Search Results (29)

This paper presents a geomechanical characterization for unwelded volcanic bimrock materials. Bimrocks are geological materials consisting of blocks of rock of different sizes embedded in a finer matrix. Many volcanic deposits and outcrops can be classified as bimrocks, and some of them correspond to unwelded bimrocks, i.e., with the absence of strong bonds between blocks of rock and matrix. The geomechanical characterization proposed is oriented towards bimrocks slopes, their stability and landslide hazard occurrence. It consists of five steps which includes the material description, the volcanic deposit classification, the definition of block size range, the computation of the volumetric block percentage, the geotechnical characterization of the blocks of rock, and the geological and geotechnical analysis of the matrix that surrounds the blocks. The geomechanical characterization proposed is applied to four slopes at the Western Cordillera of Ecuador, where slopes instabilities are common. Results show that the geomechanical characterization sets a reliable framework for geotechnically describing bimrocks materials, explaining the actual stability state of the slopes. It also enables taking appropriate and optimum decisions in the design and management of volcanic slopes, thus contributing to a sustainable approach of landslide mitigation. Full article

Detrital zircon (DZ) ages of Cretaceous sandstones in the United States contain critical spatial and temporal information on their sedimentary provenance and on the reorganization of drainage patterns. Herein, we report zircon U-Pb ages of sandstones from Lower Cretaceous and Upper Cretaceous formations of Arkansas. All Arkansas sandstones studied, except for those from the Upper Cretaceous Nacatoch Formation, display dominant Appalachian-Grenville DZ ages from among the Appalachian-Ouachita DZ grains that were studied. Our work shows that the sedimentary provenance of Arkansas sandstones started to change during the middle part of the Cretaceous. Notably, DZ grains from the Woodbine formation, which was deposited during the middle part of Cretaceous, show moderate contributions from Western Cordillera sources (275–55 Ma), and DZ grains from the Upper Cretaceous Nacatoch Formation exhibit dominant Western Cordillera sourcing. Our Arkansas-based DZ data suggest that the onset of DZ contribution of the Western Cordillera began at about 94 Ma, and the peak of the Western Cordillera source contribution occurred at about 73 Ma. Therefore, we can show that North American drainage reorganization with regard to Western Cordilleran DZ sourcing in Arkansas began during the time span 94–73 Ma, which is earlier than the previously reported onset of drainage reorganization with regard to Texas (i.e., 66–55 Ma). Full article

In the Betic-Rif Cordilleras, recent works have evidenced the existence of well-developed Eocene (Ypresian-Bartonian) carbonate platforms rich in Larger Benthic Foraminifera (LBF). Contrarily to other sectors of the western Tethys, like the Pyrenean domain in the North Iberian Margin, where these platforms started in the early Ypresian (Ilerdian), in the Betic-Rif chains, the recorded Eocene platforms started in the late Ypresian (Cuisian) after a widespread gap of sedimentation including the Ilerdian time span. In this work, the Aspe-Terreros Prebetic section (External Betic Zone) is studied. An Eocene succession with gravity flow deposits consisting of terrigenous and bioclastic turbidites, as well as olistostromes with olistoliths, was detected. In one of these turbidites, we dated (with the inherent limitations when dating bioclasts contained by gravity flow deposits) the middle Ilerdian, on the basis of LBF, representing a vestige of a missing Illerdian carbonate platform. The microfacies of these turbidites and olistoliths rich in LBF have been described and documented in detail. The gap in the sedimentary record and absence of Ilerdian platforms in the Betic-Rif Cordillera have been related to the so-called Eo-Alpine tectonics (Cretaceous to Paleogene) and sea-level variations contemporarily with the establishment of shallow marine realms in the margins of the western Tethys. Full article

The structural evolution of Andean-type orogens is strongly influenced by the geometry of the subducting slab. This study focuses on the flat-slab subduction of the Nazca Ridge and its effects on the South American Plate. The process of flat slab subduction impacts the stress distribution within the overriding plate and increases plate coupling and seismic energy release. Using the finite element method (FEM), we analyse interseismic and coseismic deformation along a 1000 km transect parallel to the ridge. We examine stress distribution, uplift patterns, and the impact of megathrust activity on deformation. To better define the crust’s properties for the model, we developed a new thermal model of the Nazca Ridge subduction zone, reconstructing the thermal structure of the overriding plate. The results show concentrated stress at the upper part of the locked plate interface, extending into the Coastal and Western Cordilleras, with deeper stress zones correlating with seismicity. Uplift patterns align with long-term rates of 0.7–1 mm/yr. Cooling from flat-slab subduction strengthens the overriding plate, allowing far-field stress transmission and deformation. These findings provide insights into the tectonic processes driving stress accumulation, seismicity, and uplift along the Peruvian margin. Full article

This study uses heavy detrital minerals to determine actualistic fluvial and beach sand provenance across the Betic Cordillera (Spain), along the coast from Almeria to Marbella. The Betic Cordillera, primarily composed of metamorphic rocks to the east, supply an assemblage dominated by almandine and graphite, with a longshore dispersal from Almeria to Malaga. Buergerite and hypersthene indicate the provenance of calcalkaline lavas east of Cabo de Gata. The western part of the Betic Cordillera, which comprises the Ronda Peridotite Complex, supplies a chromite and diopside assemblage, with a dispersal from Marbella to Algeciras. Considering these mineralogical suites, the effects of source rock compositions and weathering are evaluated. The heavy mineral species mirror the mineralogy of the source rocks of local outcrops and wider source terranes. The fluvial heavy mineral suites do not differ significantly from those in the beaches except for some unstable species. Unstable species such as olivine, pyroxene, and amphibole do not show evidence of loss because of elevated topography and semiarid climate, which do not affect heavy minerals. This contribution also evaluates the potential of some heavy detrital species as ideal pathfinders in searching for diamonds. Full article

Combined heavy mineral analysis and detrital zircon geochronology have enabled us to track detritus supplied by the ancestral river systems draining the North American continent into the deep subsurface of the Gulf of Mexico, in both the coastal plain and the offshore deep water areas. During deposition of the Paleocene–Eocene Wilcox Group, sandstones in the western part of the area are interpreted as the products of the Rosita system derived via paleo-Rio Grande material, with a large component of sediment shed from the Western Cordillera. By contrast, samples from wells further east have high proportions of zircons derived from the Yavapai-Mazatzal Province and are attributed to the Rockdale system with sediment fed predominantly by the paleo-Colorado or paleo-Colorado-Brazos. There is evidence that sediment from the Rosita system occasionally extended into the central Gulf of Mexico, and, likewise, data indicate that the Rockdale system sporadically supplied sediment to the western part of the basin. During the Late Eocene of the central Gulf of Mexico (Yegua Formation) there was a distinct shift in provenance. The earlier Yegua sandstones have a large Grenville zircon component and are most likely to have had a paleo-Mississippi origin, whereas the later Yegua sandstones are dominated by zircons of Western Cordilleran origin, similar to Wilcox sandstones fed by the Rosita system via the paleo-Rio Grande. The switch from paleo-Mississippi to paleo-Rio Grande sourcing implies there was a major reorganisation of drainage patterns during the Late Eocene. Miocene sandstones in the deepwater Gulf of Mexico were principally sourced from the paleo-Mississippi, although the paleo-Red River is inferred to have contributed to the more westerly-located wells. Full article

The Rif Cordillera, an Alpine orogen in the Western Mediterranean, was developed by the interaction of Eurasian and African (Nubia) plates. Neotectonic deformations of the Rif foreland influence the relief, especially in post-nappe basins and their boundaries with Jurassic and Cretaceous carbonate mountain massifs, and they contribute to highlighting the recent evolution of the Cordillera. The topographic and hydrological lineaments of these basins were characterised on the basis of multi-scale morphostructural data analysis, supported by digital mapping and GIS. They were correlated with geological structures, essentially with fractures. The outcrops of the Upper Tortonian and Messinian deposits depict well-defined geometric shapes with roughly rectilinear boundaries, as defined by their contacts with the massive and rigid rocks of the Jurassic and Cretaceous series. Upper Tortonian deposits evidence major regional N70°E and N40°E lineaments, which are obliquely intersected by late structures. Messinian N120°E and N25°E lineaments, associated with N140°E lineaments, are also recognised. The interpretation of these lineaments as faults indicates the activity of two systems of transtensive sinistral and then dextral brittle shearing that correspond to two episodes of neotectonic deformation that played a decisive role in shaping the reliefs of the Eastern Rif. These deformations are particularly relevant to isolate basins and likely have a key role during the closure of the South Rifian corridor during the Mediterranean Messinian Salinity crisis. Full article

The exploration of natural H₂ or white hydrogen has started in various geological settings. Ophiolitic nappes are already recognized as one of the promising contexts. In South America, the only data available so far concerns the Archean iron-rich rocks of the Mina Gerais in Brazil or the subduction context of Bolivia. In Colombia, despite government efforts to promote white hydrogen, data remain limited. This article introduces the initial dataset obtained through soil gas sampling within the Cauca-Patia Valley and Western Cordillera, where the underlying geology comprises accreted oceanic lithosphere. In this valley, promising areas with H₂ potential were identified using remote sensing tools, in particular vegetation anomalies. The Atmospherically Resistant Vegetation Index (ARVI) appears to be well adapted for this context and the field data collection confirmed the presence of H₂ in the soil in all pre-selected structures. The valley undergoes extensive cultivation, mainly for sugar cane production. While H₂ emissions lead to alterations in vegetation, unlike reports from other countries, they do not result in its complete disappearance. Soil gas measurements along the thrusts bordering the Cauca Valley also show high H₂ content in the fault zones. In the valley, the presence of sedimentary cover above the ophiolites which are presumably the H₂ generating rocks, which addresses the possible presence of reservoirs and seals to define potential plays. Drawing parallels with the Malian case, it could be that the intrusive element could serve as seals. Full article

