Pub Date : 2024-10-04DOI: 10.1016/j.jsames.2024.105179
Karen M. Panzeri , Sergio Bogan , María Sol Raigemborn , María Alejandra Pagani , Nicolás Chimento , Federico L. Agnolín , Agustín G. Martinelli
Since the 1980s, certain hemispherical structures discovered in Upper Cretaceous (Campanian-Maastrichtian) deposits of Patagonia have been interpreted as crushing teeth, variously attributed to indeterminate Teleostei or the semionotiform genus Lepidotes. This study examines the morphological, microscopic, and mineralogical characteristics of these structures, collected from the Allen, Los Alamitos, La Colonia, Loncoche, and Chorrillo formations, and compares them with modern and fossil fish crushing teeth. The external morphology, internal structure, and mineralogical composition (primarily phosphates and carbonates) of these structures, as analyzed in this study, correspond to crustacean bio-gastroliths rather than actinopterygian teeth. Microscopically, all examined gastroliths display a uniform banding pattern, while actinopterygian crushing teeth exhibit a two-layer organization with abundant dentinal tubules. These findings enhance our understanding of the distribution of crustaceans that produce gastroliths and also provide new insights into how taphonomic processes influence the mineralogical and microscopic structures of fossil gastroliths.
{"title":"Purported crushing teeth of actinopterygian fishes from the Late Cretaceous of Patagonia reinterpreted as crustacean bio-gastroliths","authors":"Karen M. Panzeri , Sergio Bogan , María Sol Raigemborn , María Alejandra Pagani , Nicolás Chimento , Federico L. Agnolín , Agustín G. Martinelli","doi":"10.1016/j.jsames.2024.105179","DOIUrl":"10.1016/j.jsames.2024.105179","url":null,"abstract":"<div><div>Since the 1980s, certain hemispherical structures discovered in Upper Cretaceous (Campanian-Maastrichtian) deposits of Patagonia have been interpreted as crushing teeth, variously attributed to indeterminate Teleostei or the semionotiform genus <em>Lepidotes</em>. This study examines the morphological, microscopic, and mineralogical characteristics of these structures, collected from the Allen, Los Alamitos, La Colonia, Loncoche, and Chorrillo formations, and compares them with modern and fossil fish crushing teeth. The external morphology, internal structure, and mineralogical composition (primarily phosphates and carbonates) of these structures, as analyzed in this study, correspond to crustacean bio-gastroliths rather than actinopterygian teeth. Microscopically, all examined gastroliths display a uniform banding pattern, while actinopterygian crushing teeth exhibit a two-layer organization with abundant dentinal tubules. These findings enhance our understanding of the distribution of crustaceans that produce gastroliths and also provide new insights into how taphonomic processes influence the mineralogical and microscopic structures of fossil gastroliths.</div></div>","PeriodicalId":50047,"journal":{"name":"Journal of South American Earth Sciences","volume":"149 ","pages":"Article 105179"},"PeriodicalIF":1.7,"publicationDate":"2024-10-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142441878","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}
Pub Date : 2024-10-02DOI: 10.1016/j.jsames.2024.105177
Edvaldo José Oliveira , Paulo A. Souza , Ana Maria Góes , Cristina M. Félix , Daiana R. Boardman , Luiz Saturnino de Andrade , Eduardo Premaor , Gelson Luís Fambrini , Afonso César Rodrigues Nogueira , Ana Karina Scomazzon
During the Permian, the northwestern portion of the supercontinent Gondwana experienced significant climate changes, among which the increasing aridity in the Parnaíba Basin, located between Brazil's northern and northeastern regions. The marine influence associated with the Panthalassa Ocean, evident in the Silurian and Devonian deposits, was progressively attenuated in the late Carboniferous, culminating in extensive continental deposits during the Permian and the Early Triassic in this region. In this paper, we present the first palynofacies analysis of the Permian Pedra de Fogo Formation, conducted concurrently with the description and association of sedimentary facies from outcrops located in the state of Maranhão, southwest of the Parnaíba Basin. A total of 15 m of sedimentary succession was described, and 28 samples were selected for palynofacies analysis. As a result, we identified six sedimentary facies, which were grouped into two distinct facies associations: Fa1 – Central Lake and Fa2 – Playa Lake. The palynofacies analysis considered the sedimentary organic matter, classifying it into amorphous organic matter, phytoclasts (subdivided into eight subgroups), and palynomorphs (with six subgroups). Integrating the results enabled an understanding of the depositional context, which is closely related to water dynamics and climate seasonality. The shallow lake system interpreted during the wet phases recorded interruptions in the normal sedimentation of the central lake due to turbidite deposits associated with ephemeral rivers. Conversely, during dry phases, salt precipitation occurred with subsequent substitution and aerial exposure of the surface when the water balance was negative. Eodiagenetic events were inferred and are considered throughout the article. The alternation of the hydrological regime allowed the deposition in proximal, transitional, and distal environments, creating a distinctive mosaic of wetland landscapes. The data presented indicate humid conditions within a context of increasing aridity in the studied location, particularly in the upper part of the Pedra de Fogo Formation.
