The use of biomarker data for determining the organic geochemical characteristics of kozlu (Zonguldak) carbonifer (westphalian-a) coal units

In this study, organic geochemical characteristics of the samples of Westphalian-A age belonging to Acılık, Domuzcu, and Büyük seams in Kozlu Formation obtained from the mines in Kozlu, Zonguldak (NW Turkey) administered by the Turkish Hard Coal Enterprises (TTK). The pyrolysis analyses to determine the organic geochemical properties demonstrated that the total organic carbon (TOC) contents were high in all three seams (average TOC was 3.65% for Acılık seam, 38.75% for Domuzcu seam, and 27.2% for Büyük seam). The source-rock potential was "very good" in Acılık seam and "excellent" in Domuzcu and Büyük seams. The type of organic matter was determined by the hydrogen and oxygen indexes (HI and OI) to be type III kerogen in Acılık seam and type II-III kerogen in Domuzcu and Büyük seams. Maturity of the samples was assessed with the Tmax and extract values determined by pyrolysis as well as the n-alkane and biomarker parameters determined by gas chromatography (GC) and gas chromatography - mass spectrometer (GC-MS) analyses. All three seams were found to be mature (Acılık seam was mature and Domuzcu and Büyük seams were mature to late mature). The analysis of the deposition medium based on the the distribution of C27, C28, and C29 steranes, sterane/hopane ratio, norhopane/hopane (C29/C30) ratio, changes in homohopane distribution, and the pristane and phytane ratios in n-alkane distributions in the biomarker data demonstrated that all three seams were composed of clastic source rocks of terrestrial origin. Domuzcu and Büyük seams were deposited under oxic conditions. Also Acılık seam were deposited unden anoxic conditions. The predominance of medium-chain n-alkanes in Acılık seam indicates the presence of vascular plants, microalgae, and cyanobacteria, and the predominance of short-chain n-alkanes in Domuzcu and Büyük seams indicates the presence of dense algae and microorganisms. In addition, the samples belonging to Acılık seam were found to have undergone biodegraded.