Journal of South American Earth Sciences最新文献

{"title":"Identification of source terranes of beach sediments from the NW Gulf of Mexico, Atlantic ocean: Constraints from geochemistry and U–Pb detrital zircon geochronology","authors":"Mayank Shukla ,&nbsp;Sanjeet K. Verma ,&nbsp;John S. Armstrong-Altrin ,&nbsp;Mayla A. Ramos-Vázquez ,&nbsp;Sumit Mishra ,&nbsp;Elson P. Oliveira ,&nbsp;Eduardo González-Partida ,&nbsp;Héctor Hernández-Mendoza ,&nbsp;Vivek P. Malviya","doi":"10.1016/j.jsames.2025.105496","DOIUrl":"10.1016/j.jsames.2025.105496","url":null,"abstract":"<div><div>This study investigated mineralogy and bulk sediment geochemistry of 24 sediment samples, and U-Pb ages of 200 zircons retrieved from the Tamiahua beach, NW Gulf of Mexico. The study aims to infer the provenance and possible source terranes supplying sediments to the beach area. The XRD and SEM-EDS studies reveal that the sediments are associated with quartz, plagioclase, calcite, and microcline. The Chemical Index of Weathering (CIW'), Th/U and Ba/Sr ratios (&gt;92, 3.75, and 2.27, respectively) indicate high intensity of weathering in the source region. The major as well as trace element-based diagrams along with elemental ratios of TiO₂/Zr (∼15–35), Al₂O₃/TiO₂ (∼120–312), La/Sc (5.31–6.01), La/Co (4.27–5.64), Th/Sc (0.96–1.06), and Cr/Th (3.04–16.24) suggest that the sediments are derived from felsic rocks.</div><div>The Th/U ratios of Tamiahua zircons indicate an igneous origin. The chondrite normalized rare earth elements (REE) patterns exhibit positive Ce and negative Eu anomalies and are depleted in light rare earth elements (LREE) and enriched in heavy rare earth elements (HREE). The sediments are dominated with Proterozoic Eon (Mesoproterozoic; 1053.95–1502.36 Ma), Mesozoic Era (Jurassic; 145.42–179.19 Ma and Cretaceous; 68.84–124.45 Ma), and Cenozoic Era (Eocene; 34.08–54.21 Ma and Oligocene; 25.39–33.71 Ma) zircons indicating their derivation from heterogenous source. The Proterozoic zircons in Tamiahua beach sediments are possibly contributed by the Mesa Central Province, which contains zircons from Chiapas and Oaxacan Massif complexes as well as Granjeno schist and Tamatán group from Sierra Madre Oriental Province. Mesozoic zircons are likely contributed by multiple sources, including undifferentiated turbidites of Mesa Central and Zacatecas, Caracol, San Felipe formations and Huizachal group of Sierra Madre Oriental and from Eastern Alkaline Provinces. Similarly, the Cenozoic zircons are supplied by the felsic to intermediate volcanic rocks and granitoids from the Mesa Central Province. The sediment transport and distribution to the beach area is facilitated by the rivers and their tributaries that flow from the source terranes. The results of this study also reveal a passive margin setting for the northwestern Gulf of Mexico.</div></div>","PeriodicalId":50047,"journal":{"name":"Journal of South American Earth Sciences","volume":"158 ","pages":"Article 105496"},"PeriodicalIF":1.7,"publicationDate":"2025-03-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143725211","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Identifying the reactivation of ancient shear zones in Sul-rio-grandense/Uruguayan shield (South America) using geomorphological index","authors":"Aline Cambri Fredere ,&nbsp;Mateus Rodrigues de Vargas ,&nbsp;Márcio Cardoso Jr ,&nbsp;Ariane Santos da Silveira ,&nbsp;José Manuel Marques Teixeira de Oliveira ,&nbsp;Nelson Ferreira Fernandes","doi":"10.1016/j.jsames.2025.105482","DOIUrl":"10.1016/j.jsames.2025.105482","url":null,"abstract":"<div><div>Cratonic/shield regions are usually considered tectonically quiescent. Fluvial geomorphology analysis has demonstrated that these areas may face continuous deformation. This study proposes the use of anomalous <span><math><msub><mrow><mi>k</mi></mrow><mrow><mi>s</mi><mi>n</mi></mrow></msub></math></span> values, related to fluvial geomorphology, to infer recent deformation in these cratonic/shield regions. This approach is validated by the joint integration of <span><math><msub><mrow><mi>k</mi></mrow><mrow><mi>s</mi><mi>n</mi></mrow></msub></math></span> anomalies with other geomorphological indexes such as