Structural interpretation of frontal folds and hydrocarbon exploration, western sulaiman fold belt, Pakistan

• Published in: Marine and petroleum geology Vol. 117; p. 104380
• Main Authors: Jadoon, Ishtiaq A.K., Ding, Lin, Nazir, Jabir, Idrees, Muhammad, Jadoon, Saif-ur-Rehman K.
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 01.07.2020
• Subjects: Fault-propagation and fault-bend folds; Foreland deformation; Hydrocarbon exploration; Out-of-sequence structures; Passive-roof duplex; Hydrocarbon exploration; Passive-roof duplex; Fault-propagation and fault-bend folds; Out-of-sequence structures; Foreland deformation
• ISSN: 0264-8172; 1873-4073
• DOI: 10.1016/j.marpetgeo.2020.104380

Seismic reflection profiles and borehole data combined with geological mapping was used to analyze foreland structures with 3-D structural variation, estimates of shortening, and kinematic evolution of western Sulaiman fold belt (SFB), Pakistan. The western SFB is interpreted with passive-roof duplex geometry. The floor thrust (décollement) is interpreted in Triassic strata rather than its inference in Precambrian-Cambrian evaporites. Whereas, the roof thrust (upper detachment) of hinterland vergence is located in Eocene Ghazij shale. Based on seismic data, the folds in the frontal duplex are interpreted as fault-propagation and fault-bend type. They are located over curved and staircase geometry of blind back thrusts. The folds-and-thrusts of EW trend show right-hand en-echelon stepping along NW-SE oriented mountain front due to drag along the western margin of the fold belt. The blind thrusts cut across the hanging-wall flat of the duplex horse with roots in base Triassic at depth of ~4–4.5 km 3D surfaces of reservoir strata show three areas of closed elliptical contours as potential prospects over blind thrusts, with maximum structural relief of ~2200 m. Shortening of 2100 (22%) and 9950 m (47%) is calculated along with thrusts in the frontal duplex with the interpretation of out-of-sequence structures. Passive roof duplex structures between foreland and hinterland vergent back-thrusts are reported from mountain belts around the world. We have identified out-of-sequence deformation in the frontal duplex with stacked structures. Identification of these features adds to our understanding of the development of mountain fronts in the context of Anderson's theory of faulting with the presence of a conjugate set of faults and foreland propagation of mountain fronts with secondary out-of-sequence deformation. Subsurface seismic data appears to be critical in their recognition for analysis of active foreland deformation and assessment of hydrocarbon plays in the fold belts. •Foreland deformation.•Hinterland-vergent fault-propagation and fault-bend folds.•Passive-roof duplex and out-of-sequence deformation.•Structural variation and shortening.•Implications on hydrocarbon exploration.