Journal of South American Earth Sciences最新文献

{"title":"Recharge area estimation by block and mountain front for the Los Humeros Geothermal Field, Puebla, Mexico: Advancing the conceptual model","authors":"Thomas Gunter Kretzschmar ,&nbsp;José Alonso Aguilar-Ojeda ,&nbsp;Enrique Iñiguez ,&nbsp;Jorge Alejandro Ávila-Olivera ,&nbsp;Julio César Cañas-Ramírez ,&nbsp;Brenda Estela García-Sánchez ,&nbsp;Gabriela Michel Vara-Castro","doi":"10.1016/j.jsames.2025.105411","DOIUrl":"10.1016/j.jsames.2025.105411","url":null,"abstract":"<div><div>The Los Humeros Geothermal Field in Mexico is recognized as one of the most important in the country due to its geological conditions and electricity generation capacity. Therefore, this study aimed to provide new data for the conceptual model through remote analysis techniques, GIS tools, and hydrogeological exploration campaigns in the areas surrounding the geothermal field. The focus was on defining the area of the mountain front and the mountain block to estimate the potential recharge through these two components. It was determined that the potential recharge areas are located in the mountain fronts and mountain blocks of six subbasins surrounding the Los Humeros geothermal field, occupying an area of 5528 km². The estimated recharge of the mountain front and mountain block ranges between 199 and 3996 million cubic meters, depending on the infiltration rates considered (5% or 100% recharge). These estimates are similar to the recharge volume estimated by the Federal Electricity Commission. This scientific study provides new knowledge about the conceptual model of the Los Humeros geothermal field, specifically regarding the definition of recharge areas from mountain fronts and blocks. The findings contribute to a better understanding of recharge mechanisms in the geothermal field and have significant implications for the sustainable management of water resources in the area.</div></div>","PeriodicalId":50047,"journal":{"name":"Journal of South American Earth Sciences","volume":"155 ","pages":"Article 105411"},"PeriodicalIF":1.7,"publicationDate":"2025-02-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143420685","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":"A new terrestrial vertebrate from the Río Nío Formation (Eocene) of northwestern Argentina","authors":"Pablo J. Gaudioso ,&nbsp;Juan C. Fernicola ,&nbsp;Raúl I. Vezzosi ,&nbsp;C.D. Corro ,&nbsp;Claudia M. Muruaga","doi":"10.1016/j.jsames.2025.105410","DOIUrl":"10.1016/j.jsames.2025.105410","url":null,"abstract":"<div><div>Northwestern Argentina exhibits numerous Paleogene fossiliferous localities. However, in Tucuman Province, this period is represented by a few fossiliferous localities of the Rio Loro Formation (early Paleocene-early Eocene?). In this context, the Río Nío Formation (Eocene) is restricted to that province and no fossiliferous locality has been reported since its formal description in 1973. Recent geo-paleontological field trips in a new locality of the Río Nío Formation in Tucumán province, have revealed new fossil remains. Here we present the first fossil records from the Río Nío Formation, based on several disarticulated osteoderms of a cingulate mammal species, exclusive to northwestern Argentina, <em>Pucatherium parvum</em> (Xenarthra, Dasypodidae). This finding provides new morphological and biogeographical information for this taxon, increasing our current knowledge. The sedimentological analysis conducted at the new locality provides valuable paleoenvironmental and stratigraphic information on the Eocene and Miocene successions in this area.</div></div>","PeriodicalId":50047,"journal":{"name":"Journal of South American Earth Sciences","volume":"155 ","pages":"Article 105410"},"PeriodicalIF":1.7,"publicationDate":"2025-02-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143403281","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":"Provenance evolution and sedimentary records in a rift basin: U-Pb Detrital zircon and petrography of sandstones of the Volta Redonda Basin (central segment of the Continental Rift of Southeastern Brazil)","authors":"Carlos Eduardo Sales de Oliveira ,&nbsp;Luiz Carlos Bertolino ,&nbsp;Mauro Cesar Geraldes ,&nbsp;Renato Rodriguez Cabral Ramos ,&nbsp;André Pires Negrão ,&nbsp;André Campos Rocha Pinto","doi":"10.1016/j.jsames.2025.105407","DOIUrl":"10.1016/j.jsames.2025.105407","url":null,"abstract":"<div><div>This study traces the evolution of provenance, paleodrainages, and sedimentary records across the Paleogene tectonic stages of the Volta Redonda Basin (central segment of the Continental Rift of Southeastern Brazil) by integrating sandstone petrography, detrital zircon U-Pb geochronology, and field observations. The basin's evolution is recorded in three tectonostratigraphic