江苏太湖平原北翼的第四纪孢粉与环境

QUATERNARY POLLEN ANALYSIS AND PALEO-ENVIRONMENTAL EVOLUTION IN THE NORTHERN PART OF TAIHU PLAIN, JIANGSU

本文根据湖东北侧 4个钻孔的孢粉分析 ,1 4 C和古地磁测试 ,并结合钙质超微化石、介形类和有孔虫所确定的海侵地层 ,将太湖地区划为 10个孢粉带 ,再参照长江下游相关资料 ,着重对 12 .7— 1.5万年以来的 4个孢粉带作了较深入的环境探讨 ,揭示出 带 (12 .7— 7.0万年 )为常绿落叶阔叶混交林 ,反映温暖湿润的亚热带气候 ,其主要温暖阶段冬温较今高 4— 5°C,当时湿度相对偏大 ,当然其中也有凉湿与干凉时段。 带 (7.0— 3.0万年 )为疏林草原 ,反映冷 (半 )干气候 ,其主要寒冷阶段年均温为 8°C左右。但仍存在剧烈的气候波动。 带 (3.0— 2 .1万年 )为温性常绿落叶阔叶混交林 ,反映温凉湿润的季风海洋性气候 ,其主要温凉阶段生长季月均温比现在低约 3°C。其中亦有更为干冷或暖湿时期。 带 (2 .1— 1.5万年 )为森林草原 -草原或干草原植被 ,其极干冷阶段年均温约 8°C,年降雨量 40 0 m

Based on the pollen analysis, 14 C dating and paleo geomagnetism of 4 cores in the north part of Taihu Plain, combined with sea transgression strata in this area, determined by calcareous nannofossil, ostracoda and foraminifera, the regional pollen assemblages are divided into 10 zones. In comparison with the pertinent environmental and dating data of the lower reach of Yangtze River, the paleo environment records from the 4 sporo pollen zones of 127-15ka BP are studied in detail and the reconstructed sequence of environmental changes is showed as follows. ①Zone Ⅵ(127-70ka BP): period of deciduous and evergreen broad leaf mixed forest, reflecting subtropical warm and wet climate. And in its main warmer stage, the winter temperature was about 4-5°C higher than today's and the humidity was relatively higher. In addition, there were fluctuations of cool wet and cool dry stages during this period. ②Zone Ⅶ(70-30ka BP): period of open forest and steppe, implying cold and semi dry climate. The average annual temperature, which fluctuated dramatically was about 8°C in its main cold stage. ③ Zone Ⅷ(30-21ka BP): period of temperate deciduous and evergreen broad leaf mixed forest, indicating that it was the monsoon marine climate characterized by cool and wet. In this main temperate cool stage, the average month temperature of growth season was about 3℃ lower than today's. And some stages of drier and colder or warmer and relatively humid in this period are found too. ④ Zone IX (21-15ka BP): period of forest steppe, steppe or drought steppe, the average annual temperature was about 8℃ and the annual average rainfall was about 400mm in extremely cold stage.