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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 künye2025Concentrations, distribution, and source appointment of heavy metal/loids in non-clastic sedimentary rocks: a case study of early jurassic chert, northeastern türkiye
Saydam Eker, Çiğdem; Kaygusuz, Abdullah; Arı, Uğur Volkan
The Current study used geochemical indicators such as the geo-accumulation index (Igeo), the Enrichment Factor (EF), and the contamination factor (CF) to evaluate the regional distributions and accumulations of various heavy metal/loids (HM; Co, Mo, Pb, Zn, Cu, Ni, As, Cd) in early Jurassic cherts in the Gümüşhane (NE Türkiye). Five stratigraphic section measurement (MS) areas (Tedaş, Alemdar, Akçakale, Tekke, and Pirahmet) and one borehole (Eskibağlar well) were selected for sampling. Major and trace element compositions of the selected 25 samples were measured by inductively coupled plasma optical emission spectrometry (ICP-OES) and inductively coupled plasma mass spectrometry (ICP-MS). Calculated geochemical indexes indicated that Alemdar, Tekke MS, and Eskibağlar well samples were polluted with Pb, Zn, Cu, As, and Cd, Tedaş, Akçakale, and Pirahmet MS samples were polluted with Cd. Pearson's correlation coefficient (PCC) and principal component analysis (PCA) suggested that Zn, Pb, and Cu contaminating the Alemdar, Tekke MS, and Eskibağlar well samples were of ore mineralization origin, As was of terrigenous input, and Cd was probably of diatom origin. PCC and PCA showed that the Cd contaminating the Tedaş, Akçakale, and Pirahmet MS samples was probably of diatom origin, and the other metals found at normal levels in the samples were due to terrigenous input. The Early Jurassic period, which was a rift environment in the Gümüşhane region, is thought to have produced the cherts of the Alemdar, Tekke MS, and Eskibağlar well samples in a graben environment, while the cherts of the Tedaş, Akçakale, and Pirahmet MS were deposited in a horst environment. δU values, Ni/Co, and Vi/(V + Ni) ratios indicated that oxic-anoxic conditions were generally prevalent in the depositional environment, but redox conditions did not affect the abundance and distribution of HMs. These findings provide critical information for assessing heavy metal/loid enrichment and contamination potential not only in clastic sedimentary rocks, river sediments, and soils but also in non-clastic sedimentary rocks.
- MakaleAçık Erişim2024The potential toxic element contents of Berriasian–Aptian carbonate rocks: distribution of elements in dolomite and limestone and possible sources (Gümüşhane/NE Türkiye)
Eker, Çiğdem Saydam; Arı, Uğur Volkan
The aim of this study is to determine the potential toxic element (PTE) content linked to the geochemical features of Berriasian–Aptian carbonate rocks commonly outcropping in Gümüşhane, along with the degree of pollution and possible sources of these toxic elements, and to compare dolomite with limestone in terms of toxic metal abundance. In the field, dolomite and limestone samples were collected by measuring stratigraphic sections around Yuvacık, Ünlüpınar, Çukutbaşı, Bağlarbaşı, Mescitli and Gülaçar (Gümüşhane). The samples were analyzed using inductively coupled plasma mass spectroscopy (ICP-MS). The mean values for Mo, Cu, Pb, Zn, Ni, As, and Co were 3.1, 23.8, 7.1, 14.5, 13.5, 30.9, and 8 mg/kg in Yuvacık; 6, 2.3, 1.1, 3.5, 8.1, 12.3 and 2.5 mg/kg in Ünlüpınar; 17.9, 1.8, 1.5, 8.6, 7.9, 13.9 and 1.7 mg/kg in Çukutbaşı; 3.7, 6.5, 31.7, 82.7, 9.5, 32.0 and 1.9 mg/kg in Bağlarbaşı; 0.7, 0.7, 7.1, 21.3, 2.6, 11.8 and 0.7 mg/kg in Mescitli; and 1.2, 1.1, 2.4, 5.2, 1.3, 4.0 and 0.2 mg/kg in Gülaçar, respectively. According to geochemical pollution parameters [geo-accumulation (Igeo), pollution index (Pi), and pollution load index (Pln)], the rocks were generally significantly polluted by Mo and As, without notable pollution by the other elements. Limestone samples from the Yuvacık, Ünlüpınar, and Çukutbaşı areas were more polluted in terms of Mo and As compared to dolomites. This pollution in Yuvacık and Ünlüpınar was identified to have geogenic sources (Pb–Zn–Cu mineralization) and in Çukutbaşı was identified to have lithogenic sources. Dolomites from the Bağlarbaşı area were more polluted in terms of As and less polluted in terms of Mo compared to limestones. In the Mescitli location, both dolomites and limestones were occasionally polluted in terms of As, while limestones were polluted in terms of Mo. In these two areas, the sources of As and Mo are geogenic (Pb–Zn mineralization), In Gülaçar, dolomites were more polluted in terms of Mo and less polluted in terms of As compared to limestones. In this locality, As and Mo are thought to have a geogenic source (Pb–Zn–Cu mineralization).
