Recent publications
Herein, we report the presence of a plant paleocommunity, dominated by ferns of the family Osmundaceae, structurally preserved from the only known Mesozoic, fossil-iferous geothermal deposits, from the La Matilde Formation (Middle-Upper Jurassic) in the Deseado Massif of Southern Patagonia, Argentina. A total of 13 siliceous chert blocks sampled in an area of approximately 250 m 2 , preserving a monotypic assemblage dominated by Osmundaceae embedded within its original swampy substrate, are documented. Additional Osmundaceae and fewer ferns and conifers are present in the stratigraphi-cally continuous, adjacent chert levels. This association is comparable to those dominated by Osmundaceae in modern swampy settings, such as in high-altitude lagoons in the Paraná Forest in Northeastern Argentina. In addition, a diverse community of mutualis-tic, parasitic, and saprotrophic microorganisms associated with the ferns and conifers in the assemblage is present. These compositional, paleoenvironmental, and trophic characteristics of the Jurassic Osmundaceae suggest a possible case of ecological stasis, where Osmundaceae-dominated plant communities apparently persisted in swamps of comparable structures, functions, and physical characteristics for over 150 million years. This suggests that Osmundaceae formed similar communities in compatible settings in the Jurassic, becoming preserved in analogous configurations.
Understanding the origin of Late Jurassic volcanism in southern Patagonia is crucial for unraveling the early Andean orogenic evolution. However, radiometric dating is not connected to stratigraphic analysis along the South Patagonian Andes, which obscures the real duration of the Late Jurassic magmatic activity. In this contribution, we present the results of a volcanic stratigraphy analysis, complemented by structural and petrographic data, on a thick succession of acidic volcanogenic rocks in the Laguna Verde district of southern Chile located along the south shore of General Carrera-Buenos Aires Lake. Through the recognition of igneous stratigraphy, we strategically sampled representative volcanogenic rocks that cover the entire duration of eruptive activity. By doing so, the new U–Pb zircon magmatic ages, combined with a compilation of U–Pb crystallization ages from the South Patagonian Andes, allows us to constrain the volcanic activity in the study area to a period of 8 My (~ 155–146 Ma, V3 stage) and 11 My considering age inherent errors. The field recognition of normal faults and the syn-kinematic emplacement of sub-volcanic bodies, which are inferred to conform to a ring-fault system, along with the presence of a thick succession of ignimbrites, suggest that the syn-extensional volcanic emplacement occurred in a caldera volcanic environment. This setting was responsible for the short-lived, voluminous eruptions. Furthermore, the high Th/U zircon ratios identified for the ~ 155–150 Ma period indicate the climax of extensional tectonics. The integration of these data supports the hypothesis that retreating-mode subduction played a major role in producing ignimbrite flare-ups.
The Devonian to early Carboniferous western margin of Patagonia (South America) includes a NW-SE-trending magmatic arc associated with a palaeo NE-dipping subduction zone. Along the Andean region of southern Patagonia, the Eastern Andean Metamorphic Complex (EAMC) developed in a forearc position, consisting of a succession of very low- to low-grade metaturbidite-metabasic rocks emplaced from the Devonian to Carboniferous periods. There are significant uncertainties surrounding this metamorphic complex, mainly related to the tectonosedimentary setting of the basin and subsequent conditions of deformation and metamorphism, which hinder our understanding of the orogenic architecture. To reveal the link between tectonics and metamorphism, we conducted a structural analysis and sampled metapelites to measure illite crystallinity along a regional structural cross-section in the EAMC. Our analysis reveals broadly Lower to Upper Anchizonal metamorphism which is roughly synchronous with deformation along northward-verging thrusts. These findings support the development of a forearc hyperextended basin that was subsequently closed during the Gondwanide orogeny (late Paleozoic), a model that reconciles previous proposals suggesting passive margin vs. back-arc basin models. This closure led to the emplacement of suprasubduction zone ophiolites and turbidites over the continent through landward migration of brittle-ductile reverse shear zones.
