COMPARATIVE PETROLEUM GEOLOGY OF SOUTHEAST TURKEY AND NORTHEAST SYRIA

Abstract

In terms of their regional tectonic setting, SE Turkey and NE Syria belong to the Persian Gulf basin, and the essential structural features of SW Iran and N Iraq are readily discernible here. Large, elongated folds of Alpine (Mio‐Pliocene) age dominate the structure of the region, and the intensity of deformation increases towards the north, in the direction of the Taurus orogenic zone.Five major depositional cycles have been recognized in the sedimentary record of SE Turkey and NE Syria, and the stratigraphy of the area has been outlined. The depositional cycles are late Precambrian, Cambro‐Devonian, Permo‐Carboniferous to Upper Jurassic, Lower‐Cretaceous to Lower Eocene and Middle Eocene to Recent in age. Important regional unconformities are present at the base of the Permo‐Carboniferous to Upper Jurassic and Lower Cretaceous to Lower Eocene cycles. The effects of the latter unconformity are particularly marked north of the Diyarbakir‐Mardin swell in southeast Turkey, and it has adversely affected the petroleum potential of this region.Several giant oilfields have been discovered in NE Syria, while in SE Turkey the accumulations are small by Middle East standards and are often only marginally commercial. The difference in size of accumulations is due to more favourable source, reservoir and caprock relationships in the former area. Many of the structures in NE Syria can be regarded as multi‐objective with Tertiary, Upper Cretaceous, Lower Jurassic and Triassic prospects, whereas in SE Turkey the effects of the late Jurassic–early Cretaceous uplift and erosion seem to have restricted the potential pay zones largely to the Upper Cretaceous–Palaeocene section.Geochemical evidence suggests separate sources for the Tertiary, Cretaceous and Lower Mesozoic crudes of NE Syria, and in SE Turkey much of the currently produced oil is believed to have been generated by late Maestrichtian–Palaeocene basinal shales. However, in both areas there is some evidence that at least part of the oils now trapped in Upper Cretaceous‐Tertiary reservoirs in certain fields may be of deeper origin.