Journal of South American Earth Sciences最新文献

The offshore portion of the Mucuri Basin, located on the eastern Brazilian margin, was mapped employing seismic, lithological and petrophysical data. Dome structures were observable in seismic sections and circular geological structures identifiable on the seismic map. Four types of domes were identified in the seismic sections, three domic features in the 3D seismic sections (Domes I, II, and III) and another dome feature in the 2D seismic section outside the 3D seismic volume (Dome IV). The first, located in the central region of the 3D seismic volume, was interpreted as a salt dome generated by a halokinesis processes. The second was interpreted as encompassing hydrothermal vents (Dome II), formed by a conduit connecting them to the sills of the Abrolhos Magmatic Province (AMP). The third comprises subvolcanic features composed of radial dikes (Dome III). The fourth was identified outside the 3D seismic volume, on a regional 2D seismic section, interpreted as a forced fold generated by sill emplacement (Dome IV). The data indicate that all domes are in some way associated to the AMP, including the salt dome, with sills mapped below the salt layer, which may have contributed to the halokinesis process. Indirect dating through stratigraphy analyses indicates that AMP magmatism probably took place during the Neogene. This assessment contributes to a better understanding of Mucuri Basin geology, which still presents many gaps concerning stratigraphy, salt movement and AMP intrusive rock emplacement. The findings confirm that the AMP may have lasted much longer than what has been widely described in the literature, with potential associations between AMP emplacement and salt movement.

Understanding and delving into the study of site effects in a region is highly important as it can reveal the main structural characteristics beneath seismic stations, which is of interest for seismic risk and/or seismic design studies. This work focuses on investigating the seismic structure of the southernmost region of Patagonia to gain insights into its evolution and current geodynamics, particularly on Tierra del Fuego Island, known for its significant seismological history. To achieve this, we analyze the near-surface crustal structure using the HVSR technique to determine resonance frequencies at different sites originated from impedance contrasts at varying depths. To characterize the site effect in the area, we examined this relationship as a function of frequency and, through inversion, obtained seismic models beneath two stations. These results improve the region's models obtained in previous studies through dispersion analysis and receiver function analysis, demonstrating an improved spatial correlation with the known tectonic features and providing valuable information for seismic hazard studies on the island.

Based on a relevant geochronological U-Pb zircon dataset (n = 47) from a sample (PBL-109) of the Cerro Punta Blanca pluton (CPB), which is part of a calc-alkaline suite, we corroborate the development of protracted magmatic activity with three major crystallization events for this Permian magmatism: 278 ± 1, 283 ± 2, and 289 ± 2 Ma, which outcrop in the Cordón del Portillo, Cordillera Frontal (CF) of Argentina. These ages can be assigned to the lower section of the magmatic record of the Choiyoi magmatism (ca., 290-265 Ma), while the age of 289 Ma represents the oldest known age for the Choiyoi, indicating the start of this magmatism during the Artinskiense. Considering these geochronological data, we postulate the presence of a deep mush reservoir where protracted magmatic activity permitted the prolonged crystallization of antecrysts (ca. 283–289 Ma). Migration of the parental magma from the mush reservoir zone occurred near the time of emplacement and culminated in the formation of an ephemeral magma chamber at shallow levels, where zircon autocrysts crystallized (ca. 278 Ma). Age spectra reported within individual samples support the idea of massive magma migration when conditions were favorable (e.g., thermally matured crust). In this view, the studied “older” Choiyoi magmatism represents a continuous magmatic event lasting 11 Ma and corresponds to a single magmatic episode rather than different periods of magmatic activity and subsequent emplacements. A later alkali-calcic magmatic event is recorded at 265 ± 4 Ma from a sample of the Cerro Bayo pluton (MH-0113), which could represent the end of the lower section of the Choiyoi magmatism. Whole-rock Sm-Nd, Rb-Sr, and Lu-Hf data in zircon, along with ages reported for the studied igneous and inherited zircon from the CPB; together with isotopic data and ages from the detrital zircon found in the Carboniferous accretionary complex of Chile, indicate that the source of the Permian parental magma in this region was a heterogeneous continental crust mainly formed by Devonian and Carboniferous rocks, related probably to a magmatic arc. However, some contribution from the Carboniferous accretionary complex of Chile to the parental magma should be consider.

