Journal of South American Earth Sciences最新文献

{"title":"Stratigraphic and paleoenvironmental significance of palustrine deposits in bioclastic successions: Morro do Chaves formation, Northeast Brazil","authors":"Marila Andrade ,&nbsp;Patrick Führ Dal’ Bó ,&nbsp;Amanda Rodrigues ,&nbsp;Julia Favoreto ,&nbsp;Leonardo Borghi ,&nbsp;Maurícius Nascimento Menezes","doi":"10.1016/j.jsames.2026.106005","DOIUrl":"10.1016/j.jsames.2026.106005","url":null,"abstract":"<div><div>The Morro do Chaves Formation (Sergipe-Alagoas Basin, NE-Brazil) represents one of the carbonate–siliciclastic successions deposited in the early Cretaceous rift-lake systems related to the opening of South Atlantic Ocean. Within this unit, palustrine intervals preserve key evidence of subaerial exposure and hydrological fluctuations, offering valuable insights into the evolution of marginal lacustrine environments. However, despite their relevance, these deposits remain poorly understood regarding their origin, spatial distribution, and relationship with base-level variations. Previous interpretations classified some of these deposits as deep-lake sediments, overlooking the pedogenic and diagenetic processes that shaped them. The aim of this study is to interpret the genesis of palustrine deposits and interpret their stratigraphic and paleoenvironmental significance in a coquina succession. The results of the study identify two main palustrine facies: nodular mudstones and micritized shellstones. Their vertical arrangement defines a protected marginal setting of backshore ponds behind shore ridges. Regionally, palustrine intervals coincide with three maximum regressive surfaces (MRS1–MRS3), marking episodes of lowered lake level and reduced accommodation space. The proposed stratigraphic model, refines the depositional and stratigraphic framework of Morro do Chaves Formation, demonstrating that palustrine deposits record repeated hydrological and climatic oscillations at the lake margins. These findings contribute to the understanding of marginal rift-lake dynamics and provide new tools for high-resolution stratigraphic correlation and reservoir characterization in hybrid carbonate–siliciclastic systems.</div></div>","PeriodicalId":50047,"journal":{"name":"Journal of South American Earth Sciences","volume":"174 ","pages":"Article 106005"},"PeriodicalIF":1.5,"publicationDate":"2026-04-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147385834","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":"3D magnetotelluric architecture of Archean nucleus São José do Campestre, Borborema Province, NE Brazil","authors":"N.C.V. Silva ,&nbsp;C. Magini ,&nbsp;E.L. Dantas ,&nbsp;F.M. da Silva ,&nbsp;R.M.G. Castelo Branco ,&nbsp;R.A. Fuck ,&nbsp;J.A. Martins ,&nbsp;V.S. Moreira","doi":"10.1016/j.jsames.2026.105995","DOIUrl":"10.1016/j.jsames.2026.105995","url":null,"abstract":"<div><div>Crustal evolution models of Archean and Paleoproterozoic lithospheres seek to determine the crust/mantle relationship, and deep geophysics techniques could identify different rheological limits between them. When applied to broadband acquisitions, the magnetotelluric (MT) method has proven extremely viable for this type of research. In MT studies carried out in the São José do Campestre Nucleus (SJCN), in the NE region of the Borborema Province, NE Brazil, the aim was to map the crustal thickness of each geological unit, its geometry, and the major lineaments that shaped the terrain of different ages. The resistivity/conductivity results show two layers: the most conductive and the most resistive, in addition to indicating the Moho surface at 18-24 km depth, related to the Archean core and the Paleoproterozoic belt surrounding it. Both are intersected by regional shear zones that served as conduits for Neoproterozoic granite bodies, the latter with a root depth of less than 7 km. The 3D model allowed visualization of these three units, of different ages and with different geoelectric responses, in both cross- and horizontal-sections.</div></div>","PeriodicalId":50047,"journal":{"name":"Journal of South American Earth Sciences","volume":"174 ","pages":"Article 105995"},"PeriodicalIF":1.5,"publicationDate":"2026-04-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147385835","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":"Bioturbation as a trigger for early diagenetic processes in miocene mixed carbonate-siliciclastic platforms: The Pirabas Formation, Equatorial Brazilian Margin","authors":"Meireanny de Albuquerque Gonçalves-Aquino ,&nbsp;Joelson Lima Soares ,&nbsp;Ailton da Silva Brito ,&nbsp;Guilherme Raffaeli Romero ,&nbsp;Renan Fernandes dos Santos ,&nbsp;Laura Estefania Garzón Rojas ,&nbsp;Bruno Scudeiro Espinosa ,&nbsp;Orangel