Ameghiniana最新文献

{"title":"Taphonomic Signature of Glycymeris longior Shells (Bivalvia) and its Potential as Paleoenvironmental Proxy for the Quaternary of Northern Patagonia (Argentina)","authors":"Sol Bayer, J. Nóbile, D. Muñoz, E. Morsan, Gisela A. Morán, E. Fucks, Sandra Gordillo","doi":"10.5710/AMGH.10.07.2023.3552","DOIUrl":"https://doi.org/10.5710/AMGH.10.07.2023.3552","url":null,"abstract":"Abstract. One of the most abundant species of bivalves found on modern beaches and Quaternary deposits in the San Matías Gulf (Argentinian Patagonia, SW Atlantic Ocean) is Glycymeris longior. Its high abundance and broad geographical distribution turn G. longior into a target species for taphonomical studies. Here, we described the taphonomic signature registered on its shells from San Antonio Bay (San Matías Gulf, Río Negro). This study will contribute to future taphonomic comparisons in the SW Atlantic Ocean, as well as in other Quaternary deposits, and provide insight into the spatial variation of the taphonomic processes influenced by the environment. Glycymeris longior valves from the Holocene Punta Delgado deposits showed two taphonomic signatures whose shell assemblages were differentiated by fragmentation, rounding and cementation intensities. Shells from PD2018A and PD2018B (two sampling localities representing similar environments) were subject to continuous and low-energy water flow. Those remained in a low-intensity hydrodynamic sediment-water interface that would favor high shell cementation. On the other hand, shells from PD2016 were also subject to continuous but more energetic water flow. Those would remain in the taphonomic active zone for enough time to confer smooth edges and to be colonized by clionid sponges but not favorable enough for carbonate precipitation. The Punta Delgado site was interpreted as a protected area during the Holocene (last 4200 yrs.), similar to the modern one, but with differences in carbonate precipitation as the product of differences in water flow intensities. Finally, the high mechanical resistance of G. longior shells, together with its abundance and broad geographical distribution, turn this species into a suitable target taxon for further taphonomic and ecologic analyses and comparisons. Resumen. Una de las especies de bivalvos más abundantes que habita en la playas y depósitos cuaternarios del Golfo San Matías (Patagonia argentina, Océano Atlántico sudoccidental) es Glycymeris longior. Su gran abundancia y amplia distribución geográfica, hacen que G. longior sea una especie objetivo para estudios tafonómicos. Por lo cual, describimos el perfil tafonómico que registran sus valvas en la Bahía San Antonio (Golfo San Matías, Argentina) con el objetivo de contribuir a futuras comparaciones tafonómicas, con material de playas actuales o de depósitos cuaternarios donde esta especie se encuentre. Las valvas de G. longior de los depósitos holocenos de Punta Delgado mostraron dos patrones de preservación diferentes caracterizados por diferencias en la intensidad de fragmentación, redondeamiento y cementación de sus valvas. Las valvas de PD2018A y PD2018B estuvieron sometidas a un flujo de agua continuo y poco intenso. Éstas permanecieron en la interfase sedimento-agua con menor intensidad hidrodinámica, lo que favorecería una alta cementación. Por otro lado, las valvas de PD2016 estuvieron sujetas también","PeriodicalId":50819,"journal":{"name":"Ameghiniana","volume":null,"pages":null},"PeriodicalIF":1.0,"publicationDate":"2023-08-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"41243912","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":"Advances in the Understanding of Neogene Mammalian Fauna in the Pampean Region (Central Argentina) Through Revising “Biozone” Hypotheses Based on New Dates and Biochronological Analyses","authors":"Cristo O. Romano, Ricardo Bonini, S. Hemming, Marcos Cenizo, U. Pardiñas, F. Prevosti","doi":"10.5710/AMGH.07.07.2023.3551","DOIUrl":"https://doi.org/10.5710/AMGH.07.07.2023.3551","url":null,"abstract":"Abstract. Fossil vertebrates, especially mammals, of the Neogene–Quaternary of