NATURE AND GEOCHEMISTRY OF OIL SHALE IN NORTHERN IRAQ: XRF AND CONFOCAL RAMAN SPECTROSCOPY METHODS

Geochemistry of oil shale is a good indicator in the determination of sedimentary basins during their formations. Oil shales are widely distributed in Iraq. Sargelu Formation (Middle Jurassic) and Barsarin Formaion (Late Jurassic) which are two of good to excellent and major petroleum source rocks were chosen for the study. Rock samples were collected from the surface outcrops located in Northern Iraq. Geochemical analyses by XRF of the oil shales were investigated and tried to interpret the depositional environments. The calculated data showed that most of the major element contents (oxides %) and the trace element contents (μg/g) are in the same range and almost no differences between the averages, but the MgO, Al₂O₃, Co, Ga, Zr, Sb, Cs, Ce, Pb and Th contents were found to be greater in Barserin Formation than in Sargelu Formation, while the SO₃, CaO, Ni, Ge, Se, Sr, Y, Mo, Cd, Ba and U contents was vice versa. The enrichment or the deficiency factors of the major and the trace elements compared with average shale were done. Raman spectroscopy analysis were used in this study, for the first time in Iraq, to understand the characteristic features of oil shale in Iraq. The results indicate that the organic matter is composed mainly of Type II and III kerogen with inorganic minerals mainly clays, calcites, dolomites and titanium oxides. Barsarin Formation are mainly carbonates (dolomite and limestone), while Sargelu Formation are organic carbonaceous mud rocks with calcite and some dolomite enrichments. The depositional environments for Sargelu Formation shown to be open marine, and the Barsarin formation shallow restricted marine or lagoon.