Research Center on Earth Sciences

We have developed a robust 2D joint inversion scheme incorporating the new concept of cross‐gradients of electrical resistivity and seismic velocity as constraints so as to investigate more precisely the resistivity‐velocity relationships in complex near‐surface environments. The results of joint inversion of dc resistivity and seismic traveltime data from collocated experiments suggest that one can distinguish between different types or facies of unconsolidated and consolidated materials, refining a previously proposed resistivity‐velocity interrelationship derived from separate inversions of the respective data sets. A consistent interpretive structural model can be obtained from the joint inversion models.

• The advent of embryophytes (land plants) is among the most important evolutionary breakthroughs in Earth history. It irreversibly changed climates and biogeochemical processes on a global scale; it allowed all eukaryotic terrestrial life to evolve and to invade nearly all continental environments. Before this work, the earliest unequivocal embryophyte traces were late Darriwilian (late Middle Ordovician; c. 463-461 million yr ago (Ma)) cryptospores from Saudi Arabia and from the Czech Republic (western Gondwana). • Here, we processed Dapingian (early Middle Ordovician, c. 473-471 Ma) palynological samples from Argentina (eastern Gondwana). • We discovered a diverse cryptospore assemblage, including naked and envelope-enclosed monads and tetrads, representing five genera. • Our discovery reinforces the earlier suggestion that embryophytes first evolved in Gondwana. It indicates that the terrestrialization of plants might have begun in the eastern part of Gondwana. The diversity of the Dapingian assemblage implies an earlier, Early Ordovician or even Cambrian, origin of embryophytes. Dapingian to Aeronian (Early Silurian) cryptospore assemblages are similar, suggesting that the rate of embryophyte evolution was extremely slow during the first c. 35-45 million yr of their diversification. The Argentinean cryptospores predate other cryptospore occurrences by c. 8-12 million yr, and are currently the earliest evidence of plants on land.

Natural dust is often associated with hot, subtropical deserts, but significant dust events have been reported from cold, high latitudes. This review synthesizes current understanding of high-latitude (50N and 40S) dust source geography and dynamics and provides a prospectus for future research on the topic. Although the fundamental processes controlling aeolian dust emissions in high latitudes are essentially the same as in temperate regions, there are additional processes specific to or enhanced in cold regions. These include low temperatures, humidity, strong winds, permafrost and niveo-aeolian processes all of which can affect the efficiency of dust emission and distribution of sediments. Dust deposition at high latitudes can provide nutrients to the marine system, specifically by contributing iron to high-nutrient, low-chlorophyll oceans; it also affects ice albedo and melt rates. There have been no attempts to quantify systematically the expanse, characteristics, or dynamics of high-latitude dust sources. To address this, we identify and compare the main sources and drivers of dust emissions in the Northern (Alaska, Canada, Greenland, and Iceland) and Southern (Antarctica, New Zealand, and Patagonia) Hemispheres. The scarcity of year-round observations and limitations of satellite remote sensing data at high latitudes are discussed. It is estimated that under contemporary conditions high-latitude sources cover >500,000 km 2 and contribute at least 80-100 Tg yr 1 of dust to the Earth system (~5% of the global dust budget); both are projected to increase under future climate change scenarios.

The origin of dust deposited in East Antarctica is not fully understood yet. This study demonstrates that, contrary to Nd, Sr isotopes are strongly fractionated in the finest‐sized material representing potential dust sources in South America. Analysis of Nd isotopes suggests that Argentine loess, Southern Ocean sediments and Antarctic dust, may all have a related origin or can represent comparable mechanisms of eolian sediment transport and deposition. This analysis also concludes that the Patagonian signature can explain a high proportion of the isotopic composition of dust trapped in Antarctic ice during glacial periods. The Puna‐Altiplano plateau emerges as the second possible important sediment contributor explaining the crustal‐like signature found in East Antarctic dust and should be considered as a potential source area when Quaternary paleoclimate is reconstructed from Argentine loess, Antarctic dust and South Atlantic sediment records.

