Characterization of upper mantle structures in the northern region of the Antarctic Peninsula, through an analysis of seismic velocity anomalies.
In order to study the seismic structure of the upper mantle underlying the South ridge of Scotia and the northern end of the Antarctic Peninsula, a joint inversion seismic tomography, based on the travel time residuals of the P and S waves, was carried out. It was based on seismographic records acquired continuously at seismological stations located in Argentine Antarctic bases, from the Argentine-Ita-lian Project for the management and maintenance of ASAIN: Antarctic Seismograph Argentinian Italian Network. The signals used correspond to local seismotectonic events of moderate to large magnitude that occurred between 2009 and 2019. The regularization method was implemented for the data discrete inversion. The results were evaluated by synthetic resolution tests. The seismic structures resolved with the tomographies were characterized and interpreted. The study was complemented by estimating the Poisson's modulus and the bulk sound velocity anomaly, which allowed the incorporation of restriction conditions and, therefore, assessment conditions in the interpretation of the tomographies. The presence of a negative S-wave velocity anomaly in the Bransfield basin sector is highlighted, in correspondence with that reported by other authors. It is interpreted as a region of the crust and mantle subjected to modifications of the rheological condition (decrease in rigidity, increase in incompressibility and increase in anelasticity) caused by an anomalous thermal flux from a source located deeper in the mantle.

The Central Andes of South America are characterized by different morphotectonic units that exhibit distinctive stratigraphic, structural, and geomorphic features. In particular, the topographic variations across the orogen are remarkably notorious. Theoretical studies on the elevation of continents have discretized distinct components that contribute to the observed elevation, among which the compositional and thermal contributions prevail. Previous investigations in the Central Andes have shown that the region presents a high variability in its crustal composition and thermal state. Such variations could exert a first-order control on the regional topography, as shown previously for the Altiplano-Puna plateau area. This study, therefore, sets out to investigate the relationship between the present-day elevation of the Central Andes, its crustal composition, and its thermal state. We first calculated the predicted thermal contribution for each morphotectonic unit based on 1D geotherms modeled on the basis of surface heat-flow data. In order to remove the compositional contribution of the crust, we then calculated a normalized elevation. This elevation was compared to the predicted thermal contribution to evaluate their fit in each morphotectonic unit. The Altiplano-Puna plateau and the Western Cordillera exhibit a good correlation, suggesting that composition and temperature control their present-day elevation. Conversely, the other areas show a significant misfit. The detailed analysis of the remaining morphotectonic units suggests that tectonic processes at the subduction zone, mantle contributions, and transient states need to be considered as important contributors to the present-day thermal state and/or elevation.

Ediacaran (or Ediacaran) is the terminal period of the Precambrian, extending from 635 to 541 million years ago (Ma). During this period the planet appears to have experienced a series of extraordinarily singular events and processes, whose actual existence and detailed characteristics are the subject of much debate and controversy. Some of the events that are more or less certainly investigated, discussed and analyzed at present are: 1) the appearance of the first complex biota of multicellular organisms in Earth's history but which would leave no successors in the Phanerozoic; 2) the largest δ13C isotopic excursion in the history of the planet (Shuram excursion) and its relationship with the evolution of the oceans; 3) the existence of a glaciation that reached low latitudes (Gaskiers glaciation) and its global paleoenvironmental impacts; 4) the chronology and kinematics of the final rupture of the supercontinent Rodinia and the subsequent formation of Gondwana; 5) the possibility of very fast true polar displacements of about 90° by exchange of the inertial axes of the planet; 6) the possibility that the magnetic poles were located for long periods at the equator; 7) an ultraweak magnetic field, with the lowest paleointensity on record; 8) a hyperactive magnetic field, with the maximum frequency of known polarity reversions; 9) the possible beginning of the formation of the Internal nucleus and the subsequent change in the mode of the terrestrial geodynamo; and many more. Through systematic paleomagnetic studies it is possible to provide valuable information to resolve many of these questions. For two decades, in the Daniel A. Valencio Paleomagnetism Laboratory of the IGEBA we have been developing systematic multidisciplinary studies in sedimentary and volcanic Ediacaran rocks of the Río de la Plata craton. These investigations are nurtured by a close and continuous collaboration with colleagues from other research groups in Argentina, Brazil and Uruguay. The studies include mainly paleomagnetic investigations in order to reconstruct the paleogeographic evolution of the Ediacaran craton and to contribute to understand the kinematics of the formation of Gondwana. Recently we are also advancing in the knowledge of the polarity reversions of the magnetic paleofield in the late Ediacaran. Accurate geochronological dating, systematic isotopic studies and recent spectacular fossil finds, in addition to paleomagnetic information, are significantly increasing our knowledge of a period that until two decades ago was almost unknown. These advances include a schematic reconstruction of the paleogeographic evolution of the La Plata River craton between approximately 600 and 550 Ma, during which time it would have migrated from low to high latitudes. With this information and that of other West Gondwana cratons, constraints on the ages of annexation with Congo-São Francisco and West Africa are emerging. They also allow speculation with more observational support on the possible existence (or not) of a big ocean called Clymene in late stages of Gondwana formation. The probable record of the Shuram excursion in calcareous sediments of the craton is a concrete possibility as chemostratigraphic studies progress. Although still incipient, the first magnetostratigraphic resultswe are obtaining suggest the apparent presence of rapid polarity reversions. This succession of new results marks limits to certain models or non-current proposals while it is compatible with others, opening an important number of new questions. In this paper we present a brief summary of the current global knowledge of many of these controversies, as well as the progress of research in our country.

