从孢粉、藻类化石组合看长江三角洲第一硬质粘土层的成因及其古环境意义

文章通过对长江三角洲南翼7个钻孔样品的孢粉、藻类分析,从晚第四纪第一硬质粘土层中提取出了种类和数量均较可观的孢粉、藻类化石,从而可以判别第一硬质粘土层形成时的沉积环境和植被类型,为长江三角洲地区硬质粘土层的成因研究提供了生物化石依据。研究结果表明,第一硬质粘土层中有多种孢粉、藻类化石组合。高含量淡水藻类的存在说明硬质粘土形成受到流水的作用,亦即硬粘土的形成环境可能为水域环境。化石组合中含量较低的海生沟鞭藻表明,长江三角洲地区在硬质粘土形成时曾受到海水影响。硬质粘土层中的禾本科-莎草科-落叶栎-松、禾本科-落叶栎-松-蒿和莎草科-落叶栎-香蒲孢粉组合指示研究区低地为平原区草甸,而周边的山地有针阔叶混交林分布,当时该地区属于温凉略湿的温带气候。

PALYNOMORPH ASSEMBLAGES,ORIGIN AND PALAEOENVIRONMENTAL SIGNIFICANCE OF THE UPPER MOST HARD CLAY IN THE DELTAIC AREA OF THE CHANGJIANG RIVER

Several layers of dark green or yellowish brown hard clay have been found in the Late Quaternary strata in the south margin of the Deltaic area of the Changjiang River, which can be used as marked layers for the stratigraphical correlation in the region due to their typical characteristics and widespread distribution. No important pollen and phytoplankton assemblages can be used to distinguish the depositional environment and type of vegetation in the developing period of the Hard Clay. Therefore it is unlikely to assemble the evidence to reach to a conclusion on the origin of the hard clay based on the known flora assemblages. A large amount of palynomorphs has been found to use to reconstruct the palaeoenvironment from the uppermost of the Hard Clay in the Deltaic area of the Changjiang River during the Late Pleistocene. The high contents of microfossil evidence, freshwater algae, indicate that the formation of Hard Clay is freshwater sediments. Whereas low content of Dinoflagellate in the palynological assemblages shows that the area might be influenced by the sea water when the Hard Clay was deposited. The sporo pollen assemblages of Gramineae Cyperaceae Quercus (deciduous trees) Pinus , Gramineae Quercus Pinus Artemisia and Cyperaceae Quercus Typha indicate that meadows were developed on the lowland plain being close to the areas where mixed broadleaved and conifer forests were developed non the mountainous area.