Abstract: The Famatina belt, Central Andes, is part of an ancient accretionary margin built along Western Gondwana in the early Palaeozoic. U–Pb ion microprobe analysis of detrital zircons and Sm–Nd whole-rock analysis of two early Palaeozoic low-grade metasedimentary units record the early evolution of this region. Detrital zircons in the Negro Peinado and Achavil formations have ages ranging from Palaeoproterozoic to Cambrian, consistent with derivation from Gondwanan sources. T DM ages suggest that the sedimentary rocks were derived from a composite source area, which separated from the mantle during the Palaeoproterozoic ( c . 1.8–1.6 Ga). Constraints from the youngest detrital grains indicate accumulation in a Mid- to Late Cambrian foreland basin adjacent to the inboard Pampean orogenic tract. The dominance of Cambrian ages in the Negro Peinado Formation suggests derivation principally from the eastern Pampean belt whereas the dominance of late Neoproterozoic ages in the Achavil Formation suggests that input from the Pampean belt was overwhelmed by older sources. The paucity of Palaeoproterozoic ages argues against direct input from older areas such as the Río de la Plata craton. The predominance of Meso- and Neoproterozoic ages over older sources suggests that a Brasiliano-age magmatic arc developed on a Mesoproterozoic basement, probably a southern extension of the Arequipa–Antofalla massif.

An almost complete skull of a carnosaur from the Allen Formation (Maasqichtian of Rio Negro Province) is described as the holotype of A belisaurus comahuensis. It is a high skull with a broad interorbital roof, a huge preorbital opening, squamosal nearly horizontal with the quadratojugal process ventraly directed, very wide infratemporal fenestra, very long quadrate, orbital opening large with almost closed orbita. The differences with Tyrannosauridae and other Cretaceous carnosaurs families appear so significant as to propose a new family, Abelisauridae, likely of gondwanic distribution. ·

New SHRIMP U-Pb zircon ages are reported for igneous and sedimentary rocks of the Famatina Complex, constraining the age of the magmatism and the ensialic basins. Together with whole-rock and isotope geochemistry for the igneous rocks from the complex, these ages indicate that the voluminous parental magmas of metaluminous composition were derived by partial melting of an older lithosphere without significant asthenospheric contribution. This magmatism was initiated in the Early Ordovician (481 Ma). During the Mid-Late Ordovician, the magmatism ceased (463 Ma), resulting in a short-lived (no more than ~20 Ma) and relatively narrow (~100–150 km) magmatic belt, in contrast to the long-lived cordilleran magmatism of the Andes. The exhumation rate of the Famatina Complex was considerably high and the erosional stripping and deposition of Ordovician sediments occurred soon after of the emplacement of the igneous source rocks during the Early to mid-Ordovician. During the upper Mid Ordovician the clastic contribution was mainly derived from plutonic rocks. Magmatism was completely extinguished in the Mid Ordovician and the sedimentary basins closed in the early Late Ordovician.

La región de Apan está situada entre los sectores este y central del Cinturón Volcánico Transmexicano (CVTM), su registro geológico muestra una interacción intermitente entre volcanismo y tectónica. Las rocas más antiguas en el área fueron emplaza- das hace 13.5 Ma, seguidas por un hiatus volcánico de casi 10 Ma. El volcanismo en el área ocurrió entre ~3.0 y 1.5 Ma; con la actividad más reciente durante el Pleistoceno Tardío (~42-31ka). Las rocas volcánicas de la región de Apan varían en composi- ción de basalto a riolita (50-75 wt.% SiO2) y muestran afinidad calco-alcalina; sus características geoquímicas indican que son productos eruptivos procedentes de una zona de subducción. Estudios geológicos y estratigráficos detallados utilizando un mapa con base digital escala 1:100 000 para la compilación de datos previos y nuevos, combinados con fechamientos K- Ar, demues- tran que la distribución de los centros volcánicos en la región de Apan está controlada en gran medida por un sistema de fallas normales NE-SW y estructuras de fosas y pilares asociadas, como resultado de un campo de esfuerzos con el esfuerzo mínimo principal (ó3) orientado hacia el NW. Los resultados de este estudio, combinados con la reinterpretación de datos geológicos y fechamientos, permitieron realizar una correlación detallada de la estratigrafía volcánica de la región de Apan con las secuencias estratigráficas de rocas volcánicas en otras áreas del CVTM. Esta correlación indica que la actividad volcánica en el CVTM inició durante el Mioceno Medio.

