New constraints on timing of Hidalgoan (Laramide) deformation in the Parras and La Popa basins, NE Mexico

摘要

The Parras and La Popa basins of northeastern Mexico together contain at least three separate types of structures that were active during Maastrichtian through Early Eocene time. These structures include salt diapirs and salt welds, E-W trending anticlines detached within the Campanian Parras shale, and large NW-SE trending anticlines detached within the Jurassic salt layers. The oldest halokinetic structure, the La Popa salt weld, began to form by Late Aptian time. This structure is parallel to the later NW-SE contractional folds, but it pre-dates regional contraction. The earliest dated contractional structures in the Sierra Madre Oriental are E-W trending folds and faults found east of the La Popa syncline. These structures were active only briefly during the deposition of the lower Maastrichtian Muerto Formation. Very similar east-west structures in the northern Parras Basin contain growth strata of upper Maastrichtian and Paleocene age. Folding of upper Paleocene beds indicates that this shortening continued into the Eocene. Very Large amplitude NW-SE trending anticlines in La Popa Basin also formed due to regional contraction, and they clearly re-fold the shallow-detached E-W set. Regional evidence suggests that all contractional deformation ceased around 40 Ma. Salt withdrawal may have continued after the cessation of contractional deformation. The contractional deformation in these basins is similar in structural style to the Sevier orogen in the U. S. A., but it is later and of shorter duration than the Sevier orogeny; it is time-equivalent to the Laramide orogeny, but it differs significantly from the Laramide structural style. Thus, the Mexican orogenic system differs from the U. S. A. orogens. This uniqueness was recognized by Guzmán and De Cserna (1963) who named this deformational event in Mexico the Hidalgoan orogeny.