Organic geochemical characteristics of the Paleocene–Eocene oil shales in the Nallıhan Region, Ankara, Turkey

Units of Paleozoic, Mesozoic and Cenozoic age are exposed in the study area which extends along the Sakarya River by the Sarýcakaya town of Eskiþehir at west and Nallýhan district of Ankara at East. Paleozoic is represented with metamorphites consisting of glaucophane schist, muscovite schist and marble alternations and granites cutting them. The Mesozoic composing of Jurassic–Cretaceous Soğukçam limestones at the northern part of the area is in tectonic contact with other units. The Tertiary is characterized by the Paleocene–Eocene Kızılçay Group which consists of the Beyköy, Çamalan and Laçin Formations. The Çamalan Formation is composed of sandstone, limestone, oil shale and locally coal bands. In the area, as a result of intense tectonic activity by the late Eocene, sedimentary sequence that compacted within the Paleozoic metamorphic rocks were folded and fractured.The Paleocene–Eocene shales have adequate organic material content to form potential source rocks. In order to determine hydrocarbon potential of the unit, various organic geochemical analysis techniques were performed. According to pyrolysis results (TOC, S1 and S2), the Paleocene–Eocene shales are perfect source rocks for oil. On the basis of Rock-Eval pyrolysis analyses, kerogens are Type I and Type II kerogens. Spore Color Index and Tmax evaluations indicate that maturity of the unit is between diagenesis and early mature oil zone and at the beginning of the oil-producing stage. Organic facies of the Paleocene–Eocene shales are A, AB and B.