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- 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.
- MakaleYalnız künye2019Jurassic acidic magmatism in a back-arc setting, eastern Sakarya Zone, Turkey: Geochemical constraints and an evolutionary model
Dokuz, Abdurrahman; Sünnetçi, Kadir
The Early Jurassic in the Sakarya Zone, Turkey, was dominated by basic magmatism. The products of this magmatic episode are found as basaltic lavas and pyroclastic rocks in the Şenköy Formation, which was deposited in an extensional basin, or as intrusives cutting Variscan crystalline basement rocks. The Olur (Erzurum) region in the easternmost part of the Sakarya Zone is one of the few locations where contemporaneous acidic rocks crop out, exposed in an area of ~50 km 2 . The acidic rocks in the eastern Sakarya Zone consist of dacitic lavas, rare pyroclastic rocks, and very rare pebble dikes. Porphyries and trondhjemites are their intrusive equivalents and crop out as dikes and small stocks within the underlying Variscan basement. These Early Jurassic rocks have modal K-feldspar contents of <10% and are trondhjemitic in character. Laser ablation–inductively coupled plasma–mass spectrometry U-Pb dating of zircons from two samples yielded formation ages for these rocks of 185.3 ± 1.0 and 184.1 ± 1.1 Ma (±2σ). Geochemically, the rocks are strongly peraluminous and display a medium- to low-K affinity and sodic compositions (K 2 O/Na 2 O = 0.03–0.49). Enrichment in large-ion lithophile elements and depletion in Nb, Ta, P, and Ti are regarded as signatures of a subduction-related setting. Moderately radiogenic I Sr ratios (0.70508–0.70877) and depleted mantle-like Ɛ Nd (t) values (−0.6 to +3.0) and Pb(t) isotopes suggest that the acidic rocks were derived from juvenile lower crust. Geochemical and isotope data imply that the partial melting of juvenile mafic lithologies of the lower crust produced K-poor tonalitic melts that later fractionated to trondhjemitic melts while ascending to the surface. Considering the available data, we suggest that the Early Jurassic bimodal magmatic rocks of the eastern Sakarya Zone were formed in a back-arc setting during the southward subduction of the Paleotethys oceanic lithosphere. These rocks are a prime example of the formation of shallow subduction products following Late Triassic ridge subduction.
- MakaleYalnız künye2011A new Early Jurassic brachiopod fauna from the Eastern Pontides (Turkey)
Vörös, Attila; Kandemir, Raif
A newly collected Early Jurassic brachiopod fauna from the Kocamantaşi section (Gümüşhane region, Eastern Pontides, Turkey) yielded 160 specimens and 13 species (4 rhynchonellids, 3 spirifennids, 6 terebratulids). Apart from some long-ranging forms, five species prove the Late Pliensbachian age of the fauna. The paleoenvironmental setting of the Kocamantaşi fauna shows analogies to the Alpine Hierlatz limestones. On the basis of common lithological characters, bedding features and sedimentary associations, this lithofacies is interpreted as a complex of submarine, biodetrital talus associated with fault-related submarine rocky slopes. The numerical comparison of the Kocamantaşi brachiopod fauna to Pliensbachian brachiopod faunas of Europe revealed that the faunal similarity was the highest to Kotel (Balkans) and the Crimea. Very strong affinity was recorded to further NW-European faunas, whereas very low, or no similarity was recognized to the Mediterranean faunas. This paleobiogeographical result supports the hypothesis that in the Late Pliensbachian the Eastern Pontide segment of the Cimmerian microcontinent was far from the Gondwana and close to the Eurasian margin of the Tethys.