Organic geochemical properties of coal units in Soylu village (Hayrabolu - Tekirdağ)

The research area is located at the intersection of Malkara and Hayrabolu district borders, 45 km west of Tekirdağ province city center, located in the Thrace Basin. While the base of the region is formed by the rocks of Paleozoic - Upper Cretaceous era, sedimentation has occurred in the study area starting from the Eocene to the Quaternary. The Thrace Basin is significant due to its coal and hydrocarbon potential. In order to determine the organic geochemical properties of coal and coal units, Total Organic Carbon, Rock-Eval pyrolysis, organic petrographic examination, and GC and GC-MS analyses were conducted. With the results, the type, quantity and aging levels of the organic matter and the properties of the sedimentary basin have been identified. The investigated coal units belong to the Oligocene aged Danişmen Formation. These units contain quartz, calcite, clay minerals, dolomite, aragonite, feldspar group minerals. Pyrite formation is abundantly seen within coal. The clay minerals observed at high rates are smectite, illite, kaolinite and chlorite in order of abundance. In accordance with the TOC and Rock-Eval pyrolysis results, the amount of organic matter varies from 0.22% to 49.83% and is generally high. In general, formation of organic materials (Type III kerogen) of terrestrial origin can be seen. According to the Tmax results, an average of 425.4°C was obtained; indicating an organic matter not aged enough. This finding is also supported by the results of vitrinite/huminite reflection. In reference to these results, it is seen that the source rock of the organic matter has a gas origin potential. With the organic petrographic examination, the presence of huminite, liptinite and inertinite maceral groups is determined. The most dominant among these is the huminite group with a presence over 54%. In accordance with the GC analyses, n-alkane distribution is between nC15-nC35 and displays bimodal or skewed n-alkane distribution towards the nC23-nC35 sequence. This indicates a high terrestrial plant input. OEP (1.80-2.63) and CPI (1.74-3.78) levels indicate immature organic matter in the OEP-CPI diagram. Normal alkane and isoprenoid data verify that the organic matter accumulates in lacustrine sediment environment conditions. The higher terrestrial/aquatic ratio (TAR) indicates more terrestrial input to the basin than aquatic sources. The TAR varies between 13.70-23.36 and indicates terrestrial input. C29/C30 ratio shows high value (9.03-19.17) in coal samples, which shows carbonate source rock. The gammacerane index varies between 0.11-0.30 and indicates salt-free or low-salt environment.