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).

Strong earthquakes (magnitude ≥7) occur worldwide affecting different cities and countries while causing great human, ecological and economic losses. The ability to forecast strong earthquakes on the long-term basis is essential to minimize the risks and vulnerabilities of people living in highly active seismic areas. We have studied seismic activities in North America, South America, Japan, Southern China and Northern India in search for patterns in strong earthquakes on each of these active seismic zones between 1900 and 2021 with the powerful mathematical tool of wavelet transform. We found that the primary seismic activity patterns for M ≥ 7 earthquakes are 55, 3.7, 7.7, and 8.6 years, for seismic zones of the southwestern United States and northern Mexico, southwestern Mexico, South American, and Southern China-Northern India, respectively. In the case of Japan, the most important seismic pattern for earthquakes with magnitude 7 ≤ M < 8 is 4.1 years and for strong earthquakes with M ≥ 8, it is 40 years. Every seismic pattern obtained clusters the earthquakes in historical intervals/episodes with and without strong earthquakes in the individually analyzed seismic zones. We want to clarify that the intervals where no strong earthquakes do not imply the total absence of seismic activity because earthquakes can occur with lesser magnitude within this same interval. From the information and pattern we obtained from the wavelet analyses, we created a probabilistic, long-term earthquake prediction model for each seismic zone using the Bayesian Machine Learning method. We propose that the periods of occurrence of earthquakes in each seismic zone analyzed could be interpreted as the period in which the stress builds up on different planes of a fault, until this energy releases through the rupture along faults and fractures near the plate tectonic boundaries. Then a series of earthquakes can occur along the fault until the stress subsides and a new cycle begins. Our machine learning models predict a new period of strong earthquakes between 2040 ± 5 and 2057 ± 5, 2024 ± 1 and 2026 ± 1, 2026 ± 2 and 2031 ± 2, 2024 ± 2 and 2029 ± 2, and 2022 ± 1 and 2028 ± 2 for the five active seismic zones of United States, Mexico, South America, Japan, and Southern China and Northern India, respectively. In additon, our methodology can be applied in areas where moderate earthquakes occur, as for the case of the Parkfield section of the San Andreas fault (California, United States). Our methodology explains why a moderate earthquake could never occur in 1988 ± 5 as proposed and why the long-awaited Parkfield earthquake event occurred in 2004. Furthermore, our model predicts that possible seismic events may occur between 2019 and 2031, with a high probability of earthquake events at Parkfield around 2025 ± 2 years.

Pampean shallow lakes naturally have water nitrogen and phosphorous concentrations that allow the development of dense beds of submerged aquatic vegetation, phytoplankton, or free-floating aquatic plants. In recent years, the eutrophication of these shallow lakes has increased due to the intensification of agriculture, use of fertilization and livestock. Phytoplankton- induced turbidity inhibits the growth of the submerged aquatic vegetation leading to phytoplankton dominance. This is the case of the Lobos shallow lake, which in a period greater than 20 years has remained as an organic turbid shallow lake, with cyanobacteria dominance. The study of the ecosystem metabolism can give relevant information about how the trophic state of a shallow lake drives production, respiration and net metabolism, and the potential consequences for aquatic biota. We evaluated the Lobos shallow lake metabolism using diel changes in dissolved oxygen concentrations during autumn and spring. Gross primary production showed lower values and variability in Autumn (1.57±1.33 g O2.m-2.day-1) than in Spring (20.45±18.00 g O2.m-2.day-1). Although there was high production during the day, respiration was also high, especially in Spring, where there was higher density of planktonic organisms principally cyanobacteria, exceeding net production in both seasons. Thus, we found mainly low or negative values for the net metabolism in Lobos shallow lake. A high oxygen consumption occurred during spring and at the lowest depth, coinciding with the highest chlorophyll-a concentrations, particulate matter, and lowest water transparency. We conclude that Lobos shallow lake was predominantly heterotrophic during study period. High nutrient concentrations will likely increase the factors that produce stress and negative impacts on aquatic fauna.