knickpoints and <span><math><mi>χ</mi></math></span>, available uplift rates, and analysis of satellite images. Our methodology was tested in the Sul-rio-grandense/Uruguayan shield, a region formed during the Neoproterozoic, and its surrounding areas, which potentially hold evidence of neotectonism. Our findings reveal that <span><math><msub><mrow><mi>k</mi></mrow><mrow><mi>s</mi><mi>n</mi></mrow></msub></math></span> anomalies coincide with tectonic-related knickpoints and follow a preferential NE-trend in the northern of the study area. In the south, several <span><math><msub><mrow><mi>k</mi></mrow><mrow><mi>s</mi><mi>n</mi></mrow></msub></math></span> anomalies are associated with elevated <span><math><mi>χ</mi></math></span> values and extend to the Quaternary sediments. In general, the NE trend observed in our joint methodology fits well with mapped Neoproterozoic shear zones and potentially reflects ongoing deformation along these ancient shear zones. Potential causes for this neotectonism include far-field stresses associated with the Andean Orogeny and tectonic plate adjustments related to the Atlantic opening, as observed in other places along the Brazilian coast. The relationship between anomalous <span><math><msub><mrow><mi>k</mi></mrow><mrow><mi>s</mi><mi>n</mi></mrow></msub></math></span> values and other geomorphological indexes supports that our methodology could be a reliable approach for mapping neotectonism at regional scales.</div></div>","PeriodicalId":50047,"journal":{"name":"Journal of South American Earth Sciences","volume":"158 ","pages":"Article 105482"},"PeriodicalIF":1.7,"publicationDate":"2025-03-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143706434","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Jurassic fern Piazopteris from the Girón Group, Colombia: A taxonomic and paleoenvironmental evaluation","authors":"Jose Manuel Torres-Parada ,&nbsp;Johanset Orihuela ,&nbsp;Carlos Mario Alarcón Gómez ,&nbsp;Jefferson Steeven Diaz Villamizar ,&nbsp;Juan Sebastián Gómez-Coronado ,&nbsp;José Javier Márquez-Prada ,&nbsp;Jorge Andrés Lizarazo-Pabón ,&nbsp;German Patarroyo","doi":"10.1016/j.jsames.2025.105488","DOIUrl":"10.1016/j.jsames.2025.105488","url":null,"abstract":"<div><div>This study investigates a new set of fossil tree ferns from the Late Jurassic Girón Group in the Eastern Cordillera of Colombia. Located on carbonaceous mudstones from the La Honda Creek, we analyzed six specimens tentatively identified as <em>Piazopteris</em> cf. <em>branneri</em> (Matoniaceae). Using thin-section petrography, scanning electron microscopy (SEM), and carbon geochemistry, including total organic carbon (TOC) and stable carbon isotope analyses (δ¹³C_org), we characterize the sedimentological context and paleoenvironmental conditions associated with these fossil remains. The lithofacies, primarily composed of dark-gray mudstone, reveal significant organic matter accumulation and suggests a low-energy depositional environment with fair organic matter preservation, likely a swampy and humid setting. Geochemical analyses, including δ¹³C_org values are consistent with this interpretation, and suggest conditions in a tropical to subtropical climate typical of the Jurassic. These findings provide new insights into the Mesozoic paleoenvironments and flora of the circum-Caribbean region and underscores the importance of the Girón Group to develop future paleobotanical studies in Colombia.</div></div>","PeriodicalId":50047,"journal":{"name":"Journal of South American Earth Sciences","volume":"158 ","pages":"Article 105488"},"PeriodicalIF":1.7,"publicationDate":"2025-03-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143682816","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"New postcranial remains of a non-mammaliaform cynodont from the Pinheiros-Chiniquá Sequence (Middle-Upper Triassic), Brazil","authors":"Leonardo Kerber ,&nbsp;Iasmim M. Michelotti ,&nbsp;Jhonata H.A. Martins ,&nbsp;Rodrigo T. Müller","doi":"10.1016/j.jsames.2025.105487","DOIUrl":"10.1016/j.jsames.2025.105487","url":null,"abstract":"<div><div>The Pinheiros-Chiniquá Sequence (<em>Dinodontosaurus</em> Assemblage Zone, Middle/Upper Triassic) of the Santa Maria Supersequence in Brazil is renowned for its rich fossil record of traversodontid and probainognathian cynodonts (Therapsida: Eucynodontia). However, despite this diversity, their postcranial anatomy remains poorly studied. In this study, we describe new postcranial remains assigned to an eucynodont from this sequence. The specimen includes three presacral vertebrae, the proximal region of the left humerus, the proximal region of the left ulna, right and left femora. The absence of associated cranial material limits a definitive taxonomic assignment. Nonetheless, the combination of distinct femoral characteristics—(i) femoral head positioned well above the greater trochanter, (ii) greater trochanter laterally protruding with a distal projection (forming a “hook”), (iii) slender diaphysis, and iv) lesser trochanter oriented posteromedially—suggests affinities with traversodontids. Future discoveries of cranial material associated with similar postcranial remains could provide critical insights, helping to clarify the taxonomic identification of this specimen.</div></div>","PeriodicalId":50047,"journal":{"name":"Journal of South American Earth Sciences","volume":"158 ","pages":"Article 105487"},"PeriodicalIF":1.7,"publicationDate":"2025-03-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143682821","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Lithostratigraphic analysis of the La Loma Formation and depositional model of the intermontane Cesar Sub-Basin (Colombia) during the Eocene: Exploring potential for CO2 storage","authors":"Dilan Arturo Martínez-Sánchez ,&nbsp;Sait Khurama-Velásquez ,&nbsp;Carlos Alberto Ríos-Reyes","doi":"10.1016/j.jsames.2025.105486","DOIUrl":"10.1016/j.jsames.2025.105486","url":null,"abstract":"<div><div>The Cesar-Ranchería Basin in Colombia presents significant knowledge gaps concerning its Eocene stratigraphy, impeding a comprehensive understanding of its geological evolution and regional correlations. This study focuses on characterizing the La Loma Formation (Eocene) using well log data, petrographic analysis, and X-ray diffraction to delineate its depositional environment and sediment provenance. The La Loma Formation comprises sandstones, conglomerates, and interbedded siltstones within the central La Loma syncline. Petrographic analysis of 100 thin sections identifies two distinct sedimentary environments: fluvial fans and a fluvial system. The Santander Massif and Serranía de Perijá are identified as primary source areas for La Loma Formation sediments. In the lower section of the La Loma Formation, sedimentary contributions primarily originated from the Santander Massif (Eastern Cordillera), indicating uplift during the early Eocene. This geological event potentially redirected drainage towards the Lower Magdalena Valley Basin and connected the Cesar Sub-basin with the Middle Magdalena Valley Basin. Conversely, the upper section of the La Loma Formation reveals a mixed sediment contribution from the Santander Massif, Serranía de Perijá, and Sierra Nevada de Santa Marta. This variation suggests significant environmental shifts and tectonic reconfigurations during the Eocene, influencing connectivity between the Middle Magdalena Valley Basin, the Lower Magdalena Valley Basin, and the Cesar Sub-basin. This lithostratigraphic analysis enhances our understanding of the La Loma Formation's role in regional stratigraphy and basin evolution within the Cesar-Ranchería Basin. Moreover, the study explores the formation's potential for carbon dioxide (CO₂) storage, emphasizing its geological stability, adequate porosity, and potential as a natural sealant, crucial for long-term CO₂ storage and climate change mitigation strategies.