The Kopet Dagh Basin is a hydrocarbon-bearing Mesozoic-Tertiary basin in the north and north-east of Iran. The Lower Cretaceous succession is poorly known but upward passage from nonmarine to marine sediments is recognised. The marine sequence includes the marly limestones and shaly marls of the Sarcheshmeh Formation and the shales and silts of the Sanganeh Formation. Both formations contain ammonites, including the families Heteroceratidae, Deshayesitidae and Desmoceratidae. Bed-by-bed collecting has facilitated the erection of a regional biozonation that can be correlated with the "standard" schemes of the Mediterranean province.
In the lower part of the Sarcheshmeh Formation the Heteroceratidae (Heteroceras and Colchidites) are dominant and indicate a very late Barremian age. The middle and upper part of the formation are mostly occupied by the Deshayesitidae, of Early Aptain age. The lower part of the Sanganeh Formation contains Parahoplitidae and Cheloniceratidae, which indicate a Late Aptain age. The upper beds have yielded Douvilleiceratidae and Leymeriellidae, of the Early Albian.
The Barremian to Aptian ammonite faunas include forms similar to species found in southwestern Iran, and are characteristic of the northern and southern margins of Tethys. In contrast, the Albian faunas are completely different from those of south-western Iran but compare with faunas from the Mediterranean and sub-Boreal provinces. The changing biogeographical relationships probably reflect the rapid rise in global sea-level during the Late Aptain to Albian.
AAPG Search and Discovery Article #90925©1999 AAPG Foundation Grants-in-Aid