Los nombres Novillo y Olvido fueron propuestos como formaciones para sucesiones de rocas sedimentarias (como unidades litoestratigráficas), de edad Jurásico. El Léxico Estratigráfico de México reconoce el nombre Novillo para designar a una unidad litodémica precámbrica formada por gneis; sin embargo, no registra al apelativo para la unidad sedimentaria del Jurásico, argumentando sinonimia de nomenclatura. El mismo Léxico no acepta a la Formación Olvido por no cumplir los requisitos que establece el Código Estratigráfico Norteamericano para designar unidades formales. El nombre Novillo originalmente fue dado a estratos de caliza, arenisca y marga con moluscos, en esta definición se incluyó un cuerpo de arenisca en la base, este cuerpo posteriormente fue segregado para incluirlo como Formación La Joya, y en ella, se omitieron pormenores para modificar a la unidad estratigráfica superior. El contacto superior de la Formación Novillo se describió subyacente a terrígenos con evaporita y caliza de la Formación Olvido. Las relaciones estratigráficas de los estratos Novillo (capas continentales abajo y yesos arriba) originaron remplazar equívocamente el nombre Novillo por el de Zuloaga y constreñir, de manera equívoca, su contenido fósil al Oxfordiano. Este criterio erróneo ocasionó correlaciones estratigráficas regionales impropias. La Formación Olvido se definió de forma lacónica para designar estratos de yeso, arenisca y caliza, motivo por el cual se restringe ser aceptada con la categoría litoestratigráfica formal. Este trabajo describe las características litológicas y cronoestratigráficas de las formaciones Novillo y Olvido para dar formalidad litoestratigráfica a estas rocas y admitir su debida inclusión en el Léxico de Nomenclatura Estratigráfica de México. En la Formación Olvido se reconocen tres miembros. Isotopía U/Pb en circones de la Formación Olvido arroja para la base edades de ~164 Ma y hacia la cima de ~155.5 Ma, que ubican su depósito entre el Caloviano y Oxfordiano. Los afloramientos estudiados permiten interpretar los ambientes de depósito y hacer las correlaciones estratigráficas regionales apropiadas con depósitos isócronos. Se acepta designar a la unidad litodémica Gneis Novillo, como Complejo Metamórfico Novillo. La revisión estratigráfica de las formaciones Novillo y Olvido se justifica por la importancia económica para la exploración de recursos naturales.
Recent investigations at Sistema Calera Cave (21°53’49”N, 98°55’52”W, 103 m a.s.l.), located in the Sierra de El Abra, San Luis Potosí, northeastern Mexico, have established the site as one of exceptional paleontological importance due to its remarkably diverse assemblage of fossilized vertebrate remains. Given the underwater depositional context, which likely contributed to collagen degradation, radiocarbon dating was performed on bioapatite, with results converted to collagen-equivalent values and calibrated to calendar years. Radiocarbon dates place specimens of Bison sp. (8423–8549 cal yr BP), Tremarctos cf. floridanus (12686–12752 cal yr BP), Glyptotherium cylindricum (12986–13166 cal yr BP), Canis dirus (13574–13666 cal yr BP), Mammuthus columbi (13729–13887 cal yr BP), Eremotherium laurillardi (23784–24065 cal yr BP), and Smilodon fatalis (31027–31178 cal yr BP) within the Late Rancholabrean. The range of dates indicates the assemblage represents a time-averaged fauna. The carbon isotopic signature (δ13C) suggests three main types of vegetation animals fed on: low-density forests, an arboreal savanna, and an ecotone between arboreal savanna to open savanna. Of 775 cataloged specimens, 37 are assigned to Xenarthra, including three sloth genera (Eremotherium, Nothrotheriops, and a megalonychid cf. Nohochichak) and one glyptodont (Glyptotherium). The co-occurrence of Nothrotheriops, typically associated with arid environments, with Eremotherium and Glyptotherium, which are linked to tropical and mixed grassland habitats, presents an unusual ecological association. Potential explanations for this uncommon association are discussed.
The La Colorada mine is characterized by a low-sulfidation epithermal Au-Ag vein system hosted within Paleozoic siliciclastic rocks and a Late Cretaceous (-75-69 Ma) volcano-plutonic complex. While this Au-Ag mineralization has been intermittently mined since 1740, the exact timing of its emplacement has remained unconstrained. Existing Ar-Ar geochronology on alteration minerals indicates an emplacement age ca. 23 Ma. However, we provide evidence for a previously undocumented, poorly preserved porphyry Cu-Mo system centered on a 72.4 Ma rhyolitic porphyry. Re-Os molybdenite dating from sulfide veinlets yielded a consistent age of 72.3 Ma. Consequently, this study redefines the La Colorada deposit as an Oligo-Miocene epithermal Au-Ag system overprinting a Late Cretaceous Cu-Mo porphyry system. Fluid inclusion petrography reveals a distinct evolution: the porphyry stage is characterized by high-salinity, L+V+S inclusions in quartz veinlets, indicating boiling of magmatic-hydrothermal fluids. In contrast, the epithermal event is dominated by liquid-rich, two-phase inclusions with lower salinities, consistent with a cooler, more diluted environment. Sulfur isotope signatures, indicated as delta 34S values, provide further constraints on the ore-forming fluids. Molybdenite from the porphyry stage yielded a delta 34S of +6.55 %o, suggesting a predominantly magmatic sulfur source with moderate heavy-sulfur enrichment. In contrast, sulfides from the epithermal overprint exhibit delta 34S values ranging from-0 to-3.02 %o, consistent with a typical magmatic-hydrothermal signature and minimal interaction with external sulfur reservoirs.
The upper Sonora River basin in northwestern Mexico is a region with active and historical mining, as well as vigorous agricultural and livestock activity. The Buenavista del Cobre mine spill that occurred in 2014 raised major concerns among residents, including food safety. In this study, potentially toxic elements, PTE, (Al, As, Ba, Cd, Cr, Cu, Fe, Ni, Pb, Zn, and Tl) and Pb isotope ratios were measured in samples of regional foods and food products [beef chorizo, shredded beef jerky, beef liver, beef top round, farmer's cheese, and red chili (powdered dried mild pepper)] collected from representative sites along the basin. Compared to international guidelines, only two out of 20 beef samples exceeded the Pb limit of 0.1 mg/kg set by FAO/WHO and the EU, mainly in prepared products (chorizo, shredded beef jerky). One liver sample exceeded the FAO/WHO Pb limit of 0.2 mg/kg. For red chili, one sample exceeded the Pb guideline of 0.6 mg/kg (FAO/ WHO). Overall, Pb levels did not surpass FAO/WHO recommendations. Pb isotope compositions in most food samples align with the range of North American rocks, indicating limited influence from mining. Variability in Pb isotope composition may be related to preparation methods and geogenic anomalies. Although the mine spill represented a major environmental disturbance, PTE concentrations measured in foods and food products are consistent with the geochemical background of the basin. This interpretation is supported by Pb isotope compositions, indicating that Pb in food and food products primarily originates from natural sources, with no clear evidence of significant contributions from mining activities.
