In Tierra del Fuego, the Magallanes-Fagnano Fault System (MFFS) accommodates a significant portion of the relative motion between the South America and Scotia plates. However, it remains unclear whether some of the deformation is partitioned southwards, along the Beagle Channel Fault System (BCFS). In this paper, high-resolution seismic reflection profiles were used to identify fault-related ruptures in the submerged Quaternary sediments of the Beagle Channel. Some faults reach the seafloor, affecting marine sediments, indicating they are Holocene in age. The correlation with outcrop data and lineaments mapped onshore suggests the post-glacial reactivation of two structures: the E-W striking BCFS and the NW-SE-trending Lapataia Fault Zone (LFZ). Whereas the BCFS displays along-strike variation in throw, the LFZ shows significant normal displacements. These results imply that deformation occurs in a wider and more complex manner than previously thought and highlight the need for a thorough hazard assessment of the area.

including turtles, crocodiles, and mammals. The age of this unit is currently under discussion given the lack of absolutechronological data, although recent works favored a middle Paleocene–early Eocene age. In this contribution, we present a leftmaxillary fragment (PVL 5901), preserving part of the M1 and the M2. A first analysis indicates a close relationship with Indalecia(Litopterna?, Indaleciidae), a genus previously recorded for the Lower Lumbrera Formation (?Ypresian; Salta Province, northwesternArgentina). Given that the Indaleciidae and the representatives of Amilnedwardsidae and Notonychopidae were considered relatedin the context of the order Notopterna, a comparison was made between PVL 5901 and these taxa, confirming its resemblancewith Indalecia. However, PVL 5901 differs from Indalecia grandensis(type and only species of the genus) by the presence of acuspule on the base of the ectoflexus, the absence of a small fossette mesial to the distolabial fossette, and a conspicuousentoflexus. Hence, we refer PVL 5901 to Indaleciasp. This is the first common faunal element between the Río Loro and LowerLumbrera formations. Nevertheless, the marked taxonomic discrepancies between the Río Loro vertebrate assemblage and otherearly Paleogene units contrast with this single common record, and a partial temporal correspondence between the Río Loro andLower Lumbrera formations is not supported here. Instead, this record indicates a more extended temporal and geographicaldistribution for the genus Indaleciain northwestern Argentina.Key words. Río Loro Formation. Lower Lumbrera Formation. Notopterna. Biostratigraphy. Northwestern Argentina.Resumen.

The gold and silver deposits of the Vetas-California mining district are hosted in Paleozoic gneisses and Mesozoic granites of the Santander massif in the Eastern Cordillera of Colombia, far from the northern Andean volcanic arc. In the California area, there is ambiguity in defining the epithermal-type metallogenic model with high to intermediate sulfidation due to the presence of Late Triassic-Early Jurassic and Miocene magmatism. The best-known hydrothermal episodes comprise two early porphyritic-style phases: a) characterized by a propylitic alteration with molybdenite of the ~10.1 Ma-old La Mascota breccia, related to granodiorite porphyries and smaller-volume rhyodacitic dykes; and b) attributed to a magmatic-hydrothermal system due to phyllic alteration associated with quartz-pyrite veins with hydrothermal sericite dated at ~3.4 Ma. These two hydrothermal episodes were followed by four epithermal phases related to the development of multiphase hydrothermal breccias and quartz-alunite alteration, defined by bornite, covellite, and chalcopyrite, alongside wolframite, enargite, and sphalerite, with gold and silver mineralization between ~2.6 and ~ 1.6 Ma. To understand the relationship of the emplacement of the porphyries and the subsequent auro-argentiferous enrichments to the deformation front observed in the Pamplona buttress, to the east of the Santander Massif, a 4D structural model of the mineralization is formulated here. This model is based on the spatial analysis of the stresses responsible for the La Baja-Angostura dextral fault in terms of the regional kinematics of the Bucaramanga sinistral fault. It is considered that the SW sector of the deposit area corresponds to a well-defined, tabular, sub-vertical body of the La Mascota breccia. On the other hand, the NE sector in the La Baja-Angostura fault is expressed as a topographically elevated right horsetail splay, which controls the more disseminated distribution of the mineralization by means of veinlet swarms arranged in an ~E-W direction. The disseminated mineralization of Vetas-California was probably favored by late thermal expansion-contraction events in the gneissic sockets, which allowed the accumulation and precipitation of boiling solutions rich in volatiles and elements of economic interest.

The Amotape Group consists of metasedimentites with varying degrees of metamorphism and Paleozoic intrusions, exposed as isolated blocks that form an NNE-SSW belt, separating the Meso-Cenozoic depocenters of the Talara (west) and Sechura and Tumbes basins (east) along the Pacific margin of NW Peru. We describe three metamorphic/tectonic episodes that produced sub-planar structures (cleavages, fractures) affecting the rocks of the Amotape Group, allowing this unit to be classified as a fractured reservoir. Field survey and multi-scale subsurface data from the Colán Block, evidence a secondary porosity system associated with fracture networks that affect both the basin fill and the basement units. This configures a complementary unconventional exploration target. Sandstone levels in lateral contact with leptometamorphic rocks of the Amotape Group define good reservoir potential due to the preferentially brittle mechanical behavior of the basement, which develops abundant fractures. The porosity values of the Amotape Group range between 4.62% and 1.23%, while permeabilities are on the order of 0.519-0.016 mD. Elevated trapping positions seem to be successfully sealed by Cretaceous units. The reservoir properties define a complementary play concept that could be extended to other positions of the technical basement in the Talara Basin and analogous regions.

