Coupling controls of neotectonism and paleoclimate on the Quaternary sediments of the Yangtze (Changjiang) coast
Coupling controls of neotectonism and paleoclimate on the Quaternary sediments of the Yangtze (Changjiang) coast
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DOI：
10.1360/04wd0089
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发表时间：
2005-08
影响因子：
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通讯作者：
Zhang Wang;Zhongyuan Chen;Zixin Wei;Zhanghua Wang;T. Wei
中科院分区：
文献类型：
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作者：
Zhang Wang;Zhongyuan Chen;Zixin Wei;Zhanghua Wang;T. Wei
探讨了新构造运动与古气候的耦合关系对长江沿岸第四纪沉积物分布和沉积相演化的控制作用。在岩石学分析的基础上，在0.4- 0.5Ma的时间尺度上，在第四纪沉积物钻孔中识别出多达6个沉积旋回。较低的沉积旋回（上新世至早更新世）主要以较厚的砾石粗砂为特征，顶部为较薄的细粉砂和粉质粘土。砾石非常有棱角，粘土质砾石占优势。沉积物通常分选性差，富含原木碎片，无微体化石。推移质负荷如C-M图所示，出现在整个剖面中。这一证据代表了盆地开始沉降时发生的冲积扇沉积。中部沉积旋回（通常包括早更新世至中更新世）由中部和上部沉积剖面的基底砾石砂和粘土质粉砂组成。分选变得相对较好，有孔虫零星出现。C-M图显示了推移质、跃移和悬浮三种输沙介质的混合，代表了早期辫状河沉积和后期曲流河沉积。上部沉积旋回（包括晚更新世至全新世）为底部砾质砂（不含全新世沉积物）和上部厚层细砂及粉质粘土。分选变得精细，有孔虫出现在整个沉积物部分。C-M图表明，泥沙断面以跃移和悬浮为主要输沙介质，推移质输沙作用减弱。这表明晚更新世和全新世时期，海侵侵入古河谷，形成了近海岸的曲流河沉积模式，常形成淹没河谷相和浅海相。值得注意的是，在旋回性顶部发育了现代三角洲相，其特征是大量的细砂和粉质粘土以及各种沉积层理。这些现象在以往冲积扇体系的基础上，增强了气候对沉积相演化的作用，主要受构造沉降背景的影响。
Attempt has been made to discuss the coupling relation of neotectonism and paleoclimate that have played a critical role in controlling the Quaternary sediment distribution and sedimentary facies evolution on the Yangtze coast. On the basis of petrological analysis, up to six sedimentary cyclicities have been identified in the Quaternary sediment boreholes on the time scale of 0.4–0.5 Ma. The lower sedimentary cyclicities (Pliocene to Early Pleistocene) are characterized largely by thicker gravelly coarse sands, topped by thinner fine silt and silty clay. Gravels are very angular and clayey gravels prevail. Sediments are usually of poor sorting, rich in log fragments and have no microfossils. Bedload as denoted by C-M plot occurs throughout the section. This evidence represents the alluvial fan sedimentation which took place as the basin began to subside. The middle sedimentary cyclicities (often including Early to Middle Pleistocene) consist of basal gravelly sands and clayey silt at the middle and upper sediment sections. Sorting becomes relatively better, and foraminifer appears sporadically. C-M plot reveals the mixture of sediment transport media via bedload, saltation and suspension, representing sedimentation of braided river system at the early stage and subsequently, the sedimentation of meandering river pattern. The upper sedimentary cyclicities (including Late Pleistocene to Holocene) comprise basal gravelly sands (exclusive of the Holocene sediment) and thick fine sand and silty clay on the upper section. Sorting becomes fine and foraminifer appears throughout the sediment section. C-M plot shows that saltation and suspension serve as the main sediment transport media in the sediment section and bedload transport weakens. These evidence the sedimentation of meandering river pattern near coast during Late Pleistocene and Holocene time, when marine transgression invaded into the paleoriver valleys, which often forms drowned-valley facies and shallow marine facies. Of note is the Recent delta facies developed on the top of the cyclicities, and characterized by a large proportion of fine sand and silty clay, and various sedimentary beddings. These phenomena have proved enhanced climate function on sedimentary fades evolution on the basis of previous alluvial fan system, largely affected by tectonic subsidence setting.