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The properties of the Miocene coal seams in the Soma Basin (W. Turkey): insights from coal petrography, rock-eval pyrolysis, mineralogy and elemental contents

Karayiğit, A., Littke, R., Querol, X., Jones, Timothy Peter, Oskay, R. and Christanis, K. 2017. The properties of the Miocene coal seams in the Soma Basin (W. Turkey): insights from coal petrography, rock-eval pyrolysis, mineralogy and elemental contents. International Journal of Coal Geology 173 , pp. 110-128. 10.1016/j.coal.2017.03.004

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The Soma Basin hosts three coal seams (kM2, kM3 and kP1) and several altered tuff layers within the Miocene sequences. This study focuses on the determination of coal petrography, Rock-Eval pyrolysis, mineralogy and elemental contents of the three coal seams from Eynez, Işıklar and Deniş sectors in the basin, and to identify the mineralogy of altered tuff layers within kM2 and kP1 seams. The routine coal quality analyses show that coal samples from the kM2 seam are characterized by lower ash yields and total S contents, and higher gross calorific values than kM3 and kP1 seams. The mineralogical composition of the bulk coal samples from the kM2 seam is made up mainly of quartz, clay minerals and lesser amounts of feldspars and carbonates. In the kM3 and as well as in the lower part of kP1 seam carbonate minerals are being dominant phases due to the existences of fossil shell-bearing bands in the coal beds and intercalations. The statistical data implies that major elements in bulk coal samples, such as Al, Fe, K, Mg and Na, and the vast majority of minor and trace elements, as we expected, have inorganic affinity. The trace element contents and elemental enrichments are generally changeable from seam to seam; nevertheless, Cs, Li and U are commonly enriched in all studied coal seams. These could be related to the differences ion ash yields and mineralogical compositions of coal beds within the seams. The mineralogical compositions of the altered tuff layers identified within the kM2 and kP1 seams display similar compositions with tonsteins; therefore, these layers are presumably in air-fall ash that were originated from synchronous felsic volcanic activities around the basin. The existences of volcanic layers also have has some influences on the mineralogical and elemental composition of both seams. The SEM data shows that clay minerals originated from these layers and certain trace elements (e.g. As and Zr) are 2 enriched in the coal layers below the tuff layers in the kM2 seam. This might be related to penetration of leached pore waters into these layers and precipitation of epigenetic minerals. The coal petrography data and coal facies diagram show that precursor peat of the kM2 seam was accumulating under telmatic, mesotrophic anoxic conditions where the water level was high and stable. The relatively low ash yields and thicker coal beds suggest the a lower clastic input ratio from the margins; therefore, the aluminosilicate affiliated elements display lower concentrations in this seam. Following periods when the, water-table fluctuated several times and covered entire mire surface; thus, peat formation ceased and several clastic and calcareous intercalations were deposited in the kM3 and kP1 seams. These imply the development of limno-telmatic conditions where fluvial influences took places during peat accumulation of both seams. Therefore, clastic inputs from the margins were high which resulted in elevated the concentrations of aluminosilicate affiliated elements. Furthermore, the mineralogical compositions of coal and intercalations of both seams also suggest the development of neutral to alkaline conditions. Considering the maceral compositions along with the thickness of coal, coal seams in the Soma Basin might have and can suggest the indicate oil generation potential; however, the data of pyrolysis analysis data shows that the studied coal seams are mainly gas-prone and only certain coal beds have mixed hydrocarbon generation capacity. Nevertheless, the changes of vegetation and depositional conditions also have reflections on the HI values. The slightly higher HI and TOC in the kM2 seems to be related to high contribution of woody material in peat and the development of more acidic conditions, whereas the predominance of herbaceous plant and alkaline conditions in the kM3 and kP1seams resulted in relative low HI and TOC values. All data presented in this study indicates that lithological features, differences in coal qualities and elemental contents in the Soma Basin were mainly controlled by changes ion the depositional conditions and as well as detrital inputs during Miocene.

Item Type: Article
Date Type: Publication
Status: Published
Schools: Earth and Environmental Sciences
Subjects: Q Science > QE Geology
Publisher: Elsevier
ISSN: 0166-5162
Date of First Compliant Deposit: 15 September 2017
Date of Acceptance: 5 March 2017
Last Modified: 29 Apr 2018 16:48

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