Abstract

The study fi eld covering an area of about 1000 km2 is located in Sorgun town of the city of Yozgat. In the region Paleozoic, Campanian-Maastrichtian, Eocene, Miocene and Quaternary units are exposed. Among these units, the lower Eocene Çeltek formation hosts coal beds and oil shale. The Eocene epoch is important for organic matter deposition regarding oil and gas productivity and anoxic depositional conditions. In order to examine the paleo-sedimentary conditions of oil shales in the study area and their relation to Total Organic Carbon (TOC) contents and major-trace element contents, a total of 29 samples were collected from two boreholes and one Measured Stratigraphic Section (MSS). Samples have TOC contents varying from 1.97 to 16.17 wt% (average 6.30 wt%). The V/Cr, V/(V+Ni), U/Th, δU and Authigenic Uranium (AU) values of the Çeltek formation oil shales (ÇFOS) reveal that the oil shales have been deposited under variable paleo-environmental conditions. For paleo-salinity the Sr/Ba ratios indicate mostly deposition in a freshwater environment. Chemical Alteration Index (CIA) values and Sr/Cu ratios indicate that paleoclimate conditions of ÇFOS were dry, hot and occasionally humid. The Fe/Ti and (Fe+Mn)/Ti ratios reveal hydrothermal activity during sedimentation of oil shales. Zr/Rb ratios of samples are indicative of very weak paleo-hydrodynamics during the deposition of oil shales. Such variable geochemical conditions in the basin resulted in variable paleo-environmental conditions.

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