units: pre-rift (Ribeirão dos Quatis Formation), which records a high-energy gravel-bed braided fluvial system; rift I (Resende Formation), deposited by an immature, sand-bed braided fluvial system with alluvial fans; rift II (Pinheiral Formation), featuring a mature braided fluvial system. U-Pb detrital zircon analyses reveal similar provenance for all units, with Neoproterozoic ages predominating (54–69%), followed by Paleoproterozoic (22–40%), Mesoproterozoic (1–14%), and minor Archean and Paleozoic contributions. Archean ages are linked to metasedimentary rocks of the Paraíba do Sul Group and orthogneisses of the Quirino and Campinho complexes. Paleoproterozoic ages are associated with orthogneisses of the Quirino, Campinho, Taquaral and Juiz de Fora complexes, and metasedimentary rocks of the Paraíba do Sul and Embu groups. Mesoproterozoic ages derive from the Embu Group. Neoproterozoic and Paleozoic ages are linked to intrusive granitoids, primarily the Rio Turvo Suite. Provenance reflects two main sediment dispersal routes: (1) from the inland side of the Bocaina Plateau, parallel to the rift axis, controlled by NE-SW-trending Precambrian basement structures, predominant during the pre-rift stage and active during the rift II stage; (2) from the Resende−Volta Redonda interbasin basement, transverse to oblique to the rift axis, controlled by NW-SE-trending transcurrent faults, predominant during rift I stage.</div></div>","PeriodicalId":50047,"journal":{"name":"Journal of South American Earth Sciences","volume":"155 ","pages":"Article 105407"},"PeriodicalIF":1.7,"publicationDate":"2025-02-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143403282","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":"The role of multiple disturbances in the morphodynamics of an alluvial fan in the north Patagonian Andean forests, Argentina","authors":"Agustín Quesada ,&nbsp;Mariano M. Amoroso","doi":"10.1016/j.jsames.2025.105409","DOIUrl":"10.1016/j.jsames.2025.105409","url":null,"abstract":"<div><div>Alluvial fans have the potential to record climatic and neotectonic events. These depositional systems, characterized by distributary river patterns, are more frequently studied in arid environments due to better exposure and easier accessibility. In this study, we applied dendrogeomorphic methods on an alluvial fan within the wet temperate north Patagonian Andean forests to reconstruct the environmental history of the Derrumbe Creek Alluvial Fan. The specific objectives were: (a) to date the activation/inactivation of different ecogeomorphic units in the alluvial fan, and (b) to interpret the relative importance of various disturbances that have shaped its recent history. The Derrumbe Creek Alluvial Fan is located in the southern bay of Puelo Lake, in the northwest of Chubut Province, Argentina. We carried out two fieldwork campaigns for tree data collection and geomorphic analysis. Using standard dendrochronological laboratory methods, we obtained establishment dates for the different geomorphic units of the alluvial fan and developed a disturbance chronology. Three main disturbance events were identified: the first in the early 1920s, clearly associated with a fire; the second between 1957 and 1959, linked to sediment deposition (colmatation) and lateral migration of the active channel; and the third between 1961 and 1963, related to an outburst flood and avulsion of the active channel. We propose that the latter two disturbance events were facilitated or conditioned by the earlier fire, emphasizing the significance of fire history in the geomorphic evolution of the alluvial fan. Our findings highlight the role of multiple disturbances in the complex dynamics of alluvial fans in the southern Andes.</div></div>","PeriodicalId":50047,"journal":{"name":"Journal of South American Earth Sciences","volume":"155 ","pages":"Article 105409"},"PeriodicalIF":1.7,"publicationDate":"2025-02-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143420688","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":"Soil development in a Maar lake basin in central Mexico based on micromorphology and magnetic mineralogy","authors":"Daisy Valera-Fernández ,&nbsp;Beatriz Ortega-Guerrero ,&nbsp;Elizabeth Solleiro-Rebolledo ,&nbsp;Arnaldo Hernández-Cardona ,&nbsp;Teresa Pi-Puig ,&nbsp;Cecilia Caballero-Miranda","doi":"10.1016/j.jsames.2025.105405","DOIUrl":"10.1016/j.jsames.2025.105405","url":null,"abstract":"<div><div>The weathering and diagenesis processes in the soils of a basin usually produce secondary minerals, which can be transported to the lake basins as part of the detrital fraction. The occurrence of magnetite in lake sediments, or the maghemitization of (Ti)-magnetites, may indicate pedogenic activity and weathering before transporting them to lakes. This study