Coal properties of Carboniferous Kurtköy coals (Zonguldak, NW Türkiye): Emphasis on rank, provenance of minerals and hydrocarbon generation potential
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Late Carboniferous coal seams in the Zonguldak Basin (NW Türkiye) underwent several tectonic movements after the Late Permian; hence, these seams exhibit rank variations. This study presents initial insights into coal rank, mineralogical compositions, and hydrocarbon generation potential of Serpukhovian-Bashkirian coals within the Alacaağzı Formation from the south-easternmost part of the basin. The examined seams are of bituminous C rank, and Tmax (442-445°C) and HI (221-288 mg HC/g TOC) values indicate that they are at the set of oil generation. However, the low PI (0.01-0.02), BI (0.03-0.06), and QI (2.2-2.9) values and the possible presence of preserved cytoplasm spore-filling within the sporinite grains may indicate that the studied coals have only gas-generation potential. The results also show that the studied coals display relatively lower random vitrinite reflectance (%Rr 0.75–0.82%) and calculated Tpeak values (113-123˚C) using %Rr and micro-Raman spectra than their counterparts in the northern parts of the basin (%Rr 1.18–1.52% and 173–206˚C). This difference seems to be related to the shallower burial depths of the studied coals or to the fact that they experienced relatively lower maximum attained temperatures than the northern parts of the basin. Furthermore, the coal petrography and SEM-EDS data also suggest that the post-coalification tectonic deformation in the study area created space for circulating Ca- and Si-rich solutions within the coal seams and controlled epigenetic mineralization. Nevertheless, the redox conditions and clastic influx into the palaeomires also controlled syngenetic mineral formations, similar to the other parts of the basin.
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