Structural evolution of southern Kohat fold and thrust belt, a case study from Karak area, Pakistan

Abstract

Structural evolution of Southern Kohat fold and thrust Belt is interpreted through a structural model and two geo-seismic balanced cross sections prepared by integrating dip domain data, seismic data of 96-SHD-

313 and well bore data of Makori East 1. The model and sections reveal the surface and geometries of folds and thrusts and variation of structural style along trend in relation to fold and thrust kinematics. Samana Suk Formation of Jurassic is taken in subsurface seismic data for which time to depth conversion is done and the values are extrapolated to cross sections. The geo-seismic balanced cross sections show that the thrust faults emanating from the sub-basal detachment within the sedimentary cover sequence, because the crystalline basement is not seen in the seismic reflection data. The tight anticlinal and broad synclinal folded structures evolved on Eocene evaporites as detachment folds were truncated by thrust faults along their limbs at surface which relates that folds formed earlier than faults. The structural models show that variation of surface structures along the trend is proved to be the result of variable displacement of thrusts along their strike. The restored cross sections show approximately 7-8 Km of shortening accommodated within the cover sequence by deformation. The research suggests that the Southern Kohat fold and thrust belt is structurally evolved in two distinct of deformation along the multiple detachment horizons. In the first phase detachment folding along Eocene evaporites had accommodated horizontal stratal shortening which is superimposed by vertical crustal telescoping by thrusting emanating from basal detachment.