Field examples of fault-related folds were observed in the south-western margin of the Sirt basin, south-central Libya. Single or paired (conjugate) monoclines, drape synclines, special drag faults can be put in a geometric and evolutionary model, which describes the propagation of basement faults to overlying sediments. At the first stage of evolution the propagating normal or oblique-slip faults show segmentation along-dip direction. Fault segments are separated by continuous, moderately to strongly bended horizons, which show different degrees of diagenesis than surrounding intervals. Fault-related folding and faulting was coeval with lithification of certain carbonate levels. Their gradual cementation increased the rigidity of layers promoting discrete faulting and breaching of fault-related folds. However, folding can be maintained up to the extent when layer dip approaches the dip of the propagating fault zone. This type of deformation can be characteristic for sequences consisted of lithified carbonates sandwiched between thicker marl/shale intervals.
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