This contribution describes basin-scale, Cretaceous (Late Aptian to Cenomanian-Early Turonian) fluvial systems outcropped over ∼30,000 km² that contain more than 7000 exhumed paleochannels in the Chubut Group, Cañadón Asfalto basin (central Patagonia), Argentina. Paleochannels are encased within a ∼350 m thick stratigraphic interval (∼20 My) including volcaniclastic and epiclastic fluvial units (Cerro Barcino and Puesto Manuel Arce formations). Geomorphologically, the exhumed paleochannels conform to isolated sandstones/conglomeratic ridges, a swarm of paleochannels, and elongated/equidimensional mesas (plateaus), characterizing much of the “mesetiform” landscape in central Chubut. The plan-view analysis of exhumed paleochannels mainly shows a mean WNW-ESE orientation (112°–292°) and predominance of narrow (83.1%) and very narrow (14.4%), low-sinuosity channels (96%). A plan-view multi-scale architectural analysis of sandbodies allows us to recognize different fluvial hierarchies: a) 3rd-order lithosomes (macroform growth increments), b) 4th-order lithosomes (point bars and crevasse-channels), b) 5th-order lithosomes (main channels), and c) 6th-order lithosomes (channel belts). Two main types of channel arrangements in the exhumed fluvial systems were recognized: fixed-channel and mobile channel belts. We observed a broad relationship between geomorphologic configurations and fluvial architectural units. Some macro spatiotemporal variation in the fluvial architecture was observed towards the youngest positions, including wider channels and a greater relative abundance of high-sinuosity channels with point bars. The basin-scale distribution of exhumed paleochannels would allow us to infer the predominance of shallow lacustrine or lagoon deposits in the western basin region, probably controlled by the inherited topography of the Jurassic- Early Cretaceous depocenters.

The central region of Sonora state, Mexico, is recognized by its different upper Paleozoic outcrops, highlighting the La Cueva Limestone and Mina México Formation. The rocks of Cerro Las Rastras and Sierra Martínez are considered among the most important Permian localities in central Sonora. This work studies the fusulinid faunas in two different sections, focusing on their biostratigraphical and paleoenvironmental relevance. Both sections comprise strata from the La Cueva Limestone and Mina México Formation. The fusulinids identified are Parafusulina sp., Paraskinnerella cf. skinneri, Praeskinnerella crassitectoria, Skinnerella cobachiensis, Skinnerella imlayi, and Eoparafusulina cf. linearis. The presence of Pa. cf. skinneri, Pr. crassitectoria, S. cobachiensis and S. imlayi indicates a lower–middle Leonardian (=upper Artinskian–lower Kungurian) age for the Las Rastras Section. The occurrence of E. cf. linearis in the base of the Sierra Martínez 2 Section suggests a youngest age of upper Wolfcampian for the bearing rocks. The microfacies analysis allowed the identification of six facies associations in the Las Rastras Section related to deep shelf, slope, and ramp-margin sand shoals. While three associations were identified in the Sierra Martínez 2 Section, indicating the deposition of open marine and slope environments. Fusulinids from both sections are classified as allochthonous elements in most facies associations (except those of open waters) since they are found in environments that are known to not been inhabited by these foraminifera. The fusulinids identified have a paleobiogeographic affinity with coeval assemblages from the North American Province.

Crustal structure models play an important role in the characterization of seismogenic zones, in the regional delimitation of geological provinces and particularly, in understanding the genesis and evolution of sedimentary basins. Despite the increasing number of new seismic surveys and seismographic networks in South America, crustal thickness measurements are still scarce and irregularly sampled, reducing the resolution of crustal model maps. To overcome these challenges, a novel approach based on machine learning techniques is proposed, in order to explore higher resolution gravity datasets in the interpolation of crustal thickness measurement points obtained from previous seismic/seismological compilations. The algorithm used in this study is based on Gaussian processes prediction methods, which allowed inferring the depth of Moho to South America. The prediction error of the model obtained from the training and testing database was 3.48 km, which is compatible with the uncertainties derived from the H-k stacking analysis. The depth range varied from 69.8 km beneath the Andes to 4.3 km in oceanic regions. The average Moho depth for the South American Platform is 39.1 km, allowing a spatial correlation of deeper and shallower Moho regions with different types of continental basins. Compared to other models, the model resulting from this study presents fine-scale features highlighting the limits of the main tectonic domains and a good agreement with the suture zones. Overall, this study demonstrates the potential of applying machine learning tools in crustal-scale imaging using sparse datasets, providing new advances in Moho modeling of the South America, as well as new perspectives on its the history and tectonic evolution.

