Evolution of Fault-Related Folds and their Hydrocarbon Trapping Potential: Kurdistan Region of Iraq

Zebari, Mjahid; Burberry, Caroline M.

The Zagros Fold-Thrust Belt in Northern Iraq has propagated ~300 km to the foreland from the collision zone at the northeastern edge of the Arabian Plate. This study concentrates on understanding the kinematic evolution of folds within a part of the Zagros Fold-Thrust Belt in the Kurdistan Region of Iraq, by constructing models for the deformation geometry of specific folds and their associated thrusts at depth. Trapping potential of these folds with respect to the related faults and deformation in sedimentary cover units is also considered. Cross-sections constructed from field data and geomorphic indices of folds measured from satellite images are used to provide data for understanding the kinematic evolution of the folds in the study area. The aspect ratio of folds and fold symmetry index, which are calculated from the hinge length of the fold, fold width and forelimb width, are 4:1-11:1 and 0.87-1.09 respectively, implying that folds are transitional between fault-bend folds and fault propagation folds. Folds are broad and box shaped with open to gentle inter-limb angles. The fold wavelength indicates that the main detachment is in the Triassic units, and that there may be some involvement of reactivated basement faults. Thus, cross-sections are constructed with the main structures as fault-bend (e.g. Harir Anticline) or fault-propagation folds (e.g. Safin Anticline). Overall shortening is calculated at ~14% in the east of the study area and ~23% in the west. The broad folds are known to act as hydrocarbon traps in the surrounding area (e.g. Shaikan) with the associated faults acting as seals at depth. Bitumen seepage through fractures and pores in the Upper Cretaceous units in the study area is due to erosion of the Tertiary seal units. Seepage is not observed along major thrusts (e. g. Harir Thrust). Thus, faults are likely to be sealing faults, and there is a high probability that the Jurassic and Triassic systems are intact at depth.

AAPG Search and Discovery Article #90163©2013AAPG 2013 Annual Convention and Exhibition, Pittsburgh, Pennsylvania, May 19-22, 2013