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- MakaleAçık Erişim2025Geochemical evaluation of black limestones in the Early Cretaceous platform carbonates of Gümüşhane (NE Turkey): An insight into petroleum source rock potential and palaeoenvironment conditions
Saydam Eker, Çiğdem; Arı, Uğur Volkan; Alemdağ, Selçuk
This study assesses the organic matter (OM) content, kerogen type, maturity, depositional environment conditions and sedimentation model of Early Cretaceous (Berriasian–Aptian) black limestones in NE Turkey using geochemical analyses, including Rock-Eval/total organic carbon (TOC), gas chromatography–mass spectrometry, gas chromatography, major and trace elements and stable carbon isotope of OM measurements. The investigated black limestones' TOC, hydrogen index and potential yield values range from 0.07 to 2.91 wt%, 76 to 636 mg HC/g TOC and 0.15 to 11.17 mg HC/g rock, respectively. These results indicate that the examined limestones have variable source rock potential, ranging from low to high. Tmax values, calculated saturated biomarkers and aromatic components suggest that the OM contained in the black limestones varies between thermally immature and mature, consistent with the potential index values. The OM found in the black limestone contained kerogen varying between type I and III. It is a composition of marine and terrigenous OM, as shown by the δ13C isotope values, biomarker components and n-alkane distributions and their parameters. This OM was deposited in a salinity water environment with marine–terrigenous (transitional) surroundings under oxic, suboxic to anoxic and arid–hot climate conditions. These findings provide critical insights for assessing the hydrocarbon potential of carbonate platforms in similar geological settings.
- MakaleYalnız künye2016Constraints of C-O-S isotope compositions and the origin of the Ünlüpinar volcanic-hosted epithermal Pb-Zn±Au deposit, Gümüşhane, NE Turkey
Akaryali, Enver; Akbulut, Kübra
The Eastern Pontide Orogenic Belt (EPOB) constitutes one of the best examples of the metallogenic provinces in on the Alpine-Himalayan belt. This study focuses on the genesis of the Ünlüpinar Pb-Zn. ±. Au deposit in the southern part of the Eastern Pontide Orogenic Belt. The main lithological units in the study area are the Early Carboniferous Kurtoğlu Metamorphic Complex the Late Carboniferous Köse Granitoid and the Early-Middle Jurassic Şenköy Formation. The studied deposit is hosted by the Şenköy Formation, which consists predominantly of basaltic-andesitic rocks and associated pyroclastic rocks that are calc-alkaline in composition. Silicic, sulfidic, argillic, chloritic, hematitic, carbonate and limonite are the most obvious alteration types observed in the deposit site. Ore microscopy studies exhibit that the mineral paragenesis in deposits includes pyrite, chalcopyrite, sphalerite, galena, gold, quartz and calcite. Electron microprobe analyses conducted on sphalerite indicate that the Zn/Cd ratio varies between 84 and 204, and these ratios point at a hydrothermal deposit related to granitic magmas. Fluid inclusion studies in calcite and quartz show that the homogenization temperature of the studied deposit ranges between 90-160. °C and 120-330. °C respectively. The values of sulfur isotope analysis of pyrite, sphalerite and galena minerals vary between 1.6‰ and 5.7‰, and the results of oxygen and carbon isotope analysis range between 8.4‰ and 18‰ and -5‰ and -3.6‰, respectively. The average formation temperature of the ore was calculated as 264. °C with a sulfur isotope geothermometer. All of the data indicate that the Ünlüpinar deposit is an epithermal vein-type mineralization that was formed depending on the granitic magmatism.