The Betic Cordillera was formed by the collision between the Alboran Domain and the South Iberian paleomargin in the frame of the NW–SE convergent Eurasia–Nubia plate boundary. The central region is undergoing a heterogeneous extension that has not been adequately analysed. This comprehensive study addressed it by collecting structural geologic, seismologic, and geodetic data. The region west of the Sierra Nevada is deformed by the extensional system of the Granada Basin, which facilitates E–W to NE–SW extension. Moreover, the southern boundary of Sierra Nevada is affected by a remarkable N–S extension related to E–W normal to normal–dextral faults affecting the shallow crust. However, geologic and geodetic data suggest that the western and southwestern Granada Basin boundary constitutes a compressional front. These data lead to the proposal of an active extensional collapse from the uplifted Sierra Nevada region to the W–SW–S, over an extensional detachment. The collapse is determined by the uplift of the central Betics and the subsidence in the Alboran Basin due to an active subduction with rollback. Our results indicate that the central Betic Cordillera is a good example of ongoing extensional collapse in the general context of plate convergence, where crustal thickening and thinning simultaneously occur. Full article

The northwest-southeast convergence of the Eurasian and Nubian (African) plates in the western Mediterranean region propagates inside the Nubian plate and affects the Moroccan Meseta and the neighboring Atlasic belt. Five continuous Global Positioning System (cGPS) stations were installed in this area in 2009 and provide significant new data, despite a certain degree of errors (between 0.5 and 1.2 mm year⁻¹, 95% confidence) due to slow rates. The cGPS network reveals 1 mm year⁻¹ North/South shortening accommodated within the High Atlas Mountains, and unexpected 2 mm year⁻¹ north-northwest/south-southeast extensional-to-transtensional tectonics within the Meseta and the Middle Atlas, which have been quantified for the first time. Moreover, the Alpine Rif Cordillera drifts towards the south-southeast against its Prerifian foreland basins and the Meseta. In this context, the geological extension foreseen in the Moroccan Meseta and Middle Atlas agrees with a crustal thinning due to the combined effect of the anomalous mantle beneath both the Meseta and Middle-High Atlasic system, from which Quaternary basalts were sourced, and the roll-back tectonics in the Rif Cordillera. Overall, the new cGPS data provide reliable support for understanding the geodynamic mechanism that built the prominent Atlasic Cordillera, and reveal the heterogeneous present-day behavior of the Eurasia-Nubia collisional boundary. Full article

Natural hydrogen is known to be generated in the crust by water/rock interactions, especially the oxidation of iron-rich rock or radiolysis. However, other sources, especially deeper ones, exist. In the context of subduction, the dehydration of the slab, the destabilization of the NH₄, and the hydration of the mantle wedge above the subducting lithosphere may generate H₂. We present here a compilation of the known gases in the central part of the Pacific subduction and the results of a first field acquisition dedicated to H₂ measurements in Bolivia between La Paz and South Lipez. Various zones have been studied: the emerging thrust faults of the western borders of the Eastern Cordillera, the Sajama area that corresponds to the western volcanic zone near the Chile border northward from the Uyuni Salar, and finally, the Altiplano-Puna Volcanic Complex in South Lipez. Soil gas measurement within and around the Salar itself was not fully conclusive. North of the Uyuni Salar, the gases are very rich in CO₂, enriched in N₂ and poor in H₂. On the opposite, southward, all the samples contain some H₂; the major gas is nitrogen, which may overpass 90% after air correction, and the CO₂ content is very limited. On the western border of the Cordillera, the δC13 isotope varies between −5 and −13‰_, and it is not surprisingly compatible with volcanic gas, as well as with asthenospheric CO₂. The methane content is close to 0, and only a few points reach 1%. The isotopes (−1‰) indicate an abiotic origin, and it is thus related to deep H₂ presence. The high steam flow in the geothermal area of South Lipez combined with the H₂ content in the water results in at least 1 ton of H₂ currently released per day from each well and may deserve an evaluation of its economic value. The nitrogen content, as in other subduction or paleo-subduction areas, questions the slab alteration. Full article

