长江口北支有孔虫组合及其环境意义

The Foraminiferal Assemblages and Its Paleoenvironmental Implications in the North Branch,Yangtze Estuary

通过对长江口北支XL1、XL2和CY孔有孔虫组合进行对比分析,综合沉积物粒度特征和环境磁学特征,探讨了长江口北支沉积环境水动力条件演变特点。揭示了长江口北支各沉积相所对应的有孔虫组合,即潮流沙脊以E.naraensis、E.magellanicum和F.decorus组合为主;潮汐水道以A.convexidorsa、E.naraensis、E.magellanicum和A.bec-cariivars.组合为主;潮滩有孔虫组合则以A.beccarii vars.、E.magellanicum、E.naraensis和滨海沼泽特征种T.inflata及J.macrescens组合为主;河口沙坝则以A.beccarii vars.、E.naraensis等组合为主的沉积特征。

On the basis of comparative analysis of foraminiferal assemblages zones for Holes XL1, XL2 and CY, integrating the characteristics of their aggradation and environmental magnetism, we probe into the evolvement of the deposit hydrodynamic condition in the North Branch, the Changjiang River Estuary. At the same time, it reveals the relation of sedimentary facies corresponding to their foraminiferal assemblages zones. That is the tidal current ridge corresponding to the E. naraensis, E. magellanicum and F. decorus assemblages zone; tidal channel to the A. convexidorsa, E. naraensis, E. magellanicum and A. beccarii vars. assemblages zone; supratidal zone to the A. beccarii vars. , E. mageUanicum, E. naraensis speciesassemblages zone, especially the T. inflate and J. macrescens are its characteristic species; sand dam to A. beccarii vars E. naraensis, et al. assemblages zone. The above sedimentary characteristics imply the function of tidal current during the burial of foraminiferal assemblage zones. Based on foraminiferal assemblages zones, magnetic properties and lithofacies, we also suggest that there are three modes of sedimentary environment for Hole XL1 , XL2 and CY in the North Branch estuary, the Changjiang River Esturary： tidal current ridge→tidal channel→supratidal zone, forming the sedimentary facial sequence of the filled estuary.