Here we describe a new notoungulate taxon, Pascualhyrax irqi sp. nov., from Eocene levels of north-western Argentina. The materials studied include cranial and dental remains and were exhumed in sediments of the Quebrada de los Colorados Formation, corresponding to the late middle Eocene (Bartonian). General traits of the referred specimens (e.g. hypsodont postcanines, nasal bulge) point to a close relationship with different typotherian taxa traditionally included among the paraphyletic ‘Archaeohyracidae’. In turn, a combination of characters indicates that the new material represents a new taxon (e.g. smaller size, deep ectoflexus in upper molars in all wear stages, maxillary process extending posterior to the caudal end of the nasals). A phylogenetic analysis was performed, based in a previously published matrix and the addition of new characters, resulting in a close relationship of Pascualhyrax irqi sp. nov. with different ‘Archaeohyracidae’ of Oligocene radiation. This fact shows the early expression of some characters until now only known for later forms, and developed in the context of a recently acknowledged diversity of hypsodont typotherians in north-western Argentina. Regarding other evolutionary issues, the strong similitude of the juvenile specimens referred to Pascualhyrax irqi sp. nov. with adult individuals of the Neogene clade Pachyrukhinae, indicates possible heterochronic (paedomorphic) traits in the later forms.

Cerro Granito is an oval shaped hill, with a maximum height of 890 m above sea level, which outcrops in the middle of Jurassic layers as an anticlinorium, marking out the regional line of the Huincul Ridge that subdivides the Neuquén basin in two. The core of Cerro Granito is composed mainly of (1) biotitic-amphibolic gray granodiorites, (2) biotitic-epidotic light gray monzogranites, (3) biotitic porphyritic pinkish gray leucogranites (4) biotitic porphyritic gray tonalites and (5) decametric dikes of gray andesites, slightly green purple, with an approximate NW-SE strike. From the central sector and towards the NE, intense fracturing, and a predominance of aplopegmatitic dikes trending NNE are recognized. In the present work, new petrographic data of five magmatic facies are provided, two of which were radiometrically dated. The 40Ar/39Ar age older than 281 Ma for the amphibolic biotitic granodiorite, together with the existence of a porphyritic biotitic tonalite facies, reinforce the proposal of linking the plutonic units of Cerro Granito with the Chachil Plutonic Complex. This igneous event would be equivalent to the one exposed in the Chilean Coastal Batholith and pre-dates the climax of the Choiyoi event. After approximately 90 Ma, the next magmatic record corresponds to an andesitic dike, which confirms that the final exhumation of the granitoids was after 190 Ma (Sinemurian - Pliesbachian) and, from all points of view, prior to the deposition of the marine sequences of the Toarcian Lajas Formation.

Pre-Hispanic production of metallurgical ceramics in Northwest Argentina has been a subject little discussed in traditional archaeometallurgical studies. Nevertheless, these ceramics, mainly molds and crucibles, were indispensable inputs of the most complex technology carried out by the pre-Hispanic societies of the area, as was the production of metallic goods. Although they have been analyzed in certain specific aspects, little research has been done on the characterization of their ceramic fabric. In this paper, we present an analysis of metallurgical ceramics from archaeological sites in the area through petrographic procedures. The sample, composed of ten specimens, contains ceramics from the Valliserrana area, covering from the province of Jujuy up to the province of San Juan. The analysis is enriched with descriptions of objects from other regions of Northwest Argentina as well as from the North of Chile. In this first stage towards a regional comparison, the results indicate that, at a regional level, the morphology of metallurgical ceramics shows an important similarity in forms and proportions, while the ceramic petrography accounts for a wide range of variability in terms of size and nature of inclusions, degree of porosity, and percentage of matrix, reflecting technological decisions, which were influenced by local geology and constrained by use as production inputs.

The present work analyzes Raman spectra of red, white, and black experimental paintings manufactured according to archeological and ethnographical data from Patagonia (South America), in order to provide reference patterns to better understand ancient signatures of rock art. Methodological insights are also presented, evaluating pitfalls and advantages of Raman spectroscopy. For this purpose, different pigments (hematite, gypsum, charcoal) mixed with binders and additives (Lama guanicoe fat, blood, urine, saliva, gypsum) were combined. Results show that, despite its high-spatial resolution, Raman analysis shows painting spectra often reflecting multicomponent signals at micrometer-scale. Results also indicate that fat and blood show well-defined spectra in paintings, whereas saliva and urine have negligible signatures, so a relatively high and low archeological preservation is expected, respectively. On the other hand, laser-related thermoalteration processes of fat and blood binders are triggered by the presence of hematite. This thermoalteration promotes conspicuous signatures in fat and blood binders related to disordered CC bonds (ca. 1,330 and 1,566 cm−1), which are also found in charcoal. Therefore, disordered carbon in the Raman spectra of rock art may not necessarily imply the presence of charcoal-bearing pigments but may also result from thermoalteration of organic materials. Evidence of blood migration through rock porosity is registered as well, with significant implications for rock art preservation, composition, and dating.

The Devonian to early Carboniferous western margin of Patagonia (South America) includes a NW–SE-trending magmatic arc associated with a NE-dipping palaeo-subduction zone. Along the Andean region of southern Patagonia, the Eastern Andean Metamorphic Complex developed in a forearc position and consists of a succession of very low- to low-grade metaturbidite–metabasic rocks emplaced from the Devonian to Carboniferous. There are significant uncertainties surrounding this metamorphic complex, mainly related to the tectonosedimentary setting of the basin and the subsequent conditions of deformation and metamorphism, which hinder our understanding of the orogenic architecture. To reveal the links between tectonics and metamorphism, we conducted a structural analysis and sampled metapelites to measure the illite crystallinity along a regional structural cross-section in the Eastern Andean Metamorphic Complex. Our analysis reveals broadly lower to upper anchizonal metamorphism roughly synchronous with deformation along northwards-verging thrusts. These findings support the development of a forearc hyperextended basin that was subsequently closed during the Gondwanide Orogeny (late Paleozoic), a model that reconciles previous proposals suggesting passive margin v. back-arc basin models. This closure led to the emplacement of supra-subduction zone ophiolites and turbidites over the continent through the landwards migration of brittle–ductile reverse shear zones.

