Clay mineralogy, chemistry, and diagenesis of Late Devonian K-bentonite occurrences in northwestern Turkey

Günal Türkmenoğlu, Asuman
Göncüoğlu, Mehmet Cemal
Unluce, Ozge
Yılmaz, İsmail Ömer
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 characteristics and diagenetic evolution. Illite is the major clay mineral in the studied K-bentonites. Additionally, kaolinite and mixed-layer illite-smectite are identified in some samples. The nonclay minerals calcite, dolomite, quartz, gypsum, feldspar, pyrite, and zircon are also found. Crystal-chemical characteristics (Kubler index, d(060) values, and polytypes of illites) from two different sampling locations do not show significant variations. Kubler index values for the Yilanli Burnu and Gavurpinari sampling locations, 0.47-0.93 (average: 0.71 Delta degrees 2 theta) and 0.69-0.77 (average: 0.72 Delta degrees 2 theta), respectively, indicate that illites were affected by high-grade diagenetic conditions. The swelling (or smectite) component (similar to 5%), crystallite size (N = 10-20 nm), and polytype (2M(1) > 1M(d)) data of illites support the same conditions. Illite d(060) values of 1.491-1.503 angstrom correspond to a range of octahedral Mg+Fe values of 0.27-0.51 atoms per formula, indicating a composition between end-member muscovite and phengite unit. Trace and rare earth element-based chemical classification of the K-bentonite samples revealed that composition of original volcanic ash is basaltic. Illitization took place by fixation of K from volcanic minerals and ash, and diffusion of elements (Mg+Fe) into and out of the beds during diagenesis. Mineralogical-chemical data point out that these K-bentonites evolved in high-grade diagenetic conditions (approximately 100-150 degrees C) from the products of volcanic eruptions of disputed sources and distances during the Late Devonian time.


Clay mineralogy and diagenesis of K-bentonites occuring in the devonian Yılanlı formation from North Western Anatolia (Bartın - Zonguldak)
Ünlüce, Özge; Günal Türkmenoğlu, Asuman; Department of Geological Engineering (2013)
Yellowish brown and gray-green colored K-bentonite horizons revealing thicknesses up to 60 cm are exposed within the limestone-dolomitic limestone successions (Middle Devonian-Lower Carboniferous Yılanlı formation) deposited on a shallow marine carbonate platform at Zonguldak and Bartın area in the western Black Sea region. In this study, bentonite samples collected from two different locations; Gavurpınarı quarry and Yılanlı Burnu quarry are investigated by means of optical microscopy, X-ray powder diffrac...
Geological features and geochemical characteristics of Late Devonian-Early Carboniferous K-bentonites from northwestern Turkey
Göncüoğlu, Mehmet Cemal; Günal Türkmenoğlu, Asuman; OKUYUCU, CENGİZ; Yılmaz, İsmail Ömer (2016-09-01)
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 optic...
Mineral chemistry and thermobarometry of Soltan Meidan basalts, North of Shahrood
Derakhshi, Morteza; Ghasemi, H.; Toksoy Köksal, Fatma (2015-06-01)
Soltan Maidan Basaltic Complex consists of a thick succession of basaltic lavas associated with some thin sedimentary interlayers that are exposed in the northwest to northeast of Shahrood. Soltan Maidan basaltic rocks has been generated from magma with transitional to mildly alkaline nature and derived by 14-20 percent partial melting of an enriched garnet peridotitic mantle source in an intra-continental rift setting during Late Ordovician to early Late Silurian. These basaltic rocks are relatively unifor...
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...
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
A. Günal Türkmenoğlu, Ö. BOZKAYA, M. C. Göncüoğlu, O. Unluce, İ. Ö. Yılmaz, and C. OKUYUCU, “Clay mineralogy, chemistry, and diagenesis of Late Devonian K-bentonite occurrences in northwestern Turkey,” TURKISH JOURNAL OF EARTH SCIENCES, pp. 209–229, 2015, Accessed: 00, 2020. [Online]. Available: