Mechanical stability model of progradational carbonate platform margins under tectonic loads: Deformation of Cretaceous carbonate platforms in the Sierra Madre Oriental fold‐thrust belt (east central Mexico)

Abstract

Shortening in the Sierra Madre Oriental fold-thrust belt (east central Mexico) is localized along the margins of Cretaceous carbonate platforms and controlled by mechanical stratigraphy. The platform margins are deformed by imbricate series of thrust ramps, whereas the coeval basins and platform interiors are deformed by map-scale detachment folds. Here we present a finite element model to evaluate the influence of the boundary geometry and boundary conditions on the style of deformation observed at these basinward progradational platform margins. We calculate the stress distribution in a linearly elastic platform-basin transition zone under the action of horizontal tectonic stress, taking into account changes of rock mechanical properties across the platform margin, as well as their dependence on direction, and infer the resulting fracture patterns based on the Mohr-Coulomb failure criterion. Stress concentrations are predicted at the contacts between the massive rocks of the platform margin and the well-layered rocks of both, the platform interior and the adjacent basin. Brittle failure of the platform border can be mostly attributed to three effects: mechanical coupling between the carbonate platform and a substratum of moderate to low viscosity, variations in layering and texture that governed the mechanical properties of the involved carbonates as well as their dependence on direction, and the development of sharp domain boundary corners associated with progradational facies changes. In contrast, the dip of the basement and a possible taper of the overlying Upper Cretaceous shale toward the basin appear to have little influence on the mechanical failure of the platform margin.

Early 19th Century Geologic Studies of the Zimapán Region, Central Mexico

“…Werner's system did not recognize motions of the continental crust as a cause of inclined strata. An increasing amount of observations of map-scale folds and faults and their geomechanical explanation would only happen some 20 years later, in the middle of the 19 th century (e.g., Darwin, 1840), and shortening by large-scale thrust faults of the Sierra Madre Oriental fold-thrust belt (Carrillo-Martínez and Suter, 1982;Suter, 1987;Suter et al, 1997;Contreras and Suter, 2015) and crustal extension by a system of major Cenozoic normal faults (Aljibes half-graben, Suter et al, 1995) would, in the Zimapán area, only be recognized in the late 20 th century. No further geologic studies seem to have been published about the Zimapán area after Galeotti's until the last third of the 19 th century, a time of scientific renovation.…”