Instituto de Geociencias

Abstract The deposits of the Solimões Formation (Acre Basin), Brazilian Amazonia, preserve a diverse vertebrate fossil assemblage. However, taphonomic studies of both the deposits and their fossil vertebrate content remain scarce. One notable example is the osteoderms of cingulates, which are relatively abundant and diverse in the South American Cenozoic record. This study describes the taphonomic signatures observed in osteoderms of a dasypodid armadillo assigned to cf. Anadasypus sp. from the Late Miocene AC64 outcrop, Solimões Formation, Acre State, western Brazilian Amazonia. Both isolated osteoderms and a sedimentary block preserving several disarticulated but spatially associated osteoderms were analyzed using a taphonomic categorization adapted from studies on modern armadillo osteoderms. This approach allowed the identification of oblique, transverse, and longitudinal fractures, bioerosion traces, and spatial arrangement patterns. The evidence best supports a low-energy fluvial depositional setting, in which the osteoderms experienced moderate trampling and minimal transport prior to burial. Paleoenvironmental conditions were reconstructed by integrating data from the associated fauna (Testudines, Crocodylomorpha, and Trichodactylidae), sedimentary structures (rhizoliths and bioturbation structures), and carbon and oxygen isotope analyses of fossil remains and associated limestone samples. These suggest a humid fluvial depositional setting dominated by C3 vegetation, with relatively stable depositional conditions.

The Kovancılar section, located to the northeast of Elazığ in eastern Türkiye records the shallow-marine sedimentation of the Kırkgeçit Formation, related to the middle-late Eocene. This study is unique in that it integrates facies analysis, micropaleontological, mineralogical, and geochemical data to reconstruct the paleoenvironmental evolution of the formation. Eight carbonate lithofacies, alongside intervals of marls, sandstones, and conglomerates, indicate a carbonate ramp environment, mainly controlled by waves, with variable energy and detrital input. A diversified larger benthic foraminifera (LBF) assemblage-including Nummulites hormoensis , Nummulites fabianii, Chapmanina gassinensis, Silvestriella tetraedra supports a Bartonian–Priabonian age. Biometric data from N. fabianii and N. hormoensis , presented here for the first time from this region, provide new constraints for biostratigraphic resolution. Stable isotopes, as well as major, trace, and REE concentrations indicate minor diagenetic alteration and paleoenvironmental signals related to changes in continental runoff and detrital input, as well as relative sea level changes. The Kırkgeçit Formation at Kovancılar was deposited in a shallow marine carbonate ramp, with a slight shallowing upward trend during the middle-late Eocene. A marly interval in the lower part of the section may represent an episode of carbonate crisis due to climatically induced enhanced runoff. A major shift towards siliciclastic facies, followed by deeper carbonate facies, occurring at the top of the section may represent an episode of marine transgression due to a regional tectonic event, with a possible contribution of global sea-level rise during the Priabonian.

The Geological Map of Colombia is periodically updated by the Colombian Geological Survey to incorporate advances in geological mapping, geochronology and tectonic interpretations. The 2023 edition integrates geological information published up to March 2022 and includes a comprehensive reassessment of isotopic ages, particularly zircon U–Pb data, within a chronostratigraphic framework. This contribution examines the impact of new geochronological constraints on the interpretation and compilation of the Geological Map of Colombia and discusses major cartographic challenges identified during its preparation. Five representative case studies are analysed: the Cajamarca Complex, the Tierradentro Gneisses and Amphibolites, the Quebradagrande Complex, high-pressure metamorphic rocks of the Central Cordillera and Jurassic metamorphic rocks in the Sierra Nevada de Santa Marta. These examples illustrate how inadequate geological mapping, inconsistencies in lithostratigraphic definitions and interpretations based solely on geochronological data can lead to erroneous chronostratigraphic assignments and misleading tectonic reconstructions. The study highlights the importance of integrating field observations, lithostratigraphic relationships, structural geology and geochronology in regional geological compilations. The reassessment of nearly 2000 isotopic ages published between 2014 and 2022 led to significant updates in the Geological Map of Colombia 2023. These include the recognition of a Permian magmatic arc along the eastern flank of the Central Cordillera and Upper Magdalena Valley, the extension of the Carboniferous plutonic record in Colombia, identification of Ordovician volcanic rocks in the Santander Massif, revision of the age and extent of the Quebradagrande Complex, and refinement of the temporal and tectonic significance of high-pressure metamorphic belts. New U–Pb ages also enabled the subdivision, redefinition and reassignment of several chronostratigraphic units previously grouped under broader geological categories. These revisions provide new insights into the tectonic and magmatic evolution of the northwestern margin of South America and demonstrate the critical role of combining geochronological information with detailed geological mapping in regional geological syntheses.

A variety of chemical and dynamical processes in the troposphere and stratosphere affect tropical total column ozone (TCO), the net effect of which may cause changes in surface UV radiation and impact human and ecosystem health. We use dynamical linear modeling to estimate changes in tropical TCO and partial column ozone (PCO) in the troposphere and three stratospheric layers to assess agreement between satellite composites and chemistry-climate model simulations from two multi-model experiments (CCMI-1 and CCMI-2022). While both model experiments show tropical TCO increases over 2000–2021, multimodel-mean CCMI-2022 changes (+2.5 DU) agree slightly better with observations (+3.3 DU) than CCMI-1 (+1.6 DU). However, this overall agreement obscures multiple systematic differences in PCO changes between the models and observations across atmospheric layers. For example, since 2000 tropical tropospheric PCO increased significantly in CCMI-2022 (+1.5 DU) but not in CCMI-1 (+0.3 DU), largely explaining the difference in TCO changes. Also, despite nearly identical stratospheric PCO changes, CCMI-2022 changes are slightly more negative than CCMI-1 in the lower stratosphere (by ∼ 0.5 DU) and more positive in the middle/upper stratosphere. Crucially, substantial differences exist between observational PCO changes, particularly in the troposphere and middle/upper stratosphere, and these disagreements limit the ability to evaluate CCM fidelity for past changes. While early and late century trends are correlated across models, suggesting a potential emergent constraint on ozone, the spread in observational trends means they are unable to provide guidance on the credibility of model projections for a given emissions scenario.

The formation of a slab window beneath southwestern North America was an inevitable consequence of major Cenozoic geodynamic events, namely the separation of the Vancouver plate from the Farallon plate by 52 Ma, and the collision of the East Pacific Rise (EPR) with the North American trench by 30 Ma. Igneous records along northwestern Mexico and southwestern U.S. are linked to mantle upwelling episodes following the formation and expansion of this slab window. Here we present a 3D model of Farallon plate subduction and fragmentation beneath North America from 60 Ma to the present, using reconstructed plate kinematics and seafloor age as boundary conditions. Our predicted slab geometry shows good agreement with subduction-related high P-wave velocity anomalies in the upper mantle. We show that the waning of subduction started between 40 and 30 Ma, as the consumption of progressively younger oceanic lithosphere straddling the nearest segment of the EPR to the trench caused the slab to thin and flatten around this region, leading to ridge abandonment and a first detachment at ∼26 Ma. A slab window then propagated northwards and southwards, facilitating pulses of upward flux below the slab-free area across northwestern Mexico and southwestern U.S. Mafic volcanic occurrences show a close spatial correspondence with the predicted slab window through time, consistent with asthenospheric decompression melting above the slab-free area. Early magmatism in southwestern North America silicic provinces predates EPR-trench collision, implying additional mechanisms –such as earlier Farallon-Vancouver boundary subduction– also contributed to the complete volcanic record of this region.