Browsing by Subject "Sierra Madre Oriental"

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Evaporite deformation in the Sierra Madre Oriental, northeastern Mexico : décollement kinematics in an evaporite-detached thin-skinned fold belt
(2012-05) Cross, Gareth Edwin; Marrett, Randall; Mosher, Sharon; Rowan, Mark; Cloos, Mark; Laubach, Stephen
Décollements are important tectonic elements in thin-skinned fold-thrust belts. However, few studies have addressed the internal structure of décollements because most are deeply buried and internal features typically cannot be resolved in seismic reflection images. Upper Jurassic evaporite exposures in the Potosí uplift of northeastern Mexico provide a unique tectonic window into the décollement of the Laramide-age Sierra Madre Oriental fold belt. In order to constrain the three-dimensional geometry of décollement structures, I mapped a ~20 km2 portion of the décollement at a scale of 1:10,000. I created a new stratigraphy for the décollement interval during mapping, and made detailed structural observations at targeted sites. The ~900 m thick décollement interval consists of gypsum with five carbonate members (up to 120 m thick) and numerous thin (<5 m) carbonate interbeds. These carbonate units delineate map-scale structural patterns and define two structural domains. The middle and upper parts of the décollement in the western domain contain map-scale folds with local map-scale boudinage and thrust faults. The eastern domain exposes the lower part of the décollement, and contains thrust repetitions of carbonate members and a regionally-persistent basal shear zone. These map relationships indicate a stratigraphic variation in structural style. Western domain folds and eastern domain thrust sheets both appear to be related kinematically to overburden folding. In contrast, the basal shear zone accommodated décollement-parallel shear strain in response to overburden translation. Folding and faulting of carbonate members and intervening gypsum units drove localization of simple shear into the basal shear zone, because only the lowermost gypsum interval maintained a favorable orientation sub-parallel to the regional transport direction throughout deformation. This investigation demonstrates that décollements have complex internal structural patterns that are below typical seismic resolution and lateral variations in structural style that cannot be reconstructed from single well cores or small outcrops. Décollement stratigraphy controls variations in strain magnitude within the décollement interval, so that previous models that invoke homogeneous strain within the décollement are incorrect. Complex, laterally-variable structural style and stratigraphic control of strain distribution could be general characteristics of décollements where the décollement interval contains significant contrasts in bed rheology.
Letter to Peter T. Flawn from H.B. Stenzel on 1963-02-13
(1963-02-13) Stenzel, Henryk B.
Soil erosion and geomorphic sensitivity under slash-and-burn agricultural systems, Sierra Madre Oriental, Eastern Mexico
(2012-05) Avwunudiogba, Augustine; Perez, Francisco L.; Hudson, Paul F., 1968-; Butzer, Karl W.; Doolittle, William E.; Maidment, David R.
The response of geomorphic systems to disturbance has been a major focus of geographic research. Nevertheless, because the sensitivity of geomorphic systems to external perturbation is complex, the response of those systems is still poorly understood for many agricultural systems in various geographic settings. This study investigates geomorphic sensitivity and soil erosion under traditional slash-and-burn cultivation. The response of soil erosion to this agricultural practice was investigated in selected plots at different stages of cultivation, representing a chronosequence of slash-and-burn cultivation for the study site. Selected physical and hydrological properties were measured in the field or determined in the laboratory from soil samples obtained from the selected plots. Soil erosion was monitored for the selected plots using bounded runoff plots. Finally, the response of soil erosion to slash-and- burn was assessed at the watershed scale by adapting the Revised Universal Soil Loss Equation to local field conditions. The study results showed that soil’s selected physical and hydrological properties differed according to the age of cultivation. In general, soil properties, such as organic matter, aggregate stability, and infiltration, showed signs of deterioration during the cultivation phase and improvement during the fallow stage of slash-and-burn cultivation. These differences in turn resulted in differences in the erodibility of the soil and the response of soil erosion at the plot scale. The soil erosion rate was observed to be higher during the cultivation stage of slash-and-burn cultivation and lower during the fallow stage. The lowest rate of erosion was recorded in natural forest plots. Overall, soil erosion rates were low considering the study site’s mountainous nature. The results of this study suggest that the response of soil erosion under the practice of slash-and burn cultivation could be minimal in a potentially sensitive humid tropical mountainous environment depending on the specific cover produced, the environmental factors, and the specific cultural management, such as cropping and tilling practices. Maintaining adequate ground cover through cropping and fallow management is the key to keeping soil erosion minimal under the practice of slash-and-burn cultivation in the study area.
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
(2005) Davis, Matthew H., 1975-; Marrett, Randall; Goldhammer, Robert K., 1957-
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