Organic-geochemical characteristics of the Miocene Lycian Basin, western Taurides, Turkey

Abstract

In the Lycian Basin (SW Turkey), the Miocene Karabayr and Karakustepe formations consist of algal limestone, conglomerate, sandstone, shale and limestone. Total organic carbon (TOC) analysis of the Miocene units show that these formations are poor in organic matter. TOC values are generally between 0.02 and 0.51%, but reach 3.47% in the Karabayr Formation. Hydrogen indices (HI) are mostly below 600mgHC/gTOC, increasing to 1200mgHC/gTOC in the Karabayr Formation. S2 vs. TOC diagrams are used to evaluate the sedimentary environments and hydrocarbon potential of the Lower-Middle Miocene sediments (the Isparta, Bucak and Korkuteli-Elmal areas). The organic material contains about 63 (type I), 35 (type II) and 29 (type II/III) pyrolysable hydrocarbons, respectively. The dominant organic matter is type II kerogens, and hydrocarbon generating potential is quite low. A positive x-intercept has been calculated in analysed samples according to S2 vs. TOC diagrams; this value shows a rock-matrix effect. Clay is the main agent of adsorption. Biomarker characteristics also verify these results. Isoprenoid rates are Pr/Ph: 2, Pr/n-C17: 1.9, and Pr/n-C18: 0.5, and a high Pr/Ph ratio (pristane/phytane) indicates an oxic environment; the terpane C29 NH/C30 H ratio is 1 for the Karabayr Formation, and this value indicates a carbonate lithology. On the other hand, the C25 NH/C30 H ratio is 1 for the Karakustepe Formation; this indicates that the hydrocarbons were derived from terrestrial organic matter. According to m/z 191 mass fragmentograms, the Miocene units contain oleanane, indicating a Tertiary age. The abundance of sterane C29C28C27 shows that the kerogens formed from algal organic matter.