Masoumeh Vatandoust

Compression of a region containing multiple detachment layers produces large-scale disharmonic folding, where individual competent units separated by detachment fold independently within the succession. Here, we present a case study of the kinematic evolution of three subsurface structures (the Karanj, Paranj and Parsi oilfields) bounded by multiple detachments, located in the southern Dezful Embayment, a major petroleum province of the Zagros Fold-Thrust Belt in SW Iran. Interpretation of seismic sections and the construction of corresponding balanced cross-sections reveals different geometries along the folds and the complete decoupling of these structures from the surface geology. This is controlled by the reactivation of basement faults, and flow of the Gachsaran incompetent units (Miocene) as the upper detachment, and the Kazhdumi (Upper Cretaceous), Pabdeh-Gurpi and Dashtak Formations as the middle detachments, respectively. Detachment folding with limb rotation started in the Middle Miocene and continued with the migration of the basal detachment horizon (equivalent Hormuz series) into the core of the anticlines. Flow of both the basal and upper detachments continued until no more material is available, whereupon the shortening is accommodated by fault development. The development of a decoupled, disharmonic folding style was controlled by the upper detachment surface through migration from the crests of the anticlines to the synclinal areas and by the reactivation of the basement faults. From NW to SE part of the area The total shortening amounts are changed between 21% and 12%.