Thematic collection: This article is part of the Ophiolites, melanges and blueschists collection available at: https://www.lyellcollection.org/topic/collections/ophiolites-melanges-and-blueschists
Supplementary material: https://doi.org/10.6084/m9.figshare.c.7160849
Over the past decade, we have conducted geochemical and isotopic monitoring of the fumarolic gases of the Peteroa volcano (Argentina‐Chile). Using the resulting data set, we constructed a conceptual model that describes the evolution of the magmatic‐hydrothermal system and identifies precursory geochemical signals of the last eruption. Our data set includes new chemical and isotopic analyses of fumarolic gas samples collected from 2016 to 2021, as well as previously published data from the 2010–2015 period. After an eruptive period in 2010–2011, the activity was characterized by low degassing rates and seismic activity. However, an increase in seismic activity and fumarolic gas emissions was observed from 2016 to 2018–2019 eruptive episode, leading to a major phreato‐magmatic eruption. Fumarole gases show different compositions during quiescent versus unrest/eruptive degassing related to the interaction of deep (magmatic) and shallow (hydrothermal) fluid contributions. During quiescent periods, fumaroles exhibited low SO2/H2S, HF/CO2, and HCl/CO2 ratios (<0.1), revealing a dominant hydrothermal contribution. In contrast, during pre‐and syn‐eruptive periods, fumaroles showed ratios up to 100 times higher indicative of an enhanced magmatic input. When compared to the evolution of the seismic activity, the increment of magmatic‐related strong acidic gases suggests repeated inputs of hot magmatic fluids, which are only partially dissolved into the hydrothermal system feeding the fumaroles. Interestingly, the ³He/⁴He and δ¹³C‐CO2 values remained relatively constant during the magmatic and hydrothermal degassing in 2016–2021, suggesting that the deep magmatic gas source did not significantly change throughout variations in Peteroa's activity.
Corundum xenocrysts from ouachititic dikes related to the ultrapotassic Puesto La Peña Complex, Mendoza, Argentina, contain inclusions of oxides, silicides, and silicates. Oxides identified are hibonite, carmeltazite, and as yet unnamed minerals consisting of ZrTiO3, (Al,Ti,Zr) oxide, and (Mn,REE) oxide. An unnamed Ti2(Mn,Fe)4Si5 phase was also recognized. Silicates include wodegongjieite and grossmanite. All minerals are enriched in rare earth elements. The formation of these mineral inclusions under extreme P-T conditions would have occurred in the primeval Earth, preserved in the lithospheric mantle and protected from oxidation by crystallization of corundum through the introduction of mantle-derived magma-transported fluids. The corundum crystals would have been transported by a rising plume in a back-arc extensional setting during the Miocene and incorporated as xenocrysts in an alkaline ouachititic magma, conferring its peraluminous signature.
This contribution presents the first study focused on the analysis of microbial mats in the Los Molles Formation (Toarcian – Early Callovian), Neuquén Basin, Argentina. This unit mainly represents offshore‐to‐shelf environments affected by storms and density currents. The Los Molles Formation is one of the oldest source rocks in the Neuquén Basin and constitutes an unconventional shale gas reservoir of great economic importance. The aim of this work was to identify the microbial activity from the description and interpretation of microbially induced sedimentary structures (MISS), to determine the paleoenvironmental and paleoecological conditions under which they formed, and to establish a possible relationship between these structures and the trace fossil Trichichnus . Samples from the levels with MISS were analyzed and described from macroscopic and binocular observations, petrographic microscope thin sections, and SEM samples with EDS analyses. The results showed several levels of microbial mats presenting diverse MISS, including biolaminations and Kinneyia ‐like wrinkles structures that were described at the macroscopic level. In thin sections, biolaminations, filament‐like microstructures with different degrees of development, oriented grains and pyrite were observed. SEM images and EDS analyses showed different types of filaments, coccoids and EPS with high concentrations of carbon. These results revealed that the studied levels fulfill the established biogenicity criteria, guaranteeing that they have a bacterial origin. The abundance of the trace fossil Trichichnus sp. throughout the section and the proximity to some Kinneyia‐ like wrinkle structures levels suggests that the same organisms may have generated them. Furthermore, they revealed that the Los Molles Formation, at the time of its deposition, experienced paleoecological and paleoenvironmental conditions appropriate for the establishment and development of microbial mats. The extensive levels of microbial mats in the study area suggest that they may have been a source of organic matter for the generation of hydrocarbons from the Los Molles Formation.
