PERMIAN TO TRIASSIC EVOLUTION OF THE SANANDAJ - SIRJAN PROVINCE OF IRAN

The geology of Iran resembles a gig-saw puzzle, consisting of eight provinces that amalgamated during the Alpine-Himalayan Orogeny (Oligocene-Miocene) to form the modern geologic characteristics of the country. These provinces include: Zagros, Sanandaj – Sirjan, Urumieh – Dokhtar, Central Iran, Alborz, Kopeh Dagh, Lut, and Makran. Each of these provinces has had its unique tectonic and sedimentary evolution. It has been documented that Sanandaj – Sirjan, Central Iran, and Lut provinces were attached to the Gowndwana until the Early Permian. At this time they detached to form the Cimmerian continent, creating the Neotethys Ocean in the process. The common interpretation is that the Cimmerian continent broke-up in Late Triassic and each of its segments followed its own unique path. Detailed stratigraphy of three sections containing nearly complete records of Late Permian to Middle Triassic Indicates that the Sanadaj – Sirjan Province may have become an isolated carbonate platform after its separation from the Gondwana. The three sections investigated include (from southeast to northwest) Shahreza, Abadeh, and Julfa.

Despite being apart for over 1200 km, the lithofacies, thickness, and depositional environments of the Upper Permian to Lower Triassic strata in these three sections are remarkably identical. The Abadehian Stage (upper Permian) in each section consists of skeletal carbonate indicative of shallow-water, photic zone sedimentation. The overlying Julfian Stage is comprised of 18 m of gray, bioturbated lime mudstone suggesting deposition in deep-water below storm wave base. The Dorashamian Stage consists of 18 m of red, nodular limestone suggestive of deep-water sedimentation. The uppermost Permian interval in all three sections is a deepening upward succession, caused by a rise in relative sea level. The lowermost Triassic in all three sections consists of gray, subtidal limestone. Except clays, siliciclastics are absent in all three sections suggestive of their distance from a landmass. The remarkable similarity in stratigraphic and sedimentologic characteristics of these three sections points to the possibility that the Sanadaj –Sirjan Province became an isolated platform after it separated from the Gondwana and may have never been attached to the Central Iran as previously assumed.