Central Argentina were fundamental to the construction of time and rock-time scales and the knowledge of the biotic evolution of southern South America. The poverty of fossiliferous localities constrained with radiometric and/or paleomagnetic data heavily complicated the correlation of different faunas and their temporal allocation. The Cerro Azul Formation (Argentina) constitutes a suitable example of this situation but also enlarged because its fossils have been collected from scattered and isolated small outcrops whose chronological ordering was based on the “stage of evolution” of some rodents. We present here new dates for the fauna/locality of Telén (La Pampa Province) plus extensive biochronological analyses covering 16 fossiliferous localities referred to Cerro Azul Formation. Two dates from an “escoria” sample gave 7.09 Ma for Telén assemblage, an age in accordance with that obtained from an independent faunal analysis. Faunal ordination and age obtained with regression analyses identify a succession of faunas/localities that cover the time range between 8–5.33 Ma. The older assemblages (e.g., Cerro Bota) appear to be transitional between Chasicoan and “Huayquerian” faunas. The first records of procyonids and cricetid rodents, two North American lineages, are not synchronic (7 and 5.7 Ma, respectively). Our results show important temporal overlapping among the proposed successive rodent”biozones”. The use of the “stage of evolution” in the analyses does not improve the results, suggesting that its application without independent chronological/biostratigraphical constraints is not appropriate. Resumen . Los vertebrados fósiles, especialmente mamíferos, del Neógeno–Cuaternario del centro de Argentina fueron fundamentales para la construcción de escalas de tiempo y tiempo-roca y el conocimiento de la evolución biótica del sur de Sudamérica. La escasez de localidades fosilíferas con datos radiométricos y/o paleomagnéticos complicó fuertemente la correlación de diferentes faunas y su asignación temporal. La Formación Cerro Azul (Argentina) constituye un ejemplo adecuado de esta situación, porque sus fósiles han sido recolectados en pequeños afloramientos dispersos y aislados cuyo ordenamiento cronológico se basó en el “grado evolutivo” de algunos roedores. Presentamos aquí nuevos fechados para la fauna/localidad de Telén (provincia de La Pampa), así como extensos análisis biocronológicos que abarcan 16 localidades fosilíferas referidas a la Formación Cerro Azul. Dos dataciones de una muestra de “escoria” dieron 7,09 Ma para el conjunto de Telén, edad concordante con la obtenida a partir de un análisis faunístico independiente. La ordenación faunística y la edad obtenida con los análisis de regresión identifican una sucesión de faunas/localidades que cubren el rango temporal entre 8–5,33 Ma. Los conjuntos más antiguos (por ejemplo, Cerro La Bota) parecen ser transic","PeriodicalId":50819,"journal":{"name":"Ameghiniana","volume":null,"pages":null},"PeriodicalIF":1.0,"publicationDate":"2023-08-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"41920730","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":"Enhanced Primary Productivity in the Brazil Malvinas Confluence Zone during the Mis 3","authors":"C. Laprida, Paula Albarracín, Silvia I. Romero, R. Martín, J. Isola, S. Kasten, N. G. Chapori","doi":"10.5710/AMGH.04.04.2023.3515","DOIUrl":"https://doi.org/10.5710/AMGH.04.04.2023.3515","url":null,"abstract":"Abstract. Micropaleontological analyses from the western South Atlantic core AU_Geo02_GC20 (45° 55' S; 58° 30' W, 2589 m water depth) revealed changes in the primary productivity and sea surface temperature (SST) during MIS 3 that point to significant changes in the Brazil Malvinas Confluence Zone dynamics. These changes led to a marked increase in the SST and the primary productivity between 44.0–36.1 ka BP, as indicated by the quantitative reconstruction of the subsurface temperature and the high relative abundance of the planktonic foraminifera Globigerina bulloides and the eutrophic index. The increase in the SST and the primary productivity