- MakaleYalnız künye2023Geochemical characterization of late Jurassic–early Cretaceous age limestones from Gümüşhane (NE-Türkiye): identification of the source of organic matter and paleo-environment conditions
Eker, Çiğdem Saydam; Arı, Uğur Volkan
Samples from late Jurassic–early Cretaceous age limestones in five different areas in the Gümüşhane region (NE-Türkiye), were studied using TOC/Rock–Eval, and some trace elements analysis, to evaluate their organic material source, type, thermal maturity, and paleo-environment conditions. The studied carbonate rocks are characterized by 90 m thick in the Bağlarbaşı section, 420 m in the Gülaçar, 584 m in the Ünlüpınar, 375 m in the Mescitli, and 272 m in the Yuvacık. The carbonate rocks are generally represented by, from bottom to top, dolomite, oolitic, sparitic, sandy, micritic, clayey, and bituminous limestones. Average total organic carbon (TOC) values are 0.14, 0.16, 0.20, 0.12, and 0.20% in the Bağlarbaşı, Gülaçar, Ünlüpınar, Mescitli, and Yuvacık sections, respectively. Organic material in the limestones consists of Type II-III kerogen, indicating that a mixture of terrigenous higher plants–marine aquatic organisms was the main source. Average Tmax values and Tmax-based vitrinite reflectance values (Ro %) are calculated as 435 and 0.67, 444 and 0.83, 431 and 0.60, 442 and 0.79, and 437 °C and 0.70 in the Bağlarbaşı, Gülaçar, Ünlüpınar, Mescitli, and Yuvacık sections, respectively, indicating that the samples have generally reached thermal maturity. The limestones in the Gülaçar, Mescitli, and Yuvacık areas are probably well-drained rocks that were extracted and originated hydrocarbon efficiently from the limestone fractures. In general, a non-marine–sometimes marine deposition environment for the carbonates is indicated by total sulfur values. V/Ni and Sr/Ba ratios indicate a stratified water column with high–low salinity and anoxic–oxic bottom water circumstances and accordingly a transitional sedimentation environment.
- MakaleYalnız künye2020Comparison of sandstone and mudstone with different methods for assessing toxic element contamination in the Early–Middle Jurassic sediments of Gümüşhane (NE Turkey)
Saydam Eker, Çiğdem; Arı, Uğur Volkan
To investigate the vertical changes of toxic elements in Jurassic sediments, sampling was performed in four sites. Samples were collected from sandstones and mudstones/marls and analyzed for some toxic elements (Cu, Pb, Zn, As, Ni and V). Results exhibited that the sediment grain size played a significant role in controlling the concentrations of the toxic elements in the sediments. The mean toxic element contents of mudstones/marls were higher than those of sandstones (except Cu). The contamination level of toxic elements was detected by enrichment factor (EF), geo-accumulation index (Igeo), potential ecological risk index (Eir), pollution index (Pi) and united pollution index (PIn). The low EF, Igeo, Eir, Pi and PIn for Cu, Pb, Zn, Ni, V in the sandstones and Cu, Zn, Ni in the mudstones/marls exhibited an absence of clear these elements pollution. The high EF, Eir, Pi and PIn for As (9.7, 73, 7 and 29, respectively, as mean values) in the sandstones and for As (49.3, 222, 22 and 75, respectively, as mean values) Pb (8.8, 24, 5 and 19, respectively, as mean values), V (8.3, 15, 7 and 39, respectively, as mean values) in the mudstones/marls indicated significant contamination. Additionally, according to the potential ecological risk (RI) values, the sandstones had low potential ecological risk for the toxic elements (RI < 150) and the mudstones/marls had moderate potential ecological risk (150 ≤ RI ≤ 300). The potential ecological risk As, Pb, V (especially As) were higher in urban areas than in agricultural activities. Therefore, the source of As, Pb, V could be gasoline combustion, burning coal and vehicle exhausts. The contents of these elements generally increased from bottom to top of the measured stratigraphic sections, which indicated transported by atmospheric conditions.