ORGANIC GEOCHEMICAL CHARACTERISTICS OF ŞIRNAK ASPHALTITES IN SOUTHEAST ANATOLIA, TURKEY

In this study, the organic geochemical properties of asphaltites in Sirnak region in Southeast Anatolia are given in detail. Total organic carbon, Rock-Eval pyrolysis, gas chromatography of saturated fractions, gas chromatography-mass spectrometry and stable carbon isotope ([δ.sup.13] C in ‰/PDB) analysis were conducted on the Sirnak region asphaltite seams. Some of these analyses were performed for the host rocks as well. It is suggested that a live oil seep occurs within asphaltites, which themselves may be formed in a multiple phase system. The amount of total organic matter in asphaltites is high as would be expected, ranging from 12 to 73%. In contrast, this amount is low in the host rocks (0.6-6.3%). The [T.sub.max] values are generally between 428°C and 451°C. The hydrogen index (HI) values vary between 270 and 541 mg HC/g TOC. The hydrogen index values and [T.sub.max] values of the host rocks are significantly lower. The GC analyses have shown that the saturated fractions of all asphaltite samples were not biodegraded. Consequently, organic geochemical parameters such as Hopane/Hopane + Moretane, [T.sub.s]/[T.sub.m], 22S/22S + 22R and the values of %[C.sub.27], %[C.sub.28], %[C.sub.29] steranes obtained as a result of GC-MS analysis were used for maturity assessments. Although the organic geochemical parameters provided some data for the origin and placing mechanism, it is concluded that they are not sufficient for an overall conclusion, especially concerning placing mechanism. Therefore, new studies particularly on local and regional geological aspects need to be undertaken.