The tectonics of Tranquitas : a field study of rift through passive margin development and Laramide deformation in Triassic and Jurassic strata of the Sierra Madre Oriental, NE Mexico

Abstract

Exposed near Galeana, Nuevo Leon are sedimentary deposits and contemporaneous structures that record the rifting and opening of the Gulf of Mexico, passive-margin development, and Laramide compression in the region. A mapping, sedimentologic, and structural study utilizing thin sections, measured sections, aerial photos and kinematics has produced a detailed stratigraphic section that records the transition from terrestrial to open marine deposition and the orientation and timing of deformational events. Triassic to Early Jurassic red beds in the Huizachal Group are composed of fluvial and marine sands. The La Boca and La Joya Formations, respectively, are separated by a polymictic cobble conglomerate. The Callovian Minas Viejas represents the initial stages of marine transgression and the overlying interbedded carbonates and evaporites of the Zuloaga and Olvido Formations respond to cyclic eustatic sea-level fluxuations. The increase of biodiversity through the upper Jurassic strata reflects a change from restricted to open-marine conditions. Rift-related tectonics and gravity driven brittle extension features within the carbonates have been overprinted by Laramide orogenesis. The red beds have been folded and faulted into a broad Laramide anticlinorium with smaller intrusion cored folds having amplitudes on the order of 10's of meters. Within the evaporite lies the decollement for Laramide thin-skinned deformation, thus there is a high degree of structural complexity represented in the overlying carbonates as tight folding patterns. By integrating concepts of depositional systems with structural deformation the hypothesis, "There is an exhumed preraft block in the Zuloaga Limestone around San Pablo de Tranquitas." will be tested