Evalution of organic matters and hydrocarbon potential in lower cretaceous mudstones: From Ulus and Kilimli formations, Northwestern part of pontides, Turkey

Lower Cretaceous mudstones are exposed Ulus and Kilimli Formations in Zonguldak (Kilimli and Kızılcakese districts) Bartın (Ulus district) and Karabük (Cumayanı district) regions, in northwestern part of Turkey. A total of seventeen outcrop samples were analyzed by Rock Eval Pyrolysis with the aim of determining quality, quantity and thermal maturity and depositional environment conditions of organic matter and hydrocarbon source rock potential of Lower Cretaceous mudstones in these regions. The TOC values ranging from 0.32 to 1.13 wt % with an average of 0.71 wt. %. HI, OI, S1, S2, S2/S3 and Tmax parameters and diagrams based on the Rock-Eval anaylsis indicate that Cumayanı, Ulus, Kilimli mudstones have overmature Type III-IV kerogen with poor, limited gas potential. While, Kızılcakese mudstones have early mature Type II-III kerogen with fair, oil-mixed gas potential. The hydrocarbons produced by the studied samples are native and have not been exposed to organic contamination by any mechanical or anthropogenic pathway. Overall, the Lower Cretaceous mudstones in Ulus and Kilimli Formations, northwestern part of Turkey, were generally deposited in sulphur limitation and reduced salinity, arid paleoclimate, C-CD-D organic facies, clastic, marine conditions as a result of a margin marine transgression which suggests frequent sealevel fluctuations in paleoenvironment. It can be deduced that the maturity and the hydrocarbon generation potential of the Kızılcakese district may increase in the deeper parts of the basin. Key words: Organic geochemistry, hydrocarbon source rock potential, Lower Cretaceous mudstones, Ulus and Kilimli Formations, northwestern Turkey