At the east of the Ventana Ranges, Buenos Aires, Argentina, outcrops the Carboniferous-Permian Pillahuincó Group (Sauce Grande, Piedra Azul, Bonete and Tunas Formation). We carried out an Anisotropy of Magnetic Susceptibility (AMS) study on Sauce Grande, Piedra Azul and Bonete Formation that displays ellipsoids with constant Kmax axes trending NW–SE, parallel to the fold axes. The Kmin axes are orientated in the NE–SW quadrants, oscillating from horizontal (base of the sequence-western) to vertical (top of the sequence-eastern) positions, showing a change from tectonic to almost sedimentary fabric. This is in concordance with the type and direction of foliation measured in petrographic thin sections which is continuous and penetrative to the base and spaced and less developed to the top. We integrated this study with previous Tunas Formation results (Permian). Similar changes in the AMS pattern (tectonic to sedimentary fabric), as well as other characteristics such as the paleo-environmental and sharp curvature in the apparent polar wander path of Gondwana, marks a new threshold in the evolution of the basin. Those changes along the Pillahuincó deposition indicate two different spasm in the tectonic deformation that according to the ages of the rocks are 300–290 Ma (Sauce Grande to Bonete Formation deposition) and 290–276 Ma (Tunas Formation deposition). This Carboniferous-Permian deformation is locally assigned to the San Rafael (Hercinian) orogenic phase, interpreted as the result of rearrangements of the microplates that collided previously with Gondwana, and latitudinal movements of Gondwana toward north and Laurentia toward south to reach the Triassic Pangea.

Two episodes of lacustrine sedimentation, separated by an erosional surface and fluvial sedimentation, took place in the southern part of the broken foreland Vinchina basin (NW Argentina) between 11 and 5 Ma. The lacustrine deposits, 768 and 740 meters thick, are recorded in the upper part of the Vinchina Formation (“Vinchina lake”) and the lower part of the Toro Formation (“Toro Negro lake”) respectively. According to sedimentological features, four sedimentary facies associations (FAs) are recognized in the lacustrine deposits: 1) thinly laminated mudstones facies association (FA 1), 2) coarsening- and thickening-upward muddy to sandy cycles (FA 2), 3) medium- to coarse-grained sandstones (FA 3), and 4) mudstones, sandstones, and oolitic limestones (FA 4). Altogether, these facies correspond to ephemeral, shallow, lacustrine systems including saline mudflats. The total thickness of each lacustrine interval, the thickness of the individual cycles and their lithology, and the overall aggradational facies arrangement suggest that both lakes developed during underfilled stages of the basin. The coarsening-upward cycles can be regarded as lacustrine parasequences representing cyclic episodes of expansion and contraction of the lake, but unlike marine parasequences these cycles do not correlate to water depth. The development of lacustrine conditions and continuous base-level rise, together with the coeval southward-directed paleoflow indicators, suggest axial drainages and that the basin was externally closed (endorheic) at that time. The large thicknesses of each lacustrine interval also points to high accommodation in the southern part of the Vinchina basin during these times. Lake filling cycles are one order of magnitude thicker than lake depth, so we postulate that subsidence (tectonic) and rise of the spill point (geomorphology) increased accommodation but not water depth. Thus, unlike marine parasequences, the analyzed coarsening-upward cycles do not correlate to water depth, but rather they are controlled by more complex basinal accommodation processes. We hypothesize that the coeval uplift of the Umango and Espinal basement block to the south, coupled with the initial doming of the Sierra de Los Colorados to the east, may have generated the damming of the southward-directed drainage and a zone of maximum accommodation, then controlling the location of the two lakes and the preservation of their thick sedimentary records. Therefore, localized accommodation was enhanced by a combination of tectonic subsidence and topographic growth. The two lacustrine intervals and the intervening fluvial deposits record changing contributions from axial to transverse drainages and different cycles of closed and open conditions in the basin. A low-frequency, closed to open and back to closed (axial to transverse and return to axial drainage) basin evolution, is envisaged by the development of the two lakes (closed stages) and the erosional surface followed by the interval of fluvial sedimentation that separates them (open stage). In addition, several high-frequency lake fluctuations (expansion–contraction) are represented by the coarsening-upward cycles within each lacustrine interval. The thick lacustrine intervals and their intermediate incision surfaces record cyclic filling and re-excavation stages and localized episodes of increased subsidence in the Vinchina basin, which seem to be a common feature of tectonically active broken foreland basins.

Sedimentology and ichnology of the middle interval of the Agua del Jagüel Formation, Carboniferous of Mendoza Precordillera: paleoenvironmental implications of the postglacial transgression. The paleoenvironmental and ichnological characteristics of the middle section of the Agua del Jagüel Formation (Carboniferous) are described in this paper. Five sedimentary facies, grouped into three facies associations illustrating the evolution of a fluvio-estuarine system, were identified. Facies association 1, composed of fluvial conglomerates and coarse-grained sandstones, rests on an erosive surface carved into postglacial diamictites, sandstones, and shales belonging to the lower part of the Agua del Jagüel Formation.

A late Pleistocene glaciolacustrine record was studied at Fagnano Lake (54°35´S, 67°20´W), central Isla Grande de Tierra del Fuego, southernmost South America. Two profiles from the Río Valdéz outcrop were collected for isotopic, geochemical, sedimentological, and geophysical analyses. The sedimentological characteristics, such as rhythmites, presence of dropstones, absence of fossil record, and scarce presence of organic matter, suggest deposition in an ice-contact lake, possibly dammed by the Fagnano paleoglacier. Organic matter of C3 plant origin suggests certain cold and wet conditions. A chronology of the late Pleistocene outcrop was obtained from five 14C ages resulting in an age-depth model. The time span covered 49.01 cal ka BP to 32.14 cal ka BP. Based on the thickness of the deposit and the calculated average sedimentation rate, the glacial environment could have been present in the study area prior to the last glacial maximum, in agreement with the Inútil-San Sebastián paleoglacier. Both glaciers flowed from the same mountain ice sheet in the Darwin Cordillera, which makes it possible to infer a different behavior of this ice cap from those of the Patagonian Andes, perhaps forced by different atmospheric dynamics and proximity to the wet and cold subantarctic air masses.

Edelmira Mórtola, the first geologist of República Argentina Edelmira Mórtola was the first female geologist of the República Argentina and in 1921 she obtained a Ph. D. in Natural Sciences from the University of Buenos Aires. She worked in the Direction of Geology and Mines between 1918 and 1923, and was the first female professional of that Institution. She taught courses on Mineralogy and Petrography in the Doctorates in Natural Sciences and Chemistry, and Civil Engineering, at the Facultad de Ciencias Exactas, Físicas y Naturales, Universidad de Buenos Aires, currently Facultad de Ciencias Exactas y Naturales (FCEN UBA). In 1956 she became the first Full Professor of that Facultad. She devoted her life to teaching and organizing the Cabinet of Mineralogy and Petrography. She fostered the development of Mineralogy in our country, which currently have numerous centers of excellence founded by her disciples. She was a relevant woman for national development, her opinion, foresight and advice were requested by the highest academics and government authorities in times of consolidation of Argentine science.

The main contribution of this paper is a new interpretation of the geomorphological evolution of the North Patagonian coast surrounding the Golfo Nuevo from Mid-to-Late Pleistocene until present. The proposed model shows how continental and marine landforms evolved during the Late Quaternary. According to this, the Golfo Nuevo depression formed during the Middle Pleistocene (>130 ka) above previous fluvial terraces, which are attributed to different stages of the Chubut river. Several pediment types and levels were also identified: (1) flanking pediment (level 1) associated with an ancient fluvial valley; (2) convergent pediment related to a previous depression of Golfo Nuevo (level 2), both assigned to Middle Pleistocene; and (3) a littoral pediment (level 3) linked to a Holocene highstand level. The height and position of accretion marine terraces are discussed, in addition to their previous dating. It can be assumed that Golfo San Matías was flooded twice as a consequence of marine transgressions (marine isotopic stage [MIS] 5 and MIS 1). Likewise, Golfo Nuevo and Golfo San José were affected only once, during the maximum Holocene transgression (MIS 1). This paper highlights the importance of reconstructing the geomorphological evolution of a coastal area of the Patagonia as a result of a combination of changes linked to sea-level variations (mainly associated with glacio-eustasy) and climate, paleo-shorelines records, and continental landforms through Late Quaternary. The proposed geomorphological model can be considered a novelty because of the complex integration of continental and marine landforms and the study of their relative relation.