洞庭盆地第四纪气候演变的沉积物地球化学记录

对洞庭盆地安乡凹陷东南部两护村ZKC1孔上新世末—第四纪沉积物的主量、微量和稀土元素以及粒度进行了分析,进而探讨洞庭盆地第四纪气候演变。曲线协变性及相关系数表明,ZKC1孔沉积物化学蚀变指数(CIA)与Cr、Ga、V、Nb、Be、Li、Sc、Th等微量元素含量呈明显的正相关。从陆相沉积物CIA及微量元素含量与温度和湿度正相关的概念出发,结合其他资料,重塑洞庭盆地第四纪气候演变过程:早更新世为冷干→暖湿→冷干→暖湿,中更新世为冷干→暖湿→冷干—温湿→暖湿,晚更新世为寒冷→温湿→寒冷,全新世总体为温湿—暖湿。这一结论与ZKC1孔孢粉组合特征反映的气候演变过程及中国东部第四纪气候演化基本吻合,说明沉积物CIA和微量元素含量较好地记录了第四纪气候演变信息。相关性分析表明洞庭盆地沉积物粒度对CIA无明显影响;CIA与沉积物粘土含量呈弱的正相关关系,应与湿热气候条件下有更强烈的风化和更多粘土矿物形成有关。

Geochemical Recording of Sediments Responding to the Quaternary Climatic Evolution in Dongting Basin

The major elements,trace elements,rare earth elements(REE) and particle size of the sediments from the core of the ZKC1 borehole at Lianghucun in southeastern Anxiang sag were analyzed systematically.On the basis of the analyses,the authors probed into the Quaternary climate evolution of the Dongting basin.The covariance and correlation coefficients of curves show that the chemical index of alteration(CIA) of the sediments from ZKC1 borehole has evident positive correlation with trace elements such as Cr,Ga,V,Nb,Be,Li,Sc,Th,etc.According to the idea that the chemical alteration index and contents of trace elements of terrestrial sediment have positive correlation with temperature and humidity,combined with other materials,the curves of CIA and contents of trace elements indicated the Quaternary climatic evolution of the Dongting basin as follows:from early to late,the climatic variations during Early Pleistocene are cool and dry → tropical and humid → cool and dry → tropical and humid,during Middle Pleistocene are cool and dry → tropical and humid → cool and dry-warm and humid → tropical and humid,during Late Pleistocene are cool → warm and humid → cool,and during Holocene are warm and humid-tropical and humid as a whole.This climatic evolution process coincides basically with climatic change indicated by sporopollen assemblages of the core from the ZKC1 borehole,and with Quaternary climatic variations of eastern China,which suggested that the CIA and trace elements of the sediments provided good constraints on the Quaternary climate evolution.Correlation analyses show that the particle size of the sediments hadn’t evident influence on CIA;CIA has weak positive correlation with the contents of clay,which suggested that there existed violent weathering and more clay minerals were formed in tropical and humid environments.