Facies, microfacies and stable isotope analyses of limestone beds in the northernmost Ñirihuau Basin, North Patagonian Andes, Argentina, document and constrain the past hydrological, sedimentological and climate conditions that prevailed during the deposition of a lacustrine system between ca 15 and 13 Ma. This palaeoenvironment is recorded in the middle section of the Ñirihuau Formation, which holds significance because: (1) It was deposited during a transition from an extensional to a compressional tectonic regime; (2) it spans the Middle Miocene Climatic Optimum and the beginning of the Middle Miocene Climatic Transition; and (3) it contains limestone beds interbedded within a 600 m thick interval of mudstones and siltstones, along with intercalated sandstone and volcaniclastic bodies. Two detailed sedimentary logs were surveyed along the Arroyo Las Bayas, at the western and eastern flank of the David Syncline. Limestones from both stratigraphic sections were sampled as well as isolated limestone beds from two other sites. One facies association was defined and interpreted as a perennial lake associated with a deltaic system and dominated by detrital clastic material. It comprises Facies 1 (Marginal lacustrine) and Facies 2 (Lower delta plain); in both, the presence of grainstones and calcimudstones stands out. Through petrography and cathodoluminescence studies of these continental carbonates, nine microfacies were identified: (a) Intraclastic grainstone, (b) Homogeneous calcimudstone, (c) Silty grainstone, (d) Disrupted micrite, (e) Birds eye micrite, (f) Bioclastic mudstone, (g) Calcimudstone with sparse detrital grains, (h) Fenestral micrite, (i) Stromatolitic boundstone. These indicate mainly bio-induced subaqueous carbonate precipitation and subordinate deposition by tractive flows with short-distance transport on a littoral lacustrine environment. Most of these microfacies exhibit very early diagenesis (eogenesis) effects. These features, and the geochemistry results, indicate that they were deposited in a palaeolake system under temperate to warm and humid conditions.

Mesosaurs were small amphibious tetrapods that lived in western Gondwana during the Early Permian or even earlier, when temperate Permo-Carboniferous conditions initiated after the glaciations that affected the southern region of Pangea. In this contribution, we applied traditional linear regression morphometrics to analyse proportions of both the skull and limb bones in more than 100 mesosaur specimens. The analyses revealed that all mesosaur bones scale remarkably close to a model of geometrical similarity (isometry), and that this pattern is particularly strong in long bones and also in the skull. These results indicate that juvenile and adult mesosaurs do not display appreciable change in bone proportions, meaning that there are few or no noticeable differences between them during growth. The well-defined isometry, and particularly, the high interrelation between metatarsals and phalanges permit us to suggest that the mesosaur hind limb is subject to notable modularity. This evidence strongly argues that the differences previously described to support three mesosaur species in Western Gondwana, might instead reflect natural intraspecific variability, taphonomic features or even possible sexual dimorphism, as recently suggested. Our study also reinforces the general plesiomorphic structure of the mesosaur skeleton, which along with some cranial specializations for ecological fitness and the evidence of strong isometric growth as we demonstrate herein, may suggest new hypotheses of relationships for mesosaurs which thus would position them as more basal amniotes than previously thought.

Environmental changes were reconstructed from a multiproxy synthesis of over 30 localities from the Isla Grande de Tierra del Fuego and Isla de los Estados, southernmost South America. At a local scale, the results from the mountain forest and gently undulating steppe areas were integrated as well as those from the marine environments of the Beagle Channel and the Atlantic coasts. At a regional scale, the results were integrated with those published for the southernmost Andean and Extra-Andean Patagonia and the Antarctic Peninsula. This study focuses on the environmental evolution during the Late Glacial-Holocene transition, the Middle to Late Holocene transgressive-regressive hemicycle and wet-dry oscillations, the Medieval Climate Anomaly, the Little Ice Age, the tephra inputs from the Patagonian Andes, and the recent climatic warming. Most paleoenvironmental changes are related to variations in the latitudinal position and intensity of the Southern Westerly Winds (SWW) while others are associated with astronomical or endogenous forcings. At a strong intensity of the SWW, a greater contribution of humidity to the forest areas and an increase in the rainfall gradient create windy and arid conditions in the steppe. At a weak intensity of the SWW, lower humidity input in the forest areas and the advection of air masses from the Atlantic Ocean promoted humid and slightly windy conditions in the steppe. Similar environmental trends are observed between terrestrial and marine environments in the center and south of Tierra del Fuego, Isla de los Estados and the Antarctic Peninsula, and between the Fuegian steppe and Extra-Andean Patagonia. The paleoclimatic evidence reveal high environmental variability in the last 10,000 years for this sector of the Southern Hemisphere.

