湖北恩施地区硒地质地球化学环境背影

我国湖北省恩施州存在一个高Ｓｅ环境区和一个低Ｓｅ环境区。它们曾分别暴发流行过人体Ｓｅ中毒和克山病。在高Ｓｅ区的地层岩石中共有５个含Ｓｅ层位，因而本区在各个地质历史时期都存在高Ｓｅ地质背景，但Ｓｅ中毒只发生于下二叠统茅口组上段和吴家坪组控制的范围内。富Ｓｅ的二叠系岩石中以硅质炭质页岩含Ｓｅ最高（平均２４７．７２×１０－６），其次为含炭硅质岩（平均５２．４×１０－６），最低为硅质白云岩（平均３．１３×１０－６）。Ｓｅ质量分数随上述岩石类型降低的趋势与这些岩石中有机炭浓度依次降低有关。高Ｓｅ区同一地层岩石在不同地点发育的土壤总Ｓｅ质量分数和水溶性Ｓｅ质量分数的分布存在明显的差异。根据这种差异可划分出３种土壤Ｓｅ的分布类型，并据此提出进行高Ｓｅ中毒危险区的地球化学预测。高Ｓｅ与低Ｓｅ土壤出露范围的大小决定于其源岩所处的地质构造、岩石性质与产状和地形坡度综合作用的结果。富Ｓｅ岩石和缺Ｓｅ岩石各自产于褶皱的两翼和向斜核部。产状平缓且与坡度方向一致，呈面状大面积出露，其派生的土壤Ｓｅ影响范围较大。在挤压褶皱两翼的富Ｓｅ岩层产状陡，呈狭窄条带出露，其派生的土壤Ｓｅ影响范围取决于搬运介质的性质、强度以及所处的地形条件。

Selenium Geological and Geochemical Environmental Background in Enshi, Hubei

There are a Se_rich area and a Se_poor area in Enshi, Hubei province, China. Human selenosis and KD cases were reported in the Se_rich area and in the Se_poor area respectively. Five Se_rich rock formations exist in the Se_rich area, but selenosis cases were only found in the areas where the Upper Maokou Formation(P 1 m ) and Wujiaping Formation(P 2 w ) of the Permian system emerge. The siliceous and carbonaceous shales of Permian system have high selenium content swith an average of 247.72×10 -6 , carbon silicalite is less abundant averaging 52.4×10 -6 , and siliceous dolomite has the lowest selenium content (3.13×10 -6 ). The selenium decreasing along with the above_mentioned various rocks is directly influenced by the decreasing of their organic carbon. In the Se_poor area, purple sandstone and mudstone, which are lack of the organic carbon material collecting selenium, have a very low selenium content. The large or small exposure areas of both Se_rich and Se_poor soils,are controlled by a comperehensive result of structure, lithologic characters and slope of landform and so on. Se_rich rocks are located in either the flanks or synclinal core. If the dip angles of rock formations are smaller and consistent with slope of landform, the exposed area of the rock will be large and the Se_rich soil derived from the rock will influence widely. If the Se_rich rock formations in flanks of compression folds have steep dip angles and narrow area of outcrop, the distribution of the soil derived from the rock is controlled by the nature and intense of the transporting media and the landscope.