Micromorphology of Secondary Calcium Carbonate Coatings in Some Arid and Semiarid Soils in Southern Alborz,Takestan-Iran



Accumulation of secondary calcium carbonates in arid and semiarid regions is a valuable tool in evaluating the degree of soil evolution, soil age, paleoenvironmental reconstruction, soil classification as well as land use. In addition, laminated pedogenic calcium carbonate coatings can provide some evidence regarding local environmental and climatic changes. In this study, pedogenic calcium carbonate coatings from southern Alborz mountains were investigated. Based on a reconnaissance survey, previous field observations and topographic maps, a transect of 10 soil profiles was selected to demonstrate the variation in physiography, land use and parent material in Takestan region, Iran. These profiles were sampled using standard techniques and then described and classified according to norms in soil taxonomy. Disturbed samples were analysed physico-chemically while undisturbed and oriented ones used for making thin sections. According to micromorphic studies, pedogenic calcium carbonate coatings were classified in the four following categories: 1) Typic Coatings, being formed as a result of super saturation of soil solution with carbonates, mostly occuring in the underside of skeletal grains, peds and void faces. Typic coatings were subdivided into three types. The first type is limpid, light monolayer calcitic coatings, composed of micritic calcite that thoroughly covers skeletal grains, like the first type, and additionally has sequences of light and dark colored lamina. Another type namely the 3rd occurs on the underside of coarse fragments, where the downward growth of calcium carbonate appears restricted by contact with the soil matrix. These coatings are either two or multilayered too. 2) The second form is carbonatic pendants; occurs as mammillary to botryoidally stalactite-like masses (segregations), which either emanate from the bottom of carbonate coats or occur on the bottoms of coarse fragments. Pendants are multi layered and composed of two to five light and dark colored layers, indicating the differences in conditions of calcite precipitation. 3) Needle-fiber calcite is the third form of coatings, which occurs in some depths near the soil surface or in upper layers of calcic horizons. This shape probably forms as a result of decomposition of in voids plant residues and of settlement of the Ca-containing components of cell walls, and also of the calcification of dead plant roots. 4) Finally, the forth form is Cappings which have the same morphology as pendants, but in contrast to pendants, occur in the upper side of coarse fragments....