Date

2013

Author

Ünlüce, Özge

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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 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 (Kübler index-KI, intensity ratios (Ir), illite polytypes (%2M1), (d060) of illite minerals from the two different sampling locations were investigated. Their KI values (for Yılanlı Burnu sampling location varying between 0.47-0.93 (with an average of 0.71 Δ°2θ); for Gavurpınarı quarry sampling location varying between 0.69-0.77 (with an average of 0.72 Δ°2θ)); % 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 Yılanlı Burnu quarry samples, whereas, these ratios are between 25-45% (with an average of 37%) for the Gavurpınarı 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 Å, (with an average of 1.499 Å) 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 °C) from the products of volcanic eruptions having yet unknown source and distance during Middle-Late Devonian time.

Subject Keywords

Clay minerals., Diagenesis., Sediments (Geology)., Sedimentation and deposition.

URI

http://etd.lib.metu.edu.tr/upload/12615587/index.pdf
https://hdl.handle.net/11511/22318

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Graduate School of Natural and Applied Sciences, Thesis