The origin and morphology of soils formed on limestone rocks in Aq- Emam area (northeast Golestan province)

The origin and micromorphology of three selected pedons in mountainous Aq- Emam area (in northeast Golestan province) were investigated. The objectives were to examine 1) physico-chemical and micromorphological characteristics of studied pedons developed in different geomorphic positions and 2) evaluate the relationship between them with underlying limestone and loessial sediment as preassumed parent materials. Our results showed that the shallow soils developed on steep upslope have a cambic horizon as a main subsurface diagnostic horizon. In contrast, more thick and clayey soils developed on sloping areal have an argillic horizon with decalcified solum indicating more eluviation due to more landscape stability. Cyclical erosion and deposition which occur on colluvial foot slope must be responsible for superimposed pedo-sedimentary complexes in this position. Mass-balance calculations and geochemical ratios show that the soils in sloping midslope have a loessial nature due to windblown source and geomorphic processes. Erosion keeps these additions to some extent from appearing on the steep upslope thus these soils have a polygenetic nature derived from loesses and limestone’s insoluble residues. In brief, we can conclude that residual origin of soils formed on limestone rocks is controversy especially for those with deep solum and we should consider other possibility of material addition to soil such as eolian contamination and geomorphic processes.