Aguilera","doi":"10.1016/j.jsames.2026.105982","DOIUrl":"10.1016/j.jsames.2026.105982","url":null,"abstract":"<div><div>During the Miocene, the mixed carbonate–siliciclastic deposits of the Pirabas Formation record decapod crustacean trace fossils that provide valuable insights into paleoenvironmental conditions and early diagenetic processes linked to bioturbation. This study integrates sedimentological, ichnological, and geochemical data to explore the interplay between substrate colonization and mineral precipitation. Facies analysis identified three associations: FA1 – tidal flat, FA2 – marginal mangrove, and FA3 – restricted lagoon. Systematic ichnological analysis recognized four ichnogenera and five ichnospecies, with bioturbation indices ranging from BI1 to BI5, corresponding to the <em>Cruziana</em> Ichnofacies, which is characteristic of shallow-marine, softground, and well-oxygenated settings. Petrographic descriptions and geochemical analyses revealed three main types of trace fossil infill—calcite, pyrite, and siderite—corresponding to distinct early diagenetic redox zones: oxic/suboxic, oxic/anoxic. These results highlight the role of decapod activity in modifying shallow-marine substrates and mediating biogeochemical cycles, offering new perspectives on the interactions between bioturbation, paleoenvironmental dynamics, and early diagenesis in Miocene mixed carbonate platforms of the equatorial Brazilian margin.</div></div>","PeriodicalId":50047,"journal":{"name":"Journal of South American Earth Sciences","volume":"174 ","pages":"Article 105982"},"PeriodicalIF":1.5,"publicationDate":"2026-04-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146175032","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 Pampia terrane: its original definition, alternative proposals and present interpretations","authors":"Lisandro Gastón Rodríguez ,&nbsp;Mónica Patricia Escayola","doi":"10.1016/j.jsames.2026.105972","DOIUrl":"10.1016/j.jsames.2026.105972","url":null,"abstract":"<div><div>The <em>Pampia</em> terrane is envisaged as a large piece of continental crust that was gradually accreted to Gondwana, firstly to the Amazonian craton, in the Mesoproterozoic, and then to the Río de La Plata craton, in the early Cambrian. Evidences are upheld by remarkable tectonic relationships with other South American cratonic blocks across multiple orogenic belts and deformational episodes. However, in recent years, its geodynamic history has been extensively debated among the scientific community, leading to diverse interpretative frameworks, some of which even claiming its non-existence. This contribution, dedicated to Professor Victor Ramos, offers a historical overview of the <em>Pampia</em> terrane's evolution, from its earliest conception to the diverse alternative proposals put forth over the years. Based on an extensive compilation of U-Pb, Lu-Hf and Sm-Nd isotopic dataset from the Pampean rocks, we address the uncertainties and the compelling evidence of <em>Pampia</em>, as well as the feasibility of the alternative tectonic models. Additionally, this research incorporates new Sm-Nd geochronological results from xenoliths hosted by cretaceous basalts on the easternmost Sierras Pampeanas. These novel data strengthen the interpretation of <em>Pampia</em> as a sialic terrane, and endeavors to resolve outstanding questions about the region's geological history.</div></div>","PeriodicalId":50047,"journal":{"name":"Journal of South American Earth Sciences","volume":"174 ","pages":"Article 105972"},"PeriodicalIF":1.5,"publicationDate":"2026-04-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146175031","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 hydrothermal enrichment in the Pratápolis sedimentary phosphorite deposit, Minas Gerais, Brazil","authors":"E.S.V.C. Leme ,&nbsp;C.G. Porto ,&nbsp;J.A.C. Nascimento ,&nbsp;M.B. Abram ,&nbsp;S.Q. de Sousa ,&nbsp;J.P.P. de Oliveira ,&nbsp;P.K. Pufahl","doi":"10.1016/j.jsames.2026.105998","DOIUrl":"10.1016/j.jsames.2026.105998","url":null,"abstract":"<div><div>The Pratápolis sedimentary phosphate deposit, located southwestern Minas Gerais, is a relatively recent discovery that began production in 2016. Its development has had a major impact on regional agribusiness, driven by the growing demand for phosphate fertilizers. This study aims to understand the geological processes responsible for the mineralization and its implications for sedimentary phosphate exploration, particularly within Brazil's Bambuí Group. The deposit is situated in the geological context of the Passos Nappe, within the southern, structurally complex portion of the Brasília Fold Belt. Field descriptions, field data and whole-rock lithogeochemical analyses reveal the ore is a metasedimentary sequence hosted mainly in metasiltstones, tectonic breccias, and