{"title":"Deciphering Permian wetland deposits of the Parnaíba Basin through an integrated study of lithofacies and palynofacies in Western Gondwana","authors":"Edvaldo José Oliveira , Paulo A. Souza , Ana Maria Góes , Cristina M. Félix , Daiana R. Boardman , Luiz Saturnino de Andrade , Eduardo Premaor , Gelson Luís Fambrini , Afonso César Rodrigues Nogueira , Ana Karina Scomazzon","doi":"10.1016/j.jsames.2024.105177","DOIUrl":"10.1016/j.jsames.2024.105177","url":null,"abstract":"<div><div>During the Permian, the northwestern portion of the supercontinent Gondwana experienced significant climate changes, among which the increasing aridity in the Parnaíba Basin, located between Brazil's northern and northeastern regions. The marine influence associated with the Panthalassa Ocean, evident in the Silurian and Devonian deposits, was progressively attenuated in the late Carboniferous, culminating in extensive continental deposits during the Permian and the Early Triassic in this region. In this paper, we present the first palynofacies analysis of the Permian Pedra de Fogo Formation, conducted concurrently with the description and association of sedimentary facies from outcrops located in the state of Maranhão, southwest of the Parnaíba Basin. A total of 15 m of sedimentary succession was described, and 28 samples were selected for palynofacies analysis. As a result, we identified six sedimentary facies, which were grouped into two distinct facies associations: Fa1 – Central Lake and Fa2 – Playa Lake. The palynofacies analysis considered the sedimentary organic matter, classifying it into amorphous organic matter, phytoclasts (subdivided into eight subgroups), and palynomorphs (with six subgroups). Integrating the results enabled an understanding of the depositional context, which is closely related to water dynamics and climate seasonality. The shallow lake system interpreted during the wet phases recorded interruptions in the normal sedimentation of the central lake due to turbidite deposits associated with ephemeral rivers. Conversely, during dry phases, salt precipitation occurred with subsequent substitution and aerial exposure of the surface when the water balance was negative. Eodiagenetic events were inferred and are considered throughout the article. The alternation of the hydrological regime allowed the deposition in proximal, transitional, and distal environments, creating a distinctive mosaic of wetland landscapes. The data presented indicate humid conditions within a context of increasing aridity in the studied location, particularly in the upper part of the Pedra de Fogo Formation.</div></div>","PeriodicalId":50047,"journal":{"name":"Journal of South American Earth Sciences","volume":"148 ","pages":"Article 105177"},"PeriodicalIF":1.7,"publicationDate":"2024-10-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142420366","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}
In central-western Argentina, sedimentological and paleontological studies have identified changes in sea levels during the Pennsylvanian period. After the late Serpukhovian-early Bashkirian postglacial transgression, two main flooding events occurred. Among these, Pennsylvanian transgressions 1 and 2 are considered the most significant. New palynological samples recovered from the T1 transgression in Puesto Volcán, western Precordillera (San Juan province) reveal the presence of the Raistrickia densa-Convolutispora muriornata (DM) Biozone. The palynofloras are characterized by the recognition of Ahrensisporites cristatus, Lundbladispora spp., Raistrickia densa, Spelaeotriletes ybertii, and monosaccate pollen grains. The composition of the assemblages includes some taeniate pollen grains suggesting their assignment to the Subzone B. A new orthoconic cephalopod was also identified in the same stratigraphic interval, which adds to the invertebrate faunal record and confirms the marine environment. Imprints of foliage of Fedekurtzia argentina complete the paleofloristic assemblage. A late Bashkirian-earliest Moscovian age is suggested according to the well constrained radiometric control of the palynostratigraphy in the region.
