Inorganic and Organic Geochemical Characteristics of the Naokelekan Formation in Northeastern Iraq: Implications for Paleoredox Conditions and Organic Maturity

An inorganic and organic geochemical study of rocks of the Naokelekan Formation (Upper Jurassic) from an Imbricated Zone (Halabja section) and a High Folded Zone (Barzinja section) in northeastern Iraq was performed to determine ancient redox conditions and assess hydrocarbon maturity. There are no obvious differences in major oxides and trace elements between the two studied sections. The formation rocks showed a high content of calcium oxide followed by silica oxide, reflecting the dominance of carbonate minerals, as well as a high concentration of trace elements Sr, Ba, V, and Ni. The presence of carbonate minerals as well as clay minerals reflects the effect of oxidation and weathering of organic matter in both study sections. The geochemical parameters of redox conditions V/V+Ni, V/Ni, V/Cr, and U/Th indicate that the formation was deposited under oxygenic conditions and organic matter of continental origin. On the other hand, the organic geochemical study showed the post-maturity conditions due to an increase in Tmax and a decrease in S2 value. In addition, the samples are in the type IV of kerogen due to a decrease in the hydrogen index value, which reflects the effect of high oxidation of both studied sections in the Halabja and Barzanja areas.