could indicate frequent or more persistent southward penetration of subtropical waters over the north Patagonian margin due to a southward extension of the Brazil Current and a weakening of the Malvinas Current. The high primary productivity resulted in the intensive use of phosphate during spring. Conversely, benthic assemblages do not reflect high surface productivity. The dominance of calcareous nannoplankton over diatoms as primary producers, which allows inferring the shoaling of the nutricline and the thermocline, justifies the decoupling between planktonic and benthic communities as a consequence of reduced efficiency of the biological pump. The deposition of the pelagites during the period of enhanced primary productivity indicates a slowing down of the bottom circulation, probably due to a weakening of the Atlantic Meridional Overturning Circulation. Resumen. Los análisis micropaleontológicos del testigo AU_Geo02_GC20 (45° 55' S; 58° 30' W, 2589 m de profundidad del agua), Atlántico Sudoccidental, revelaron cambios en la productividad primaria y la temperatura del agua superficial (SST) durante el MIS 3 que implican cambios significativos en la dinámica de la Zona de Confluencia Brasil Malvinas. Estos cambios condujeron a un marcado aumento en la SST y en la productividad primaria entre 44,0 y 36,1 ka AP, como lo indican la reconstrucción cuantitativa de la temperatura sub-superficial, la elevada abundancia relativa del foraminífero planctónico Globigerina bulloides y el índice de productividad eutrófica. La alta productividad primaria condujo a un uso intensivo de fosfato durante la primavera. El aumento de la SST y de la productividad primaria podrían indicar una frecuente o más persistente penetración de aguas subtropicales sobre el margen norte patagónico debido a una extensión hacia el sur de la Corriente de Brasil y el concurrente debilitamiento de la Corriente de Malvinas. Por el contrario, los ensambles de foraminíferos bentónicos no reflejan una alta productividad superficial. El dominio de cocolitofóridos sobre diatomeas como productores primarios, que permite inferir la somerización de la nutriclina y la termoclina, justifica el desacople entre las comunidades planctónicas y bentónicas como consecuencia de una menor eficiencia de la bomba biológica. La deposición de pelagitas calcáreas","PeriodicalId":50819,"journal":{"name":"Ameghiniana","volume":null,"pages":null},"PeriodicalIF":1.0,"publicationDate":"2023-06-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"47133278","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"New Insights on Benthic Mg/Ca Paleothermometry in the Western South Atlantic","authors":"N. G. Chapori, R. Martín, J. Groeneveld, P. Albarracin, C. Laprida","doi":"10.5710/AMGH.25.03.2023.3513","DOIUrl":"https://doi.org/10.5710/AMGH.25.03.2023.3513","url":null,"abstract":"Abstract. Close relationship exists between the Mg/Ca ratio in foraminiferal shells and the calcification temperature. Even when most paleoceanographic studies focused on near-surface property reconstructions leaving the deep ocean less explored, during the last years, new Mg/Ca-temperature calibrations were established for the benthic genera Uvigerina and Cibicidoides. Among the main conclusions, it has been established that secondary factors exist affecting the Mg incorporation into the benthic shells, particularly at low temperatures. In order to establish a potential relationship between the Mg/Ca ratios of the aforementioned genera for the western South Atlantic and tropical Atlantic, 38 core-top samples are analyzed here. Our results confirm the existence of other parameters than just temperature affecting Cibicidoides and Uvigerina Mg/Ca, suggesting that the effect of all these other parameters together produces a variable “offset” between both genera that can be linearly approached. We develop an algorithm that allows transforming the Mg/Ca data measured on one of these two genera into the other. This not only would allow performing a continuous Mg/Ca record independent of which benthic genera is available for study but also potentially leads