alterites. These lithologies were enriched in phosphate by hydrothermal fluids that circulated through zones of discontinuity. The ore content ranges from 4.64 to 38.1% P₂O₅, with an average of 9.25%. The metasiltstones, in particular, are believed to have been hydrothermally enriched over a zone of primary mineralization, allowing them to partially retain a geochemical signature (ΣREY and Sr anomalies) that is distinct from the other lithologies. Based on petrographic, X-ray diffraction (XRD), Scanning Electron Microscopy (SEM), and Cathodoluminescence (CL) analyses, a mineral succession scheme was developed. These analyses also identified fluorapatite as the sole ore mineral, which occurs in four main textural types. This study suggests that the phosphate rocks are associated with the Bambuí Group. This conclusion is consistent with the established Neoproterozoic metallogenic period of phosphatization, though their exact stratigraphic position remains uncertain.</div></div>","PeriodicalId":50047,"journal":{"name":"Journal of South American Earth Sciences","volume":"174 ","pages":"Article 105998"},"PeriodicalIF":1.5,"publicationDate":"2026-04-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147385828","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-landscape relationship in a topolithosequence over meta-limestone rocks and schist in Monteiro, PB","authors":"Emanuel da Costa Cavalcante ,&nbsp;Milton César Costa Campos ,&nbsp;Rodrigo Santana Macedo ,&nbsp;Robson Vinício dos Santos ,&nbsp;Joálison de Brito Silva ,&nbsp;Marcelo Metri Corrêa ,&nbsp;Letícia Moro ,&nbsp;Antônio Augusto Sousa ,&nbsp;Jean-Thomas Cornelis ,&nbsp;Flávio Pereira de Oliveira","doi":"10.1016/j.jsames.2026.106006","DOIUrl":"10.1016/j.jsames.2026.106006","url":null,"abstract":"<div><div>The Western Cariri region of Paraíba has a wide geomorphological and lithological variation, and the diversity of soils in this region makes pedological surveys costly and laborious. Thus, aimed to study the soil-relief-parent material relationship in a topolitosequence over meta-limestone rocks and schists in the Cariri Ocidental Paraibano, Brazil. In each slope positions a soil profile was described and sampled. The physical and chemical attributes were evaluated. Mineralogical analyses of the sand, silt, and clay fraction were conducted by X-ray diffraction, and the total contents of major elements were determined by X-ray fluorescence. The soils were classified as Hypereutric Sideralic Cambisol (Loamic, Humic) (P1), Hypereutric Sideralic Cambisol (Loamic, Ochric, Saprolithic) (P2), Haplic Lixisol (Loamic, Differentic, Hypereutric, Saprolithic) (P3), and Hypereutric Sideralic Cambisol (Clayic, Humic) (P4). The moderate depth allied to the considerable contents of coarse sand and silt in the soils indicates a low degree of weathering under semi-arid conditions. The soils located at the summit and in the shoulder (metal-limestone) are eutrophic, have higher SiO₂ contents, and present minerals 2:1 (bissialitization), while the soils in the backslope and footsope (schist) are dystrophic, have higher contents of Al₂O₃ and are predominantly kaolinitic (monossialitization). The elutriation and in situ clay formation processes created conditions for forming a textural gradient in the backslope. Variation in the morphological, physical, and chemical attributes of soils on material of similar origin confirms the important action of relief in installing specific pedogenetic processes.</div></div>","PeriodicalId":50047,"journal":{"name":"Journal of South American Earth Sciences","volume":"174 ","pages":"Article 106006"},"PeriodicalIF":1.5,"publicationDate":"2026-04-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147385837","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":"Cenozoic exhumation of the Frontal Cordillera revisited: Insights from low-temperature thermochronology studies and other geological constraints","authors":"Ana C. Lossada ,&nbsp;Laura B. Giambiagi ,&nbsp;Chelsea Mackaman-Lofland ,&nbsp;Julieta Suriano ,&nbsp;Macarena Bertoa del Llano","doi":"10.1016/j.jsames.2026.106009","DOIUrl":"10.1016/j.jsames.2026.106009","url":null,"abstract":"<div><div>The Frontal Cordillera is a prominent north–south-trending morphostructural feature in the southern Central Andes, characterized by high topography and relief, monotonic lithologic exposures of Late Paleozoic to Triassic volcanic and intrusive rocks, and thick-skinned deformation. It spans from ∼27 to 28°S, where it gradually transitions into the Puna Plateau, to 34.8°S, where it terminates abruptly. Most of the along-strike exposure of this tectonic domain coincides spatially with the modern Argentina-Chile (Pampean) flat-slab subduction segment (27–33°30′S). Early studies attributed the construction of the Frontal Cordillera to enhanced transmission of compressional stresses to the overriding plate during the Middle Miocene–Recent southward migration of flat-slab subduction, and the associated propagation of deformation to the foreland. However, recent studies have questioned north-to-south diachronism in the structural evolution of the Frontal Cordillera, as well as the extent to which uplift and exhumation were controlled by flat-slab subduction. The timing of deformation in the Frontal Cordillera has been primarily constrained through the analysis of synorogenic sedimentary records and crosscutting structural relationships. Thermochronological studies have emerged as additional, powerful tools for quantifying the exhumation of ranges that comprise the Frontal Cordillera. Despite the proliferation of structural, sedimentological, geo/thermochronological, and geomorphic studies in recent years, fundamental aspects –including the timing and patterns of rock uplift and exhumation in the Frontal Cordillera, and the overall vergence of the Andean orogenic wedge at these latitudes– remain topics of debate. This contribution presents an updated review of thermochronological studies carried out in the Frontal Cordillera in recent years, and the implications of these data for regional tectono-thermal evolution in the context of other, independent geologic constraints. Our data compilation reveals that the main phase of rock uplift and exhumation preceded the onset of flat-slab subduction and occurred largely synchronously along strike during the Early to Middle Miocene. This phase of deformation overlapped with the final stages of contraction in the Principal Cordillera to the west, suggesting an east-directed propagation of deformation. The results also point to a period of pronounced crustal shortening during the Early Miocene, marked by the simultaneous activity of multiple tectonic domains within the Andean wedge.</div></div>","PeriodicalId":50047,"journal":{"name":"Journal of South American Earth Sciences","volume":"174 ","pages":"Article 106009"},"PeriodicalIF":1.5,"publicationDate":"2026-04-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147385924","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":"Revisiting the coronitic gabbros of the deep Famatinian magmatic-arc section (Sierra de Valle Fértil, NW Argentina): New insight from U-Pb zircon geochronology","authors":"C.D. Ramacciotti ,&nbsp;J.A. Murra ,&nbsp;M.E. Benítez ,&nbsp;S.O. Verdecchia ,&nbsp;E.G. Baldo ,&nbsp;C. Casquet","doi":"10.1016/j.jsames.2026.106010","DOIUrl":"10.1016/j.jsames.2026.106010","url":null,"abstract":"<div><div>Mafic–ultramafic cumulates from the Sierra de Valle Fértil (Sierras Pampeanas, NW Argentina) preserve well-developed olivine–plagioclase coronitic textures that record the interplay between magmatic crystallization and subsequent high-temperature metamorphism during the evolution of the Famatinian arc. We present new U–Pb zircon geochronology from coronitic and amphibole gabbros exposed at Las Juntas creek. Coronitic gabbros are troctolites with concentric reaction rings between olivine and plagioclase consisting of the sequence: olivine | orthopyroxene | amphibole | amphibole ± clinopyroxene + spinel symplectite | plagioclase. A multistage origin for these coronas comprises: (1) a magmatic stage, in which intercumulus melts reacted with early-formed olivine and plagioclase to produce orthopyroxene, clinopyroxene, and Cr-rich spinel; and (2) a metamorphic stage, characterized by the development of amphibole and Cr-poor spinel symplectites formed during high-temperature, low-pressure overprinting. New SHRIMP U–Pb zircon ages from coronitic and related amphibole gabbros constrain the main magmatic episode to ca. 470 Ma, with antecrystic zircon populations at ca. 490 Ma and minor inherited Proterozoic components. Amphibole-spinel symplectites were probably formed at ca. 445 Ma, evidenced by zircon overgrowths and Pb loss, and were likely linked to the Rinconada orogenic phase of the Famatinian orogeny.</div></div>","PeriodicalId":50047,"journal":{"name":"Journal of South American Earth Sciences","volume":"174 ","pages":"Article 106010"},"PeriodicalIF":1.5,"publicationDate":"2026-04-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147385927","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":"Neotectonics in Lago Roca, Santa Cruz province, Argentina","authors":"Stefania D. Bunicontro ,&nbsp;Florencia B. Restelli ,&nbsp;Diego A. Winocur ,&nbsp;Donaldo M. Bran ,&nbsp;Jorge G. Lozano ,&nbsp;Marco Menichetti ,&nbsp;Yasmin S. Gutierrez ,&nbsp;Luca Baradello ,&nbsp;Emanuele Lodolo ,&nbsp;Alejandro A. Tassone","doi":"10.1016/j.jsames.2026.105992","DOIUrl":"10.1016/j.jsames.2026.105992","url":null,"abstract":"<div><div>Lago