Mechanical stratigraphy and folding style of the Lurestan region in the Zagros Fold–Thrust Belt, Iran

Abstract

Abstract: The structural style of the folds from the central part of the Lurestan salient located in the NW portion of the Zagros Fold–Thrust Belt has been studied by constructing a regional balanced cross-section from field data, existing geological maps, seismic profiles, stratigraphic surface sections and well data. The regional balanced structural cross-section that is constructed from the High Zagros Fault to the Mountain Front Fault highlights the difference in the folding style across the area. The vertical and lateral changes in the style of the folding indicate the influence of mechano-stratigraphic contrast between the sedimentary units. Three main décollement levels (the basal Lower Palaeozoic, the intermediate Triassic, and the upper Upper Cretaceous–Lower Palaeocene) have been interpreted. Folds developed during the Zagros Fold–Thrust Belt evolution above and below these décollement horizons are decoupled from each other and are different in both geometry and size. Similarly, thickness and facies changes of some formations across the region cause lateral variation in folding pattern from the north to the south. Polyharmonic folds exist in the south, where the different structural levels are relatively strongly coupled. To the north, however, strongly disharmonic folding occurs where a combination of increased décollement thickness and decreased mechanical competence has led to decoupling at different structural levels. This change in folding style has a direct impact on hydrocarbon exploration in the area. To reduce structural risk in exploration, the incorporation of high-resolution deep seismic data with the surface geology is recommended for future hydrocarbon exploration activities within the Lurestan region.