Stratigraphy, structure and hydrocarbon potential of the Ordovician-Devonian succession of northern Iraq: a multidisciplinary, field-based study

Geological research in Iraq has been restricted by conflict and a lack of investment. One consequence of this lack of local data is that many of the geological models and stratigraphic interpretations applied to Iraq are interpolated from adjoining countries. Most recent geological research in Iraq has focussed on the important Mesozoic petroleum plays in the south east of the country. However, the Paleozoic succession of Iraq also contains proven and potential hydrocarbon plays that require further research. Paleozoic sediments outcrop only in the Western Desert (Rutbah-Ga’ara area) and the Taurus Mountains. Recent publications on the Paleozoic stratigraphy of Iraq are based primarily on subsurface data and, to date, the most complete field descriptions of the Paleozoic outcrops of northern Iraq are those published in the 1950’s (Van Bellen et al., 1959; Wetzel and Morton, 1952; Wetzel, 1950).

This study is based on observations and measurements made at the Khabour and Ora sections in the Taurus Mountains of Northern Iraq during 3 field seasons, combined with analysis of samples collected both at outcrop and from the Akkas-1, Akkas-3 and KH5/1 wells. The main results are: 1) Detailed sedimentological observations provide new insights into Paleozoic depositional environments at the northern margin of Gondwana. 2) Palynology studies can help to constrain the age of the Paleozoic succession at outcrop and to improve correlation between the outcrops in northern Iraq and the subsurface. 3) TOC/pyrolysis and geochemical analysis of shale samples from both the Khabour (Ordovician) and Akkas (Silurian) formations indicate they have good source potential. Silurian “hot” shales in Iraq are part of a regionally important source interval and are proven source rocks in the Akkas region, but have been eroded in northern Iraq. The source potential of shales in the Khabour Formation is less well understood but they are present in northern Iraq. 4) Petrographic, heavy mineral provenance and mineral geochemistry data provide new information on the composition, provenance, diagenetic history and reservoir characteristics of sandstones in the Khabour, Akkas and Pirispiki (Devonian) formations. Sandstones in the Khabour and Akkas formations are proven reservoirs in the Akkas region. 5) A structural transect through the Taurus mountains helps to constrain the nature, intensity and extent of Paleozoic deformation events in northern Iraq as a first step toward quantifying their impact on sedimentation patterns and hydrocarbon systems. The results of this research shed new light on the formation and subsequent evolution of Paleozoic sedimentary basins along the northern margin of Gondwana, however, many fundamental questions remain regarding the Paleozoic of Iraq and its petroleum systems.