Hydrocarbon generation potential, palynofacies examination and 1D basin modeling of the Middle Jurassic–Lowermost Cretaceous intervals, Mesopotamian Foredeep Basin, Iraq

This study evaluates hydrocarbon generation, palynofacies, and burial-thermal evolution of Middle Jurassic-Lowermost Cretaceous source rocks in the Ajeel Field, located in the Mesopotamian Foredeep Basin of Iraq. Through Rock-Eval pyrolysis, Total organic carbon (TOC) analysis, and palynofacies, a comprehensive investigation of 109 core and cutting samples in wells 8 and 12 was supported by one-dimensional (1D) basin modeling. The geochemical data show a TOC maximum of 23.0 wt.%, with reported mean concentrations of 6.22 wt.% in the Sargelu Formation and 10.09 wt.% in the Naokelekan Formation. The Chia Gara Formation bears a broad range of TOC values, as shown by the heterogeneous depositional environment. Hydrogen Index (HI) values reach 457 mg HC/g TOC, indicating dominance of oil-prone Type II kerogen, particularly in the Naokelekan and Chia Gara formations, and with minor Type II/III kerogen content in the Sargelu Formation interval. The calculated Tmax (428–448 °C) plus the estimated vitrinite reflectance (% Ro: 0.53–0.85 %) can define the maturity range that is characterized by early and peak oil window maturities. Palynofacies data confirm the deposition in suboxic–anoxic environments on the marine shelf, and amorphous organic matter (AOM) varies widely between 1 and 98 %. This has been confirmed as the Bajocian-Berriasian age and marine provenance as demonstrated by the presence of diagnostic palynomorphs. Basin modeling shows that hydrocarbons originated in the Oligocene (∼27 Ma) and were expelled during the Miocene (21-15 Ma). This is also supported by the higher transformation ratio (%TR) values, which reached up to 83 % for Sargelu, up to 70 % for Naokelekan Formation, and up to 50 % for the Chia Gara Formation. These findings confirm the identified formations as the main oil-producing horizons in the basin and emphasize their significance as potential oil exploration activities in northern Iraq.