Early Miocene larger benthic foraminifera from the northwestern Tethyan Seaway (NW Iran): new findings on Shallow Benthic Zone 25

The lower Miocene marine units of NW Iran (Hamedan–Miandoab area) were studied to establish a high-resolution biostratigraphy framework in the context of European standard biozonation (SBZ zonal scheme). The units are dominated by larger and small benthic foraminifera together with coralline algae and corals. Due to its position in the Tethyan Seaway between the Mediterranean and Indo-Pacific, the investigated area has high significance in palaeobiogeography. Seven species of benthic foraminifera were described, including Miogypsina globulina, Amphistegina bohdanowiczi, Elphidium crispum, Elphidium sp. 1, Borelis curdica, Austrotrillina asmariensis, and Peneroplis thomasi. The occurrence of Miogypsina globulina in the shallow-marine carbonates of the studied sections documents the Burdigalian SBZ 25 Zone. Austrotrillina asmariensis and Peneroplis thomasi occur with M. globulina. Simultaneously, their stratigraphical range is extended to the Burdigalian in the Middle East. Based on the discovery of lower Miocene deposits in the Hamedan–Miandoab area (previously mapped as Oligocene–Miocene units), the stratigraphy of northwest Central Iran is revised. The biostratigraphic results also present a more precise chronology for the marine transgression in the study area, initiating in the late early Miocene. The coralline algal assemblages and the abundance and diversity of larger benthic foraminifera indicate that shallow-marine Qom Formation got deposited in tropical to subtropical warm waters.