</div></div>","PeriodicalId":50047,"journal":{"name":"Journal of South American Earth Sciences","volume":"158 ","pages":"Article 105486"},"PeriodicalIF":1.7,"publicationDate":"2025-03-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143724627","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Interpolation and artificial neural network to estimate soil spatial variability affected by land use and altitude","authors":"Fatemeh Taghipour,&nbsp;Seyed Mostafa Emadi,&nbsp;Majid Danesh,&nbsp;Mehdi Ghajar Sepanlou","doi":"10.1016/j.jsames.2025.105485","DOIUrl":"10.1016/j.jsames.2025.105485","url":null,"abstract":"<div><div>Finding the most suitable methods, which may predict soil spatial variability is essential for proper handling of agricultural lands affected by land use types and altitude. There is not much data on the use of artificial neural network (ANN) outperforming the traditional methods such as the interpolation methods for predicting soil spatial variability. Accordingly, the interpolation methods of inverse distance weighting (IDW), kriging, and co-kriging, as well as ANN were tested to predict soil spatial variability of pH, salinity (EC), and cation exchange capacity (CEC) affected by land use type (cultivated and uncultivated lands, orchard, forestry and rangeland) and altitude (-20-0 (A1), 0–100 (A2), 100–500 (A3), and &gt;500 m (A4)) in a 9545 km² research area. The chemical properties of the 249 soil samples (0–15 cm) were determined. Land use type indicated pH of 6.56 (forestry) to 7.32 (cultivated land), EC of 1.10 (forestry) to 2.87 dS/m (rangeland), and CEC of 17.71 (uncultivated land) to 37.01 meq/100 g soil (forestry). Altitude resulted in pH of 6.72 (A4) to 7.35 dS/m (A2), EC of 1.31 (A4) to 1.90 (A2) dS/m, and CEC of 20.07 (A1) to 34.45 meq/100 g soil. Although cross-validation method (using mean error (ME) and root means square error (RMSE)) indicated the accuracy of interpolation methods to predict soil spatial variability, ANN was the most suitable one. The proper training of ANN may precisely predict the spatial heterogeneity of soil chemical properties affected by land use type and altitude, useful for the appropriate handling of agricultural lands.</div></div>","PeriodicalId":50047,"journal":{"name":"Journal of South American Earth Sciences","volume":"157 ","pages":"Article 105485"},"PeriodicalIF":1.7,"publicationDate":"2025-03-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143631977","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Paleomagnetism of the Permian De la Cuesta formation (Narváez Range, NW Argentina): Apparent polar wander path and paleogeography of Gondwana and Pangea","authors":"Cecilia Mariel Spagnuolo ,&nbsp;Augusto Ernesto Rapalini ,&nbsp;Ricardo A. Astini ,&nbsp;Sabrina Y. Fazzito","doi":"10.1016/j.jsames.2025.105468","DOIUrl":"10.1016/j.jsames.2025.105468","url":null,"abstract":"<div><div>Permian times were characterized by distribution of land masses forming a supercontinent called Pangea. Although its existence has been accepted for many decades, there is still debate about its configuration. In order to provide new constraints on the position of Gondwana during late Paleozoic times, a paleomagnetic study was carried out on Carboniferous-Permian red beds exposed in the Famatinian Ranges, western Argentina (27°43′S 67°58′W). Eighty four oriented samples (11 sites) were submitted to standard stepwise demagnetization procedures. Magnetic analysis was complemented by acquisition of isothermal remanent magnetization (IRM), backfield curves and anisotropy of magnetic susceptibility (AMS) on selected specimens. Inclination shallowing due to compaction was evaluated by application of oriented acquisition of IRM and demagnetization experiments. The high-temperature magnetic components of sites are characterized by southward declinations with positive inclinations that yield a positive fold test. A new paleomagnetic pole is calculated and suggests an age of magnetization between 300 and 270 Ma, thatmatches with a Pangea B distribution although a Pangea A2 model can not be ruled out if the magnetization age is restricted to 280-270 Ma.