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CLAY MINERALOGY AND DIAGENESIS OF K-BENTONITES OCCURRING IN THE DEVONIAN YILANLI FORMATION FROM NORTH WESTERN ANATOLIA (BARTIN-ZONGULDAK) &Uuml / nl&uuml / ce, &Ouml / zge M. Sc., Department of Geological Engineering Supervisor: Prof. Dr. Asuman G&uuml / nal T&uuml / rkmenoglu January 2013, 80 pages 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 Yilanli formation) deposited on a shallow marine carbonate platform at Zonguldak and Bartin area in the western Black Sea region. In this study, bentonite samples collected from two different locations / Gavurpinari quarry and Yilanli Burnu quarry are investigated by means of optical microscopy, X-ray powder diffraction analyses (XRD), both scanning electron microscopy (SEM) and energy dispersive X-ray (EDX) analysis, high resolution transmission electron microscopy (HR-TEM) and inductively coupled plasma mass spectrometry (ICP-MS) in order to reveal their mineralogicalgeochemical characteristics and understand their origin and evolution. Illite is determined as the major phyllosilicate mineral in K-bentonites. Additionally, kaolinite and illite-smectite mixed-layer clay minerals are also detected in some samples. As non-clay minerals calcite, dolomite, quartz, gypsum, feldspar, pyrite and zircon are present in these K-bentonites. Crystal-chemical characteristics (K&uuml / bler index-KI, intensity ratios (Ir), illite polytypes (%2M1), (d060) of illite minerals from the two different sampling locations were investigated. Their KI values (for Yilanli Burnu sampling location varying between 0.47-0.93 (with an average of 0.71 &Delta / &deg / 2&theta / ) / for Gavurpinari quarry sampling location varying between 0.69-0.77 (with an average of 0.72 &Delta / &deg / 2&theta / )) / % of swelling component (smectite-max 5%) and crystallite thickness (N=10-20 nm) indicate that these illites were affected by high-grade diagenetic conditions. Similarly, illite polytype ratios (%2M1/(2M1+1Md)) range between 20-50% (with an average of 36%) for the Yilanli Burnu quarry samples, whereas, these ratios are between 25-45% (with an average of 37%) for the Gavurpinari limestone quarry samples. Illite polytpe data also supports a high-grade diagenetic origin possibility of K-bentonites. Illite d060 values ranges between 1.491-1.503 &Aring / , (with an average of 1.499 &Aring / ) which reflect the octahedral Mg+Fe compositions are varying between 0.27-0.51 and thus approach the ideal muscovite-phengite values close to dioctahedral muscovite composition. Based on the data obtained from this study, volcanic ash was firstly transformed into a smectitic I/S mineral in early stages of sedimentation and burial diagenesis. This initial smectite was then be transformed into a highly illitic I/S, and finally illite by diffusion of elements into and out of the bed, during Devonian. Mineralogical-petrographical data points out that these K-bentonites evolved in a high-grade diagenetic environment (approximately 100-150 &deg / C) from the products of volcanic eruptions having yet unknown source and distance during Middle-Late Devonian time.

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