高级检索

    化学风化指数和磁化率对洞庭盆地第四纪古气候变化的响应

    Chemical weathering index and magnetic susceptibility of deposits and their responses to the Quaternary climate in Dongting Basin

    • 摘要: 提要:在安乡凹陷东南部两护村新施工揭穿第四系的ZKC1孔,孔内第四系为河流和湖泊沉积,地层组成自下而上依次为上新世—早更新世华田组、早更新世汨罗组、中更新世早期—中期洞庭湖组、晚更新世坡头组以及全新统等。对钻孔岩心进行了系统的主量元素及磁化率分析,进而从陆相沉积物化学风化指数(CWI)与温度和湿度正相关、磁化率与温度和湿度负相关的理论出发,探讨洞庭盆地第四纪气候演变。结合其他资料,CWI曲线特征指示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CWI对第四纪气候演变具有较好的响应。变化曲线及相关系数(-0.32)表明磁化率值与CWI值呈较明显的负相关,暗示温度和湿度对磁化率具有明显的控制作用。但可能受盆地升降等因素的影响叠加,磁化率曲线未能如CWI一样明确反映出第四纪气候的阶段性变化。

       

      Abstract: Abstract:The drilling of ZKC1 borehole was carried out at Lianghucun in southeastern Anxiang sag. The Quaternary alluvial and lacustrine sediments in the borehole are composed of Pliocene-Early Pleistocene Huatian Formation, Early Pleistocene Miluo Formation, early-middle Middle Pleistocene Dongtinghu Formation, Late Pleistocene Potou Formation and Holocene strata. The major elements and magnetic susceptibility of the core from the borehole were analyzed systematically. According to the idea that the chemical weathering index (CWI) of terrestrial sediments has a positive correlation with temperature and humidity, and that the magnetic susceptibility has a negative correlation with temperature and humidity, the authors probed into the Quaternary climate evolution of the Dongting basin. Combined with other materials, the curve of CIA indicates that the Quaternary climatic evolution of the Dongting basin was from early to late in order of cool and dry → tropical and humid → cool and dry → tropical and humid during Early Pleistocene; cool and dry → tropical and humid → cool and dry-warm and humid→ tropical and humid during Middle Pleistocene; cool → warm and humid → cool during Late Pleistocene, and warm and humid-tropical and humid during Holocene. This climatic evolution process coincides basically with climatic change indicated by sporopollen assemblages of the core from the ZKC1 borehole, and also accords with Quaternary climatic variations of eastern China, which suggests that the CWI of the sediments shows a good responses to the Quaternary climate evolution. Curves and correlation coefficient of -0.32 between CWI and magnetic susceptibility of the sediments show that the magnetic susceptibility has a negative correlation with CWI, which suggests that temperature and humidity controlled evidently the magnetic susceptibility. Impacted probably by the uplift and subsidence of the basin, the curve of the magnetic susceptibility fails to show the same phasic variations as CWI.

       

    /

    返回文章
    返回