Folding/faulting interaction in thrust sheet development

Folding and faulting in thrustbelts are interdependent and/or competing processes that have been described in terms of models of fold–thrust interaction (e.g., Berger and Johnson, 1982; Suppe, 1983; Williams and Chapman, 1983; Suppe and Medwedeff, 1984; Jamison, 1987). Over the past decade, several quantitative geometric models, described later, have been developed for thin-skin thrustbelts providing specific relationships between the fault and fold geometries, such as faultbend, fault-propagation and detachment folding (Suppe, 1983; Suppe and Medwedeff, 1984; Jamison, 1987; Chester and Chester, 1990; Erslev, 1991; Epard and Groshong, 1995). In general, these geometric models are based on line-length or area balancing and assume kink-type or tri-shear folding, where flexural slip is the dominant deformation mechanism. Some models have been expanded by adding localized thickening or thinning within the fold, translation along imbricate thrust faults or over ramps, and progressive changes in fold geometry with displacement (e.g., Jamison, 1987; Mitra, 1990, 2002; Suppe and Medwedeff, 1990; Erslev, 1991; Erslev and Mayborn, 1997; Hardy and Ford, 1997; Almendinger, 1998). The models provide guidelines for seismic interpretation and construction of balanced cross sections. They have become valuable tools for defining trap geometry in the subsurface (e.g., Suppe and Namson, 1979; Mitra, 1986; Namson and Davis, 1988; Mount et al., 1990). Because of their geometric basis, however, the models do not allow one to determine why, when, and where a particular process, such as imbrication or detachment, occurs. Neither do they allow the determination of the exact geometrical response of the deforming section, which is unique for each mechanical stratigraphy and character of the faults involved.