The extinct dromornithids, gastornithids and phorusrhacids are among the most spectacular birds to have ever lived, with some giants exceeding 500 kg. The affinities and evolution of these and other related extinct birds remain contentious, with previous phylogenetic analyses being affected by widespread convergence and limited taxon sampling. We address these problems using both parsimony and tip-dated Bayesian approaches on an expansive taxon set that includes all key extinct flightless and flighted (e.g. Vegavis and lithornithids) forms, an extensive array of extant fowl (Galloanseres), representative Neoaves and palaeognaths. The Paleogene volant Lithornithidae are recovered as stem palaeognaths in the Bayesian analyses. The Galloanseres comprise four clades inferred to have diverged in the Late Cretaceous on Gondwana. In addition to Anseriformes and Galliformes, we recognize a robust new clade (Gastornithiformes) for the giant flightless Dromornithidae (Australia) and Gastornithidae (Eurasia, North America). This clade exhibits parallels to ratite palaeognaths in that flight presumably was lost and giant size attained multiple times. A fourth clade is represented by the Cretaceous Vegavis (Antarctica), which was strongly excluded from Anseriformes; thus, a crucial molecular calibration point needs to be reconsidered. The presbyornithids Wilaru (Australia) and Presbyornis (Northern Hemisphere) are robustly found to be the sister group to Anatoidea (Anseranatidae + Anatidae), a relatively more basal position than hitherto recognized. South America's largest bird, Brontornis , is not a galloansere, but a member of Neoaves related to Cariamiformes; therefore, giant Galloanseres remain unknown from this continent. Trait analyses showed that while gigantism and flightlessness evolved repeatedly in groups, diet is constrained by phylogeny: all giant Galloanseres and palaeognaths are herbivores or mainly herbivorous, and giant neoavians are zoophagous or omnivorous.

Abstract This study provides a detailed description of the sources, transport, dispersion, and deposition of two major dust events originating from the high‐altitude subtropical Puna‐Altiplano Plateau (15–26°S; 65–69°W) in South America. A long and severe drought provided the right conditions for the onset of both events in July 2009 and 2010. Dust was transported SE and deposited over the Pampas region and was observed to continue to the Atlantic Ocean. Dust monitoring stations located downwind recorded both events, and samples were characterized through chemical and textural analysis. Through a combination of meteorological data and satellite observations (CALIPSO and MODIS detectors), we estimate the emission flux for the 2010 event. This estimate was used to constrain the Hybrid Single Particle Lagrangian Integrated Trajectory (HYSPLIT) transport model and simulate the dust event. Both satellite imagery and model results agree in the location and extension of the dust cloud. CALIPSO detected dust between ~6000 and ~8500 m a.s.l., which remained at this height during most of its trajectory. The dust cloud mixed with a strong convective system in the region, and the associated precipitation brought down significant amounts of dust to the ground. Dust particle size analysis for both events indicates that near the sources dust samples show median modes of 12.4–14.1 µm, similar to modes observed 1300 km away. Chemical composition of sediments from potential dust sources shows distinct signatures within the Puna‐Altiplano Plateau, the Puna sector being clearly different from the Altiplano area. In addition, both sources are markedly different from the Patagonian chemical fingerprint. These results have important implications to improve the interpretation of paleo‐environmental archives preserved on the Argentine loess, Antarctic ice cores, and Southern Ocean marine sediments.

The role played by Paleoproterozoic cratons in southern South America from the Mesoproterozoic to the Early Cambrian is reconsidered here. This period involved protracted continental amalgamation that led to formation of the supercontinent Rodinia, followed by Neoproterozoic continental break-up, with the consequent opening of Clymene and Iapetus oceans, and finally continental re-assembly as Gondwana through complex oblique collisions in the Late Neoproterozoic to Early Cambrian. The evidence for this is based mainly on a combination of precise U-Pb SHRMP dating and radiogenic isotope data for igneous and metamorphic rocks from a large area extending from the Rio de la Plata craton in the east to the Argentine Precordillera in the west and as far north as Arequipa in Peru. Our interpretation of the paleogeographical and geodynamic evolution invokes a hypothetical Paleoproterozoic block (MARA) embracing basement ultimately older than 1.7 Ga in the Western Sierras Pampeanas (Argentina), the Arequipa block (Peru), the Rio Apa block (Brazil), and probably also the Paraguaia block (Bolivia).

Present knowledge of Late Triassic tetrapod evolution, including the rise of dinosaurs, relies heavily on the fossil-rich continental deposits of South America, their precise depositional histories and correlations. We report on an extended succession of the Ischigualasto Formation exposed in the Hoyada del Cerro Las Lajas (La Rioja, Argentina), where more than 100 tetrapod fossils were newly collected, augmented by historical finds such as the ornithosuchid Venaticosuchus rusconii and the putative ornithischian Pisanosaurus mertii. Detailed lithostratigraphy combined with high-precision U-Pb geochronology from three intercalated tuffs are used to construct a robust Bayesian age model for the formation, constraining its deposition between 230.2 ± 1.9 Ma and 221.4 ± 1.2 Ma, and its fossil-bearing interval to 229.20 + 0.11/- 0.15-226.85 + 1.45/- 2.01 Ma. The latter is divided into a lower Hyperodapedon and an upper Teyumbaita biozones, based on the ranges of the eponymous rhynchosaurs, allowing biostratigraphic correlations to elsewhere in the Ischigualasto-Villa Unión Basin, as well as to the Paraná Basin in Brazil. The temporally calibrated Ischigualasto biostratigraphy suggests the persistence of rhynchosaur-dominated faunas into the earliest Norian. Our ca. 229 Ma age assignment to Pi. mertii partially fills the ghost lineage between younger ornithischian records and the oldest known saurischians at ca. 233 Ma.

