Abstract
Over the past few decades, hydrocarbon exploration has considerably improved our understanding of foreland deformation. This study used the interpretation of seismic reflection profiles and cross-section balancing techniques to understand the passive-roof duplex geometry of foreland structures in the Western Sulaiman Fold Belt (SFB), Pakistan. Seismic reflection profiles were interpreted to show the presence of hinterland-vergent fault-propagation and fault-bend folds as prospects over a detachment located at a depth of ∼6 km in the pelitic Triassic succession. Cross-section balancing showed intraplate deformation in the hanging-wall flat of the frontal duplex. Clear seismic reflectors above 3 s two-way travel time (TWT), estimates of stratigraphic and tectonic thicknesses with field geology and isopach mapping were used to locate the décollement in the pelitic Permo-Triassic strata at a depth of ∼11 km and interpret stacked duplexes at the mountain front. The foreland deformation of the western SFB was compared with that of the central/eastern SFB. The comparison shows the presence of discovered gas fields, with intraplate deformation of the duplex in the western, and pop-ups in the roof-sequence in eastern SFB depicting the complexity of deformation for the assessment of hydrocarbon prospectivity in the fold belt. The 33 km deformed balanced cross-section was restored to ∼71 km, with 38 km (54%) shortening in the foreland. Approximately 12 km (17%) of shortening was passively accommodated by the hinterland-vergent out-of-sequence passive backthrust in the frontal horse. This description of foreland deformation using the example of the SFB adds to our understanding of the structures of the mountain front that are recognized as zones of prolific hydrocarbon prospects.
Published Version
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