Roca is located in southwestern Santa Cruz Province, Argentina, ∼40 km southwest of El Calafate, within Los Glaciares National Park. The study area lies within the internal fold-and-thrust belt of the Austral Basin, a structurally complex region shaped by N-S oriented thrusts and folds and intersected by NE-SW trending transfer zones such as the Lago Argentino Transfer Fault. Although the region has been considered of low seismic hazard, shallow earthquakes of moderate magnitude (e.g., Mw 5.4 in 2021) have been recorded, indicating the potential for ongoing neotectonic activity, which remains poorly constrained. This study aims to improve knowledge of recent tectonic activity in Lago Roca and its implications for local geological hazard. We reinterpreted existing high-resolution seismic profiles from the lake, analyzed a high-resolution digital elevation model of the surrounding subaerial area, and examined soft-sediment deformation structures (SSDS) in exposed lacustrine deposits. Our results identify at least four paleoseismic events preserved in the lake infill, expressed as Mass-Transport Deposits (MTDs), megaturbidites, and SSDS. These features are spatially and stratigraphically associated with normal and reverse faults affecting multiple sedimentary units. Additional normal faults mapped in the subaerial sector (S1–S4) are possible linked to the most recent event, while the SSDS in undisturbed units may correspond to the last event or an earlier one. Chronostratigraphic data constrain the onset of lacustrine sedimentation—and therefore deformation—to after 13,350–12,280 cal yr BP. The distribution of seismicity and structural trends suggests a genetic link between the observed deformation and neotectonic activity along the Lago Argentino Transfer Fault.</div></div>","PeriodicalId":50047,"journal":{"name":"Journal of South American Earth Sciences","volume":"174 ","pages":"Article 105992"},"PeriodicalIF":1.5,"publicationDate":"2026-04-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146175095","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":"Rudists as paleoenvironmental tools: Multi-proxy records of Late Cretaceous shells from the western Tethys (Cárdenas formation, Mexico)","authors":"E. Aldrin Juárez-Aguilar ,&nbsp;Francisco Sánchez-Beristain ,&nbsp;Pedro García-Barrera ,&nbsp;Andreas Pack ,&nbsp;Juan Pablo Bernal ,&nbsp;Orlando Hernández-Cristóbal ,&nbsp;José Ramón Torres-Hernández","doi":"10.1016/j.jsames.2026.106000","DOIUrl":"10.1016/j.jsames.2026.106000","url":null,"abstract":"<div><div>Rudist bivalves are valuable archives of Late Cretaceous paleoenvironmental conditions, although their geochemical signals may be modified by diagenesis and terrigenous contamination. This study examines the paleoenvironmental significance of well-preserved rudist shells from the Late Maastrichtian of northern Mexico, focusing on specimens recovered from the Cárdenas Formation. Major and trace element concentrations, rare earth element (REE) distributions, and stable isotope compositions were analyzed in selected growth increments of nine rudist specimens representing five taxa. Shell preservation was assessed through a combined approach of petrographic analysis, Energy Dispersive X-ray Spectroscopy, and Laser Ablation Inductively Coupled Plasma Mass Spectrometry. Microstructural observations, together with geochemical screening criteria (Ca &gt;38 wt%, Si &lt; 1 wt%, Mn &lt; 300 ppm, Fe &lt; 1000 ppm, Mn/Sr &lt; 0.2) and weak to moderate correlations among Mn-, Fe-, and Al-based proxies, indicate limited diagenetic alteration and minimal terrigenous contamination restricted to specific shell domains. REE patterns exhibit seawater-like signatures with variable redox-sensitive anomalies, suggesting predominantly marine conditions during shell formation and minimal post-depositional overprinting. The REE systematics is characterized by positive La_SN, Gd_SN and Y_SN anomalies, negative Ce_SN anomalies, slight enrichment of heavy REE relative to light REE, and superchondritic Y/Ho ratios (&gt;40). Oxygen isotope-derived temperatures indicate warm sea surface conditions (∼28–31 °C) in the western Tethys Ocean, consistent with tropical settings. These findings confirm that rudist shells can reliably record marine geochemical conditions when rigorous screening is applied and highlight the complementary value of REE systematics alongside conventional elemental proxies in reconstructing Late Cretaceous paleoenvironments.</div></div>","PeriodicalId":50047,"journal":{"name":"Journal of South American Earth Sciences","volume":"174 ","pages":"Article 106000"},"PeriodicalIF":1.5,"publicationDate":"2026-04-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147385919","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}