</div></div>","PeriodicalId":50047,"journal":{"name":"Journal of South American Earth Sciences","volume":"157 ","pages":"Article 105468"},"PeriodicalIF":1.7,"publicationDate":"2025-03-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143631976","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Rainfall variability, land use and land cover dynamics, and implications for climate risk through a theoretical-conceptual model for the Eastern Northeast of Brazil","authors":"Micejane da Silva Costa ,&nbsp;José Francisco de Oliveira Júnior ,&nbsp;Bárbara Godoy de Barros ,&nbsp;Luís Felipe Francisco Ferreira da Silva ,&nbsp;Kelvy Rosalvo Alencar Cardoso ,&nbsp;Akza Hellen dos Santos Silva ,&nbsp;Ana Carla do Santos Gomes ,&nbsp;Maytê Duarte Leal Coutinho ,&nbsp;Edson de Oliveira Souza ,&nbsp;Michelyne Duarte Coutinho de Morais ,&nbsp;Ninu Krishnan Modon Valappil ,&nbsp;Vijith Hamza ,&nbsp;Sudhir Kumar Singh ,&nbsp;Punyawi Jamjareegulgarn ,&nbsp;Munawar Shah","doi":"10.1016/j.jsames.2025.105470","DOIUrl":"10.1016/j.jsames.2025.105470","url":null,"abstract":"<div><div>The study assessed the variability of rainfall, land use and land cover (LULC), the influence of meteorological systems and their interactions, followed by the increase in climate risks in Maceió – Alagoas – ENEB. Monthly rainfall data were obtained from the 64-year historical series (1958–2022) of the TerraClimate platform. The TerraClimate precipitation data were validated ANA and SEMARH data, resulting in R² = 0.72 and r = 0.85. Spatially, the highest rainfall accumulations occurred from April to July (rainy season), with May and June being the wettest months (&gt;800 mm). In contrast, the months from October to February (dry season) and March, August, and September (transition season) recorded lower rainfall, with November and December being the driest months (150–201 mm). The seasonal occurrence of rainfall and the relief in Maceió were associated with areas of climate risk. Maceió is a region vulnerable to extreme rainfall events due to its geographical location, the influence of the Atlantic Ocean and the Mundaú/Manguaba Lagoons, and the interaction with multi-scale meteorological systems. With LULC, there was an expansion of forest areas in rural areas and a reduction of agricultural areas, followed by increased urbanization in neighborhoods in the western part of the city (coastal plateau). The theoretical-conceptual model of climate risk provides essential information for planning and supports decision-making for public policies. The ability to assess the impacts of extreme rainfall underscores the importance of adaptive responses by local communities through the management of public policies and strategies for adapting to climate risk.</div></div>","PeriodicalId":50047,"journal":{"name":"Journal of South American Earth Sciences","volume":"158 ","pages":"Article 105470"},"PeriodicalIF":1.7,"publicationDate":"2025-03-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143682820","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Geochemical analysis of lateritic duricrust formation in the Cuesta and Paulista Peripheral Depression sectors of São Paulo State, southeastern Brazil","authors":"Everton Tiago Sulato ,&nbsp;Karen Luko-Sulato ,&nbsp;Daniel Godoy ,&nbsp;Reiner Neumann ,&nbsp;Vania Rosolen","doi":"10.1016/j.jsames.2025.105473","DOIUrl":"10.1016/j.jsames.2025.105473","url":null,"abstract":"<div><div>This study aims to investigate rare earth elements (REE), U, Th, Pb concentrations, and Pb isotopic ratios in lateritic weathering profiles from the Cuesta and Paulista Peripheral Depression, Brazil. Sample analysis provided geochemical and mineralogical indicators of element mobilization and distribution, enhancing the understanding of weathering processes and parental inheritance in lateritic profiles. The lateritic duricrusts are composed of goethite, hematite, kaolinite, quartz, and rare magnetite, with a significant loss of basic cation, indicating intense weathering and leaching. However, weathering fronts show limited advancement toward intense laterization, likely controlled by climate, topography, parent rock composition, and drainage. A mineralogical trend distinguishes lateritic duricrusts by elevation, with hematite predominating at mid-to-high (Cuesta) and goethite predominating at low-to-mid (Peripheral Depression) elevations. REE concentrations correlate more with mineralogy than parent rock composition, with lower REE levels in hematite-rich lateritic duricrusts at higher elevations and higher REE content in goethite-rich ones from all elevations, influenced by the alteration stage of goethite-rich lateritic duricrusts. Light REE enrichment over heavy REE is observed in lateritic duricrusts, soils, and parent rock, with soils showing greater mobility and differential accumulation. Pb redistribution occurs during weathering, with lateritic duricrusts retaining intermediate isotopic signatures and soils exhibiting the most radiogenic Pb, while ²⁰⁷Pb/²⁰⁶Pb and ²⁰⁸Pb/²⁰⁶Pb ratios suggest parental inheritance among all matrices. Higher elevation lateritic duricrusts exhibit an inverse relationship between U and Pb or Th, likely driven by mineralogical stabilization, selective adsorption, and the radioactive decay of U and Th into Pb over time.