656 research outputs found

    The past to unravel the future: Deoxygenation events in the geological archive and the anthropocene oxygen crisis

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    Despite the observation that we are witnessing a true oxygen crisis, the ocean deoxygenation theme is getting less attention from the media and population compared to other environmental stressors concerning climate change. The current ocean oxygen crisis is characterized by a complex interplay of climatic, biological, and oceanographic processes acting at different time scales. Earth system models offer insights into future deoxygenation events and their potential extent; however, their capacity to precisely constrain these events is complicated by the intricate interplay of various interconnected feedback mechanisms. The Earth's geological history has been punctuated by regional and global deoxygenation events, which are usually expressed by organic-rich sediment in the geological record and can be useful past analogues of the present-day and future oxygenation crisis related to current climatic stress. Accordingly, we provide an overview of the key elements characterizing past deoxygenation events, aiming for a better understanding of the Anthropocene oxygen crisis and its potential evolution. We suggest that past global deoxygenation events during hypethermals may bear similarities to present-day dynamics in the open ocean. Additionally, we explore the significance of regional deoxygenation events with cyclical occurrences for better constraining environmental dynamics and ecological impacts in semi-enclosed, restricted, and marginal basins. Despite the unprecedented magnitude and rate of current anthropogenic pressures, it is essential to consider the comparison of triggers and feedbacks from ancient deoxygenation events when investigating the future of this concealed but ecologically impactful problem

    The skeletal completeness of the Palaeozoic chondrichthyan fossil record

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    Chondrichthyes (sharks, rays, ratfish and their extinct relatives) originated and diversified in the Palaeozoic but are rarely preserved as articulated or partly articulated remains because of their predominantly cartilaginous endoskeletons. Consequently, their evolutionary history is perceived to be documented predominantly by isolated teeth, scales and fin spines. Here, we aim to capture and analyse the quality of the Palaeozoic chondrichthyan fossil record by using a variation of the skeletal completeness metric, which calculates how complete the skeletons of individuals are compared to estimates of their original entirety. Notably, chondrichthyan completeness is significantly lower than any published vertebrate group: low throughout the Silurian and Permian but peaking in the Devonian and Carboniferous. Scores increase to a range similar to pelycosaurs and parareptiles only when taxa identified solely from isolated teeth, scales and spines are excluded. We argue that environmental influences probably played an important role in chondrichthyan completeness. Sea level significantly negatively correlates with chondrichthyan completeness records and resembles patterns already evident in records of ichthyosaurs, plesiosaurs and sauropodomorphs. Such observed variations in completeness highlight the impact of different sampling biases on the chondrichthyan fossil record and the need to acknowledge these when inferring patterns of chondrichthyan macroevolution

    Evidence for Placoderms from the Mid-Palaeozoic Sandon Beds of North-western New South Wales, Australia

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    Armoured jawed Ô¨Āshes known as placoderms are a well-documented group with a fossil record spanning the Silurian to end-Devonian. They have a global distribution and a marked diversity within Devonian deposits of Australia. Despite their notable Gondwanan fossil record, new material is occasionally identiÔ¨Āed and can present important stratigraphic information for otherwise under-explored deposits. A unique Ô¨Ānd from the so-called Sandon beds is presented here and expands the record of placoderms from New South Wales. This specimen presents insight into a previously unknown macrofossil record from the deposit and suggests a more Devonian age for the unit, rather than the previously suggested Carboniferous date. We also summarise the macrovertebrate record of Devonian placoderms from Australia, highlighting and discussing changes in their Gondwanan taxonomic diversity across the time period

    2017 GREAT Day Program

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    SUNY Geneseo’s Eleventh Annual GREAT Day.https://knightscholar.geneseo.edu/program-2007/1011/thumbnail.jp

    Life through an Ediacaran glaciation: Shale- and diamictite-hosted organic-walled microfossil assemblages from the late Neoproterozoic of the Tanafjorden area, northern Norway

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    New organic-walled microfossil (OWM) assemblages are reported from upper Neoproterozoic glacial and interglacial siliciclastic deposits in Finnmark, northern Norway. A nearly continuous sedimentary succession of the Vestertana Group contains two glaciogenic units, the Smalfjorden and Mortensnes formations, interpreted as end-Cryogenian Marinoan and Ediacaran glaciations, respectively. We investigated the OWM record in the Nyborg, Mortensnes, and St√°hpogieddi formations to assess the impact of a glacial interval on the diversity of microscopic eukaryotes. A modified acid-extraction technique was applied to recover OWM from the diamictite matrix. The upper Nyborg Formation contains morphologically complex Doushantuo-Pertatataka acritarchs (DPA), restricting the age of the Nyborg Formation to early-mid Ediacaran. DPA occur below the dolostones that record a negative carbon isotope excursion correlated with the Shuram anomaly and below a glacial diamictite. A decline in species richness and compositional change is observed in the Mortensnes glacial assemblage. DPA are replaced by bacterial filaments and cell aggregates. The overlying Indreelva Member, St√°hpogieddi Formation contains Ediacara-type biota and palaeopascichnids, but only a depauperate OWM assemblage of leiosphaerids and flask-shaped microfossils characteristic of the late Ediacaran.The succession of assemblages in the Vestertana Group demonstrates a turnover from large eukaryotic OWM to a microbial community in the glacial interval, to a low diversity post-glacial assemblage during the rise of macroscopic life. We compared the Vestertana record to global DPA occurrences. Although one DPA assemblage zone postdates the Shuram excursion, no DPA occur above Ediacaran glacial diamictites in successions where those deposits are present. Considering this, and the community changes in the Vestertana succession, we suggest that DPA were affected by the onset of an Ediacaran glaciation. Lastly, we combined the biostratigraphic markers in the Vestertana Group to constrain the age of the Mortensnes diamictite

    Broad snouted cladoselachian with sensory specialization at the base of modern chondrichthyans

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    Throughout the Silurian and Devonian, cartilaginous fish successively evolved their specialized skeletal and dental characteristics, and increasingly refined their sensory systems. The Late Devonian shark taxon Maghriboselache mohamezanei gen. et sp. n. from the eastern Anti-Atlas of Morocco is known from multiple specimens preserving most of its skeletal features, which in some instances are preserved in three dimensions. Key details of the dentition, jaws, and pectoral skeleton are shared with the iconic genus Cladoselache. Phylogenetic analyses place the family Cladoselachidae as the sister group of symmoriiforms and these groups as sister group of the holocephalans. Further phylogenetic results corroborate that the initial evolutionary radiation of crown chondrichthyans occurred within or before the Late Devonian. Remarkably, this new stem holocephalan is equipped with a wide snout and large laterally separated nasal capsules: the earliest known example of this condition in the chondrichthyan and (perhaps) gnathostome record. This suggests sensory specialization approaching that of extant broad-rostrum elasmobranchs and represents a significant addition to increasingly apparent ecomorphological diversity among early chondrichthyans

    2014 GREAT Day Program

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    SUNY Geneseo’s Eighth Annual GREAT Day.https://knightscholar.geneseo.edu/program-2007/1008/thumbnail.jp

    Secuencias tectono-estratigráficas y reconstrucción de la cuenca sinorogénica cenozoica de San Antonio de los Cobres, Noroeste Argentino

