Paleosols of Devonian Padeha Formation in the Estern-Alborz Zone, NE Iran: Textural, mineralogical and geochemical characteristics

Paleosols of the study area is a part of the Eastern-Alborz Zone which is located about 50 km southeast of Azadshahr. These paleosols developed on floodplain and lacustrine facies of the Devonian Padeha Formation. Based on the field and textural evidences, two major paleosol horizons identified as A and B horizons. The A horizon consists of calcrete and noncalcrete paleosols which is located in the floodplain facies of the Padeha Formation. The B horizon identified in the lacustrine facies and consists of calcrete paleosols. Quartz, calcite, dolomite, microcline, hematite, albite, sericite, illite, chlorite and montmorilonite were identified in the paleosols. Geochemical analyses of the paleosols reveal the enrichment of immobile elements and depletion of mobile elements. Investigations of chemical alteration and effective chemical alteration indices indicate intermediate weathering in the study area. The occurrences of noncalcrete and calcrete paleosols suggest a climate change from humid to dryer condition occurred during soil formation. Combinations of textural, mineralogical and geochemical data indicate an origin of basic igneous rocks for the paleosols of the study area.