to new and more accurate Mg/Ca-temperature calibrations allowing to get more, high-resolution bottom water temperature reconstructions. Resumen. Existe una cercana relación entre el Mg/Ca de las conchillas de foraminíferos y la temperatura de calcificación de las mismas. Aun cuando la mayoría de los estudios paleoceanográficos se enfocaron en la reconstrucción de las propiedades cercanas a la superficie, dejando al océano profundo menos explorado, durante los últimos años se establecieron nuevas calibraciones de temperatura en base a Mg/Ca para los géneros bentónicos Uvigerina y Cibicidoides. En base a las mismas, se estableció que existen distintos factores que afectan la incorporación del Mg a las conchillas bentónicas, particularmente a bajas temperaturas. A fin de establecer una potencial relación entre el Mg/Ca de los géneros mencionados previamente, se analizan aquí 38 muestras de sedimento superficial (core-tops) del Atlántico Sudoccidental y del Atlántico Tropical. Nuestros resultados confirman la existencia de otros parámetros, además de la temperatura, afectando el Mg/Ca de Cibicidoides y Uvigerina, sugiriendo que el efecto de todos estos parámetros juntos produce un “offset” variable entre ambos géneros que podría aproximarse de forma lineal. Desarrollamos un algoritmo que permite transformar los datos de Mg/Ca medidos en uno de estos géneros en datos del otro. Esto no solo permitiría analizar un registro de Mg/Ca de forma continua, independientemente del género bentónico que se encuentre disponible, sino que también conduce potencialmente a nuevas y más precisas calibraciones de temperatura en base a Mg/Ca permitiendo más reconstrucciones de la temperatura del agua del fondo.","PeriodicalId":50819,"journal":{"name":"Ameghiniana","volume":null,"pages":null},"PeriodicalIF":1.0,"publicationDate":"2023-06-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"44132976","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 Rise and Fall of Ancient Neornithes. Paleogene Fossil Birds – 2nd Edition.","authors":"F. Degrange","doi":"10.5710/1851-8044-60.4.389","DOIUrl":"https://doi.org/10.5710/1851-8044-60.4.389","url":null,"abstract":"","PeriodicalId":50819,"journal":{"name":"Ameghiniana","volume":null,"pages":null},"PeriodicalIF":1.0,"publicationDate":"2023-06-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"41998277","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":"Gondwanan Perspectives: Mesozoic and Cenozoic Micropaleontology of South America, Progresses and Applications","authors":"A. Concheyro, E. Bernasconi","doi":"10.5710/amgh.28.04.2023.3557","DOIUrl":"https://doi.org/10.5710/amgh.28.04.2023.3557","url":null,"abstract":"","PeriodicalId":50819,"journal":{"name":"Ameghiniana","volume":null,"pages":null},"PeriodicalIF":1.0,"publicationDate":"2023-06-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"49202060","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":"Maastrichtian Microfossils of the Shallow Marine Umir Formation, Northeastern Colombia","authors":"G. Patarroyo, K. Kochhann, R. M. Guerra, L. Alegret, Daiane Ceolin, J. M. Torres","doi":"10.5710/AMGH.02.03.2023.3525","DOIUrl":"https://doi.org/10.5710/AMGH.02.03.2023.3525","url":null,"abstract":"Abstract. During the Late Cretaceous, northern South America was characterized by broad epicontinental seas, with variable surface productivity and changing bottom-water oxygenation. Global sea-level fluctuations and local tectonic shifts caused their disappearance in the latest Cretaceous. We present an integrated micropaleontological and geochemical study of a section comprising the Umir Formation and its lower stratigraphic contact with the La Luna Formation, in the Middle Magdalena Valley, northeastern Colombia. Foraminiferal assemblages were moderately diverse and mainly dominated by benthic taxa, characterizing the biozones Siphogenerinoides bramlettei and Ammobaculites colombiana (Maastrichtian). Planktonic foraminiferal assemblages were less diversified, being species assigned to Heterohelicidae and scarce keeled forms (Globotruncana spp.) the most recurrent taxa. Ostracod