Stratigraphic, geophysical, and remote sensing evidence shows that the basement of northern Iraq is fragmented at various scales. Two large blocks have been recognized: the northern Mosul block, south of the east-west to west-northwest-east-southeast-trending Taurus suture zone; and the Kirkuk block, southwest of the northwest-southeast-trending Zagros suture zone. These blocks are in turn subdivided into smaller longitudinal blocks (relative to the fold trends). The Mosul block was less stable and more uplifted relative to the Kirkuk block and, therefore, its stratigraphic record is characterized by wider and more extensive erosion and/or periods of nondeposition. This led to a relatively poor development of the Middle Jurassic-Upper Cretaceous potential source rocks ove the Mosul block. The difference in hydrocarbon resources between the Mosul and Kirkuk blocks is apparent from the estimated reserves of oil and gas in each. Development of grabens or half grabens enhanced the already favorable stratigraphic circumstances for the deposition and preservation of potential source rocks in the Kirkuk block and locally improved the otherwise inhibiting environment in the Mosul block. These features show significant difference in their plan shape and relative arrangement in the two blocks. In addition, within each of the large blocks, the synorogenic differential movement on longitudinal basement faults (fault stacking) had a great effect on hydrocarbon generation, migration, and entrapment.

The difference in basement tectonics between the Mosul and Kirkuk blocks reflects a regional difference in the Afro-Arabian plate margin history along the Taurus and Zagros belts.