</div></div>","PeriodicalId":50047,"journal":{"name":"Journal of South American Earth Sciences","volume":"157 ","pages":"Article 105473"},"PeriodicalIF":1.7,"publicationDate":"2025-03-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143577557","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Sediment provenance signatures of the largest river in the Andes (Marañón River, Peru): Implications for signal propagation in the Amazon drainage system","authors":"Lily J. Jackson ,&nbsp;Brian K. Horton","doi":"10.1016/j.jsames.2025.105471","DOIUrl":"10.1016/j.jsames.2025.105471","url":null,"abstract":"<div><div>The transcontinental Amazon River system carries vast amounts of sediment from the Andes Mountains and South American craton to the Atlantic Ocean. However, diagnostic provenance signatures for Andean headwater rivers and Amazonian lowland tributaries remain poorly defined. The Marañón River, the longest Andean river with the largest upland drainage area, is proposed here to be the principal tributary and contributor of orogenic sediment to the modern Amazon River. The intermontane Marañón River flows axially (longitudinally) northward for ∼550 km from 10° to 5°S in the high-relief hinterland region between the flanking 3000–6000 m high Western Cordillera and Eastern Cordillera in the Andes of Peru. Detrital zircon U-Pb ages from 18 samples (1922 analyses) of modern river sands collected at 235–3120 m altitude reveal the provenance signatures for the major sediment sources within the Marañón River drainage system. Detrital zircon U-Pb age distributions from the mainstem river and selected tributary watersheds (∼280–6600 km²) exhibit a large proportion of Precambrian to early Paleozoic grains, including prominent 1600–1400 Ma (Rondonia-San Ignacio), 1300–900 Ma (Sunsás), and 700–450 Ma (Brasiliano-Famatinian) age groups, with subordinate Permian-Triassic (300–200 Ma) and Cenozoic (66–0 Ma) ages. The detrital zircon age distributions can be linked to extensive outcrops of late Neoproterozoic-early Paleozoic metamorphic basement, Mesozoic sedimentary rocks, and Cenozoic sedimentary and volcanic deposits in the Andean fold-thrust belt. Limited variations in detrital signatures along the mainstem Marañón River match the uninterrupted exposures of chiefly pre-Cenozoic units along the length of the Western and Eastern Cordilleras. However, a greater downstream proportion of Cenozoic ages corresponds to expanded Cenozoic deposits in tributary catchments of northernmost Peru. For one tributary (Crisnejas River), we present zircon U-Pb ages from 9 bedrock source samples (866 analyses) to assess the degree to which river sand age distributions reflect the bedrock units exposed in the corresponding drainage area. A remarkable agreement between observed and predicted age distributions from sediment provenance unmixing models suggests that modern river sands faithfully preserve the relative proportions of contributing rock units. Further comparisons of U-Pb age signatures for the intermontane Marañón River with other Andean tributaries and downstream lowland segments of the Amazon River (7603 analyses of 67 samples) reveal striking similarities between Marañón and Amazon results, with many shared characteristic age components, suggesting that Amazon River provenance may be determined principally by Andean headwater tributaries such as the Marañón River.</div></div>","PeriodicalId":50047,"journal":{"name":"Journal of South American Earth Sciences","volume":"157 ","pages":"Article 105471"},"PeriodicalIF":1.7,"publicationDate":"2025-03-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143592544","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}