Abstract Two end‐member models have been proposed for the Paleogene Andean foreland: a simple W‐E migrating foreland model and a broken‐foreland model. We present new stratigraphic, sedimentological and structural data from the Paleogene Quebrada de los Colorados ( QLC ) Formation, in the Eastern Cordillera, with which to test these two different models. Basin‐wide unconformities, growthstrata and changes in provenance indicate deposition of the QLC Formation in a tectonically active basin. Both west‐ and east‐vergent structures, rooted in the basement, controlled the deposition and distribution of the QLC Formation from the Middle Eocene to the Early Miocene. The provenance analysis indicates that the main source areas were basement blocks, like the Paleozoic Oire Eruptive Complex, uplifted during Paleogene shortening, and that delimits the eastern boundary of the present‐day intraorogenic Puna plateau. A comparison of the QLC sedimentary basin‐fill pattern with those of adjacent Paleogene basins in the Puna plateau and in the Santa Bárbara System highlights the presence of discrete depozones. These reflect the early compartmentalization of the foreland, rather than a stepwise advance of the deformation front of a thrust belt. The early Tertiary foreland of the southern central Andes is represented by a ca . 250‐km‐wide area comprising several deformation zones (Arizaro, Macón, Copalayo and Calchaquí) in which doubly vergent or asymmetric structures, rooted in the basement, were generated. Hence, classical foreland model is difficult to apply in this Paleogene basin; and our data and interpretation agree with a broken‐foreland model.

The fungus Blumeria graminis f. sp. tritici causes wheat powdery mildew disease. Here, we study its spread and evolution by analyzing a global sample of 172 mildew genomes. Our analyses show that B.g. tritici emerged in the Fertile Crescent during wheat domestication. After it spread throughout Eurasia, colonization brought it to America, where it hybridized with unknown grass mildew species. Recent trade brought USA strains to Japan, and European strains to China. In both places, they hybridized with local ancestral strains. Thus, although mildew spreads by wind regionally, our results indicate that humans drove its global spread throughout history and that mildew rapidly evolved through hybridization.

, a well-studied coastal model diatom, grows more rapidly, and with higher photosynthetic efficiency, with input of glaciogenic particulates compared to that of nonglaciogenic particulates due to these differences in Fe mineralogy. Monod nutrient accessibility models fit to our data suggest that particulate Fe(II) content, rather than abiotic solubility, controls the Fe bioavailability in our Fe fertilization experiments. Thus, it is possible for this diatom to access particulate Fe in dusts by another mechanism besides uptake of unchelated Fe (Fe') dissolved from particles into the bulk solution. If this capability is widespread in the Southern Ocean, then dusts deposited to the Southern Ocean in cold glacial periods are likely more bioavailable than those deposited in warm interglacial periods.

Soil physical quality is fundamental for the sustainability of agro ecosystems. Soil physical quality assessment must be developed using parameters that describe physical behavior. S, a new soil physical parameter has recently been introduced for assessing the soil physical quality. A good soil physical quality has been associated with values of S > 0.035 in soils from temperate climates. However, S has not been evaluated in tropical soils yet. Therefore we tested the hypothesis that S is a reliable soil physical quality indicator of a Typic Hapludox cropped with maize under no-tillage (NT) and conventional tillage (CT). Undisturbed samples were collected from each tillage system in the row and interrow positions. Soil bulk density was determined in the samples and the S parameter was calculated using a pedotransfer function from the same samples. The parameter S was able to differentiate tillage and position with S NT < S CT independent of the row and interrow sampling positions. Higher S values were verified in row position than in the interrow in both tillage systems. With the use of a pedotransfer function it was also possible to establish a negative relationship between S and soil compaction. The results confirmed our hypothesis and suggest that further studies should be carried out to evaluate S in other tropical soils and management systems.

