Thrace Basin: An Extensional Tertiary Sedimentary Basin in an Area of Major Plate Convergences, Northwest Turkey

Suleyman Turgut, Erkan Atalik

The Thrace basin forms one of the largest Tertiary basins in Turkey. Paleontological and sedimentological evidence suggests sedimentation and basin formation commenced by a major transgression from the southwest in the middle to late middle Eocene. The basin formed over an extremely deformed crustal block. It straddles an Upper Cretaceous suture zone which later became a major mobile belt in Turkey. Syndepositional fault patterns and sedimentary thickness indicate the basin was evolved tectonically by north-south extension. Large listric normal faults and east-west depositional axis are evidence of this extension.

Early marine sedimentation in the basin was accompanied by an intense volcanism which poured large quantities of ash into the depositional environment. Normal basement faults were active and great thicknesses of clastic sediments accumulated along faults. Reefal to shallow marine carbonates were deposited on shelves and over intrabasinal paleohighs. Sedimentation became regressive in the early Oligocene. Alternation of marine and nonmarine clastic deposition continued without interruption until the end of the Oligocene.

By the late Oligocene to early Miocene, the whole basin was subjected to intense tectonism that caused uplift and faulting. Seismic reflection profiles reveal a very complex tectonic style in the basin. Fault-related inversion and flowage structures involving shale diapirism are quite common.

Eocene and Oligocene shales are mature enough to generate economical quantities of hydrocarbons. Their source quality is fair to poor. Sand bodies in the Eocene-Oligocene series and reefal carbonates form the reservoir facies, and they are targets for exploration.

AAPG Search and Discovery Article #91032©1988 Mediterranean Basins Conference and Exhibition, Nice, France, 25-28 September 1988.