Uncertainties of balanced sections and the role of basement in the southern Fars area, Iran

Abstract

The frontal Zagros fold belt in the Fars area of Iran is generally considered to be detached on the Hormuz salt. Shortening rates and the proportion of thick-skinned deformation are debated and published balanced sections show large differences in style and amount of deformation. We believe that the main uncertainties are related to stratigraphic thickness variations, the degree of thick-skinned deformation and/or the flexural response of the crust. We analysed the stratigraphic thickness ranges interpreted from seismic data and conclude that the interpretational uncertainties, combined with the uncalibrated interval velocities of the largely undrilled Paleozoic strata, yield a wide range of outcomes for the total Phanerozoic thickness (9.5–16.5 km). With an area balancing approach, we show that geological surface cross sections could be matched by various structural subsurface scenarios, including pure thin-skinned deformation with flexure and/or thick-skinned deformation. Given the input uncertainties, we discuss the merits and shortcomings of our balanced sections and propose a geological model including a subtle control on the deformation style by the inherited pre-salt basin morphology. Given the uncertainties, we conclude that the contribution of thick-skinned deformation to the structural evolution remains indefinite and published shortening values may be much more unconstrained than typically specified.