recovery was very scarce, and we could only identify the genus Actinocythereis. In contrast, calcareous nannofossil assemblages were moderately diversified along the section, and composed of typical Late Cretaceous low-latitude taxa such as Micula staurophora, Cribrosphaerella ehrenbergii, Gartnerago segmentatum. The identified microfossils indicate a transition from middle-inner shelf conditions, with moderately oxygenated bottom waters within the La Luna Formation, to a shallower marine setting within the Umir Formation. This interpretation is supported by Sr/Ba and log(Fe/Ca) ratios measured in bulk sediment, which indicate increased continental runoff and terrigenous input in the upper part of the section. Moreover, a significant biotic turnover was identified at the base of the section, suggesting the presence of a xenoconformity at the La Luna-Umir contact, which has been previously described and proposed as a regional stratigraphic feature. Resumen. El Cretácico Tardío del norte de Sudamérica estuvo dominado por mares epicontinentales extensos, con fluctuaciones de la productividad superficial y oxigenación del agua de fondo. Cambios en los regímenes tectónicos locales y descensos globales en el nivel del mar, llevaron a la desaparición de dichos ambientes hacia fines del Cretácico. Presentamos un estudio micropaleontológico y geoquímico integrado de una sección de la Formación Umir y su contacto basal con la Formación La Luna en el Valle Medio del Magdalena, noreste de Colombia. Las asociaciones de foraminíferos fueron moderadamente diversas y estuvieron dominadas por formas bentónicas que definen las biozonas de asociación locales Siphogenerinoides bramlettei y Ammobaculites colombiana (Maastrichtiano). Las formas planctónicas, menos diversas, incluyeron ejemplares de Heterohelicidae y escasas formas quilladas (Globotruncana spp.). El registro de ostrácodos fue muy escaso, sólo pudimos reconocer al género Actinocythereis. En contraste, las asociaciones de nanofósiles calcáreos fueron moderadamente diversas y comprendieron formas típicas de bajas latitudes del C","PeriodicalId":50819,"journal":{"name":"Ameghiniana","volume":null,"pages":null},"PeriodicalIF":1.0,"publicationDate":"2023-06-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"46050042","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":"Late Triassic Calcareous Nannofossils from the Pucará Group, Peru: A New Biostratigraphic Tool for Regional Correlation in Western South America","authors":"J. P. Pérez Panera, Lydia Calvo Marcilese, D. Boggetti, E. Ottone, Josefina Cuello, P. Giampaoli","doi":"10.5710/AMGH.06.02.2023.3516","DOIUrl":"https://doi.org/10.5710/AMGH.06.02.2023.3516","url":null,"abstract":"Abstract. Micropaleontological investigations performed at four sections in the Pucará Group, northwestern Peru, revealed the presence of late Triassic calcareous nannofossils. Recovered assemblages are poorly preserved and show low abundance and species richness. However, these findings represent one of the three records outside the Tethyan Realm and allow independent biostratigraphic constraints for the Pucará Group. In the Cantera Tello section, Chambará Formation, only the genus Prinsiosphaera was observed, suggesting a late Norian age for the lower part, and the occurrence of Eoconusphaera zlambachensis indicates a Rhaetian age for the upper part. In the Río Cocahuayco section, Chambará, and Aramachay formations, only the genus Prinsiosphaera was recovered, indicating the late Triassic. In Ricardo Palma section, Aramachay Formation, the presence of E. zlambachensis indicates a Rhaetian age. The Aguas Verdes section, Condorsinga Formation, yields an assemblage with P. triassica and E. zlambachensis, indicating that, at least in this part of the basin, the lower section of this Formation is Rhaetian. Resumen. Estudios micropaleontológicos realizados en cuatro secciones del Grupo Pucará, noroeste de Perú, revelaron la presencia de nanofósiles calcáreos del Triásico Tardío. Los ensambles recuperados están mal preservados y muestran baja abundancia y riqueza específica. Sin embargo, estos