Geochemical properties and heavy metal contents of carbonaceous rocks in the Pliocene siliciclastic rock sequence from southeastern Denizli-Turkey

Pliocene-aged carbonaceous rocks of varying thicknesses, alternating with siliciclastic and carbonate rock units, are located on the northern border of the cameli-Acipayam basin (in southwestern Turkey), which is filled with thick Neogene sediments. Organic and inorganic geochemical properties of carbonaceous rocks were examined to evaluate their hydrocarbon production potential and paleo-depositional conditions (provenance, paleoclimate, paleosalinity, paleoredox, weathering, heavy metal contents, etc.). Based on organic geochemical analysis, carbonaceous rocks show good to excellent source rock potential and have gas production potential. Organic substances are mostly of allochthonous origin, and their thermal maturity degree is quite low. Carbonaceous rocks have a high amount of inorganic substance (minerals) composed of quartz, clay + mica minerals (mostly illite and a lesser amount of smectite, chlorite, and kaolinite), feldspar, and opaque minerals (pyrite and ilmenite). Although carbonaceous rocks have similar major oxide and trace element concentrations, they show clear differences in terms of Fe2O3, MgO, and some heavy metals (such as Ni, Cr, Co, V, and Sc). The major oxide, trace element concentrations, various element ratios of carbonaceous rocks bear the characteristics of mafic/ultramafic magmatic rocks formed on the active continental margin. In addition, carbonaceous rocks were precipitated in a brackish water environment under oxic conditions. The sediments, which were rapidly stored without recycling in the deposition environment where hot/humid climatic conditions are effective, did not undergo intense decomposition in the source area.