Articulated fossil ophiuroids from South America were reported for the Devonian, Cretaceous, Eocene, and Miocene. Here
we report the first Jurassic record of an articulated ophiuroid from the Sierra Chacaicó Formation (early Pliensbachian–
Sinemurian) in Neuquén Basin, Argentina, and discuss the taphonomic processes that allowed its preservation. The Sierra
Chacaicó Formation represents the onset of the Early Jurassic extensive marine transgression in the basin. The basal
section comprises shoreface and offshore Gilbert-type delta system, which was affected by hyperpycnal discharges. The
middle and upper sections are represented by offshore deposits, affected by storms and eroded by hyperpycnal channel-levee
systems. The ophiuroid specimen was found in levels of massive, fine, tuffaceous sandstone beds and covered
by coarse sandstone containing a large amount of plant debris and organic matter. It was preserved articulated, with a
complete disc and almost complete arms. Based on the microstructure of the spine-bearing lateral arm plates, the ophiuroid
is assigned to Sinosura, an extinct genus of the family Ophioleucidae, widespread in the Lower Jurassic deposits
of Europe but previously unknown from other parts of the world. The posture of the ophiuroid, with one arm curved
distally and extended in one direction and the other four arms symmetrically oriented in the opposite direction, suggests
a walking or escape movement frozen in time. This implies that the ophiuroid was buried alive by sediment thick enough
to prevent successful escape. The taphonomic and sedimentologic evidence indicates that the fossil material was found in
hyperpycnal deposits accumulated in offshore positions, which carried a high concentration of sediment in suspension.
The presence and evolution of a late Paleozoic mountain chain with a paleogeographic disposition similar to the present-day Andean Cordillera is analyzed in this paper. This mountain range, here named Ancestral Andes, was formed during the Gondwanan orogeny (Permian) and separated the Paleopacific Sea from the eastern retroarc basins in this part of South America. Three basement types are involved in the roots of the Ancestral Andes: 1. poorly exposed Mesoproterozoic-Neoproterozoic high-grade metamorphic rocks probably remains of the Chi-Cu terrane, 2. Cambrian-Silurian sedimentary and metamorphic rocks formed during the Famatinian orogeny, and 3. Neoproterozoic to early Carboniferous sedimentary and metamorphic rocks originated during the Chanic orogenic cycle. According to tectonic activity, sedimentary facies, and magmatic record, the Gondwanan cycle comprises seven tectosedimentary stages: 1) Late Mississippian-Early Pennsylvanian (post-Chanic orogeny marine sedimentation), 2) late Early Pennsylvanian (sea-level fall and progradation of sandy wedges in an extensional pre-orogenic period), 3) Middle-Late Pennsylvanian (sea level fluctuations at the end of the pre-orogenic phase), 4) latest Pennsylvanian-early Cisuralian (active tectonism during the beginning of the uplift of the Ancestral Andes, 5) middle Cisuralian (continental and shallow marine sedimentation during the main phase of the Ancestral Andes uplift), 6) late Cisuralian-Guadalupian (continental sedimentation and beginning of the post-orogenic volcanism), 7) late Guadalupian-Lopingian (most active post-orogenic volcanism). The stages 1, 2, and 3 correspond to the pre-orogenic phase of the Gondwanan cycle recorded in the Agua Negra Formation, which is mainly marine with thin continental intercalations. Stages 4 and 5 represent the orogenic conditions that promoted the uplift of the Ancestral Andes and a sudden change from mainly marine (Agua Negra Formation) to continental (San Ignacio Formation) facies. Finally, stages 6 and 7 show the intense magmatic activity developed during the Guadalupian-Lopingian and probably early Triassic times (Choiyoi Group, anaorogenic conditions).
