Publications
Structural restoration of complex stratal geometries: reconstructing the evolution of a flared salt diapir, La Popa Basin, Mexico, Geological Society of London, Modern developments in structural interpretation, validation and modelling II, 2000, Mark G. Rowan, Timothy F. Lawton, Katherine A. Giles, Robert A. Ratliff
El Papalote diapir is an exposed salt stock located in La Popa Basin, northwest of Monterrey, Mexico. It is elliptical in plan view (approximately 1x2 km) and is surrounded by deformed rocks of Maastricthian to Eocene age. These strata include marine to nonmarine sandstones, siltstones, and shales deposited in the foreland basin of the Sierra Madre Oriental, as well as local carbonate "lentils" that rimmed and/or covered the bathymetric high created by the growing passive diapir. The edge of El Papalote is approximately vertical on three sides, where it is flanked by vertical strata that gradually return to regional dip within less than 1 km from the diapir. However, on the southeastern flank the diapir flares laterally, with the edge dipping 35 degrees to the northwest. Adjacent stratal geometries are highly complex. The lentil and associated siliciclastics that immediately border the diapir are folded through vertical to completely overturned, subhorizontal dips. This overturned flap is truncated by a presently vertical unconformity at the base of the next lentil/siliciclastic halokinetic sequence. The vertical beds are in turn completely overturned before being truncated by another vertical unconformity, overlain by strata that gradually decrease in dip away from the diapir. Established techniques for structural restoration are inadequate for reconstructing the evolution of El Papalote diapir and its adjoining strata: vertical and inclined shear fail where bedding is parallel to the shear direction, which must be the case for all shear angles because of the range of bedding dips; flexural slip, appropriate for constant-thickness strata, imposes slip surfaces at high angles to bedding; and block rotation creates space problems because of the lack of accommodating faults. We therefore apply complex geometry, a new kinematic model that provides a more accurate representation of the observed geometry and its deformation history owing to its ability to arbitrarily mix vertical/inclined shear with non-parallel flexural slip. The restored configurations and predicted strain distributions realistically illustrate the progressive pattern of repeated subsidence and deposition, inflation and erosion, and salt extrusion and associated stratal deformation along the flank of El Papalote diapir.