analyzes the differences in soil development in the Laguna de Majahual Maar Lake catchment soil profiles under a tropical-humid climate. Three soil profiles were sampled at different depths in the rim lake basin of Laguna de Majahual (MJ1, MJ2, and MJ3). Magnetic mineralogy and micromorphology analyses were completed, complemented by color, grain size, and mineralogy from the bulk sample and the clay fraction by X-ray diffraction (XRD). The basin's local topography variability influences the Laguna de Majahual soils' magnetic properties and degree of pedogenesis. The two soils in the upper part (MJ1 and MJ2) are formed mainly by the A, AB, and C horizons, suggesting several sedimentations and pedogenesis cycles. At the same time, the MJ3 profile close to the lake's surface shows well-developed Bt and Btg horizons. The micromorphology of the A and AB horizons of MJ1 and MJ2 showed abundant fresh plant fragments and a granular structure, while in the Bt and Btg horizons of MJ3, illuviation of clays and accumulation of Fe oxides was identified. The identification of clays in the MJ1, MJ2, and MJ3 horizons revealed the presence of halloysite. In the MJ1 and MJ2 horizons, this is likely due to hydrothermal alteration of volcanic materials. However, in the MJ3 horizon, halloysite formation is more likely the result of extensive leaching in soil profiles under tropical humid climates. Regarding their magnetic mineralogy, titanomagnetite (soft detrital minerals), and magnetite (soft pedogenic minerals) were found, whereas hematite (hard pedogenic mineral) was found exclusively in the MJ3 profile. It is now clearer that the contribution of titanomagnetite and magnetite in the MJ1 and MJ2 profiles is due to the incorporation of new volcanic material deposits, and hematite in the MJ3 profile related to pedogenic processes.</div></div>","PeriodicalId":50047,"journal":{"name":"Journal of South American Earth Sciences","volume":"154 ","pages":"Article 105405"},"PeriodicalIF":1.7,"publicationDate":"2025-02-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143376708","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":"Coastal dynamics: Assessing erosion and progradation patterns in Campeche coastal region using machine learning techniques for geological insights","authors":"Palanikkumar D ,&nbsp;Eatedal Alabdulkreem ,&nbsp;Nuha Alruwais ,&nbsp;Abdulsamad Ebrahim Yahya","doi":"10.1016/j.jsames.2025.105406","DOIUrl":"10.1016/j.jsames.2025.105406","url":null,"abstract":"<div><div>This study examines shoreline dynamics along the Campeche coastal region from 1974 to 2024, using machine learning techniques to analyse long-term trends in erosion and accretion. Integration of machine learning with geological analysis enables precise evaluation of shoreline changes, enhancing the understanding of coastal dynamics. Spanning 50 years, the research utilizes satellite imagery, historical maps, remote sensing, and GIS to assess shoreline changes and their geological significance. Results show that 93% of the coastline is experiencing accretion, while 7% is undergoing erosion. Accretion rates range from a minimum of 2.36 m (0.05 m/year) to a maximum of 1136.61 m (22.73 m/year), while erosion rates vary from −2.56 m (−0.05 m/year) to −131.41 m (−2.63 m/year). This study identifies key coastal changes, with Zona Centra and Koben regions experiencing significant accretion, while South San Lorenzo faces the highest erosion activity. Understanding these dynamics is crucial for coastal management and mitigation strategies. Campeche's coastline predominantly features carbonate-rich sediment deposits, influenced by ocean currents, sediment supply, and coastal morphology, resulting in widespread accretion. Localized erosion hotspots are linked to human activities and disruptions in sediment transport. Machine learning models identified spatial patterns and quantified the influence of stratigraphy on shoreline changes, highlighting the benefits of combining modern techniques with traditional methods for accurate coastal analysis. Campeche's rich geological diversity and extensive data availability make it an ideal case study for exploring machine learning applications in coastal management and assessing coastal vulnerability. This comprehensive approach offers valuable insights for sustainable development and addressing coastal erosion challenges.</div></div>","PeriodicalId":50047,"journal":{"name":"Journal of South American Earth Sciences","volume":"155 ","pages":"Article 105406"},"PeriodicalIF":1.7,"publicationDate":"2025-02-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143403608","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":"Climate and anthropic agents lead to changes in groundwater-surface water interactions in a semi-arid maar lake","authors":"Raúl A. Silva-Aguilera ,&nbsp;Oscar Escolero ,&nbsp;Javier Alcocer ,&nbsp;Eric Morales-Casique ,&nbsp;Selene Olea-Olea ,&nbsp;Gloria Vilaclara ,&nbsp;Socorro Lozano-García ,&nbsp;Alex Correa-Metrio","doi":"10.1016/j.jsames.2025.105398","DOIUrl":"10.1016/j.jsames.2025.105398","url":null,"abstract":"<div><div>Groundwater and surface water form a complex and interconnected system influenced by geomorphology, geology, hydrology, and climate factors. Human activities, particularly intensive groundwater exploitation, add further complexity to these systems, especially in arid regions. Understanding groundwater-surface water interactions is essential for effective management and conservation. Maar lakes are unique surface bodies specifically connected to groundwater flow systems. In this study, we developed a conceptual model of the groundwater-surface water interaction of a semi-arid maar lake over space and time. Our objective was to understand the changes in the system and the relative influence of external forcing factors. The study focuses on Lake Alchichica, located in a semi-arid, endorheic basin in central Mexico, which has experienced a decline in water levels over recent decades. We employed a multiproxy methodology that includes the characterization of space-time variability in effective precipitation, regional hydrogeochemical patterns, isotopic and physicochemical patterns within the lake, dynamic changes in phreatic levels, and an overall assessment of anthropogenic pressures relative to natural variability. The hydrogeochemical patterns indicate that the groundwater flow path feeding Lake Alchichica is part of the regional groundwater flow system. This shows hydrogeochemical evolution from the Sierra Madre Oriental to the regional base level at playa lake Tepeyahualco. Isotopic composition and hydrochemical patterns near the lake provide evidence of groundwater-lake interactions, with increasing concentrations of various ions along the flow path, likely due to intense evaporation within the lake. From 2017 to 2021, phreatic levels declined by approximately 37.8 cm, indicating a decrease in the total volume of groundwater entering the lake, which affects the lake's water balance and level. This decline was not directly attributed to meteorological changes, suggesting alterations in the regional system. Although no significant changes in groundwater chemical composition were observed, other studies have reported changes in the chemical composition and temperature of the lake, indicating potential threats to the lake's habitat due to modifications in the groundwater-surface water interaction system.</div></div>","PeriodicalId":50047,"journal":{"name":"Journal of South American Earth Sciences","volume":"156 ","pages":"Article 105398"},"PeriodicalIF":1.7,"publicationDate":"2025-02-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143436529","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":"Water quality modulations under influence of rainfall and land cover in a mountain basin in southeast Brazil","authors":"Felipe Soter de Mariz e Miranda,&nbsp;André de Souza Avelar","doi":"10.1016/j.jsames.2025.105403","DOIUrl":"10.1016/j.jsames.2025.105403","url":null,"abstract":"<div><div>In the context of climate change, there are projections of an increase in storm occurrence and larger periods of drought that threaten water resources for human supply and ecosystems in South America. Based on this problem, this study aimed to understand how rainfall affects different water quality parameters and its relationship with changes in land cover. To this end, rainfall data were cross-referenced with water quality monitoring, and it was compared at two sampling points on the Rio Preto: upstream and downstream from a human settlement (Maromba District). The parameter thermotolerant coliforms was the parameter that showed the most divergence between the two sampling points, which often exceeded Brazilian legislation limits for supply and recreational use, and their variability over time was not related to rainfall. Dissolved oxygen and nitrates were the most correlated parameters with rainfall. Turbidity increases correlated to rainfall only downstream, being the parameter with the greatest difference between points in response to rain. However, the parameters that correlated in some way with rainfall remained within satisfactory values in the Maromba District. We believe that the virtual absence of agriculture in the basin is the key factor for maintaining satisfactory values of eutrophic parameters downstream, but it is noteworthy that human activity linked to tourism threatens water quality due to coliform contamination.</div></div>","PeriodicalId":50047,"journal":{"name":"Journal of South American Earth Sciences","volume":"154 ","pages":"Article 105403"},"PeriodicalIF":1.7,"publicationDate":"2025-02-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143349585","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":"Thermal conductivity of igneous rock cores estimated from shallow wells drilled within the Las Tres Vírgenes volcanic complex, BCS, Mexico","authors":"Gómez-Ávila Marianggy ,&nbsp;Gómez-Arias Efraín ,&nbsp;Rodríguez-González Claudia Alejandra ,&nbsp;Hernández-Paz Juan Francisco ,&nbsp;Lira-Martínez Manuel Alejandro","doi":"10.1016/j.jsames.2025.105404","DOIUrl":"10.1016/j.jsames.2025.105404","url":null,"abstract":"<div><div>In this study, the thermal properties of volcanic igneous rock cores were experimentally measured, considering them ceramic materials (that allows heat transfer conduction efficiently). Five shallow wells (with depths between 42 and 55 m) were drilled, from which different samples of volcanic core rocks (including pumice, tuff, rhyolites, basalts, and basaltic andesite) were recovered. To measure the thermal properties of these materials, the cores were cut using a diamond-tipped rock cutter and dried in an oven between 105 and 120 °C for approximately 12 h to remove excess lubrication fluids. The thermal properties of the rocks (thermal conductivity, thermal diffusivity, and volumetric heat capacity) were measured in twenty-one rock core samples (from five shallow wells) by a Hot Disk Thermal Constants Analyzer. The sample thermal conductivities experimental results were corrected as a function of the log-temperature depths, showing a variation based on the depth at which they were obtained. For example, the thermal conductivity for tuff is 0.73 W/mK at 5.81 m and 1.40 W/mK at 10.20 m for the Refugio well; for pumice is 0.62 W/mK at 3.14 m and 0.52 W/mK at 11.40 m in La Reforma 1 well, and 0.52 W/mK at 3.53 m and 0.56 W/mK at 5.86 m in la Reforma 2 well; for basalt is 0.98 W/mK at 43.53 m and 1.09 W/mK at 43.98 m in La Reforma 1 well, and 1.11 W/mK at 43.30 m in La Reforma 2 well; thermal conductivity of rhyolite is 1.42 W/mK at 55.05 m in La Reforma 2 well; and for the basaltic-andesite rocks, 1.32 W/mK at 43.46 m in El Azufre well, 1.09 W/mK at 6.29 m in La Fumarola well, and 1.674 W/mK at 27.88 m in Refugio Well.</div></div>","PeriodicalId":50047,"journal":{"name":"Journal of South American Earth Sciences","volume":"154 ","pages":"Article 105404"},"PeriodicalIF":1.7,"publicationDate":"2025-02-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143349592","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":"Concealed morphological diversity revealed by new fossils of Chelus (Testudines, Chelidae) from the Upper Miocene of the Acre Basin, Brazil","authors":"Donato J. Martucci Neto ,&nbsp;Annie Schmaltz Hsiou ,&nbsp;Edson Guilherme ,&nbsp;Leonardo A.T. Costa ,&nbsp;Gabriel S. Ferreira","doi":"10.1016/j.jsames.2025.105408","DOIUrl":"10.1016/j.jsames.2025.105408","url":null,"abstract":"<div><div>The Solimões Formation, in the Acre Basin, which outcrops between the states of Acre and Amazonas, northern Brazil, contains the country's most diverse fossil fauna of Neogene amniotes. The outcrops are mainly found on the erosive margins of the Purus, Acre, and Juruá rivers, among others, since the 19th century. So far, as recorded in other Neogene deposits in northern South America, most of the fossil turtles of the Brazilian Amazon are represented mainly by the clades Chelidae, Podocnemididae, and Testudinidae. The genus <em>Chelus</em> (Chelidae) — popularly known as mata-mata —, represented by two extant species, <em>Chelus fimbriata</em> and <em>Chelus orinocensis</em>, traditionally also includes two extinct species: <em>Chelus colombiana</em> and <em>Chelus lewisi</em>. In Brazil, fossils attributed to the genus <em>Chelus</em> have been reported since the late 19th century. Still, the first valid identifications were made in the 1980s and 1990s, and later in the 2000s, with the proposed presence of <em>C. colombiana</em> and <em>C. lewisi</em> observed in Miocene strata of the Brazilian Amazon. Here, we describe recently discovered fossils housed at the Laboratório de Pesquisas Paleontológicas at the Universidade Federal do Acre (Campus Rio Branco) and assign them to <em>Chelus.</em> Our comparative analyses show that features traditionally and recently used to diagnose the two extinct taxa are present in the same individual. This overlap leads us to question the consistency of these characteristics and consequently the validity of <em>C. lewisi</em>.</div></div>","PeriodicalId":50047,"journal":{"name":"Journal of South American Earth Sciences","volume":"155 ","pages":"Article 105408"},"PeriodicalIF":1.7,"publicationDate":"2025-02-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143395420","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}