Abstract Microbialites comprise the mineralized record of early life on Earth and preserve a spectrum of fabrics that reflect complex physical, chemical, and biological interactions. The relatively rarity of microbialites in modern environments, however, challenges our interpretation of ancient structures. Here we report the occurrence of microbial mats, mineral precipitates, and oncoids in the Laguna Negra, a high-altitude hypersaline Andean lake in Catamarca Province, Argentina. Laguna Negra is a Ca-Na-Cl brine where abundant carbonate precipitation takes place. Extreme environmental conditions, including high UV radiation, elevated salinity, and temperature extremes, restrict multicellular life so that mineralization reflects a combination of local hydrologic conditions, lake geochemistry, and microbial activity. The resulting carbonates consist of micritic laminae, botryoidal cement fans, and isopachous cement laminae that are strikingly similar to those observed in Proterozoic stromatolites, providing insight into mechanisms of mineralization. Here, increased saturation with respect to carbonate minerals reflects mixing of spring-fed inlets and lake waters, favoring microbialite formation and preservation. This highlights the importance of hydrological mixing zones in microbialite formation and as taphonomic windows to record microbial activity. Recent discoveries of minerals related to evaporating playa-lake systems on Mars further highlights the potential of Laguna Negra to provide critical insight into biosignature preservation in both terrestrial and extraterrestrial settings.

Carbonate microbialites provide a window to understand microbe-mineral interactions in modern environments and in the geological record. Unraveling microbial versus physicochemical controls and biogeochemical signatures is not always straightforward. Environmental and laboratory studies have shown that microbial activity can play a central role in calcium carbonate precipitation. Most studies have focused on the effects of Bacteria and Archaea activity on carbonate precipitation processes (e.g., cyanobacteria, sulfate-reducing bacteria, sulfide-oxidizing bacteria and iron-reducing bacteria). The influence of eukaryotic activity, such as diatoms and other microalgae, on carbonate precipitation and microbialite formation has been the focus of less attention.

Mourasuchus is a Miocene alligatorid endemic to South America, and is represented by four species. Together with the closely related Purussaurus, it is a peculiar crocodylian taxon of neogene Caimaninae and one of the most bizarre forms among eusuchian crocodiles. The phylogenetic relationships between Mourasuchus species have not been explored, and detailed skull descriptions are scarce. The goal of this study is to provide new data on skull morphology and cranial recesses in Mourasuchus nativus, including a new tomography analysis (3D modeling). We observed that several diagnostic characters of Purussaurus, such as lack of contact between the nasal and lacrimal, separation of the nasal and frontal by the prefrontals, and the posterior dorsal margin of the skull table, are shared with Mourasuchus. M. nativus is characterized by the presence of solid transverse squamosal eminences, large posttemporal fenestrae, and a quadrate laterocaudal bridge separating V(2) -V(3) trigeminal openings. Compared with other crocodylians, the endocast of M. nativus is similar in shape but quite sigmoid in lateral view, the canal of the supraorbital ramus of V(2) is more vertically oriented, the thick tympanic branch canal opens in a large foramen aligned with trigeminal foramen, and the canal of the vagal (X) tympanic ramus is also very wide. Contrary to extant alligatorids, the median pharyngeal recess remains paired throughout its course and only connects its opposite fellow near the external ventral opening. The knowledge of the internal skull anatomy of Mourasuchus contributes to the understanding of the general morphology of alligatorids, Caimaninae, and their variation.

The phylogenetic relationships of the recently described genus † Ticinolepis from the Middle Triassic of the Monte San Giorgio are explored through cladistic analyses of the so far largest morphological dataset for fossil actinopterygians, including representatives of the crown-neopterygian clades Halecomorphi, Ginglymodi and Teleostei, and merging the characters from previously published systematic studies together with newly proposed characters. † Ticinolepis is retrieved as the most basal Ginglymodi and our results support the monophyly of Teleostei and Holostei, as well as Halecomorphi and Ginglymodi within the latter clade. The patterns of relationships within these clades mostly agree with those of previous studies, although a few important differences require future research. According to our results, ionoscopiforms are not monophyletic, caturids are not amiiforms and leptolepids and luisiellids form a monophyletic clade. Our phylogenetic hypothesis confirms the rapid radiation of the holostean clades Halecomorphi and Ginglymodi during the Early and Middle Triassic and the radiation of pholidophoriform teleosts during the Late Triassic. Crown-group Halecomorphi have an enormous ghost lineage throughout half of the Mesozoic, but ginglymodians and teleosts show a second radiation during the Early Jurassic. The crown-groups of Halecomorphi, Ginglymodi and Teleostei originated within parallel events of radiation during the Late Jurassic.