In addition to the study of sedimentary facies, the reconstruction of paleoenvironments depends on a detailed understanding of the taphonomy of a fossil accumulation. The Capianga Member of the Aliança Formation (Middle to Late Jurassic of the Jatobá Basin, northeastern Brazil) reveals vertebrate fossil accumulations composed predominantly of disarticulated bone and osteoderms, scales, spines and isolated teeth from a lacustrine paleoenvironment. However, the taphonomic history of the accumulation has not yet been studied extensively. The present work aims to interpret taphonomic facies based on lithological data and the systematic collection of fossils from the Capianga Member of the Aliança Formation, located in the northeastern portion of the Jatobá Basin, mainly in the municipality of Ibimirim. Six lithofacies were identified: Fm – massive claystones, Fl – Shale laminated Lt – calcilutites, Lc – calcarenites, Gf – fibrous gypsum and Scl – calciferous sandstones. Two primary taphonomic classes were recognized, consisting essentially of disarticulated elements, including (1) incomplete, semi-complete, or rarely complete bioclasts (such as osteoderms and fish scales) and (2) small-sized, occasionally complete bioclasts (osteoderms and scales) that sometimes compose bonebeds. According to the vertebrate taphonomy characteristics, three taphofacies were identified, with the Taphofacies A and B occurring in calcarenites and the Taphofacies C in calcilutites. The interpretation of these taphofacies reveals a multi-episodic history of the lacustrine environment. The integrated model suggests that the genesis of the identified taphofacies is linked to the action of lowering the water level of the paleolake, as well as the agents responsible for transport and disarticulation. These agents are related to pre-burial sub-aerial exposure, the action of unidirectional turbidity currents in shallow waters, and the likely influence of storms.

In recent decades, Miocene marine transgressions in South America have sparked ongoing debates concerning their boundaries, number of events, regional connectivity, and the existence of an epicontinental sea formed during the Andean orogeny. The bed-by-bed analysis of the Late Miocene Paraná Formation deposits in Entre Ríos Province (Argentina) allow defining six facies associations: (i) beach ridge, (ii) tidal inlet channel and washover fan, (iii) outer estuarine bioherms, (iv) central estuary, (v) tidal bar and sandflat, and (vi) tidal mudflat and creek deposits. Architectural and stacking pattern analyses reveal transgressive-regressive sequences typical of the coastal strip, encompassing shallow marine to estuarine sub-environments. The analysis identified diverse ecological guilds, including bivalve and gastropod assemblages in bioherms, and crustacean traces in tidal flats. Regressive units are characterized by wave-dominated shoreface deposits, while transgressive units comprise fine-grained estuarine deposits interbedded with bioclastic sandstones and storm deposits. The paleoenvironmental and paleoecological data indicate normal salinity marine environments with macroinvertebrates and estuarine components and suggesting tropical brackish conditions. Plant remains point to a range of vegetative communities, including mangroves, palm forests, grasslands, humid riparian forests, and dry upland forests, reflecting tropical to subtropical and humid to semiarid environments. This study concludes that the Paraná Formation correspond to a third-order transgressive system tract influenced by the Miocene Paranaense Sea. The basin-scale implications suggest that the distal Chaco-Paraná basin was affected by eustatic changes due to its low accommodation and topographic relief. The Chaco-Paraná foreland basin's evolution was driven by interactions between tectonic, climatic, and eustatic processes. The comprehensive analysis of sedimentary and fossil records provides a detailed paleogeographic reconstruction of the Miocene marine transgression in southern South America.

This work describes for the first time a fauna of micromorphic brachiopods from Mexico. The biota comprises Permian species of the order Productida: Dyoros (Dyoros) extensiformis, Quadrochonetes girtyi, Rugaria hessensis, Fimbrinia ovata, as well as a productid indeterminate. The samples were located in the Calnali 2 section, belonging to the Tuzancoa Formation. The Kungurian (upper Cisuralian) relative age of the section was established by employing brachiopods, which were associated with bivalves, crinoids, trilobites, and bryozoans. The rocks with invertebrates are interbedded with strata bear plant remains. Sedimentological traits and preservation of brachiopods and associated fauna suggest that the marine community was deposited in a subtidal shallow and restricted environment with very low energy and continuous terrigenous input. On the other hand, the productid indeterminate is the largest brachiopod and displays the worst preservation, with evident traits suggesting that it was transported from a faraway region of the coast. Given that all taxa were previously identified in different units of Texas, considered a region where the Grandian Province was extended, it can be proposed that brachiopods of the Tuzancoa Formation also belonged to the same province. Thus, apart from New Mexico and Texas (USA), Huehuetenango (Guatemala), Palmarito (Venezuela), and Coahuila and Chiapas (Mexico), also Hidalgo's early Permian fauna could be included in the same biotic province.

The Vitória-Trindade Ridge, situated in the central South Atlantic Ocean, is the longest aseismic ridge. The ridge comprises alkaline volcanic formations, including seamounts such as Davis, Colúmbia, Congress banks, Jaseur, Montague, and Vitória. The VTR resulted from a mantle plume, making it structurally complex. A study was conducted to investigate the structure of the VTR using gravity anomalies and bathymetric data. The study revealed the 3D structure of seamounts in terms of their density, depth, and volume. The results showed that the volume of seamounts with depth of VTR ranges from 10 to 14 km. Additionally, the uneven distribution of density contrast indicates the complex structure of the VTR region.