Basement-Involved Structural Styles along the Eastern Sulaiman Ranges Front, Pakistan

Sajjad, Ahmad; Irfan Mohammad, Khan; Gohar, Rehman; Abdul, Qayyum

An approximately 320 km long belt of Mesozoic-cored folds is situated along the eastern topographic front of the Sulaiman ranges abutting the Sulaiman foredeep and Indus basin in the east. This fold belt is about 20 km wide, north-northeast oriented and display en echelon geometric pattern. Despite the fact that all major anticlines are characterised by greater structural uplift, yet most of them are not associated with major surface faults. To better constrain the structural style of this important fold belt, the Fort Munro anticline was studied in detail taking into account the available 2-D seismic, remote sensing and surface geological data. The Fort Munro anticline is an asymmetric, doubly plunging and east-facing anticline with a strike length of about 95 km. The axial trace of the anticline is curvilinear, north-northeast oriented with a clear convexity towards east-southeast. Back limb dips are in the range of 8°-15° whereas its fore limb dips are recorded in the range of 45°-60°. The back limb of Fort Munro anticline is very long having 13 km of map length whereas contrastingly its fore limb is very short up to 3 km long and lacks any prominent emergent fault. Its longer back limb appears like westward dipping monocline and the profile shape slightly resemble the geometry of a monoclinal anticline. 2-D-3-D structural modelling of Fort Munro anticline shows that its genesis is related to a basement-related, steeply west dipping reverse fault. The displacement in basement at depth along the fault is consumed in folding at higher structural levels with attenuation in Triassic and Jurassic shales. It is inferred that the Mesozoic-cored fold belt occupying the eastern topographic front of the Sulaiman ranges is characterised by basement involved deformation with concomitant left lateral wrenching. This belt may be having significant hydrocarbon accumulations in four way closures at Jurassic and older rocks being located in close proximity to the Indus basin kitchen in the east.

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