The late Paleozoic paleofloras recovered from different stratigraphic intervals into the Ancestral Andes allow establishing that stages 1, and 2, bear remains of the Nothorhacopteris-Botrychiopsis-Ginkgophyllum (NBG) Biozone (latest Mississippian-Early Pennsylvanian). Stage 3 yielded Late Pennsylvanian plant remains and invertebrates while the Stage 5 provided silicified trunks of Cuyoxylon (San Ignacio Formation) and palynofloras characterized by Lueckisporites (La Puerta Formation) of Cisuralian age.
Fine-grained sediments deposited under oxygen-deficient conditions are enriched in organic matter and hold considerable economic interest as unconventional reservoirs. The present analysis integrates sedimentological, ichnological, and geochemical datasets to understand depositional processes in the Upper Jurassic–Lower Cretaceous Vaca Muerta Formation (Argentina), the most important economical unconventional play outside North America. For this purpose, cores from eight wells and one outcrop were examined. The succession comprises thirteen facies associations corresponding to marginal-marine, basin, drift, and slope environments, deposited in a mixed carbonate-siliciclastic, shelf-margin, subaqueous clinoform system. Estuarine circulation during warm and humid climates produced a stable stratification. Sediment delivery was dominated by pelagic processes in the bottomset, and hemipelagic processes and fluid mud flows in the foreset. However, the typical estuarine circulation changed to weakened estuarine or anti-estuarine during cool and arid climates, triggering wind- and thermohaline-driven contour (bottom) currents that reworked and oxygenated the complete clinoform system. The analysis suggests that distal-proximal trends are of lesser importance for the delineation of sedimentary environments in settings with contrasting basin circulation regimes and provides several insights to understand sediment partitioning in fine-grained clinoform systems.
Supplementary material: Stratigraphic context of the Vaca Muerta Formation, example of facies distribution in a well, trace-fossil descriptions, and XRD and TOC geochemical data is available at https://doi.org/10.6084/m9.figshare.c.6294914
This work aims to study the interaction between two of the most representative structural systems controlling the Caviahue-Copahue volcanic complex. To achieve this objective, a structural analysis based on outcrop-scale fault-slip data field surveys and analogue models were carried out. The deformation regime acting on the studied area was characterized, and the associated paleostresses were obtained from the kinematic data inversion.
The performed analysis in Caviahue-Copahue volcanic complex allowed to define two main sets of faults controlling the deformation of the area: NE-SW to ENE-WSW, and WNW-ESE to NW-SE, respectively. The first group comprises high-angle normal faults, resulting in a horst-and-graben setting with along-strike lengths up to 2 km. The second group shows strike-slip kinematics with a minor normal component. These NW-SE faults are related to the Miocene-Pliocene fissure-related volcanism and define the major caldera axis direction. In the geothermal area, the obtained paleostress orientation shows a consistent vertical σ1, denoting a local extensional regime. Regarding the geothermal field, the NE-SW extensional fault system is proposed as the main circulation pathways for hydrothermal fluids rising to the surface. The major NW-SE faults would act as barriers for this circulation.
The set of analogous experiments was used to contrast the obtained local structural kinematic results. Two non-coaxial extensional events were established to achieve a local scale approach to the structural configuration observed in the area. Simulations aimed to understand the structural behavior of the superposition of non-coaxial extensive events; they allowed us to assess the role of the different fault sets surveyed in the field within the system. Particularly, our findings support that the NW-SE-oriented structures compartmentalize the subsequent NE-SW-oriented faults, acting on occasions as transfer zones.
We have carried out the zircon U–Pb SHRIMP dating of the Cerro de los Viejos (CLV) Granite of southern La Pampa province, Argentina, which has yielded a concordia age of 468.0 ± 2.7 Ma, and determined the average Hf TDM model age of the dated zircon grains at 1491 Ma (Lower Mesoproterozoic; Calymmian), with an average epsilon Hf value of −3.13. Given the Ordovician (Darriwilian) crystallization age newly obtained for the CLV Granite, it becomes apparent that its previously known muscovite K–Ar Permian age of ca. 261 Ma would likely represent the age of the conspicuous shearing/mylonitization distinctive of this granitic body.
