中国南方碳酸盐岩上覆红土形成机制研究进展

碳酸盐岩上覆红土在中国南方分布广泛,已提出的用于解释其形成机制的有溶蚀-残积说、溶蚀-交代说和外来沉积说,溶蚀-残积说应该是红土形成的真正机制。形成红土消耗的原岩可能是质纯碳酸盐岩,但更可能是含有泥质碳酸盐岩,甚至碎屑岩或粘土岩。红土中粘土矿物来源应该有二,一是原岩所夹粘土矿物,二是原岩中硅酸盐矿物溶解形成的次生粘土矿物;铁氧化物应该来自原岩中黄铁矿的次生演化。完整的红土剖面应该由红土层、杂色粘土层和碳酸盐岩腐岩组成。碳酸盐岩腐岩形成于包气带,由原岩中的碳酸盐溶解后再次沉淀形成,主要由钙华和残余碳酸盐晶体组成。红土地区的石漠化趋势主要与红土向地下岩溶空间渗漏有关。

A REVIEW OF ADVANCES AND OUTSTANDING ISSUES IN RESEARCH ON THE FORMING MECHANISM OF LATERITE IN SOUTH CHINA

The laterite overlying carbonate rocks is distributed extensively in South China. So far dissolution-residuum, dissolutionmetasomatism and foreign sediments theories have been put forward for the forming mechanisms of laterite. The dissolution-residuum theory should be the real forming mechanisms of laterite. Clay minerals in the laterite come directly from carbonate rocks and secondary evolution of silicates in carbonate rocks. A complete laterite profile should be made up of laterite layer, parti-color clay layer and carbonate rock saprolite. Carbonate rock saprolite is formed in zones of alteration and made up of travertine and residual carbonate crystals. The tendency of rocky desertification in laterite districts is mainly related to the laterite leakage into underground karst spaces.