Paleosols and bauxites in the Eastern Alborz and implications for Devonian-Permian paleoclimate

Eastern Alborz zone contains paleosols and bauxites that demonstrate paleoclimatic changes in addition to widely geological events in this zone. The Khoshyeilagh region is located about 50 km southeast of Azadshahr. Stratigraphic sequence in this region contains calcrete paleosols in Devonian sandstones of the Padeha Formation and a karst bauxite horizon along the contact zone of Permian limestones and Triassic dolomitic limestones. Textural and mineralogical evidences indicate the formation of paleosols in arid to semi-arid climate and the formation of bauxites in warm and humid climate. Also, range of weathering indices point out increasing of chemical weathering from Devonian paleosols to Permo-Triassic bauxites. Geochemical data combined with the geological evidences suggest that the basaltic rocks of the Soltanmeidan Formation are the parent rock of the studied paleosols and bauxites. Combination of textural, mineralogical and geochemical data show that paleosol formed in low temperature, low rate of precipitation, and low chemical weathering. In contrast, high temperature and high precipitation rate led to formation of chemical weathering during bauxites formation. Devonian paleosols of the Padeha formation and Permo-Triassic bauxites of the study area are good indicators for recognition of paleoclimatic conditions in this area.