hallazgos representan uno de los tres registros fuera del Reino de Tethys y aportan un control bioestratigráfico independiente para el Grupo Pucará. En la sección Cantera Tello, Formación Chambará, la sola presencia del género Prinsiosphaera sugiere una edad noriana tardía para la parte inferior, y la presencia de Eoconusphaera zlambachensis indica una edad retiana para la parte superior. En la sección Río Cocahuayco, formaciones Chambará y Aramachay, solo se recuperaron especímenes del género Prinsiosphaera, indicando el Triásico Tardío. En la sección Ricardo Palma, Formación Aramachay, la presencia de E. zlambachensis indica una edad retiana. La sección Aguas Verdes, Formación Condorsinga, contiene un ensamble con P. triassica, y E. zlambachensis, indicando que, al menos en esta parte de la cuenca, la sección inferior de esta Formación corresponde al Rhaetiano.","PeriodicalId":50819,"journal":{"name":"Ameghiniana","volume":null,"pages":null},"PeriodicalIF":1.0,"publicationDate":"2023-06-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"41909203","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":"Fossil Diatom Study Reveals Significant Freshwater Input in Miocene Coastal Marine Environments of the Southwestern Atlantic (Patagonia, Argentina)","authors":"Aylén Allende Mosquera, J. Cuitiño, M. Espinosa","doi":"10.5710/AMGH.03.03.2023.3517","DOIUrl":"https://doi.org/10.5710/AMGH.03.03.2023.3517","url":null,"abstract":"Abstract. A 209 m-thick sedimentary succession exposed at Estancia Redonda Chica locality (northeastern Patagonia, Argentina) includes both the Gaiman Formation (Early Miocene) and the Puerto Madryn Formation (Late Miocene). Based on the sedimentologic analysis, the Gaiman Formation is interpreted as accumulated in a marine inner shelf to shoreline environment, whereas an estuarine to terrestrial environment is interpreted for the Puerto Madryn Formation. Fifteen samples were processed and analyzed for diatoms, providing for the first time a micropaleontological record for these units, allowing us to go deeper into the paleoenvironmental interpretations. Fourteen diatom species, two diatom genera, and chrysophyte stomatocysts were identified. The dominant diatom elements among the samples are Paralia sulcata, Lemnicola hungarica, Cocconeis placentula, and Pseudopodosira sp., together with chrysophyte stomatocysts. Paleoecological information drawn from diatom assemblages is consistent with paleoenvironmental interpretations based on sedimentological analysis for both units. However, diatom analysis for the Gaiman Formation suggests a strong freshwater influence in an inner shelf environment, which went unnoticed by utilizing other proxies. We suggest a high-productivity marine zone may have developed as a consequence of nutrient supply from rivers favoring diatom growth. This could explain the unique great abundance of macroinvertebrates and marine vertebrates preserved in the sedimentary succession. Resumen. Se estudió una sucesión sedimentaria de 209 metros de espesor, la cual aflora en la localidad de Estancia Redonda Chica (noreste de Patagonia, Argentina). Dicha sucesión expone los depósitos de la Formación Gaiman (Mioceno Temprano) y de la Formación Puerto Madryn (Mioceno Tardío). La Formación Gaiman corresponde a depósitos de plataforma marina interna hasta un ambiente más cercano a la costa. Por otro lado, la Formación Puerto Madryn es interpretada como depósitos de ambientes estuarinos a terrestres. Quince muestras fueron procesadas y analizadas con el objetivo de constatar la presencia de diatomeas y proporcionar, por primera vez, un registro micropaleontológico para la localidad, y a su vez, profundizar la interpretación paleoambiental de los depósitos neógenos de Patagonia. Se pudieron reconocer 14 especies y dos géneros de diatomeas, y estomatoquistes de crisofitas. Las especies Paralia sulcata, Lemnicola hungarica y Cocconeis placentula, y Pseudopodosira sp., junto con los estomatoquistes de crisofitas son dominantes. La información paleoecológica extraída de los ensambles de diatomeas es consistente con la interpretación