The present study contributes to bridging the gap in research related to the presence and distribution patterns of carnivore mammals in western México and identifies priority areas for biodiversity conservation in western Michoacán, México. The distribution of 11 carnivore species (Canis latrans; Urocyon cinereoargenteus; Herpailurus yagouaroundi; Leopardus pardalis; Leopardus wiedii; Puma concolor; Panthera onca; Conepatus leuconotus; Bassariscus astutus; Nasua narica; Procyon lotor) in western México was modeled through the application of a two-scale approach, including a large modeled region that corresponded to the western part of the country, for which consensus models were obtained that represent the species’ bioclimatic envelopes (historic occurrence records); and the second modeled study area that includes only the western portion of the state of Michoacán in which compounded models of the species’ habitat suitability (field occurrence records) for this region were proposed. Using species’ habitat suitability models as biodiversity units, prioritization exercises were carried out on important areas for the conservation of these species, as well as the comparison and analysis of the existing natural protected areas (NPA) and existing proposed conservation areas in the study area. The different exercises for prioritizing areas for conservation yielded similar results and show the potential percentages of the landscape that can be subjected to conservation programs. The highest conservation priority values were mainly located in the Costas del Sur and Cordillera del Sur provinces. This study signifies a flexible basis from which future studies on planning and designing a network of natural protected areas can be carried out in this region. Full article

Based on the results of a preceding species-delimitation analysis for the diploid representatives of the genus Leucanthemum (Compositae, Anthemideae), the present study aims at the elaboration of a specific and subspecific taxonomic treatment of the tetraploid members of the genus. Following an integrative taxonomic approach, species-level decisions on eight predefined morphotaxon hypotheses were based on genetic/genealogical, morphological, ecological, and geographical differentiation patterns. ddRADseq fingerprinting and SNP-based clustering revealed genetic integrity for six of the eight morphotaxa, with no clear differentiation patterns observed between the widespread L. ircutianum subsp. ircutianum and the N Spanish (Cordillera Cantábrica) L. cantabricum and the S French L. delarbrei subsp. delabrei (northern Massif Central) and L. meridionale (western Massif Central). The inclusion of differentiation patterns in morphological (leaf dissection and shape), ecological (climatological and edaphic niches), and geographical respects (pair-wise tests of sympatry vs. allopatry) together with the application of a procedural protocol for species-rank decisions (the ‘Wettstein tesseract’) led to the proposal of an acknowledgement of the eight predefined morphotaxon hypotheses as six species (two of them with two subspecies). Nomenclatural consequences following from these results are drawn and lead to the following new combinations: Leucanthemum delarbrei subsp. meridionale (Legrand) Oberpr., T.Ott & Vogt, comb. nov. and Leucanthemum ruscinonense (Jeanb. & Timb.-Lagr.) Oberpr., T.Ott & Vogt, comb. et stat. nov. Full article

Glaciation has been a powerful determiner of species distributions and the genetic structure of populations. Contemporary distributions of many organisms in North America’s Western Cordillera reflect the influence of Pleistocene glaciation. We identified a pattern of north–south differentiation in the genus Prosimulium of western North America, which reflects the separation of northern and southern populations by the North American Ice Sheet during the Pleistocene Epoch. The taxonomic implication is that new species exist within nominal species, requiring formal description or revalidation of names currently in synonymy. We morphologically and cytogenetically examined populations of one nominal species of black fly, Prosimulium esselbaughi Sommerman, over its known range from Alaska south to California and Colorado. Chromosomal and morphological evidence supports the presence of two species, P. esselbaughi sensu stricto from Alaska to at least southern British Columbia, and a new species, Prosimulium supernum in the central Rocky Mountains and high Sierra Nevada range of the United States. The new species is described in all life stages above the egg, along with its polytene chromosomes. The existence of differentiated populations of other nominal species of black flies in northern and southern North America provides a system for investigating possible co-differentiation of vectors and parasites. Full article

The historic western edge of the bison (Bison bison) range and the ecological processes that caused its formation are frequently debated with important implications for bison restoration across North America. We test the hypothesis that a combination of bottom-up habitat suitability and top-down harvest pressure from Indigenous peoples were important processes in forming the western edge of bison distribution. Using 9384 historical journal observations from 1691–1928, we employ MaxEnt ecological niche modelling to identify suitable bison habitat across the Western Cordillera from bottom-up climatic, land cover, and topographic factors. We then use mixed-effect logistic regression to test if bison occurrence in journal records can be in part explained by the abundance of humans, wolves, or grizzly bears, in addition to MaxEnt-derived habitat suitability. We find support for our hypothesis because of the limited suitable habitat in the Rocky Mountains that likely prevented westward bison dispersal from their core habitat, and there was a negative relationship between bison occurrence and human harvest pressure. On this basis, we propose that intensive human harvest from large populations in the Western Cordillera, subsidized by other wildlife, salmon, and vegetation resources, is an underappreciated socioecological process that needs to be restored alongside bison populations. Co-managing bison with Indigenous peoples will also mitigate the adverse effects of overabundant bison populations and maximize the ecological and cultural benefits of bison restoration. Full article