918 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

    Comparing thallium isotopes to paleosalinity and Mo-U isotope paleoredox proxies: A case study of the Upper Devonian Kettle Point Formation, Ontario

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    Black shale formations are utilised to reconstruct ancient global ocean redox conditions by analyzing and inferring their geochemical and isotopic compositions. However, the accuracy of these reconstructions can decrease if regional and local influences overprint global signals. This study utilizes the novel thallium (Tl) isotope paleoredox proxy, in conjunction with the well-studied molybdenum (Mo) and uranium (U) isotope redox proxies, to reconstruct the depositional environment of black shales from the Famennian Kettle Point Formation of southern Ontario. The Mo-U isotope ratios of these black shales have been previously inferred by Kendall et al. (2020) to reflect a local redox change from strongly to weakly euxinic conditions within the bottom-waters of the Chatham Sag sub-basin. Paleosalinity proxies were also interpreted by Kendall et al. (2020) as an increase in the Chatham Sag’s basin restriction during the Late Famennian. Authigenic Tl concentrations were obtained through leaching of black shale rock powder using 2 M nitric acid and have a range of 0.72 - 14 μg/g. Units 1 to 3 contained low Tl concentrations (0.72 - 4.3 μg/g) and Unit 4 had relatively high Tl concentrations (3.2 - 14 μg/g). Authigenic Tl isotope ratios were measured against NIST SRM 3158 (0 ε units; statistically identical to NIST SRM 997) and range between –7.1 and –2.0 ± 0.4 ε units (2SD). Authigenic Tl concentrations have a strong negative correlation (r = –0.79; p < 0.001) with authigenic Tl isotope ratios, which indicate low concentrations contain heavier Tl isotope compositions and high concentrations contain lighter Tl isotope compositions. Thallium isotopes have a very strong negative correlation with U isotope ratios (r = –0.89; p < 0.001) and a strong positive correlation with Mo isotopes (r = 0.71; p < 0.001). The positive correlation with Mo isotopes suggests that the Fe-Mn oxyhydroxide particulate shuttle did not influence Tl and Mo isotope expression. Three distinct groups of samples are apparent in the cross plots of Tl - U and Tl - Mo isotopes. In stratigraphically ascending order, these groups are described as the high Tl - low U - high Mo group of Unit 1 to lower Unit 3 (ε205Tlmean = –2.7 ± 0.4, 2SD, n = 13), the transitional group of upper Unit 3 to lower Unit 4 (ε205Tlmean = –4.1 ± 0.5, 2SD, n = 5), and the low Tl - high U - low Mo group of upper Unit 4 (ε205Tlmean = –6.1 ± 0.6, 2SD, n = 17). Together with the paleosalinity proxies, these groups represent redox and salinity changes within the Chatham Sag throughout the Famennian. Unit 1 to lower Unit 3 experienced increased basin restriction that promoted strong euxinia in the deep basin and the predominance of river inputs as the main source of Tl to the Chatham Sag, which is reflected by average ε205Tl values comparable to modern rivers. Low trace metal (TM) accumulation and marine paleosalinity during this time suggests that the Chatham Sag was still somewhat connected to the open ocean, and received infrequent inputs of oceanic water to replenish the TM reservoir and maintain marine salinity at the sediment-water interface. During upper Unit 4 deposition, the Chatham Sag’s source of TMs shifted to mainly oceanic inputs, indicated by average ε205Tl values comparable to the modern ocean, and suggests a relative decrease in basin restriction. Increased hydrographic connectivity to the open ocean during Unit 4 deposition also increased sedimentary TM accumulation. Additionally, decreased basin restriction and increased freshwater inputs, which is indicated by brackish paleosalinity, diluted aqueous hydrogen sulfide concentrations of the bottom-waters to weakly euxinic conditions. The transitional period between these two environmental regimes occurred during upper Unit 3 to lower Unit 4 deposition, which was coincident with the Late Famennian eustatic transgression of Algeo et al. (2007). The decrease in paleosalinity during the transitional period may have been caused by glacial meltwater outwash from the Acadian highlands to the paleo-south, but an increase in regional precipitation frequency and intensity caused by a shift in regional climate is also considered a potential mechanism. Overall, the application of the Tl isotope paleoredox proxy to the Kettle Point Formation black shales reveals that local and regional environmental factors have a strong influence on Tl isotope expression, and global-scale redox reconstructions using this proxy can be widely inaccurate if smaller scale factors are not considered

