Progressive Rollover Fault-Propagation Folding: A Possible Kinematic Mechanism to Generate Regional-Scale Recumbent Folds in Shallow Foreland Belts

The occurrence of strongly overturned to recumbent anticlines in shallow foreland thrust-fold belts is not well explained by the available geometric models of thrust-related folding when a very large amount of forward shear cannot be assumed and, for growth anticlines, when the tectonic uplift rate is greater than the sedimentation rate. We have developed new geometries for fault-propagation folding (progressive rollover fault-propagation folding) that are suitable for overcoming these problems. In our configuration an outer, right-way-up sector and an overturned sector can grow simultaneously in the forelimb of the tip anticline. They are linked to a recumbent leading syncline. A semiquantitative computation of fracture strain during folding allowed us to define six homogeneously strained rock panels. The location of the most strained panels suggests that an anticlinal breakthrough or a synclinal breakthrough is likely to affect the structure later in its evolution. The outer morphology of the tip anticline in progressive rollover fault-propagation folding resembles a fault-bend fold. This model produces geometries suitable for hydrocarbon trapping