CARBONATES IN THE ADIYAMAN REGION, SE TURKEY: AN ASSESSMENT OF BURIAL HISTORY
AND SOURCE-ROCK POTENTIAL
I. H. Demirel* and S. Guneri**
*Hacettepe University, Faculty of Engineering, Dept. of Geology, 06532, Ankara, Turkey.
** Turkish Petroleum Corporation, Exploration Group, Ankara, Turkey.
The burial history and source-rock potential of Cretaceous carbonates in the Adiyaman region of SE Turkey have been investigated. The carbonates belong to the Aptian-Campanian Mardin Group and the overlying Karabogaz Formation. The stratigraphy of these carbonates at four well locations was recorded. At each well, the carbonate succession was found to be incomplete, and important unconformities were present indicating periods of non-deposition and/or erosion. These unconformities are of variable extent. When combined with the effects of rapid subsidence and sedimentation which took place in the SW of the Adiyaman region during end-Cretaceous foredeep development, they have resulted in variations in the carbonates present-day burial depths, thereby influencing the regional pattern of source-rock maturation and the timing of oil generation. Burial history curves indicate that the carbonates maturity increases from SW to NE, towards the Late Cretaceous thrust belt. Predicted levels of maturity for the Mardin Group are consistent with measured geochemical data from three of the wells in the study area (the exception being well Karadag-1).
Three potential source-rock intervals of Cretaceous age have been identified. Two of these units -- the Derdere and Karababa Formations of the Mardin Group -- are composed of shallow-water carbonates which were deposited on the northern margin of the Arabian Platform. The third source-rock unit, the overlying Karabogaz Formation, is composed of pelagic carbonates which were deposited during a regional transgression. These potential source-rock intervals contain marine organic matter dominated by Type II kerogen. Total organic carbon contents range from 0.5 to 2.9 %. Time-temperature analyses indicate that the Mardin Group carbonates are immature to marginally mature at well locations in the SW of the study area, and are mature at western and NE well locations. The onset of oil generation in these Cretaceous source rocks took place between the middle Eocene (48 million yrs ago) and the Oligocene (28 million yrs ago).