{"title":"Paleontology of Pennsylvanian transgressive deposits in northwestern Precordillera, San Juan province, Argentina","authors":"V.S. Perez Loinaze , S.N. Césari , C.O. Limarino , L. Fauqué","doi":"10.1016/j.jsames.2024.105178","DOIUrl":"10.1016/j.jsames.2024.105178","url":null,"abstract":"<div><div>In central-western Argentina, sedimentological and paleontological studies have identified changes in sea levels during the Pennsylvanian period. After the late Serpukhovian-early Bashkirian postglacial transgression, two main flooding events occurred. Among these, Pennsylvanian transgressions 1 and 2 are considered the most significant. New palynological samples recovered from the T1 transgression in Puesto Volcán, western Precordillera (San Juan province) reveal the presence of the <em>Raistrickia densa-Convolutispora muriornata</em> (DM) Biozone. The palynofloras are characterized by the recognition of <em>Ahrensisporites cristatus</em>, <em>Lundbladispora</em> spp., <em>Raistrickia densa</em>, <em>Spelaeotriletes ybertii</em>, and monosaccate pollen grains. The composition of the assemblages includes some taeniate pollen grains suggesting their assignment to the Subzone B. A new orthoconic cephalopod was also identified in the same stratigraphic interval, which adds to the invertebrate faunal record and confirms the marine environment. Imprints of foliage of <em>Fedekurtzia argentina</em> complete the paleofloristic assemblage. A late Bashkirian-earliest Moscovian age is suggested according to the well constrained radiometric control of the palynostratigraphy in the region.</div></div>","PeriodicalId":50047,"journal":{"name":"Journal of South American Earth Sciences","volume":"148 ","pages":"Article 105178"},"PeriodicalIF":1.7,"publicationDate":"2024-10-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142420367","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}
Pub Date : 2024-09-29DOI: 10.1016/j.jsames.2024.105176
Spencer G. Lucas , Charles M. Henderson , Karl Krainer , James E. Barrick , Stephen J. Reynolds
Lower Permian marine strata in the American Southwest (Arizona, New Mexico and Texas, USA) identify three extensive marine seaways, one of Wolfcampian age and the other two of Leonardian age. These are strata deposited on the Mogollon shelf and in the Holbrook basin of Arizona, the Pedregosa basin of Arizona-New Mexico and northern Mexico, the Orogrande basin of New Mexico, the Delaware basin of New Mexico-Texas and the Midland basin of Texas. Age control of these strata, based primarily on fusulinids and conodonts, including new conodont data presented here, correlates Wolfcampian (mostly Asselian to Sakmarian) marine strata from the Pedregosa basin to the Midland basin, lower to middle Leonardian (upper Artinskian to mid-Kungurian) marine strata that extend from the Mogollon shelf to the Delaware basin and upper Leonardian to lower Guadalupian (upper Kungurian to lower Roadian) marine strata that extend from the Mogollon shelf to the Midland basin. Active regional Ancestral Rocky Mountain tectonism affected Wolfcampian marine deposition by providing accommodation in which to preserve both non-marine and marine facies within multiple transgressive-regressive sequences associated with the most extensive part of the late Paleozoic ice age, when global sea level would have been low. In contrast, two Leonardian seaways were likely driven by global tectono-eustatic events. Identification of the three Early Permian seaways in the American Southwest underscores the need for more precise correlations as well as integrated sequence stratigraphic interpretations of the deposits of these seaways from Arizona to Texas.
{"title":"Early Permian seaways in the American Southwest","authors":"Spencer G. Lucas , Charles M. Henderson , Karl Krainer , James E. Barrick , Stephen J. Reynolds","doi":"10.1016/j.jsames.2024.105176","DOIUrl":"10.1016/j.jsames.2024.105176","url":null,"abstract":"<div><div>Lower Permian marine strata in the American Southwest (Arizona, New Mexico and Texas, USA) identify three extensive marine seaways, one of Wolfcampian age and the other two of Leonardian age. These are strata deposited on the Mogollon shelf and in the Holbrook basin of Arizona, the Pedregosa basin of Arizona-New Mexico and northern Mexico, the Orogrande basin of New Mexico, the Delaware basin of New Mexico-Texas and the Midland basin of Texas. Age control of these strata, based primarily on fusulinids and conodonts, including new conodont data presented here, correlates Wolfcampian (mostly Asselian to Sakmarian) marine strata from the Pedregosa basin to the Midland basin, lower to middle Leonardian (upper Artinskian to mid-Kungurian) marine strata that extend from the Mogollon shelf to the Delaware basin and upper Leonardian to lower Guadalupian (upper Kungurian to lower Roadian) marine strata that extend from the Mogollon shelf to the Midland basin. Active regional Ancestral Rocky Mountain tectonism affected Wolfcampian marine deposition by providing accommodation in which to preserve both non-marine and marine facies within multiple transgressive-regressive sequences associated with the most extensive part of the late Paleozoic ice age, when global sea level would have been low. In contrast, two Leonardian seaways were likely driven by global tectono-eustatic events. Identification of the three Early Permian seaways in the American Southwest underscores the need for more precise correlations as well as integrated sequence stratigraphic interpretations of the deposits of these seaways from Arizona to Texas.</div></div>","PeriodicalId":50047,"journal":{"name":"Journal of South American Earth Sciences","volume":"148 ","pages":"Article 105176"},"PeriodicalIF":1.7,"publicationDate":"2024-09-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142420369","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}
Pub Date : 2024-09-29DOI: 10.1016/j.jsames.2024.105175
Nicole Delaunay , Eduardo Duarte Marques , Alexis Rosa Nummer , Vinicius Tavares Kutter , Emmanoel Vieira Silva-Filho , Ingrid Carvalho Lage
The global demand for water sources for human consumption has been increasing over the last century. The degradation of water bodies and aquifers has made the planning and management of these natural resources crucial. In this context, this study focuses on the hydrogeochemical characterization of aquifers surrounding the of Guanabara Bay Hydrographic Region (GBHR), located in Rio de Janeiro, which stands out as an area with a high population density associated with elevated levels of environmental degradation. A total of 228 wells were analyzed, separated by aquifer types, resulting in 138 fissured and 90 porous aquifers, predominantly sodium-rich groundwaters. This predominance this hydrochemical facies can be attributed to the influence of the saline influence, given the proximity to the ocean, and anthropogenic activities, such as the discharge of industrial and urban effluents, which alter the chemical composition of groundwater. From the mixing diagram, it was found that most of the sampled wells are in the field of silicate rocks for both types of aquifers. In porous aquifers, a significant number of wells under greater influence of effluents/evaporites were observed in the eastern portion of GBHR, whereas in fissured aquifers, effluents/evaporites are predominantly concentrated in the western portion of the study area. The high variability of the Inorganic Chemical Index may indicate zones of point or diffuse pollution, influenced by effluent discharges, surface runoff, and contaminant infiltration. This variation reveals a distinctive pattern related to land use and aquifer type in the studied region when observed spatially. The use of a multivariate statistical technique (factor analysis) corroborates the influence of natural processes, like weathering and seawater intrusion in wells close to the coast and the anthropogenic processes, such as domestic/agricultural/industrial effluents influence in wells far from the coast. This study highlights the importance of understanding the hydrogeochemistry of aquifers in urban and industrial areas, not only for the preservation of the local ecosystem but also for public health and sustainable development. The results point to the need for integrated water resource management policies that consider both environmental conservation and economic development, thus ensuring a balance between the use and protection of groundwater around Guanabara Bay.
{"title":"Hydrogeochemical characterization and indicators of anthropogenic influence in groundwater around Guanabara Bay, Rio de Janeiro, Brazil","authors":"Nicole Delaunay , Eduardo Duarte Marques , Alexis Rosa Nummer , Vinicius Tavares Kutter , Emmanoel Vieira Silva-Filho , Ingrid Carvalho Lage","doi":"10.1016/j.jsames.2024.105175","DOIUrl":"10.1016/j.jsames.2024.105175","url":null,"abstract":"<div><div>The global demand for water sources for human consumption has been increasing over the last century. The degradation of water bodies and aquifers has made the planning and management of these natural resources crucial. In this context, this study focuses on the hydrogeochemical characterization of aquifers surrounding the of Guanabara Bay Hydrographic Region (GBHR), located in Rio de Janeiro, which stands out as an area with a high population density associated with elevated levels of environmental degradation. A total of 228 wells were analyzed, separated by aquifer types, resulting in 138 fissured and 90 porous aquifers, predominantly sodium-rich groundwaters. This predominance this hydrochemical facies can be attributed to the influence of the saline influence, given the proximity to the ocean, and anthropogenic activities, such as the discharge of industrial and urban effluents, which alter the chemical composition of groundwater. From the mixing diagram, it was found that most of the sampled wells are in the field of silicate rocks for both types of aquifers. In porous aquifers, a significant number of wells under greater influence of effluents/evaporites were observed in the eastern portion of GBHR, whereas in fissured aquifers, effluents/evaporites are predominantly concentrated in the western portion of the study area. The high variability of the Inorganic Chemical Index may indicate zones of point or diffuse pollution, influenced by effluent discharges, surface runoff, and contaminant infiltration. This variation reveals a distinctive pattern related to land use and aquifer type in the studied region when observed spatially. The use of a multivariate statistical technique (factor analysis) corroborates the influence of natural processes, like weathering and seawater intrusion in wells close to the coast and the anthropogenic processes, such as domestic/agricultural/industrial effluents influence in wells far from the coast. This study highlights the importance of understanding the hydrogeochemistry of aquifers in urban and industrial areas, not only for the preservation of the local ecosystem but also for public health and sustainable development. The results point to the need for integrated water resource management policies that consider both environmental conservation and economic development, thus ensuring a balance between the use and protection of groundwater around Guanabara Bay.</div></div>","PeriodicalId":50047,"journal":{"name":"Journal of South American Earth Sciences","volume":"148 ","pages":"Article 105175"},"PeriodicalIF":1.7,"publicationDate":"2024-09-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142420364","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}
Pub Date : 2024-09-26DOI: 10.1016/j.jsames.2024.105172
Wolf Uwe Reimold
The recent 13th South American Symposium on Isotope Geology (SSAGI) in May 2024 in Buzios (Brazil) was an excellent conference, showcasing the current diversity and high standard of isotope geochemistry and geology at universities and research institutions across Latin America. Three days of oral and poster presentations provided a great forum for scientific and social exchange. This conference, however, also further supported observations made at earlier events that many oral and poster presentations by postgraduate students and docents alike suffer from a number of problems. There is ample scope for improvement, in the interest of more efficient information transfer and better exchange with colleagues. The main problem areas noted (e.g., overloading of powerpoint slides, and of posters, with diagrams and/or text; application of poor color, etc.) are discussed here, and suggestions are made how to avoid these issues and improve our scientific communication.
{"title":"Oral and poster contributions for conferences: Some observations and recommendations","authors":"Wolf Uwe Reimold","doi":"10.1016/j.jsames.2024.105172","DOIUrl":"10.1016/j.jsames.2024.105172","url":null,"abstract":"<div><div>The recent 13th South American Symposium on Isotope Geology (SSAGI) in May 2024 in Buzios (Brazil) was an excellent conference, showcasing the current diversity and high standard of isotope geochemistry and geology at universities and research institutions across Latin America. Three days of oral and poster presentations provided a great forum for scientific and social exchange. This conference, however, also further supported observations made at earlier events that many oral and poster presentations by postgraduate students and docents alike suffer from a number of problems. There is ample scope for improvement, in the interest of more efficient information transfer and better exchange with colleagues. The main problem areas noted (e.g., overloading of powerpoint slides, and of posters, with diagrams and/or text; application of poor color, etc.) are discussed here, and suggestions are made how to avoid these issues and improve our scientific communication.</div></div>","PeriodicalId":50047,"journal":{"name":"Journal of South American Earth Sciences","volume":"148 ","pages":"Article 105172"},"PeriodicalIF":1.7,"publicationDate":"2024-09-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142420363","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}
Pub Date : 2024-09-21DOI: 10.1016/j.jsames.2024.105169
Moreno Florencia, Mestre Ana, Heredia Susana
In this contribution, we describe and interpret the microfacies of the upper levels of the San Juan Formation in the Río Francia section of the Central Precordillera, Argentina, for the first time. Several studies in this section identified the Lenodus antivariabilis, Lenodus variabilis, Lenodus crassus, and Lenodus pseudoplanus zones, thereby limiting this stratigraphic interval to the early Darriwilian age. Five microfacies were recognized: M1 burrowed bioclastic wackestone, M2 bioclastic mudstone-wackestone, M3 intrabioclastic grainstone, M4 crinoidal wackestone-packstone, and M5 bioclastic wackestone-packstone. These microfacies indicate a shallow subtidal inner platform environment with variations in hydrodynamic energy ranging from low to moderate conditions below the fair-weather wave base level. The vertical arrangement of these sub-environments suggests a gradual transgressive setting during the lower Darriwilian for the carbonate beds of the San Juan Formation. The Baños de Talacasto, Ancha Creek, and Don Braulio sections are correlated with the section studied in this work, where conodont zones were documented, and microfacies analyses revealed shallow subtidal environments with low-energy conditions and occasional high-energy episodes. Differences in redox conditions were observed between the Don Braulio section (anoxic) and the Río Francia section (well-oxygenated), interpreted as the result of a rapid sea-level rise, though diachronic across the platform. Microfacies analysis, combined with precise conodont biostratigraphy, provides a powerful tool for reconstructing the Middle Ordovician carbonate platform.
