ABSTRACT Upper Triassic and Lower to Middle Jurassic strata in the Plomosas uplift of central Chihuahua accumulated in backarc and rift settings, respectively. The succession, as much as ~3250 m thick, consists of four stratigraphic units. The Cerro El Carrizalillo Formation (Carnian–Norian), a volcanic-lithic shallow-marine succession deposited in the (newly named) El Carrizalillo backarc basin, is characterized by predominantly Triassic detrital zircon ages. The overlying Plomosas Formation consists of three members: (1) the Cerro de Enmedio Member (Hettangian–Toarcian), a succession of conglomerate, siltstone, and shallow-marine carbonate strata deposited during the onset of extension in Chihuahua; (2) the Cerro Nevado Ignimbrite Member (176 ± 1 Ma; late Toarcian), a widespread ash-flow tuff; and (3) La Sofía Member (Aalenian–Callovian?), consisting of alluvial-fan conglomerate, fluvial sandstone, tidal sandstone and siltstone, and delta-plain red beds characterized by rapid facies changes, lithic compositions, and diverse Proterozoic, Paleozoic, and Triassic detrital zircon ages characteristic of a rift-basin setting. The extensional basin in which the Cerro de Enmedio and La Sofía members accumulated is termed the Plomosas basin. Improved age control provided by U-Pb maximum depositional ages from detrital zircon and U-Pb zircon analyses of the ignimbrite indicates that the Cerro El Carrizalillo Formation is partly correlative with the Chinle Formation of the Colorado Plateau, and the Plomosas Formation is equivalent to eolianites of the Glen Canyon and San Rafael Groups of the Colorado Plateau. Detrital zircon ages and sandstone textures are consistent with both proximal and distal sediment sources along the Laurentia-Gondwana suture and adjoining Grenville basement of Laurentia, including sources in northern Mexico and the composite Appalachian orogen. Although the depositional setting of the Cerro El Carrizalillo Formation was not connected to fluvial systems of the Chinle Formation, subsequent eolian transport of voluminous sediment to the overlying Cerro de Enmedio and La Sofía members from the Colorado Plateau ergs is suggested by the composition and texture of some sandstone, thick siltstone accumulations, and detrital zircon characteristics that broadly resemble those of the Colorado Plateau eolianites. Thick siltstone in the upper part of La Sofía Member is interpreted as deflated fine-grained sediment that was transported downwind from a time-equivalent erg to accumulate in shallow-marine and coastal-plain settings of the Plomosas basin.

Abstract The mine caves of Naica (Chihuahua, Mexico) are famous because they host large gypsum crystals. Mine works intersected new caves hosting the largest crystals in the world in the year 2000. From 2006 these caves became the object of a multidisciplinary research project with the goal of inferring their ages, the boundary conditions for their formation and the mechanisms inducing their development. Several other scientific aspects were also considered, including palynology, mineralogy, microbiology, physiology, hydrogeology and astrobiology. From 2006 to 2009, scientists and explorers tried to ensure the complete documentation of these natural wonders because they were expected to be accessible for only a few years. As a result of their location c. 160 m below the natural groundwater level, they were predicted to be flooded with thermal water as soon as dewatering of the mine ceased. This occurred at the end of 2015, so that the lower part of the mine is already submerged and in the near future the giant crystal caves will also disappear. Theoretically, it is still possible to maintain these incredible wonders for future generations, but this seems highly unlikely. Soon the crystals will be submerged below c. 150 m of hot water, restarting their incredible slow growth.

Tascotal Mesa fault is the principal component of Tascotal Mesa transfer zone within the Rio Grande rift of Texas (USA) and Chihuahua (Mexico). Strata and structures along the zone attest to ~290 m.y. of tectonic and magmatic activity, from at least late Paleozoic time onward. The transfer zone comprises the Tascotal Mesa and newly documented Christmas Mountains–Grapevine Hills faults, as well as the Terlingua Creek pull-apart complex at the right step between those two dextral zones. Strike-slip (to ~1 km) and dip-slip (to ~735 m) displacements have occurred in the zone during the past 30–27 m.y.; young faults of the transfer zone displace mid-Pleistocene caliches. Stable isotope and palynologic data from travertines in the transfer zone indicate ascent of warm waters (25°–35 °C) along faults as recently as mid- to late Pleistocene time. Older, basement-rooted structural anisotropies are present in the Tascotal Mesa transfer zone but not all have been reactivated during Cenozoic rifting. Geophysically constrained physical models integrated with field data demonstrate that the Terlingua Creek pull-apart basin likely formed in cover strata that were detached from basement, as the orientations of surficial and buried basement structures differ markedly. Dip-slip displacement predominates on pull-apart faults, with significant dextral slip. Analysis of the role of the Tascotal Mesa transfer zone in Rio Grande rifting revealed that it and the flanking grabens (Presidio to the northwest; Redford to the southeast) are all parts of the Border Corridor transform zone. This transform zone interconnects rift segments from Mesilla graben to the Sunken Block and includes both transfer zones and grabens. Right-transtensional deformation, as manifested in historic earthquakes, accounts for differing orientations of transform (northwest) versus rift (north) grabens. Petrographic and geochronologic data indicate ascent of lavas of rift geochemical character in both the Tascotal Mesa transfer zone and the Border Corridor transform zone from ca. 30 Ma onward. K-Ar ages were determined for basalt (24.73 ± 1.96 Ma) and trachyte (25.42 ± 0.64 Ma) emplaced within the Tascotal Mesa transfer zone. Magmatism is bimodal; olivine basalt and/or hawaiite predominates. Basalts at the junctions of rift grabens and the Border Corridor transform zone entrain mantle and lower-crustal xenoliths.

Abstract Of all the countries in the world considered to be oil rich, Mexico is the only one that consistently has been losing production and reserves in the last ten years. Even though Mexico has five major producing provinces: two for oil (the Southeast and the Tampico–Misantla basins) and three for gas (the Sabinas, Burgos and Veracruz basins), and has seven more with potential, (California, Gulf of Cortès, Chihuahua, Sierra Madre Oriental, Sierra de Chiapas, Progreso shelf, and the deep Gulf of Mèxico), its output and reserves have declined consistently. Many reasons can be attributed for these results, and as this note proves, least of them is the country’s endowment of oil and gas resources. The problem is that Mexico, since 1938, has had only one oil company responsible for all of its upstream activities and even though Pemex’s performance is comparable with that of most of the majors’ (it is world’s third largest in terms of production), it is impossible that all the remaining potential of the entire country can be found and produced with only one company, no matter how large, wealthy, efficient, technologically advanced, and successful it can be. The good news is that once the country opens up for third-party participation in exploration, which will eventually take place, results are going to be spectacular. So far there has only been a timid opening for development and exploitation opportunities.