Foraminiferal Biostratigraphy and Paleoecology of the Southeasternmost Outcrops of the Oligocene Qom Formation, SE Iran

Abstract

Abstract The Qom Formation is deposited along more than 1800 km of the NE margin of the Tethyan Seaway in the Oligocene-Early Miocene during the final sea transgression on the Iranian Plate. We present (foraminiferal-based) biostratigraphic data from three exposed sections near the northwestern Jazmurian Lake, as the southeasternmost outcrops of the Qom Formation. Larger benthic foraminifera are mainly represented by nummulitids (Nummulites, Operculina, Heterostegina), lepidocyclinids (Nephrolepidina, Eulepidina, Lepidocyclina), and Amphistegina. The presence of Nummulites fichteli/intermedius and Nummulites vascus in the lower parts of the study sections together with lepidocyclinids indicates that their basal deposits could be attributed to the late Rupelian. The Qom Formation is of late Rupelian-Chattian in age in all three stratigraphic sections. Also, the presence of Nummulites- bearing tuffaceous limestones and tuff unit in the lower part of the Bozadan section is indicative of contemporaneous volcanic activity. Most parts of the study sections with an association of large and flat perforate foraminifera were deposited in normal saline waters. These parts are presented by large and flat nummulitids, lepidocyclinids, and Amphistegina. These large and flat perforate foraminifera often dominate in the lower part of the photic zone. The abundance of larger benthic foraminiferal and coralline red algae and the coral facies indicates a tropical-subtropical palaeoenvironment.