Geological features and geochemical characteristics of Late Devonian-Early Carboniferous K-bentonites from northwestern Turkey

Newly discovered K-bentonite beds, interstratified with limestones/dolomitic limestones of the Upper Devonian-Lower Carboniferous Yilanli Formation, are exposed in the northwestern Black Sea region of Turkey, around Zonguldak and Bartin. K-bentonite samples collected from four different locations: the Gavurpinari and Yilanli Burnu quarries from the Bartin area, the Cimsir Cukurlari quarry from the Sapca area, and the Gudullu and Gokgol highway tunnel section near Zonguldak city were investigated using optical microscopy, X-ray diffraction and inductively coupled plasma mass spectrometry in order to reveal their mineralogical and geochemical characteristics and understand their origin and evolution. The K-bentonites occur at different levels in the Yilanli Formation as 2-40 cm-thick, greenish to yellowish beds cropping out several hundred metres along strike. Preliminary biostratigraphic data suggest that the protoliths of the Bartin (Gavurpinari and Yilanli Burnu) and Gudullu K-bentonites were deposited at around the boundary between the Frasnian and Famennian, whereas those in the Sapca and Gokgol sections are slightly younger (Devonian-Carboniferous boundary interval). The lithofacies types of the host carbonate rocks suggest an 'epeiric' shallow carbonate platform environment. Illite and mixed-layer illite-smectite were the major clay minerals in the K-bentonites. The K-bentonites from the Bartin area display a high degree of illitization and consist mainly of illite indicating high-grade diagenesis, whereas illite-smectite-rich samples from the Sapca and Gokgol tunnel locations reflect relatively lower diagenetic conditions. According to their geochemical compositions, two groups of K-bentonites were distinguished, one with alkali basalt (Bartin area and Gudullu locations) and one with trachyte affinities (Gokgol tunnel and Sapca locations). Geochemical fingerprinting of K-bentonites by trace and rare earth element (REE) data suggest that tephras with alkali basalt composition have been derived by a source formed in a 'continental back-arc' setting, whereas the source of K-bentonites with trachytic precursors is related to 'continental within-plate rifting'. An evaluation of the global Late Devonian and Devonian-Carboniferous volcanism suggests that the bentonite precursors may be related to late-Variscan magmatism in Laurussia.


Geological, mineralogical and geochemical characteristics of Mississippian K-bentonites from southern Turkey: A correlation with coeval tephras from Gondwana-derived terranes
Bozkaya, Ömer; Günal Türkmenoğlu, Asuman; Göncüoğlu, Mehmet Cemal; Okuyucu, Cengiz (2021-09-01)
Five thin (5–15 cm) and yellowish green tephra (K-bentonite) layers are exposed along two sections in the south of Akşehir (Konya, southern Turkey) within the Early Carboniferous (Mississippian) red dolomite-dolomitic limestone succession of the Sultandağ Unit in the central Tauride Belt. K-bentonites exhibit typical porphyritic texture with euhedral plagioclase phenocrysts replaced by fine-grained white K-micas and sparry dolomite crystals. The intensively sericitized volcanic matrix has vitrophyric textur...
Clay mineralogy, chemistry, and diagenesis of Late Devonian K-bentonite occurrences in northwestern Turkey
Günal Türkmenoğlu, Asuman; BOZKAYA, ÖMER; Göncüoğlu, Mehmet Cemal; Unluce, Ozge; Yılmaz, İsmail Ömer; OKUYUCU, CENGİZ (2015-01-01)
Thin beds of tephra (K-bentonites) formed by the diagenesis of volcanic ash are exposed within the limestone-dolomitic limestone successions of the Yilanli formation at Zonguldak and Bartin in northwestern Turkey. They were deposited on the Middle Devonian-Lower Carboniferous shallow carbonate platform of the Zonguldak terrane. In this study, K-bentonite samples collected from Gavurpinari and Yilanli Burnu limestone quarries are investigated in order to reveal their mineralogical and geochemical characteris...
Ellero, Alessandro; Ottria, Giuseppe; Sayıt, Kaan; Catanzariti, Rita; Frassi, Chiara; Göncüoğlu, Mehmet Cemal; Marroni, Michele; Pandolfi, Luca (2015-01-01)
In the Central Pontides (Northern Turkey), south of Tosya, a tectonic unit consisting of not-metamorphic volcanic rocks and overlying sedimentary succession is exposed inside a fault-bounded elongated block. It is restrained within a wide shear zone, where the Intra-Pontide suture zone, the Sakarya terrane and the Izmir-Ankara-Erzincan suture zone are juxtaposed as result of strike-slip activity of the North Anatolian shear zone. The volcanic rocks are mainly basalts and basaltic andesites (with their pyroc...
Demirel, Serhat; Göncüoğlu, Mehmet Cemal; Topuz, Gueltekin; IŞIK, VEYSEL (2009-08-01)
A hydrothermal breccia zone 6 km long and 2 km wide, crossed by quartz-tourmaline veins, occurs to the south of the Late Cretaceous Kerkenez granite-monzonite massif in the northern part of the Central Anatolian Crystalline Complex, Yozgat, Turkey. This breccia zone is characterized by numerous veins, a few millimeters to 1 meter in width, and display typical microtectonic features of multiple brecciation. Trace amounts of albite, K-feldspar, epidote, muscovite and rutile are associated with quartz and tour...
Geology and geochemistry of the pre-Early Cambrian rocks in the Sandikli area: Implications for the Pan-African evolution of NW Gondwanaland
Gursu, S; Göncüoğlu, Mehmet Cemal; Bayhan, H (2004-10-01)
The pre-Early Cambrian Sandikli Basement Complex in western Central Anatolia comprises a low-grade metasedimentary succession (Guvercinoluk Formation) and meta-rhyolites intruded by meta-quartz porphyry rocks (Kestel Cayi Porphyroid Suite). The Guvercinoluk Formation consists of alternation of meta-siltstones and meta-sandstones with olistostromal conglomerates, rare black chert and cherty meta-dolomite lenses. The Kestel Cayi Porphyroid Suite is a deformed, highly sheared dome-shaped rhyolitic body with qu...
Citation Formats
M. C. Göncüoğlu, A. Günal Türkmenoğlu, C. OKUYUCU, and İ. Ö. Yılmaz, “Geological features and geochemical characteristics of Late Devonian-Early Carboniferous K-bentonites from northwestern Turkey,” CLAY MINERALS, pp. 539–562, 2016, Accessed: 00, 2020. [Online]. Available: