The amalgamation of southwestern Gondwana during the late Neoproterozoic Brasiliano/Pan-African orogenic cycle involved the tectonic interaction of the Congo, Kalahari and Rio de la Plata cratons, together with numerous smaller basement fragments scattered throughout South America. A comprehensive review of U-Pb and Lu-Hf spot analyses in zircon provides new insights on the pre-Brasiliano crustal growth of the main tectonic domains of the southern South American Platform from the Archean to the early Neoproterozoic. The results highlight similarities between five basement fragments, from south to north: the Nico P´erez Terrane, Tijucas Terrane, Camboriú Complex, Luis Alves Terrane and Curitiba Terrane. Whereas these units have variable characteristics, especially concerning differing degrees of tectonic reworking in the late Neoproterozoic, they share similarities in their geological evolution. They were all originally accreted in the Archean, as evidenced by Hf TDM model ages and zircon inheritance, and later experienced intense orogenic reworking during the Rhyacian and Orosirian. The Paleoproterozoic record is diverse and indicates a complex episodic evolution instead of a single orogenic event. Conspicuous diachronic magmatic events took place locally in the Late Paleoproterozoic and Mesoproterozoic, interrupting an otherwise relatively stable tectonic setting until the Neoproterozoic. The Archean origin and strong crustal signatures of the main Paleoproterozoic units distinguish these terranes from the Rio de la Plata Craton, evidencing instead stronger affinities with African crustal blocks such as the Congo and Kalahari cratons. This relationship has implications for the geodynamic reconstruction of southwest Gondwana that extend into the early Neoproterozoic, as it contextualizes the genetic link between the main Tonian events in the region, namely the formation of the S˜ao Gabriel Terrane and the emplacement of the magmatic protoliths of the basement of the Punta del Este Terrane. They can be understood as marginal and within-plate manifestations of an accretionary orogen, respectively. The basement of the Punta del Este Terrane has signatures compatible with the recycling of ancient crust through the mixture of mantellic magmatic input with the partial melting

Coupled U–Pb and Lu–Hf LA-ICP-MS detrital and igneous zircon data were obtained from etasedimentary sequences (Kaserer Formation, Schmirntal Quartzite, Seidlwinkel Formation, Bündnerschiefer Basin, Riffler Basin) of the western Tauern Window (Eastern Alps). Results show maximum deposition ages between the Late Permian and the Triassic, indicating protracted sedimentation and magmatism between the Late Paleozoic and the Mesozoic. The Lu–Hf fingerprint shows a change from subchondritic to variable subchondritic to suprachondritic compositions at ca. 290 Ma, possibly documenting the transition from Late Paleozoic Variscan post-collisional processes to intracontinental extension. Lithospheric thinning and magmatic underplating may explain the observed Hf isotopic evolution as the result of mixing of crustal and mantellic sources. From a paleogeographical perspective, results confirm that the Tauern Window was situated between Alpine basement units (South Alpine, Austroalpine and External Massifs) and the Bohemian Massif during the Permian–Triassic.

We present the first palynological assemblages collected from the fine-grained variegated beds that overlie the De La Cuesta Formation at Puerta de Las Angosturas, Sierra de Narváez, Catamarca Province, Argentina. Five samples from two different stratigraphic levels provided spores, non-taeniate, taeniate, and sulcate pollen grains referred to the Lueckisporites/Weylandites (LW) Biozone. The palynofloras are equivalent to those previously reported for the Los Jumes area and, therefore, the variegated sequences that overlie the De La Cuesta Formation at both flanks of the Sierra de Narváez are entirely equivalent, not only lithologically but also in fossiliferous content and age. These assemblages are analogous to those isotopically dated at 278.84±0.22 Ma (Kungurian) in the Valle Hermoso area (La Rioja Province), which constitute a key stratigraphic horizon to link the initial phases of the Permian volcanic arc and the sedimentation in the retroarc basins. The recognition of diagnostic taxa of the LW Biozone confirms earlier correlations with the Striatites Biozone of the Chacoparaná Basin and the Lv Biozone from Brazil. The different ages recently reported for the succession analyzed here in Sierra de Narváez and La Veteada Formation, suggest that these units should not be correlated. Moreover, while the strata overlying the De La Cuesta Formation records the Permian post-orogenic sedimentation in the Paganzo Basin, the La Veteada Formation accounts for the transition to the rifting conditions that characterized the triassic basins of northwestern Argentina.

Palynology is one of the most useful tools for constructing biostratigraphic charts in the late Paleozoic basins of South America, but the lack of radiometric ages often makes it difficult to establish the precise age of the biozones. This paper focuses on two points: (i) the description of new Argentinian palynological assemblages referred to the Lueckisporites/Weylandites (LW) Biozone and (ii) the application of a new isotopic age that enables more confident large-scale correlations with the neighboring Paraná Basin of Brazil. The palynofloras were recovered from the upper part of the De La Cuesta Formation that crops out in the retroarc basin of the Paganzo Basin, more specifically obtained from mudstones intercalated with limestones, cherts, and tuffs interpreted as being deposited in a shallow water body. The assemblages are characterized by an abundance of bi-taeniate pollen grains of the Lueckisporites complex and multitaeniate pollen grains such as Lunatisporites, Protohaploxypinus, Striatopodocarpidites, Tornopollenites, and Vittatina. Colpate pollen grains are also represented by Marsupipollenites and Pakhapites. A U-Pb CA-ID-TIMS age of 278.84 ± 0.22 Ma, obtained from a tuff level interstratified with the fossiliferous strata, allows the age of the LW Biozone in the Paganzo Basin to be constrained for the first time and the adjustment of the record Lueckisporites virkkiae in Gondwana. Moreover, this date enables precise correlations with other basins, such as the San Rafael Basin (Yacimiento Los Reyunos Formation) in Argentina and the Brazilian Paraná Basin (Iratí Formation).

Lago Roca is a NE–SW elongated lacustrine body located to the south of Lago Argentino, the largest lake of the UNESCO ‘Los Glaciares’ National Park. An extensive high-resolution seismic survey carried out within the Lago Roca, integrated with geological information gathered in the area, have allowed to produce: (a) a complete bathymetric map of the lake; (b) a basement topography map and a structural map; and (c) an analysis of the geometry, distribution, and thickness of the sedimentary infill. Two sub-basins were recognized in Lago Roca, separated by a central basement high that shows a pop-up structure. The northern and southern margins of the lake basement are bounded by NE–SW trending strike-slip faults that constitute subsidiary faults strands of the regional structural lineament known as the ‘Lago Argentino transfer fault’. The shallow, low magnitude seismicity recorded in the area supports the interpretation that this fault segment is active at the present. The relative motion along the fault led to the deformation of the sedimentary infill of the lake, which was also affected by several subsidiary normal faults oriented parallel to the Lago Argentino transfer fault. Data show the peculiar asymmetry in the sedimentary filling of Lago Roca, typical of those of pull-apart basins generated along transform margins. A simplified model for the evolution of Lago Roca is also here proposed, based on the analysed data and the regional tectonic background.

In this study, we examine the external part of the Magallanes-Malvinas Fold and Thrust Belt in offshore areas, including a portion in Tierra del Fuego onshore, in southern South America. Our investigations focus on the interaction between a thin-skinned fold and thrust belt and the basement in that deformation, considering pre-existing structures acting as stress risers and localizing a possible tectonic inversion. The data is composed of around 14,000 km of 2-D multichannel seismic lines and three exploratory wells, used to analyse the anticlines of the fold and thrust belt in the area. The strike of these folds progressively evolves from NW-SE trending in western onshore regions, to WSW-ENE trending in eastern offshore areas. The fold and thrust belt shows a buttressing effect against the Río Chico Arch. The most shortening is seen in the apex of the Río Chico Arch around 67° W, in the coast of Tierra del Fuego, and gradually decreases eastwards in offshore regions. A connection between basement-involved faults and folds offshore is inferred from the analysis of the Géminis and Ciclón anticlines, developed during the N–S last compressional stage of deformation in the late Oligocene/early Miocene. The Géminis anticline is a fault propagation fold with a total shortening of 205 m with a piggyback basin developed over its backlimb. The location and ENE-WSW strike-direction of the fold have been controlled by a basement-involved fault. The Ciclón anticline is a subtle fold trending WNW-ESE developed as a result of the slight tectonic inversion of a negative flower structure.

The Matachines field, located in the Girardot subbasin, Upper Magdalena Valley (Valle Superior del Magdalena – VSM) basin, has a morphology characterized by antiforms arranged along a N–S axis. These antiforms involve multipha-se tectono-sedimentary sequences with half-graben geometries associated with Mesozoic sequences reactivated by at least three Andean phases. Bedding surfaces are mechanically active planes that contribute to the flexural slip that is generated by the folding of multilithologic sequences. In the Matachines field, the bedding planes help to improve the petrophysical characteristics of the reservoirs by incorporating a significant number of discontinuities, which comple-ment the fluid connectivity. Thus, the subhorizontal planes are linked to subvertical fractures preferentially arranged in the ENE–WSW direction, generated by horizontal compressive stress. In particular, these effects are magnified on the western flank and hinge zone of the anticline structure, where they contribute greatly to the connectivity of the production wells. In naturally fractured reservoirs, the correct 4D technical and economic evaluation of the quality and arrangement of discontinuities is essential to determine their actual contribution to improving the petrophysical properties of such reservoirs. Accordingly, many methods often used to study wells from core samples or images identify, along with different types of fractures, the presence of bedding surfa-ces, although they evaluate them separately, so they overlook petrophysical factors that affect the porosity and permeability of the wells. The present study discusses the genetic and morphological aspects of bedding surfaces that enhance the petrophysical potential of reservoirs, which usually have limited primary values of permeability and porosity, to meet the economic expectations of specific resources in hydrocarbon exploration and/or production activities.

Rosselia socialis were studied in the Ordovician Áspero Formation, in order to explore their sedimentary and diagenetic fingerprint in the substrate. These trace fossils are found forming crowded Rosselia ichnofabrics, described for the first time in pre-Quaternary strata of Argentina. We identified three microstructures corresponding to the central shaft complex, the burrow lining and the host rock of a trace fossil assigned to a terebellid polychaete. The infill of the central shaft complex represents downwards advection of surficial deposits located close to the burrow opening: fine-grained fecal mounds, and sandy mounds and lag deposits of manipulated, non-ingested material. Abundant phylosillicates in the central shaft complex and burrow lining evidence mechanical selection of particles with high specific surface area by the tracemaker. The fine-grained composition and multilayered organically bound structure of the burrow lining generate an impermeable and reinforced burrow, which combined with crowding grants physical and chemical stability to its inhabitants. This is especially advantageous in the high energy environments with shifting substrates where crowded Rosselia ichnofabrics are typically found. The central shaft complex and burrow lining are enriched in secondary iron minerals with respect to the host rock. Mineralized bacterial structures in the burrow lining evidence biologically induced precipitation of iron oxides and possibly sulphides. This coupled with the distribution of iron minerals in the burrow lining and central shaft complex suggests the occurrence of early diagenetic processes of organic matter decomposition and precipitation of authigenic iron minerals in Rosselia burrows, as observed in modern terebellid polychaetes.