Abstract The Minas Viejas Formation consists of carbonates and sulfates that are the first evidence of marine incursion into northeastern Mexico during the Late Jurassic (Oxfordian). In the area southwest of Galeana, Nuevo Leon, this evaporite sequence is intensively deformed, but a consistent stratigraphic succession and separation of two members is recognizable. In addition to the Las Minas Member that was defined by Götte (1988), we introduce the La Primavera Member. Our data suggest that only one largely evaporitic succession exists in the region and that the terms Minas Viejas and Olvido are synonyms for the same stratigraphic unit. Lateral and vertical changes of facies in the Minas Viejas Formation are the result of syndepositional normal faulting and relate to the onset of sea-floor spreading in the Gulf of Mexico. Alkaline volcanic rocks occur in the La Primavera Member of the Minas Viejas Formation. This Oxfordian volcanism is hitherto undescribed in the area and links the tectonostratigraphic evolution of northeastern Mexico to early sea-floor spreading in the Gulf of Mexico. In addition, barite deposits in the Galeana area likely are related to this Late Jurassic volcanism. Barite mineralization is restricted mainly to stratigraphic levels older than the alkaline volcanism in the Minas Viejas Formation and is not the result of magmatism of Tertiary age. Apparently, carbonatite magmatism that provided the source for barium by hydrothermal activity was associated with Late Jurassic volcanism.

Abstract The San Luis Basin encompasses the largest structural and hydrologic basin of the Rio Grande rift. On this field trip, we will examine the timing of transition of the San Luis Basin from hydrologically closed, aggrading subbasins to a continuous fluvial system that eroded the basin, formed the Rio Grande gorge, and ultimately, integrated the Rio Grande from Colorado to the Gulf of Mexico. Waning Pleistocene neotectonic activity and onset of major glacial episodes, in particular Marine Isotope Stages 11–2 (~420–14 ka), induced basin fill, spillover, and erosion of the southern San Luis Basin. The combined use of new geologic mapping, fluvial geomorphology, reinterpreted surficial geology of the Taos Plateau, pedogenic relative dating studies, 3 He surface exposure dating of basalts, and U-series dating of pedogenic carbonate supports a sequence of events wherein pluvial Lake Alamosa in the northern San Luis Basin overflowed, and began to drain to the south across the closed Sunshine Valley–Costilla Plain region ≤400 ka. By ~200 ka, erosion had cut through topographic highs at Ute Mountain and the Red River fault zone, and began deep-canyon incision across the southern San Luis Basin. Previous studies indicate that prior to 200 ka, the present Rio Grande terminated into a large bolson complex in the vicinity of El Paso, Texas, and systematic, headward erosional processes had subtly integrated discontinuously connected basins along the eastern flank of the Rio Grande rift and southern Rocky Mountains. We propose that the integration of the entire San Luis Basin into the Rio Grande drainage system (~400–200 ka) was the critical event in the formation of the modern Rio Grande, integrating hinterland basins of the Rio Grande rift from El Paso, Texas, north to the San Luis Basin with the Gulf of Mexico. This event dramatically affected basins southeast of El Paso, Texas, across the Chisos Mountains and southeastern Basin and Range province, including the Rio Conchos watershed and much of the Chihuahuan Desert, inducing broad regional landscape incision and exhumation.

Abstract Middle Eocene compression resulted in formation of the Sierra Madre Oriental fold and thrust belt and end-early Miocene compression resulted in formation of the Chiapas-Campeche fold and thrust belt. These events mask the importance of other periods of deformation, principally in the Middle–Late Jurassic, Late Cretaceous, and Paleogene. Deformation is represented by folding, thick-skinned thrusting, basin inversion, and development of major angular unconformities. Associated features include development of karstification, production of breccias, onlap, lowstand wedges, seeding of carbonate platforms, entry of siliciclastic sediments into carbonate basins, significant switches in input directions of clastic sedimentary systems, initiation of extensional tectonism basinward of the compressive deformation front and igneous activity. We propose that, during the late Mesozoic and the Cenozoic, Pacific plate-margin compressive deformation often extended eastward into the Gulf of Mexico. Two main belts of deformation are identified, which are linked back to Pacific plate-margin processes by postulated deep-seated faults. The first and outer (easternmost) belt is seen on regional seismic lines as a long-wavelength, easterly facing, monoclonal fold that developed close to the transition of thick into thinned continental crust. The Sierra Madre Oriental is the second belt of which the structural history already has been well described in the literature. Where salt is present at depth, compressional events are expressed only as laterally propagated thin-skinned folds and thrusts. These events are of critical importance in that they contribute many unique geologic features that cumulatively give Mexico a world-class petroleum system.