ABSTRACT: Structural Controls on Source Rock Distribution and Maturation in Southeast Turkey

Jackie D. Reed, Vicki V. Ottensman, Grant W. Cushing, Sezgin Aytuna

Production from the western part of the Zagros fold and thrust belt in southeastern Turkey is character by high-sulfur (2-3%) oils from the middle Cretaceous Mardin Formation. The oils are generated from two carbonate sources, one from the middle Cretaceous passive margin sequence and one deposited as a part of the Upper Cretaceous foreland basin sequence. Both sources are associated with transgressive events coincident with two recognized Cretaceous oceanic anoxic events in the Cenomanian-Turonian and Coniacian-Santonian. Geochemical markers in the oils substantiate the restricted, anoxic conditions characteristic of their source rock deposition.

During the Upper Cretaceous compressional event, horsts formed buttresses to advancing oceanic thrust sheets. The oceanic thrust sheets consisted of the Karadut and Kocali formations, oceanic equivalents of the Mesozoic shelf. The middle and Upper Cretaceous source facies were rapidly and deeply buried by the tectonically thickened thrust sheets adjacent to the buttresses. Thick burial by the oceanic rocks was critical for thermal maturation of the sources. Geohistory modeling shows oil generation occurred during the Tertiary coincidental with tectonic activity that probably allowed oil migration to occur along new or reactivated Cretaceous faults.

AAPG Search and Discovery Article #91003©1990 AAPG Annual Convention, San Francisco, California, June 3-6, 1990