    AN ECOLOGICAL SURVEY OF EAST TEXAS SALAMANDERS ACROSS THE CAMP TYLER OUTDOOR FIELD SCHOOL IN SMITH COUNTY, TEXAS

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    Amphibians are a unique class of organisms with a very long and storied evolutionary history of survival. Many modern amphibian clades occupy several vital ecological roles within their native freshwater environments. One of these roles, typically includes functioning as an ecological indicator species, whereby the presence of stable and diverse populations of many amphibian species, including salamanders, within a freshwater ecosystem have long been considered ecological indicators of good habitat quality and stable ecosystem health. Similarly, salamanders also function as important members of their local food webs and act as valuable mediators of complex trophic hierarchies to facilitate nutrient cycling between trophic levels throughout their equally complex life histories. However, countless amphibians today are experiencing significant population declines – with many sensitive and endemic species currently facing the imminent threat of widespread extinction events that are primarily driven by anthropogenic activities. Concerningly, this could also spell disaster for numerous other clades and communities within these same freshwater ecosystems. These changes in amphibian distribution and diversity are only one small component in many broad scale declines in global biodiversity that have been recognized in recent decades. These collective declines have been described as a “sixth mass extinction.” Because of their status as ecological indicator species, the widespread reduction in many amphibian communities may also serve as a harbinger of further biological crises in the near future. As a result, an updated record of sensitive amphibian species, especially salamanders, needs to be collected and compiled for use in assessing, tracking, and maintaining the health and well-being of many vital freshwater ecosystems. Here, a field survey of several East Texas salamander species was conducted from October of 2022 through April of 2023 – during their peak activity season – to create an updated inventory of historic and anecdotal salamander populations previously reported at the Camp Tyler Outdoor School, a local non-profit field school for grades K-12, located in Smith County, Texas. All three target salamander species were observed and identified during this period, although current findings seem to indicate that some these animals, especially the previously documented population of Western lesser sirens (Siren intermedia nettingi) may have experienced significant population declines since they were last surveyed. This is likely the result of a variety of ecological factors that have changed over time, including an increased anthropogenic presence within the area, land use changes, possible degradations in water and habitat quality, changing climatic conditions, and out competition with more tolerant clades in their aquatic environment

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

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    Armoured jawed fishes 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 identified and can present important stratigraphic information for otherwise under-explored deposits. A unique find 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

    Paleoenvironmental variations during the Late Cambrian: implications from Zn isotopes and I/(Ca+Mg) ratios

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    The Upper Cambrian at the Martin Point section partially spans the coeval Tuckers Cove (Shallow Bay Formation) and the Martin Point (Green Point Formation) members of the Cow Head Group of western Newfoundland (eastern Laurentia), Canada. These units comprise alternating shale, minor conglomerate beds and limestone rhythmites of a toe-of-slope apron. Earlier studies of the C-isotope profile, based on the lime mudstone interbeds, documented global negative δ¹³ Ccarb shifts (from old to young: NL1, NL2, HERB) correlated with the lowermost Proconodontus posterocostatus, Proconodontus muelleri and base of Eoconodontus notchpeakensis conodont zones, respectively. Samples were extracted from the most micritic spots, where the micritic to near-micritic grain size (≤ 4 μm−10 μm) and fabric retention confirm petrographic preservation. Insignificant correlations of diagenetic proxies with their environmental counterparts support high degree of geochemical preservation. The zinc-isotope (δ⁶⁶Zn) signatures (0.09 – 0.73 ‰ JMC Lyon) and iodine-to-calcium-plus-magnesium (I/(Ca+Mg)) ratios (0.02 – 0.48 μmol/mol) vary consistently throughout the studied events and were employed to shed light on paleoenviromental conditions. The decrease in δ⁶⁶Zn values seems to denote inhibition of bioproductivity in a dysoxic water column, consistent with warm and humid climate during general transgressive settings and shoaling of organic matter into the shallow environment. On the contrary, slight increases in δ⁶⁶Zn (<0.8 ‰ JMC Lyon) might reflect weak bioproductivity and possible influence of carbonate weathering input during minor fluctuations (episodic falls) in sea level during the main course of the transgression. The low I/(Ca+Mg) ratios (< 0.5 μmol/mol) reinforce this interpretation, suggesting general dysoxic settings along the entire section

