Burial history and thermal maturity assessment of Upper Cretaceous–Lower Tertiary formations in the Çankırı Basin, Turkey

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Abstract A burial history and thermal maturity investigation has been carried out on Upper Cretaceous–Lower Tertiary deposits from the Cankiri Basin. This basin, which contains post-deformational deposits of Campanian–Maastrichtian to Pliocene ages, forms part of a rich hydrocarbon province defined by the presence of potential hydrocarbon source rocks. The stratigraphic sequence was recorded at the Cankiri, Bayat areas and Topuzsaray-1 and Sagpazar-1 wells. At each area, the 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. A potential source-rock interval of Upper Ypresian and Lutetian, the Yoncali Formation which has only the organic-rich strata among the other formations in the Cankiri Basin, has been identified. It is composed of laminated dark gray shales dominated by Type III kerogen with turbiditic sandstones, which were deposited in relatively deep water conditions. Total organic carbon content values range from 0.5 to 1.0%. Assessments of time–temperature index (TTI) values indicate that the top of the main zone of oil generation is at a depth of 3000–3250-m, and the onset of oil generation window, for the Bayat area, took place in the Miocene (10.5 My ago) and continued into the present. Coal samples collected from the Karabalcik Formation of Lutetian age are high in ash and sulfur. Petrographic identifications on the polished blocks in reflected light indicate that the coal samples include abundant huminite/vitrinite group macerals. Mean random huminite/vitrinite reflectance values of the coal samples are between 0.51 and 0.53 %Rrandom oil (av. 0.52 %Rr oil), indicating low-rank coals (subbituminous A/high volatile C bituminous) according to the ASTM classification.