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    Tesis (DCG)--FCEFN-UNC, 2023Fil: Ledesma, Jonathan Hern√°n. Universidad Nacional de C√≥rdoba. Facultad de Ciencias Exacts F√≠sicas y Naturales; ArgentinaLa cuenca intermontana de San Antonio de lo Cobres (SAC), se ubica en el l√≠mite entre la Puna y Cordillera Oriental, a los 24¬įS ‚Äď 66¬į15‚ÄôO, y a una altitud aproximada de 3600 m.s.n.m. Est√° limitada por bloques de basamento relacionados a sistemas de fallas inversas regionales. El l√≠mite sur de la misma lo constituye el lineamiento regional Calama-Olacapato-El Toro (COT), que a su vez marca la transici√≥n entre la Puna austral y septentrional. Mediante el estudio de las sucesiones sedimentarias, se propuso un nuevo esquema estratigr√°fico Cenozoico. El relleno sedimentario de antepa√≠s est√° compuesto por la Formaci√≥n Geste (Eoceno Medio? ‚Äď Oligoceno?) del Grupo Pastos Grandes, el Conglomerado Los Patos (Mioceno Medio), la Ignimbrita Vizcachayoc (Mioceno Medio) y la Formaci√≥n San Antonio de los Cobres (Mioceno Superior ‚Äď Plioceno?). La Formaci√≥n Geste se asienta en discordancia sobre el Subgrupo Santa B√°rbara y representa la depositaci√≥n en un ambiente fluvio-aluvial. El an√°lisis de procedencia indica un aporte desde las rocas que componen el basamento en los bordes de cuenca, as√≠ como desde las unidades del Grupo Salta, especialmente desde la Formaci√≥n Yacoraite. La identificaci√≥n de estructuras de deformaci√≥n sin-sedimentaria, junto con la discordancia basal con el Subgrupo Santa B√°rbara, permite interpretar que la sedimentaci√≥n inicial de la Formaci√≥n Geste fue sincr√≥nica con per√≠odos de deformaci√≥n del Eoceno. Adem√°s, el hallazgo de restos f√≥siles de notoungulados en la secci√≥n basal de la Formaci√≥n Geste ser√≠an correlacionables con los hallados en la Formaci√≥n Quebrada de los Colorados en Cordillera Oriental, de edad Eocena media. Se interpreta al Conglomerado Los Patos como depositado en ambiente de abanicos aluviales, en una cuenca de tipo extensiva (strike-slip). Esta unidad se encuentra limitada en su techo por la Ignimbrita Vizcachayoc. Se describe formalmente a la Formaci√≥n San Antonio de los Cobres, compuesta por dos miembros. El Miembro basal (Miembro Corte Blanco) se caracteriza por una sucesi√≥n de areniscas e√≥licas, limitadas en su base y techo por dos unidades ignimbr√≠ticas. Tanto la ignimbrita inferior (Ignimbrita Corte Blanco), como la ignimbrita superior (Ignimbrita Ramadas), limitan la edad del Miembro al Mioceno Superior (7,4 ‚Äď 6,4 Ma respectivamente). El an√°lisis de procedencia indica detritos derivados a partir de la disecci√≥n del arco magm√°tico y del basamento metam√≥rfico. Adem√°s, el estudio de paleovientos sugiere un flujo predominantemente desde el noroeste y una velocidad m√°xima calculada de aproximadamente 70 km/h. Estos datos son coincidentes con el patr√≥n de circulaci√≥n y r√©gimen de los vientos actuales en la regi√≥n de la Puna. El Miembro superior (Miembro Mu√Īano) se caracteriza por una sucesi√≥n grano-creciente areno-conglomer√°dica. Presenta evidencias de estratos de crecimiento en el √°rea de Corte Blanco que acompa√Īan un anticlinal, lo que documenta la depositaci√≥n sintect√≥nica desde el Mioceno Superior. El relleno sedimentario Cenozoico de la cuenca de SAC presenta m√ļltiples evidencias sobre la estructuraci√≥n del antepa√≠s del NOA. El hallazgo de discordancias, estructuras de crecimiento y deformaci√≥n sinsedimentaria en las distintas unidades litoestratigr√°ficas, sugiere una evoluci√≥n relacionada a los eventos de deformaci√≥n e inversi√≥n tect√≥nica que ocurrieron durante el Eoceno en el NOA.Fil: Ledesma, Jonathan Hern√°n. Universidad Nacional de C√≥rdoba. Facultad de Ciencias Exacts F√≠sicas y Naturales; Argentin
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