paleoambiental previamente realizada a partir del análisis sedimentológico para ambas unidades. Sin embargo, la fuerte influencia de agua dulce observada para la Formación Gaiman a partir del análisis diatomológico, aparece como una nueva evidencia para dicha unidad. Se sugiere el posible desarrollo de una zona mar","PeriodicalId":50819,"journal":{"name":"Ameghiniana","volume":null,"pages":null},"PeriodicalIF":1.0,"publicationDate":"2023-06-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"48034170","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":"Correlation of Middle to Upper Eocene Units from High Latitude Southwestern Atlantic Sites","authors":"C. Amenábar, G. R. Guerstein, Marta I. Alperin, G. Daners, S. Casadío, Martín Rodríguez Raising","doi":"10.5710/AMGH.25.02.2023.3514","DOIUrl":"https://doi.org/10.5710/AMGH.25.02.2023.3514","url":null,"abstract":"Abstract. To understand the important significant climatic and paleoceanographic changes occurred in the Southern Hemisphere during the Paleogene, and especially those related to the opening of the Drake Passage, is essential to correlate the Eocene lithostratigraphic units in areas adjacent to this passage, such as those from the Austral-Magallanes and James Ross basins, to the north and to the south, respectively. For many years, there was no correlation between these units due to the absence of reliable chronostratigraphic and biostratigraphic information. Recently, other authors published U/Pb data for the Austral-Magallanes Basin and introduced important modifications to the previous stratigraphic scheme. Subsequently, due to reinterpretating the available isotope data together with U/Pb ages, the chronostratigraphic model has modified again, also including the James Ross Basin. In light of an updated quantitative dinoflagellate cyst dataset from the units adjacent to the Drake Passage, we performed a Principal Component Analysis (PCA) to discuss the correlation between the studied sections. The PCA groups assemblages with a high contribution of Antarctic taxa (e.g., Enneadocysta dictyostila, Deflandrea antarctica) containing in the Upper Member of the Río Turbio Formation (lower part), Man Aike, Leticia, and La Meseta formations, being Bartonian in age. The other group joined assemblages with younger ages, Priabonian, dominated by Antarctic species (Vozzhennikovia-Spinidinium) and cosmopolitan taxa, corresponding to the Upper Member of the Río Turbio Formation (upper part). This study reinforces the most recent chronostratigraphic proposal and proves the biostratigraphic useful of some taxa for sites near the Drake Passage. Resumen. Para comprender los cambios climáticos y paleoceanográficos ocurridos durante el Paleógeno en el Hemisferio Sur y especialmente aquellos relacionados con la apertura del Pasaje de Drake, es esencial correlacionar las unidades litoestratigráficas de áreas adyacentes a dicho pasaje como las de las cuencas Austral-Magallanes y James Ross, al norte y sur, respectivamente. Por muchos años, no se contó con una correlación de dichas unidades debido a la ausencia de información crono y bioestratigráfica confiable. Recientemente, otros autores publicaron edades U/Pb para la Cuenca Austral-Magallanes e introdujeron importantes modificaciones en el esquema estratigráfico previo. Posteriormente, en base a la reinterpretación de datos isotópicos disponibles junto con las edades U/Pb, el modelo cronoestratigráfico fue nuevamente modificado incluyendo además a la Cuenca James Ross. A la luz de un conjunto actualizado de datos cuantitativos de quistes de dinoflagelados de las unidades adyacentes al Pasaje de Drake, realizamos un Análisis de Componentes Principales (PCA) para discutir la correlación entre las secciones estudiadas. El PCA agrupa asociaciones con una alta contribución de taxones antárticos (e.g., Enneadocysta dict","PeriodicalId":50819,"journal":{"name":"Ameghiniana","volume":null,"pages":null},"PeriodicalIF":1.0,"publicationDate":"2023-06-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"70945679","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}