    GAC-MAC-SGA 2023 Sudbury Meeting: Abstracts, Volume 46

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    The rise and fall of the Malvinoxhosan (Malvinokaffric) bioregion in South Africa: Evidence for Early-Middle Devonian biocrises at the South Pole

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    Global reconstructions, inclusive of environments and ecosystems, and biodiversity counts for the Devonian Period are often done so at the expense of high latitude regions given a historical lack of data presented from these areas. This has bearing on the recognition of biocrises (events marked by extinctions and faunal turnovers) at high latitudes as well as their controls and potential correlation with global, regional, and local tempos. The appearance and disappearance of high-latitude endemic Malvinoxhosan (synonymous with the “Malvinokaffric Realm” which it supersedes) marine invertebrate faunas from West Gondwana are often overlooked, in part owing to difficulties in correlating fossil-bearing strata with global frameworks given the absence and rarity of several key index taxa as well as detailed biostratigraphic appraisals in which to draw regional interbasinal correlations and comparisons. The Early to Middle Devonian Series of South Africa (upper Table Mountain, Bokkeveld and lower Witteberg groups) are a classic Malvinoxhosan-bearing section recording the rise of these endemic faunas, as well as their decline and replacement by cosmopolitan faunas. A detailed biostratigraphy of this interval was created following an assessment of fossil material curated at the Council for Geoscience and Iziko South African Museum, Cape Town as well as from literature. These data suggest that the Malvinoxhosan bioregion persisted as a cohesive unit during Rietvlei-Baviaanskloof to Waboomberg deposition (Pragian/Emsian-early Givetian) given that many representative taxa are found in these strata, however showing a trend of decreasing diversity with little origination through time. Above this interval, few representative taxa are known to continue into the upper Bokkeveld and Witteberg groups, disappearing entirely by the deposition of the Blinkberg Formation. The few fossils that are known in these strata and those succeeding it (e.g., the Swartruggens Formation) are entirely cosmopolitan in identity. Using novel multivariate statistical methods (non-metric multidimensional scaling and cluster analysis) in conjunction with network analysis (NA), the data were interrogated to indicate potential groupings of strata according to their fossil content as well as to track faunal changes through time. These analyses suggest the presence of at least seven to eight interval assemblage biozones housed within at least three larger faunal complexes (Eo-Malvinoxhosan, Malvinoxhosan and Post-Malvinoxhosan) based on their constituent faunal makeup. A closer inspection of these faunal complexes and interval assemblage biozones show a stepped decline in biodiversity with little to no origination and recovery through time that may be correlated with local base-level change at varying orders of magnitude. Declines in biodiversity show selectivity for taxa with epifaunal and semi-infaunal habits with respect to infaunal, deep infaunal and nektonic taxa. Environmental conditions associated with the collapse of the Malvinoxhosan bioregion are thought to have been catastrophic as few new (often short-ranging) immigrants are registered in Post-Malvinoxhosan strata. Further to this, those faunas that are prevalent in Post-Malvinoxhosan strata (e.g., Tropidoleptus) those with known high environmental tolerance and were already present in the region prior to the collapse of the Malvinoxhosan bioregion. Lastly, the observed biodiversity changes in South Africa with respect to local base-level show remarkable similarities with several time equivalent locales in South America suggesting that the decline and extinction of the Malvinoxhosan biota was regional and that the biostratigraphy presented herein has regional application. Here, it is thought regional tectonic controls are suggested to have brought on sea-level changes and entrained warmer waters into higher latitudes against the backdrop of overall rising temperatures from the late Givetian onwards. Whilst the decline of the Malvinoxhosan bioregion might associated with global Middle Devonian biocrises (e.g., Kačák; Taghanic) insufficient age constraints for these strata are available at present to make direct comparisons. Furthermore, an adequate driver for global sea-level change during the Devonian Period, needs to be established to tease out global and local signals in constructed local sea-level curves to establish if these changes (and their effects in changes in biodiversity) are truly global in extent

    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 Stáhpogieddi 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, Stáhpogieddi 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

    2015 GREAT Day Program

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    SUNY Geneseo’s Ninth Annual GREAT Day.https://knightscholar.geneseo.edu/program-2007/1009/thumbnail.jp
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