在这篇论文中，我们首次描述并解释了阿根廷前缘山脉中部 Río Francia 地段圣胡安地层上层的微地貌。在该区段进行的几项研究确定了 Lenodus antivariabilis、Lenodus variabilis、Lenodus crassus 和 Lenodus pseudoplanus 区，从而将该地层区间限定为达里维利早期。确认了五种微地层：M1钻孔生物碎屑瓦基岩、M2生物碎屑泥岩-瓦基岩、M3生物碎屑内粒岩、M4碎屑瓦基岩-包岩、M5生物碎屑瓦基岩-包岩。这些微岩相表明，潮下浅层内平台环境的水动力能量变化范围从低到中等，低于全天候波浪基底水平。这些子环境的垂直排列表明，圣胡安地层的碳酸盐岩床是在下达里维利期逐渐形成的。Baños de Talacasto、Ancha Creek 和 Don Braulio 剖面与本研究中的剖面相关联，在这些剖面中记录了锥齿动物区，微岩相分析表明浅潮下环境具有低能量条件和偶尔的高能量事件。在 Don Braulio 段（缺氧）和 Río Francia 段（高氧）之间观察到了氧化还原条件的差异，这被解释为海平面快速上升的结果，尽管在整个平台上是非同步的。微地层分析与精确的同系生物地层学相结合，为重建中奥陶世碳酸盐平台提供了强有力的工具。
{"title":"Microfacies of the San Juan Formation (lower Darriwilian) in the Rio Francia, Central Precordillera, Argentina","authors":"Moreno Florencia, Mestre Ana, Heredia Susana","doi":"10.1016/j.jsames.2024.105169","DOIUrl":"10.1016/j.jsames.2024.105169","url":null,"abstract":"<div><div>In this contribution, we describe and interpret the microfacies of the upper levels of the San Juan Formation in the Río Francia section of the Central Precordillera, Argentina, for the first time. Several studies in this section identified the <em>Lenodus antivariabilis, Lenodus variabilis, Lenodus crassus</em>, and <em>Lenodus pseudoplanus</em> zones, thereby limiting this stratigraphic interval to the early Darriwilian age. Five microfacies were recognized: M1 burrowed bioclastic wackestone, M2 bioclastic mudstone-wackestone, M3 intrabioclastic grainstone, M4 crinoidal wackestone-packstone, and M5 bioclastic wackestone-packstone. These microfacies indicate a shallow subtidal inner platform environment with variations in hydrodynamic energy ranging from low to moderate conditions below the fair-weather wave base level. The vertical arrangement of these sub-environments suggests a gradual transgressive setting during the lower Darriwilian for the carbonate beds of the San Juan Formation. The Baños de Talacasto, Ancha Creek, and Don Braulio sections are correlated with the section studied in this work, where conodont zones were documented, and microfacies analyses revealed shallow subtidal environments with low-energy conditions and occasional high-energy episodes. Differences in redox conditions were observed between the Don Braulio section (anoxic) and the Río Francia section (well-oxygenated), interpreted as the result of a rapid sea-level rise, though diachronic across the platform. Microfacies analysis, combined with precise conodont biostratigraphy, provides a powerful tool for reconstructing the Middle Ordovician carbonate platform.</div></div>","PeriodicalId":50047,"journal":{"name":"Journal of South American Earth Sciences","volume":"148 ","pages":"Article 105169"},"PeriodicalIF":1.7,"publicationDate":"2024-09-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142311435","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}
Pub Date : 2024-09-21DOI: 10.1016/j.jsames.2024.105174
P. Rossel , M. Suárez , D. Morata , R. De la Cruz
Los Leones Granite represents a calc-alkaline tonalite-granodiorite tabular stock of ∼3 km2 intruded within Paleozoic metasedimentary rocks from the Eastern Andean Metamorphic Complex. Two newly obtained zircon SHRIMP U-Pb ages reveal a Middle Mississippian (340-335 Ma) crystallization age, contrasting with previously accepted K-Ar Pennsylvanian age. Isotopic analysis indicate derivation from a depleted source with minimal influence of continental crust contamination (eHf(i) ∼14), which experienced hydrothermal alteration at high temperatures (δ18O ∼4.13). New data coupled with contemporaneous subduction-related rocks in Western Patagonia and Antarctica suggest the existence a broader Lower Carboniferous subduction zone extending at least from Northern Patagonia, to Western Antarctica. On the other hand, isotopic signatures depict a tectono-magmatic framework with a thermal configuration of the margin that was modified by the presence of a local slab tear or the progressive horizontalization of the isotherms as result of the ∼20 myr. of magmatic quiescence in the area.
