洞庭盆地安乡凹陷CZ04孔第四纪孢粉记录及其古环境意义

CZ04钻孔位于洞庭盆地安乡凹陷的西南部,孔中第四纪沉积总厚201.63 m。本文通过对CZ04孔孢粉组合特征及各科属含量变化特点的分析,识别出了13个孢粉组合带,详细讨论了洞庭盆地第四纪植被演替过程,并结合CIA等气候代用指标,重塑了洞庭盆地第四纪气候演变过程:早更新世为冷干→温干→冷干→暖湿,中更新世为温凉偏干→热湿→凉湿→温湿偏暖→冷湿→干热,晚更新世为凉湿→温干→凉湿,全新世总体为凉湿→温略干。铁杉属及松属自洞庭湖组下段中部开始总体含量增加,可能与中更新世中期安乡凹陷西缘沉降及湖盆扩张有关。

Quaternary Palynological Record from the Borehole CZ04 in the Anxiang Sag of the Dongting Basin and Its Palaeoenvironmental Significance

The borehole CZ04 is located in the southwestern Anxiang Sag of the Dongting Basin,and the thickness of Quaternary deposits in this core is 201.63 m.This study of pollen and spores from the borehole CZ04 recognizes thirteen palynological assemblages.A record of vegetation change covering the whole Quaternary period is provided by the study.Based on the palynological analysis and the chemical index of alteration(CIA),the Quaternary climatic evolution of the Dongting Basin is concluded as follows:cold and dry→warm and dry→cold and dry→warm and humid during the Early Pleistocene;in the Middle Pleistocene,warm and dry→hot and humid→cool and humid→warm and humid→cold and humid→hot and dry;cool and humid→warm and dry→cool and humid during the Late Pleistocene;in the Holocene,cool and humid→warm and slightly dry.Pinus and Tsuga largely increased in the middle part of the lower member of the Dongtinghu Formation which may relate the subsidence of the west periphery of Anxiang Sag as well as the expansion of the basin in middle Middle Pleistocene.