Based on the new geochronologic and isotopic study of the CLV Granite, which also bears juvenile Rhyacian or “Transplatense” inheritance (aged at ca 2116 Ma, with average Hf TDM 2.4 Ga and average epsilon Hf value + 4.23) –an inheritance not known to occur in the neighbouring Patagonia or Pampia terranes–, as well as on comparisons with all the available geochronologic, isotopic, geophysical and geological data of the study region, in addition to broader tectonic considerations, we view the Ordovician CLV Granite as derived from the autochthonous, early Mesoproterozoic (Calymmian) southwesternmost portion of the Río de la Plata craton.
The location of the CLV Granite would indicate that the peraluminous Ordovician magmatism of the southern La Pampa province, Argentina, straddles the Cambrian tectonic boundary between the Pampia terrane and the Río de la Plata craton.
The CLV Granite would have been intruded in the immediate western continuation of the unexposed, E-W elongated upper crustal high/block recently identified by geophysical methods slightly to the east of the CLV Granite, the delineation of this block following the persistent sub-latitudinal structural fabric of the southern Río de la Plata craton, having also been reinforced by its probably late Middle Permian uplift coeval with the shearing of the CLV Granite.
This study analyzes the dynamics in which structural vulnerabilities are shaped and expressed in the day-to-day lives of people making a living from a garbage dump in Argentina. It is a mixed methods case study, qualitative driven with a collaborative cycle (2016-2021). The study is embedded in medical anthropology, social epidemiology and Latin America Social Medicine, with the focus on the ways people respond to inequalities locally. The findings contribute to the field of health disparities in three directions: 1) the description of patterns of segregation in South America peripheries, shedding light on cumulative disadvantages and multiple exposures; 2) the experience of living enmeshed in places with strong stigmas, revising the ways this source of discrimination become social suffering; and 3) the detection of the impact of collective action and social capital in providing material and symbolic resources for restoring dignity and honour that challenge depreciated status.
The Río Damas Formation is an Upper Jurassic volcano-sedimentary succession, whose outcrops are largely distributed between 33°S and 35.30°S in Chile and Argentina, as part of the retroarc Neuquén Basin fill. This unit was deposited during an important marine regressive phase of the basin. We studied the Río Damas Formation exposures at the Los Gateados creek valley, in the Alto Atuel depocenter (34°40′S; westernmost Malargüe fold and thrust belt), next to the Argentinean-Chilean border. This area represents a key location where the formation interdigitates with the nonmarine red beds of the time equivalent Tordillo Formation, representing a continentalization episode of the Neuquén Basin. This paper presents a lithofacial characterization of the Río Damas Formation, a new U–Pb igneous crystallization age, and a paleographic reconstruction for this period. The Río Damas Formation in the Alto Atuel depocenter consists of porphyritic basaltic and andesitic lavas, interbedded with fine-grained sandstones, conglomerates, volcanic lithic breccias, and pyroclastic deposits. Based on field and petrographic analyses, we associate the Río Damas Formation with a piedmont environment where sedimentary fluvial and alluvial setting coexisted with volcanic effusive and pyroclastic activity. A regional comparison of the Río Damas and Tordillo Formations along the Argentinian-Chilean border shows that the composition and thickness of these units present important latitudinal and longitudinal variations. The increase in thickness and the volcanic component of the Río Damas Formation towards the west could be associated with the proximity to the Jurassic magmatic arc.
