Biostratigraphy and Depositional History of the Paleozoic Deposits in the South of Central Alborz Basin, Based onForaminifera

Paleozoic sediments of a section in south of Central Alborz Mountains near the village of Aru were studied in order to determine faunal assemblages, their precise ages and the history of the basin. A sum of 120 samples was collected from four different formations of Jeirud, Mobarak, Doroud and Ruteh. A total of 150 thin sections were prepared and analyzed. Fifty species of Foraminifera were identified and classified in 38 genera. From the biostratigraphic and lithostratigraphic evidence presented here it is clear that excep for the upper contact of the Jeirud Formation, the upper and lower contacts of each of the other three formations cropping out in the Aru area are disconformable and, during the Paleozoic, the sedimentary basin underwent a few major and minor transgressive and regressive events. The absence of Middle - Upper Cambrian, Ordovician, Silurian and Lower Devonian sediments is a result of post-orogenic erosional processes of the Caledonian Orogeny, while the absence of Upper Carboniferous sediments was a result of the Hercynian Orogeny.