Structural Style in the Zagros: Implications for Hydrocarbon Systems

The Zagros mountain belt through Iran and the Kurdistan Region of Iraq is characterised by world class structural traps and stacked fractured reservoirs. Despite the apparent simplicity of many four-way traps seen at surface in satellite imagery, most anticlines show significant structural complexity, arising from a combination of several key factors:
1. The pronounced mechanical stratigraphy of the cover sequence, characterised by mechanically strong platform carbonates, alternating with thick packages of weak shales, mudstones and evaporites. This exerts a fundamental control on folding and thrusting, the resultant trap geometry and integrity, and the development of pervasive fracture networks.
2. Structural inheritance, both from reactivation of early regional fracture sets seen in basement rocks of the Arabian shield, and the postulated inversion of Tethyan rift structures that remain poorly imaged at present.
3. The oblique close of the Tethys ocean, and the consequent transpressional development of the Zagros.
Collectively these factors have a profound effect on hydrocarbon systems through the region, and make the structural style of the Zagros very different to classic fold and thrust belts such as the Rockies, Alps or Himalayas.