The evolution of central Patagonia is associated with episodic shortening and extension that have greatly affected the topography of the Cordillera and intraplate belt. The San Jorge Basin is a site of sediment accumulation in the foreland that is surrounded by igneous and broken foreland relief. The latter originated from episodic deformation and reactivation of inherited structures associated with a period of slab shallowing that allowed the far-field transmission of Andean stresses to the foreland. Thus, due to of its location, the San Jorge Basin provides an exceptional opportunity to study the denudation of both Cordilleran and intraplate topography during the Cenozoic, particularly during the late Eocene–early Miocene interval of mild deformation. In this study, we use a single-grain geochronological approach combining apatite fission tracks and UPb dating on apatite, along with maximum deposition ages obtained from UPb zircon dating for Neogene foreland basin deposits, to distinguish between two distinctive sediment source regions in central Patagonia during the Cenozoic, despite the persistent volcanic signal. A compilation of previously published cooling ages combined with our new data define: (i) a dominant local source from the northern broken foreland from the late Eocene until the early Miocene; and (ii) a widespread source in the Cordillera during the Miocene based on a very uniform thermochronological signal observed throughout the entire foreland. Therefore, this study provides new insights into the variation of in sediment sourcing in the central Patagonian foreland. This variation is primarily controlled by the decrease of post-orogenic erosional processes during a period of relative tectonic quiescence following the highly active Early Cretaceous–middle Eocene time interval.
The Latin American Association of Volcanology (ALVO) arose in 2010 as a regional network, promoting regional cooperation, the exchange of experiences and the strengthening of local capacities in the field of volcanology. In 2020, ALVO organized its first scientific congress under the slogan ‘Volcanology in and for Latin America’ (1er Congreso ALVO: Volcanología en y para Latinoamérica). The Special Issue, Volcanism in Latin America, hosts several works presented at this Congress. The articles that constitute this Special Issue cover a broad spectrum of topics studied by many research groups and institutions working on volcanology in the region. Such topics include disciplines like physical volcanology, geochemistry, seismology, remote sensing, volcano observatories, instrumentation, and volcanic hazards and risks, among others. These papers represent good examples of the state-of-the-art of volcanology research in Latin America.
The basal succession of the Lajas Formation at Trasandino section, Arroyo Covunco area, constitutes an excellent example of proximal prodelta facies cut by sediment-waves formed during a complete acceleration-deceleration hyperpycnal discharge cycle. The main outcome of this contribution was to present a new studied locality in which the Lajas Formation outcrops. Nine mudstones and fine-grained heterolites levels deposited during the waning stage, were sampled to palynological analysis. The recovered assemblages are dominated by sporomorphs, which are characterized by a great diversity of the trilete spores. Among them, is interesting to highlight the first mention of Manumia variverrucata and the extension of the last occurrence of Striatella seebergensis until to Callovian in Argentina. Based on selected key taxa a Late Bathonian–Callovian age is proposed for the Lajas Formation at the Trasandino section in this area. The Trasandino section spore assemblages show the greatest similarity with the Arroyo Covunco section spore associations when they are compared with the Lajas Formation of other studied localities. The endemic development of certain types of bryophyte (sensu lato) spores, e.g. Taurocusporites quattrocchiensis, was favored by locally humid conditions inferred at the Arroyo Covunco area. Large abundance of phytoclasts, sporomorphs and fresh-water algae characterize the recovered organic matter suggesting a high input of continental organic particles to the basin, as the result of fluvial-derived density discharges. Three palynofacies type (PT) had been identified which allow to evaluate the hydrodynamic characteristics of the flow, taking into account the differential buoyancy of the opaque particles. The large amount of equidimensional opaque particles recognized at the PT-B, characterizes the beginning of the deceleration phase of the flow and the abundance of blade-shape opaque particles, identified in the PT-A, point out a deposition from the final buoyant plume of hyperpycnal flow. The PT-C shows transitional features between these two conditions.
In the Cenozoic Central Volcanic Zone of the Andes, the genetic relationships between regional deformation, volcanic activity, and epithermal mineralization are not fully established. In order to shed some light on the matter, we present new macro and mesoscopic structural data, fault-slip data inversion and ⁴⁰Ar-³⁹Ar geochronology for volcanic rocks, hydrothermally altered equivalents and epithermal Ag–Pb–Zn mineralization of the Quevar Volcanic Complex, which is located in the Puna plateau of NE Argentina.
