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通过对澧阳平原大量的野外考察、典型剖面玉成(YC)黑褐色土壤剖面的系统取样和室内粒度、稀土元素地球化学分析,以及OSL和AMS14C年代测定,探讨了黑褐色土的稀土地球化学特征,揭示了黑褐色土的形成年代、形成过程与形成环境.研究结果表明,黑褐色土层ΣREE变化范围分布在184.63～264.26μg.g-1,其平均值为207.93μg.g-1;低于剖面的ΣREE总平均值219.87μg.g-1,与洞庭盆地的红土ΣREE平均值(211.6μg.g-1)大体相当,但明显高于镇江下蜀黄土(207.7μg.g-1)和黄土高原黄土(159.2μg.g-1),表明YC剖面黑褐色土上经过了相对较强的风化成壤作用.YC剖面黑褐色土的稀土分布模式与该剖面黄土层、黄土高原黄土、镇江下蜀黄土和洞庭盆地风成红土等典型风成沉积物的分布模式具有一致性,而与河流沉积物、湖泊沉积物和基岩风化红土在稀土的分布模式上具有明显差别.而且,YC剖面沉积物粒度频率曲线呈明显的单峰分布,与典型河流相的双峰粒度频率分布存在显著差异;YC剖面位于澧阳平原中部台地上,比周边高5～10m,不可能是洪水作用沉积物;野外调查进一步表明,沉积物无水流作用痕迹;OSL和AMS14C年代测定表明,黑褐色土层形成的年代对应于23.8～10.6kaBP,此年代对应于末次冰期的晚期,其形成于相对冷湿的气候环境.因此,黑褐色土层及其上、下部的黄土层均为风成堆积物.
The rare earth geochemical characteristics of dark brown soil were discussed through extensive field investigation in the Yangyang Plain, systematic sampling of the dark brown soil profile of the YC section, indoor grain size, REE geochemical analysis, and OSL and AMS14C dating , Revealing the formation age, formation process and formation environment of dark brown soil.The results show that the range of ΣREE varies from 184.63 to 264.26μg.g-1, with an average of 207.93μg.g-1 The average ΣREE of the profile in the section is 219.87μg.g-1, which is roughly the same as that of the terrestrial ΣREE in the Dongting Basin (211.6μg.g-1), but significantly higher than that of the Xiashi loess (207.7μg.g-1) and The Loess Plateau loess (159.2μg.g-1) shows that the YC profile of dark brown soil has undergone relatively strong weathering and pedogenesis.The rare earth distribution pattern of YC profile dark brown soil is similar to that of the Loess Plateau, Loess Plateau, The distribution patterns of the typical aeolian sediments such as the lateritic loess and the Dongting basin are quite consistent with those of the river sediments, the lake sediments and the bedrock weathered red earth, and the YC profile Sediment particle size The curve shows a unimodal distribution, which is significantly different from the bimodal particle size distribution of the typical fluvial facies. The YC profile is located on the platform of the central part of the Xingyang Plain, 5 ~ 10m above the periphery, and can not be a flood sediment. Furthermore, the sediments showed no trace of water flow. The dating of OSL and AMS14C indicated that the formation of dark brown soil layer corresponded to 23.8 ~ 10.6 kaBP, which corresponded to the late stage of the last glacial stage and formed in relatively cold and humid climate. Therefore, the dark brown soil layer and its upper and lower loess layers are the wind into the accumulation.