The Frente Llanero of the Eastern Cordillera of Colombia exhibits a great remaining hydrocarbon potential based on the interpretation of exploratory objectives essentially controlled by the morphology of its various tectonic traps. These structures recognized on surface and subsurface suffered the effects of Andean transpressional inversion of normal faulting associated with the accommodation of Mesozoic depocenters. Based on limited surface and subsurface information, the balanced cross sections are the widely used technique for interpretation based mainly on subhorizontal faulting placed subparallel to compression. Basic mechanics and geometric principles are simplified to facilitate their making. These include considering the involved sequences as perfectly tabular with uniform deformation responses, despite their heterogeneous lithologies with different rheologies. Additionally, the spatial relationships between the dominant stress field and the fractures (joints and faults) established by Anderson's Law are not contemplated. Furthermore, multiple evolution sequences with inversions or transcurrent components are not allowed since the previous discontinuities of the underlying basement located in a preferred orientation for their reactivation are not considered. This paper summarizes the main tectonic characteristics of the Colombian Frente Llanero, and structural aspects of faulting based on analog models, mechanical principles of deformation, the influence of pre-existing discontinuities, and the postulates and limitations of analog modeling concepts are discussed. In this way, alternative and less subjective tectonic interpretations are proposed to study the exploratory potential of the hydrocarbon resources of the Colombian Frente Llanero and similar tectonic regions.

A new Permian lithostratigraphic unit denominated Puerta de Las Angosturas Formation is defined for the Paganzo Basin. The new formation is mainly composed of variegated mudstones and sandstone beds, among which several levels of chert, limestone, and tuff are interstratified. The area of Las Angosturas (Sierra de Narváez, Catamarca province) is set as its type section, in which six stratigraphic intervals were distinguished and described. Stratigraphic interval 1, formed by massive or laminated red and purple sandstones (23 m thick), overlies eolian deposits belonging to the De La Cuesta Formation through a low-relief erosive unconformity. Interval 2 comprises 55 meters of purple to grayish-brown mudstones and fine-grained sandstones that transitionally cover interval 1 or overlap on the red beds of the De La Cuesta Formation. Interval 3 is made of interbedded sandstone and limestone beds with millimeter levels of chert; the whole interval reaches 110 m of thickness. Interval 4 (70 m) shows similar lithological characteristics to 3 but differs in the predominance of mudstones over sandstone and the presence of thin and recurrent tuff levels. Interval 5 is very thin, 35 m thick, and shows marked lithological changes concerning those previously described intervals since it is formed by medium- to coarse-grained cross-bedded sandstones. Finally, interval 6 (76 m) corresponds to a fine-grained sequence in which mudstones, very fine-grained sandstones, limestone, and a few tuff beds alternate. The Puerta de Las Angosturas Formation is covered in unconformity by the red beds of the Talampaya Formation. Intervals 2, 3, and 4 of the Puerta de Las Angosturas Formation have provided palynological assemblages corresponding to the Lueckisporites/Weylandites biozone that suggests a Kungurian age, at least for the lower half of the unit.

This paper analyzes an extended eolian field developed during the Oligocene-Early Miocene along the eastern flank of the Andes. This eolian episode, herein named OMEB (Oligocene-Miocene Eolian Belt), is recorded in several units, including Mariño, Pachaco, Cuculí, Vallecito, El Crestón, Tambería, Angastaco, Quiñoas, Las Chacras, and Vizcachera Formations. Eolian accumulation occurred in five environments: 1. Sand sheet and extradune, 2. Dune field, 3. Dune and draas, 4. Deflationary eolian fields, and 5. Wadi and fore-eolian areas. While sand sheet deposits are composed of horizontally laminated and low-angle cross-bedded sandstones, dune and draas environments comprise giant- and large-scale cross-bedded sets and dune fields by stacked sets of cross-bedded sandstones. In contrast, the deflation field environment exhibits low-relief irregular surfaces carved in dune and extradune environments. Finally, the wadi and fore-eolian deposits correspond to the eolian dune interbedded with fluvial conglomerates and muddy sediments deposited mainly by low-energy fluvial currents on the interdunes. Towards the end of the Early Miocene, the OMEB declined in almost all the foreland area, and fluvial and lacustrine sediments replaced eolian deposits. Although the stratigraphic expression of this change was different along the region, three principal patterns of change are recognized: 1. Different degrees of fluvial incisions, 2. Fluvial replacement of eolian deposits without evidence of significant incision, and 3. interbedding of eolian, fluvial, and occasionally playa-lake deposits. In the first pattern, conglomerates forming lenticular channels abruptly incise into the dune deposits. In pattern 2, fluvial channels are dominantly sandy, and incision surfaces are poorly defined. The third pattern, contrasting with the two previously described, results from the recurrent interstratification of eolian, fluvial, and playa lake deposits. This type of eolian-fluvial transition was studied in detail in the Tambillos creek (Northeastern Sierras de Los Colorados), where a sequential model for the eolian fluvial transition using the position of the water table is proposed. This model allows defining four primary states: 1. Low water table, 2. High water table (below the surface), 3. High water table (at or slightly above the surface) with partial flooding and damming, and 4. Runoff for fluvial channels.