Sedimentological Study of the Hartha Formation in Selected Oilfields, Northern Iraq

Abstract

The Hartha Formation (late Campanian–Maastrichtian) is one of the most important carbonate hydrocarbon reservoirs in Iraq. Previous studies have focused on stratigraphic and lithological characteristics of the Hartha Formation in the middle and southern parts of Iraq, while this study focuses on the reconstruction of its facies architecture and stratigraphic successions in five oilfields the north and northwestern parts of Iraq. Its thicknesses were recorded for all of the wells studied, along with the occurrences of benthonic foraminifera, rudists, echinoderms, coral, algae and peloids. The main diagenetic processes affecting the formation include dolomitization, cementation, silicification, compaction and micritization. Eleven microfacies are recognized, representing four facies association: outer shelf (I), fore reef and shoal (II), rudist reef and restricted platform (III) and (IV) lagoon. These facies associations occur in a predictable order reflecting regressive shallowing-upward sequences. Lateral facies variation shows that fore reef and shoal environments dominate the Hartha succession, suggesting that it corresponds to a ramp-type carbonate platform depositional model.