{"title":"Low-δ18Ο in mississippian los leones granite (46°S). Tectonic implications for the understanding of late paleozoic evolution in patagonia","authors":"P. Rossel , M. Suárez , D. Morata , R. De la Cruz","doi":"10.1016/j.jsames.2024.105174","DOIUrl":"10.1016/j.jsames.2024.105174","url":null,"abstract":"<div><div>Los Leones Granite represents a calc-alkaline tonalite-granodiorite tabular stock of ∼3 km<sup>2</sup> intruded within Paleozoic metasedimentary rocks from the Eastern Andean Metamorphic Complex. Two newly obtained zircon SHRIMP U-Pb ages reveal a Middle Mississippian (340-335 Ma) crystallization age, contrasting with previously accepted K-Ar Pennsylvanian age. Isotopic analysis indicate derivation from a depleted source with minimal influence of continental crust contamination (eHf<sub>(i)</sub> ∼14), which experienced hydrothermal alteration at high temperatures (δ<sup>18</sup>O ∼4.13). New data coupled with contemporaneous subduction-related rocks in Western Patagonia and Antarctica suggest the existence a broader Lower Carboniferous subduction zone extending at least from Northern Patagonia, to Western Antarctica. On the other hand, isotopic signatures depict a tectono-magmatic framework with a thermal configuration of the margin that was modified by the presence of a local slab tear or the progressive horizontalization of the isotherms as result of the ∼20 myr. of magmatic quiescence in the area.</div></div>","PeriodicalId":50047,"journal":{"name":"Journal of South American Earth Sciences","volume":"148 ","pages":"Article 105174"},"PeriodicalIF":1.7,"publicationDate":"2024-09-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142315947","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}
Pub Date : 2024-09-20DOI: 10.1016/j.jsames.2024.105173
Adilson Oliveira dos Santos , Webster Ueipass Mohriak , Alanna Costa Dutra , Anderson Costa dos Santos
There are numerous inquiries regarding the origin and development of the Vitória-Trindade Ridge (VTR) in eastern Brazil, a major tectonic feature composed of seamounts, guyots, banks, and islands, prompting extensive studies in the region. These investigations aim to create a more precise crustal model to aid in understanding various geological phenomena, such as the separation of South America from Africa, the interaction between continental and oceanic crusts, and the behavior of oceanic fracture zones. These zones may have served as conduits for magma feeding into the ridge and adjacent areas, or the seamounts could have formed due to a fixed mantle plume related to the West-East trend. This study focuses on exploring the tectonic structure of the region, particularly the subsurface of the VTR, utilizing geophysical data modeling techniques. This includes data from topography, gravimetric and magnetic anomalies, and analysis of reflection seismic lines. The research aims to accurately characterize the geological and geophysical context of the continental margin and some igneous features in the offshore region of the Espírito Santo and Bahia states. The anomalous hotspots correlate with pre-existing fracture zones resulting from the Mesozoic rifting of South American and African continents, which due to later tectonic episodes, have masked traces of deep-seated tectonic structures. The integration of geophysical methods, particularly gravimetry and magnetometry, when combined with reflection seismic data and 2D modeling techniques, offer insights into the geodynamic processes involved in the formation of the volcanic ridge. The results obtained showed the interference generated by magmatism in the oceanic crust and the transition zone. The seismic data allowed the visualization of the approximate geometries and interrelationships of some volcanic edifices that are compared with the Davis Bank, located in the central region of the VTR.