The Martín García Complex, which crops out at the homonymous island of the Río de la Plata Estuary, is composed of intermediate to silicic orthogneisses and granitoids, hornblende and olivine gabbros, and felsic dykes of Paleoproterozoic and Mesoproterozoic ages, as well as serpentinized ultrabasic rocks of unknown age. A major part of this igneous-metamorphic basement is covered by sediments and vegetation, hiding the relationships between the different rock units, and hindering their study. Therefore, a ground magnetic survey and the consequent 3D geophysical modeling were conducted to elucidate the geometry of the ultrabasic bodies in the subsurface. Normal and reverse dipolar sub-circular and elongated (∼ENE-WSW) magnetic anomalies were identified. It is proposed that Cr-rich spinels would be responsible for some of the detected magnetic anomalies. Our results suggest the existence of three magnetic units with a dyke-type geometry, all of them with ∼ENE-WSW trend and steep dip. The magnetic survey and 3D modeling allowed us to confirm the continuity and extension in the subsurface of the ultrabasic bodies cropping out discontinuously on the surface. According to their crosscutting relationships, a post-Stenian age is proposed for these rocks. Magnetic patterns identified in Martín García Island are similar to those observed in western Uruguay, suggesting that the Martín García Complex would be part of the Piedra Alta Terrane (Río de la Plata Craton).

The fluvial-aeolian interaction field of the Guandacol valley (northwest Argentina) is studied through different methodologies that comprise satellite, drone and GPR images, bedform descriptions, and grain-size analysis. The obtained information allowed the recognition of five depositional subenvironments: 1. Dune patches; 2. Aeolian sand sheets; 3. Muddy plains; 4. Active channels; and 5. Abandoned and secondary channels. Moreover, the lithofacies pattern, sedimentary structures and geometry of the beds permitted the definition of ten architectural elements in both channel and interchannel areas. The channel architectural elements comprise active channels with intercalations of aeolian deposits (CHe), abandoned or secondary channels (CHa), aeolian sand ramp (CHsr), lateral bars (CHlb), and aeolian mesoforms (CHem). The architectural elements in the interchannel area include active dunes (Fad), fixed or low-migration rate dunes (Fsd), partially flooded interdunes (Ffd), sandy flats (Fsf), and muddy plains (Fmp). A model of the evolution of fluvial-aeolian interaction environment is proposed in which three types are recognized: dry, intermediate, and wet. Migratory dunes and sand sheets environments dominate the dry interaction systems in the floodplain (Fad, Fsf). At the same time, during the intermediate stage, Fsd and Fsf architectures prevail, together with fluvial bars with thin aeolian intercalations into the channels (CHe and CHa). The wet systems consist of flooded interdunes, muddy plains, and different types of aeolian mesoforms in the channel (Fmp, Ffd and CHem). The analysis of present-day depositional subenvironments in the Guandacol valley and the definition of architectural elements serve as a potential analogue for studying ancient fluvial-aeolian interaction environments.

The concepts of progressive and polyphase deformation have been widely applied by structural geologists to explain complexly deformed rocks, particularly for ductile conditions. Interpreting complex structural patterns as the result of progressive deformation is mainly based on structural and kinematic evidence, applying the Ockham’s razor principle: single-phase progressive deformation is the simplest and thus most plausible explanation in many cases. Processes such as strain partitioning and localization are commonly considered to explain such patterns. In this contribution, guidelines to distinguish between progressive and polyphase deformation processes are presented, mainly based on a critical discussion of advantages and pitfalls of P-T-D-X-t (pressure – temperature – deformation – composition – time) data. Such information not only allows for a robust reconstruction on the timing and rates at which deformation operates, but also provides insights into the progressive or polyphase evolution of pressure-temperature conditions and fluid flow. For example, complex structural patterns are common in transpressional and transtensional settings, particularly (but not only) for non-steady progressive deformation, which seems to be the rule in nature. Consequently, assessing the structural and microstructural context is a must, because analytical data commonly record only distinct stages in the protracted evolution of deformation. CPO data are useful to disentangle complex structural histories, particularly in the case of changing deformation mechanisms and related conditions. For petrochronology, it is thus highly relevant to understand equilibrium conditions and mechanisms of intracrystalline deformation and (re)crystallization of dated minerals, in order to properly link the obtained ages with specific deformation stages and mineral reactions. In a similar way, structural facies characterization is critical to interpret geochronologic data linked to ductile and brittle deformation. Though poorly explored, microstructural information of fluid inclusion data is a valuable tool to understand the role of fluids in deformation-assisted settings. The recognition of phases is ultimately related to their tectonic significance and, therefore, may not be easy in cases of overlapping tectonic processes (e.g., subduction during a post-collisional phase) and transitional stages that may not necessarily imply a dramatic change in the deformation pattern (e.g., post-orogenic collapse and intracontinental rifting).