The drilling of the Alejandrina hydrogeological well at 209 m bbp, below the usual depth of water wells in the area, reached a sandy level of the Zapallal Formation with unexpected gas content that caused strong blow-up, venting, liquefaction of the ground, collapse of the drilling equipment and contamination of the traditionally producing levels of the confined aquifer. To mitigate this invasion of gas and it upwelling to the surface, the following wells were drilled: i) Papayal interference well, to carry out capture and cementing maneuvers with 5 horizontal attempts until intercepting the Alejandrina well, and ii) Curumuy 1X exploratory well to reduce the pressure of the gas invasion and discover its possible abnormal origins at such shallow depths. The objective of the work is to present the stratigraphy of this potentially exploratory sector with proved gas resources of the Sechura basin and to describe the sequence of events of the interference in the management and relationships between the hydrogeological and gas resources that share the same sandstone reservoirs of the Zapallal Formation. For this, petrophysical data are provided from the drilling records of the Alejandrina, Papayal and Curumuy 1X wells and a simulated model of loading and handling of the gas responsible for the contamination. In this way, a case of interference of different subsoil objectives is presented with the intention of preserving and reestablishing the behavior of the producing wells of the aquifer and at the same time producing gas.

The present study reviews the main geological features, with emphasis on structural controls, affecting the geoeconomic potential of the green schist-hosted talc deposits of the western sector of the San José Belt (Colonia Department, Uruguay) located in the Narancio, Dante Ramos and Zafiro Sector mines. The analysis of the regional geology allows us to define two complementary genetic models for the talc deposits: i) hydrothermal alteration of basic volcanic rocks rich in magnesium, and ii) metasomatic processes in the contact between dolomites and acidic intrusive rocks. Finally, the productive history of the Narancio Mine is synthesized and the geometry, the volume of the lenticular bodies and the quality of the talc deposits of the Zafiro Sector are discussed with the purpose of allowing a better evaluation of its economic potential.

The very thick (up to 6000 m thick) Miocene Vinchina Formation was deposited between 16 and 8 Ma ago and later covered by more than 2500 m of Pliocene-Pleistocene sediments in a broken foreland basin. The very thick sedimentary pile accumulated in a medium to low-gradient basin must have suffered intense mechanical compaction during burial.

Seventy thin sections of unaltered sandstones collected in three sections along the depositional strike of the Vinchina Formation at the Sierra de Los Colorados, La Rioja Province, northwestern Argentina, were analyzed under the microscope for determining compactional paths and controls.

The role of compaction in sandstone diagenesis was firstly assessed using the change in intergranular volume (IGV), which is the sum of all cement and remaining primary porosity. It is clear from the IGV analysis that most of the studied sandstones lose more porosity by compaction (COPL) than by cementation (CEPL). In general compaction increased from the upper to the lower member of the Vinchina Formation (i.e with depth) and there is a clear trend of the compaction index ICOMPACT increase from the northern, shorter Los Pozuelos to the central, thicker La Troya sections. Surprisingly, the thickest southern El Yeso section shows anomalous results possibly due to the extensive development of cements as indicated by the highest CEPL values. Cements are related to the depositional environment (gypsum, calcite) and clast composition (zeolites). Early cements may have prevented further compaction while late cements may have produced open fabrics by dissolution of matrix and framework clasts. Both cases show that diagenetic processes are not homogeneous basin-wide and that the diagenetic pathways are not only controlled by the increase in burial depth but also by characteristics associated with depositional environments and framework clast composition.

We also attempted to relate compaction to burial depth based on the nature (point, long, concave-convex and sutured contacts) and the number (contact and packing indexes) of grain-to-grain contacts in the studied sandstones. The sandstones present predominance of concave-convex grain-to-grain contacts and IC indexes mostly between 3 and 4. Sutured contacts are uncommon, and stylolites were not observed at all. Persistence of open fabrics, floating textures and point grain-to-grain contacts at different depths are the result of dissolution-cementation processes. A clear trend of increasing mechanical compaction with depth is only seen along the northern coarser-grained but thinner Los Pozuelos section. Although compaction seems to have increased with depth and also from north to south, the thickest but overall finer-grained El Yeso (southern) section do not show a clear pattern of change with depth. This behavior seems to be the result of at least four main factors: 1) mean sandstone grain-size, 2) thickness of muddy intervals, 3) development of early diagenetic cements, and 4) depth of burial.

Comparison with comparable examples suggests that similar compactional characteristics are achieved between 3.5 and 6 km of maximum burial depths. However, cumulative thickness of the Vinchina basin-fill indicate that the base of the Vinchina Formation may have been buried at 8.5 km deep but preliminary backstripping models suggest that by 5 Ma this surface may have reached up to 10 km depth. Alternatively, recorded repetitive episodes of deformation, uplift, and erosion (progressive unconformities) in the Vinchina basin may have prevented the sedimentary pile to be deeply buried and therefore allow to reconcile the observed compactional textures with depth of burial.

