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The geochemistry of oil shale units of Hançili Formation in the Çankırı-Çorum Basin (Central Turkey) was studied using various chemical analyses. The mineralogical composition of the samples were preliminarily investigated using Pearson's correlation coefficients of selected elements, indicating that the samples contain abundant clay minerals as well as K-feldspar and carbonate. The K 2 O/Al 2 O 3 and SiO 2 /Al 2 O 3 ratios indicate that the major proportion of clay minerals is composed of smectite. Si, Al, Ti, K, Na, and Fe reside in clay minerals, while Ca, Mg, and Mn are mostly associated with carbonates (e.g., calcite and dolomite) and phosphorous (P) is present as apatite. The total REE content of the oil shale range from 19 to 113 ppm. The chondrite-normalized patterns of the oil shale show LREE enrichments, HREE deficits, negative Eu anomalies and negligible Ce anomalies. In general, major, trace and rare earth element abundances suggest that the studied oil shale in the Çankırı-Çorum Basin are mainly from the intermediate rocks, mixed with small amounts of basic rocks, and that their source rocks are mostly deposited in the continental collision setting. The REE geochemistry of the oil shale suggests that these samples were derived from a consistent terrigenous source and the Eu anomaly was inherited from the source rocks. The paleoclimate index (C-value), varies between 0.07 and 1.22 reflecting a generally semi-arid to humid conditions. In addition, Rb/Sr (~ 0.22) and Sr/Cu (~ 9.09) ratios support the idea that warm and humid conditions prevailed during deposition of the Hançili Formation. Sr/Ba ratios (0.54–3.7) of the studied samples suggest a paleoenvironment with variable salinity. The co-variation among this factor and paleoclimate indicators suggest that variations in climatic conditions exerted a primary control on salinity. The substantially low C-value and Rb/Sr ratio and significantly high ratios of Sr/Cu and Sr/Ba and also elevated carbonate content of four samples indicate that these samples were deposited during hot and arid periods and that the paleoclimate controlled the terrigenous sediment flux to the lake basin. The chemical index of alteration (CIA), A-CN-K ternary diagram, and high Th/U ratios indicate that the parent rocks of the oil shale experienced moderate chemical weathering (steady state). [ABSTRACT FROM AUTHOR]

The study area is situated in the imbrication zone (northwest of Adıyaman–Gölbaşı, Helete–Savran) of the Southeast Anatolian orogen, part of the Mediterranean–Himalayan orogenic belt. This area is characterized by NEE/SWW-trending, northward-dipping imbricated thrust slices located low in the nappe zone that was finally emplaced onto the Arabian platform during the Mid-Miocene. From top to bottom the main units in the study area are: (1) the Malatya Metamorphics- (2) the Harami Formation- (3) the Göksun Ophiolite–Esence Granitoid- (4) the Helete volcanics and (5) the Savran–Alacık Formation, Hompur–Lice Formation and Midyat Formation. This study contains the Upper Cretaceous–Eocene tectono-magmatic succession (ophiolitic rocks and related felsic intrusions and volcanic rocks), which are located in the Helete area. The unmetamorphosed ophiolitic rocks display an irregular ophiolitic sequence. These rocks are represented by tectonites, cumulated gabbros, isotropic gabbros and sheeted dyke complex and were intruded locally by felsic intrusions (granite, granodiorite, tonalite, dacite, and aplite). These ophiolites locally contain tectonically disrupted thin amphibolitic rocks. The mineral chemistry and geochemical features of these ophiolites indicate that these rocks exhibit sub-alkaline characteristics, and they are similar to those of island arc tholeiites formed in a supra-subduction zone. These ophiolitic rocks, located in the imbrication zone, are interpreted as being the equivalent of the Göksun Ophiolites. The felsic intrusions, which cut these ophiolitic rocks, correspond to the calc-alkaline Esence Granitoids which formed in an arc setting. Based on the 40Ar/39Ar dating method, a plateau age of 80.92 ± 0.29 Ma was obtained from a granite sample that cuts the gabbroic rocks. The Helete volcanics, which have a tectonic relationship with the Göksun Ophiolite and the Esence Granitoid, are represented by andesite-basalt (locally pillow lavas), and are overlain by nummulitic carbonate sediments. Geochemical data indicated that, the Helete volcanics evolved from a tholeiitic parental magma and formed in a subduction-related setting. [ABSTRACT FROM AUTHOR]