Evidence of pre-Triassic normal faulting in the Abgarm Mountains, northwest of central Iran

The Permian period is associated with an extensional tectonic regime during which the Neotethys oceanic basin developed between the central Iranian blocks and the Arabian Plate. In this study, the effects of this extensional regime on developing the normal faults and associated syndepositional sequences have been investigated in the Abgarm region at NW Iran. There is a huge gap in the stratigraphic sequence of the region from the Cambrian to the Devonian. This discontinuity is seen in some areas as concordant and some areas as angular. In addition to the Cenozoic and younger thrust and strike-slip faults system, faults with the major northwest-southeast trends are seen that extend only to Paleozoic units and are not observed in units of Triassic or younger age. Field observations document the normal kinematics of these faults. They have cut and displaced pre-Permian sequences. The Permian rock units including the Dorud and the Ruteh Formations have generally thickened toward these normal faults that document the syndepositional normal activity of faults. The normal faults have been covered by the Upper Permian and Triassic and younger deposits including Doroud, Ruteh, and Elika formations document the pre-Permian timing of the extensional regime in this part of the central Iranian basin.