The lower parts of the Oligo–Miocene Qom Formation in the Kegharaki (SE Jiroft) and Shurab (SE Qom) areas: biostratigraphy, microfacies, and depositional environments

In order to determine the transgression time of the Tethyan Seaway in the Jiroft and  Qom areas, and to analyzis depositional conditions at the same time, the basal parts of two exposed sections (Kegharaki and Shurab) were studied in terms of biostratigraphy, microfacies, and depositional environments. In the Kegharaki section, larger benthic foraminifera are mainly represented by nummulitids, lepidocyclinids, and Amphistegina.  In the Shurab section foraminifera are mainly represented by miliolids, Operculina, Amphistegina, and textularids. The presence of Nummulites fichteli/intermedius, Nummulites vascus, and lepidocyclinids in the lower parts of the Kegharaki section indicates that the basal deposits could be attributed to the late Rupelian. The basal part of the Shurab section is indicative of the late Rupelian?–Chattian.  Besides, the presence of tuffaceous layers in the study sections is indicative of contemporaneous volcanic activity. Ten microfacies were identified in the basal parts of the study sections. Microfacies associations of the Kegharaki section cover a range of subdepositinal environments from open marine to open lagoon environments. Coral patch reefs are present, but there is no reef complex with sigmoidal geometries. Microfacies cover a range of subenvironments from restricted lagoons to open marine environments in the Shurab section. Most parts of the Kegharaki section with an association of large and flat perforate foraminifera were deposited in normal saline waters in open marine environments (in the middle ramp). The Shurab section was deposited mainly in the restricted lagoons to open marine environments. The abundance of larger benthic foraminiferal and coralline red algae and coral facies indicates a tropical-subtropical palaeoenvironment.

The lower parts of the Oligo–Miocene Qom Formation in the Kegharaki (SE Jiroft) and Shurab (SE Qom) areas: biostratigraphy, microfacies, and depositional environments Keywords:

Oligo , Miocene , Larger benthic foraminifera , biozonation , Tethyan Seaway , Iran