These data allow us to establish a first evolutionary stage with the eruption of the lavas and pyroclastic deposits of the Quevar Dacite in the Tortonian (9.9–8.7 Ma), when the volcanic activity was controlled by the NW-trending Calama-Olacapato-Toro lineament (COT). A second stage included the implantation of a hydrothermal alteration system and the related formation of the epithermal mineralization in the Messinian (7.7–6.3 Ma). These processes were contemporaneous with an ENE to E-directed shortening regime, which produced the reactivation of the COT and the formation of a left-lateral strike-slip stepover between WNW-trending regional faults. The third stage included the cessation of the hydrothermal activity and the erosion of the volcanic edifice. During this stage, mineralized veins and strike-slip faults were reactivated as normal faults by a NNW-directed extensional regime.
The Pliocene is considered an analog for future climate. Insolation is found the dominant forcing for Asian precipitation over the late Pliocene, evidenced by magnetic enhancement of Chinese loess caused by formation of nanometer‐scale ferrimagnetic grains during pedogenesis corresponding to high precipitation. However, lack of European loess limits understanding of Pliocene European climate. We identified likely similar magnetic enhancement mechanism between Pliocene alluvial sediments from Spain and Chinese loess despite different depositional settings. This provides an opportunity to improve understanding of Pliocene climate in Europe. Spectral analysis shows that European wet‐dry variations during the early Pliocene were forced by insolation and during the late Pliocene by both insolation and ice sheets development. During the Quaternary, in contrast, the forcing was dominantly from high latitude. These results demonstrate the importance of insolation during warm climates and the growing importance of ice sheets with global cooling in controlling Northern Hemisphere precipitation changes.
The changes in physical properties leading up to a volcanic eruption provide clues to processes occurring within volcanoes and may reveal premonitory signals. The Sierra Negra shield volcano, located in the Galápagos Islands, erupted on 26 June 2018 after months of continued inflation and escalating earthquake activity. We applied ambient noise interferometry to five months of continuous seismic data from 12 broadband stations to calculate crustal shear‐wave velocity changes before and during the eruption. Using the Moving Window Cross‐Spectral technique and a pre‐eruption stack of ambient seismic data as reference, we found a −0.27% decrease in velocity 17 days before the eruption in station‐pairs that pass beneath the caldera's north‐eastern sector. Sensitivity kernels suggest that the velocity changes of this precursory signal are greatest at depths corresponding to the shallow sill (∼2 km) beneath the wide caldera. Our results, considered in light of geodetic, seismicity, and petrological results, suggest that this velocity decrease is in part caused by dilatation from a ML 4.8 earthquake, and degassing after a possible magma intrusion below or at the base of the sill. The precursory velocity decrease within the sill region offers an important tool for forecasting future eruptions at Sierra Negra.
The current study presents new bed‐by‐bed brachiopod δ¹³C and δ¹⁸O records from Öland, Sweden, which together with previously published data from the East Baltic region, constitutes a high‐resolution paired brachiopod and bulk rock carbon and oxygen isotope archive through the Lower to Upper Ordovician successions of Baltoscandia. This new data set refines the temporal control on the global Ordovician δ¹⁸O‐trend considerably, improving paleoenvironmental reconstructions through the main phase of the Great Ordovician Biodiversification Event (GOBE). The new brachiopod carbon and oxygen isotope records from Öland display strong similarity with the East Baltic records, elucidating the regional consistency as well as global correlation utility of the ensuing composite Baltoscandian Lower to Middle Ordovician carbon and oxygen isotope record. The carbon isotope record from Öland indicates that the widely reported Middle Ordovician carbon cycle perturbation—MDICE (Mid‐Darriwilian Carbon Isotope Excursion)—is recorded in both brachiopods and bulk carbonates. The oxygen isotope record reveals a long‐term Lower to Upper Ordovician trend of increasingly heavier brachiopod δ¹⁸O values, with a pronounced increase during the Middle Ordovician Darriwilian Stage. We interpret this trend as dominantly reflecting a paleotemperature signal indicating progressively cooler Early to Middle Ordovician climate with glacio‐eustasy. Our Baltic δ¹⁸O values are therefore consistent with postulations that the biotic radiations during the GOBE and climatic cooling during the Darriwilian were strongly linked.
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