长江中游阳逻砾石层沉积环境分析

本文在野外调查的基础上，选择典型剖面，通过剖面沉积学、岩相划分和粒度分析研究，对长江中游“阳逻砾石层”沉积环境进行了讨论。研究表明，阳逻砾石层的岩性主要砾石层夹砂层，由Gm，Sh和Sp沉积相类型组成；   大多数频率曲线图形态为双峰，且以不对称曲线为主；   概率累积曲线大都为上三段式，以滚动总体为主，约占50%～60%，斜率较大，在35°～45°；   悬浮总体约占20%～30%，斜率在 40°以上；   跳跃总体约占20%～30%，斜率较小，多在 10°～20°。跳跃总体和滚动总体之间均存在有混合带，分选性较差。综合分析认为，阳逻砾石层沉积环境为具有辫状河特点的河流沉积。根据电子自旋共振测年（ESR）得到阳逻砾石层的形成年龄为1.12～1.56MaB.P.，表明阳逻砾石层形成于第四纪早更新世。
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SEDIMENTARY ENVIRONMENT OF GRAVEL BED IN YANGLUO TOWN IN THE MIDDLE REACHES OF YANGTZE RIVER

Gravel beds from Yangluo，Jiujiang，and Anqing as well as from Yuhuatai in Nanjing are the earliest deposits after the Cretaceous Tertiary redbed deposition in the hilly areas of two banks of the lower middle reaches of Yangtze River，representing the highest river terrace of this part of the river. Through field investigation and lithoface and granularity analysis of sediments from two typical sections，we discussed the sedimentary environment of the gravel bed in Yangluo Town. The result shows that the bed is mainly composed of gravels and sands. Three sedimentary facies，Gm，Sh，and Sp can be recognized. Most frequency curves are of two peaks and are asymmetry. Most probability cumulative curves are of up three segments type and the main ones are the rolling collectivities which are of about 50% to 60%. Their slope angle is between 35° and 45°. The suspending collectivities take the second place，which are of about 20％ to 30％，with their slopes angle exceeding 40°. The proportion of the jumping collectivities is about 20％ to 30％，with slope angle between 10° and 20°. There exists mixed zone between the jumping and the rolling collectivities，in which it is difficult to distinguish collectivities. Comprehensive analysis suggests that the sedimentary environment of the gravel bed in Yangluo Town is a braided river. The result of ESR shows the age of gravel bed in Yangluo Town is between 1.12MaB.P. and 1.56MaB.P. This shows that gravel bed in Yangluo Town were formed in Early Pleistocene of Quaternary.