊动力因子有关。本区N(50克干样)等值线图表明,在淤蚀多变的强潮环境里,N值主要不是与沉积速率有关,而是与沉积体的年龄有关。 弶港附近湖滩有孔虫埋葬群的特殊组合及其特征参数分布模式,为在地层中辨认这类近岸强潮环境提供了参考标志。

tidal sand ridge,storm surge,confluence belt of tidal currents,diversity, taphocoenoses,Jiangsu The foraminiferal taphocoenoses of surface sediments from some strong tidal environ-ments near Jianggang of Jiangsu Province, including marshes,intertidal banks and tidal sandridges,are composed of 41 genera and 98 species. The taphocoenoses may be divided into twoforaminiferal assemblages as follows: Ⅰ. Ammonia beccarii vars. Assemblage in the northern part; Ⅱ. Ammonia convexidorsa--Epistominella naraensis Assemblage in the southwestern part(inshore tidal flats). Based on the taphonomic distribution of the taxa in Assemblage I,three subzones may be distinguished: Ia. Dongsha Subzone(tidal sand ridge), Ib. Tiaozini Subzone (tidal flats), Ic. West Jiangjiasha Subzone(tidal sand ridge). These subzones are characterized by the components of foraminiferal genera and speciesand their distinct characteristic parameters. Average compound diversity H(S) in these subzones varies between 2. 4 and 2. 99. Theyfar exceed H(S) values of general marine marsh and intertidal zones of the Yellow Sea andthe East China Sea inshore areas. Within all of sampling sites the highest H(S) value is 3. 31registered from Station 534 situated in the marsh, which is immediately contiguous to landand at the highest level of the tidal flat. The lowest value of H(S) is 1. 68 registered fromStation 233 situated in the external margin of the lower intertidal zone. The abnormal distribution of high values of H(S) and its reversed gradient in this dis-trict has no relation to some environmental factors, such as salinity, depth and temperature,but is related to special dynamic factors,such as strong tide,storm surge and confluence beltof tidal currents from different directions. The foraminiferal individual number N (in 50g dry sample) isopleth indicates that verylikely it has no relation to sedimentation rate, but is related to the age of the sedimentarybody, because depositional and erosional processes are proceeding too fast in these environ-ments. The special assemblages and distributional model of characteristic parameters from theforaminiferal taphocoenoses of tidal flats adjacent to Jianggang provide some reference for de-termining such strong tidal environments from the strata.