Paper No. 1
Presentation Time: 8:00 AM
Style and Timing of Laramide Deformation in Northeastern Mexico
The style of Late Cretaceous and Paleogene crustal shortening in northeastern Mexico, broadly termed Laramide or Hidalgoan deformation, was strongly preconditioned by basement structure and pre-Laramide Mesozoic stratigraphy. Three structural styles comprise the Laramide province, which includes the Sierra Madre Oriental orogen and its foreland, a region of inverted extensional basins: (1) Large-scale upright, isoclinal folds detached on Jurassic evaporite and involving the entire preserved post-Callovian stratigraphic section; (2) west-trending detachment and fault-propagation folds of moderate scale with multiple decollements in Upper Cretaceous shale; (3) steep basement faults with dominant reverse displacement that accommodated partial inversion of Jurassic extensional basins in the foreland. Large-scale detachment folds are dominant in the former salt basins of the Sierra Madre and the Sabinas and La Popa basins in the foreland, whereas moderate scale folds dominate in the Parras basin, which lacks Jurassic salt. Steep faults that core large-scale folds flank several large basement blocks in the foreland. Lack of a regional detachment surface suggests that basement shortening accompanied development of salt-detached folds across the foreland.
Timing of shortening, although not well constrained throughout the orogen, appears to have been controlled by the development of a strongly coupled, subducted Farallon slab following Cretaceous consolidation and accretion of oceanic rocks in western Mexico. Flexural subsidence that records development of the Sierra Madre fold belt began in the Campanian. Early Maastrichtian influx of volcanogenic sediment with near-depositional detrital zircon ages suggests that foreland shortening was coeval with, and thus related to, voluminous magmatism in western Mexico. Refolding patterns indicate that shale-detached folds in the Parras basin predate salt-detached folds in La Popa and, by extension, Sabinas basins. La Popa folds began to form in mid-Maastrichtian time and continued through the middle Eocene, the age of youngest preserved strata in the foreland.