{"title":"Geophysical characterization and 2D gravimetric modeling: Application to tectonic control of the Vitória-Trindade Ridge (VTR–ES, Brazil)","authors":"Adilson Oliveira dos Santos , Webster Ueipass Mohriak , Alanna Costa Dutra , Anderson Costa dos Santos","doi":"10.1016/j.jsames.2024.105173","DOIUrl":"10.1016/j.jsames.2024.105173","url":null,"abstract":"<div><div>There are numerous inquiries regarding the origin and development of the Vitória-Trindade Ridge (VTR) in eastern Brazil, a major tectonic feature composed of seamounts, guyots, banks, and islands, prompting extensive studies in the region. These investigations aim to create a more precise crustal model to aid in understanding various geological phenomena, such as the separation of South America from Africa, the interaction between continental and oceanic crusts, and the behavior of oceanic fracture zones. These zones may have served as conduits for magma feeding into the ridge and adjacent areas, or the seamounts could have formed due to a fixed mantle plume related to the West-East trend. This study focuses on exploring the tectonic structure of the region, particularly the subsurface of the VTR, utilizing geophysical data modeling techniques. This includes data from topography, gravimetric and magnetic anomalies, and analysis of reflection seismic lines. The research aims to accurately characterize the geological and geophysical context of the continental margin and some igneous features in the offshore region of the Espírito Santo and Bahia states. The anomalous hotspots correlate with pre-existing fracture zones resulting from the Mesozoic rifting of South American and African continents, which due to later tectonic episodes, have masked traces of deep-seated tectonic structures. The integration of geophysical methods, particularly gravimetry and magnetometry, when combined with reflection seismic data and 2D modeling techniques, offer insights into the geodynamic processes involved in the formation of the volcanic ridge. The results obtained showed the interference generated by magmatism in the oceanic crust and the transition zone. The seismic data allowed the visualization of the approximate geometries and interrelationships of some volcanic edifices that are compared with the Davis Bank, located in the central region of the VTR.</div></div>","PeriodicalId":50047,"journal":{"name":"Journal of South American Earth Sciences","volume":"148 ","pages":"Article 105173"},"PeriodicalIF":1.7,"publicationDate":"2024-09-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142323432","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}
Pub Date : 2024-09-19DOI: 10.1016/j.jsames.2024.105164
Santiago N. González , Gerson A. Greco , Darío L. Orts
This study presents new evidence of a major, regional strike-slip fault system linked to the emplacement of the Somún Curá Large Igneous Province in central Patagonia, Argentina. Employing a combination of remote sensing techniques and fieldwork, we provide additional insights into the structural complexities underlying this magmatic province, shedding light on its geological evolution. Our findings indicate a compelling correlation between the magmatic products of the Somún Curá Large Igneous Province and the left-lateral strike-slip fault system, resembling similar relationships observed in other magmatic large igneous provinces. Moreover, the strike-slip tectonics delineated in this study likely represent the culmination of the fault system's evolution, possibly originating from a longstanding basement fault and extending beyond the limits of the Somún Curá basaltic plateau.
{"title":"Unveiling a major strike-slip fault system associated with the Somún Curá Large Igneous Province in central Patagonia, Argentina","authors":"Santiago N. González , Gerson A. Greco , Darío L. Orts","doi":"10.1016/j.jsames.2024.105164","DOIUrl":"10.1016/j.jsames.2024.105164","url":null,"abstract":"<div><div>This study presents new evidence of a major, regional strike-slip fault system linked to the emplacement of the Somún Curá Large Igneous Province in central Patagonia, Argentina. Employing a combination of remote sensing techniques and fieldwork, we provide additional insights into the structural complexities underlying this magmatic province, shedding light on its geological evolution. Our findings indicate a compelling correlation between the magmatic products of the Somún Curá Large Igneous Province and the left-lateral strike-slip fault system, resembling similar relationships observed in other magmatic large igneous provinces. Moreover, the strike-slip tectonics delineated in this study likely represent the culmination of the fault system's evolution, possibly originating from a longstanding basement fault and extending beyond the limits of the Somún Curá basaltic plateau.</div></div>","PeriodicalId":50047,"journal":{"name":"Journal of South American Earth Sciences","volume":"148 ","pages":"Article 105164"},"PeriodicalIF":1.7,"publicationDate":"2024-09-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142315948","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}
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