The results obtained in this work show that the analysis of mechanical compaction in sandstones constitutes a complex task and in occasions there is not a linear relationship between the contact indexes and depth of burial. Sandstone compaction is controlled not only by the depth of burial but also by other factors such as, time, geothermal flow, matrix content, the development of early cements, the ratio between ductile and rigid lithic fragments and, in tectonically active basins the development of progressive unconformities. Therefore, in most cases, it is very speculative to extend diagenetic conditions to basin-wide scales. In particular, the porosity-depth relationship must be based on primary porosity only.

During the Late Cretaceous Andean orogeny, the compressive deformation associated with the shallowing of the subducting slab caused the development of the arc-related igneous rocks known as the Naunauco Belt. This study presents petrographic, mineralogical and anisotropy of magnetic susceptibility data for the Varvarco Intrusives (the Varvarco Tonalite, Butalón Tonalite and Radales Aplite), which crop out in the Cordillera del Viento, Neuquén Province, Argentina. The assembly of plutons was formed by mafic magma episodic injection. Amphibole and biotite compositions suggest that the Varvarco Tonalite is related to calc-alkaline, I-type magmas, typical of subduction environments. Different geothermobarometers based on amphibole and plagioclase compositions for the Varvarco Tonalite suggest shallow emplacement conditions (∼2–3 kbar, equivalent to ∼12 km depth). Apatite fission-track analyses give exhumation ages of 67.5 ± 8 Ma for the Varvarco Tonalite and 50.3 ± 5.9 Ma for the Butalón Tonalite. A calculated continuous fast exhumation rate of at least 330 °C Ma−1 is consistent with the shallow emplacement conditions, textural data and geobarometric estimations. In agreement with the thermal profile, the magmatic system was exhumed by ∼12 km within c. 2.1 Ma implying a geothermal gradient of ∼62.5 °C km−1. The last step of exhumation occurred between ∼65.3 and 56.9 Ma. The magmatic fabrics observed in the studied plutons reflect mostly magma chamber processes. The Varvarco Intrusives represent satellite calc-alkaline plutons of the North Patagonian Batholith which were emplaced syn- to post-tectonically with respect to a major deformation stage of the Southern Central Andes.

This work presents new biostratigraphic data based on calpionellids and calcareous dinoflagellate cysts for the Tithonian in Central Chile. This stratigraphic interval is mostly represented by a thick marine succession of limestone and sandstone known as Baños del Flaco Formation. This formation originated in the shallow-water setting of a carbonate ramp and correlates with other well-studied units in the Neuquén basin of Argentina. Calpionellids and calcareous dinogflagellate cysts are studied on the Chilean side of the Andes for the first time. The recognition of several calpionellids and calcareous dinogflagellate cyst species within the lower Baños del Flaco Formation allowed the identification of a preliminary microbiostratigraphic zonation. Calcareous dinoflagellate cysts include eleven species that defines the Colomisphaera tenuis, and Colomisphaera fortis zones, whereas six chitinoidellid species allowed the identification of the Chitinoidella and Crassicollaria zones, with the Slovenica, Boneti and Remanei subzones. These new microbiostratigraphic data suggest a latest early to earliest late Tithonian age for the studied interval.

Some recent models challenge the position and extension of the assumed oceanic basins formed through the break-up of Rodinia, and the tectonic processes involved in the Gondwana assembly, making the investigation of the Early Neoproterozoic record of great relevance. Within the South-American Atlantic margin, the Punta del Este Terrane (PET) of the Dom Feliciano Belt (DFB) comprises a unique Tonian to Ediacaran record, and has a strategic position to reconstruct spatio-temporal relationships with the southern African orogenic belts. Novel zircon U–Pb and Lu–Hf data from the PET basement orthogneisses display Tonian magmatic ages (805–760 Ma) and Hf isotopic signatures indicative of mainly crustal/metasedimentary sources, (Nd TDM ages: 2.2–1.9 Ga, and εHf(t): − 12 to − 4). The basement paragneisses yielded late Paleoproterozoic to Neoproterozoic U–Pb ages, but dominantly positive εHf(t) values. The presented results confirm the correlation of the PET with the Coastal Terrane of the Kaoko Belt, and discard the idea of the Nico Pérez Terrane as a source. Detrital zircon U–Pb and Lu–Hf data from the Rocha Formation yielded a main peak at ca. 660 Ma, with the Neoproterozoic grains showing a εHf(t) between + 1 and + 14. The deposition age of the Rocha Formation is constrained by the youngest detrital zircon age peak (660 Ma), and the beginning of the deposition of the Sierra de Aguirre Formation (580 Ma). The data indicate common sources with the Marmora Terrane, and it is thus proposed that the Rocha Formation belongs to the Gariep Belt, and it was juxtaposed during the Ediacaran to the DFB.