849 research outputs found

    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

    2017 GREAT Day Program

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

    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

    2019 GREAT Day Program

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    SUNY Geneseo’s Thirteenth Annual GREAT Day.https://knightscholar.geneseo.edu/program-2007/1013/thumbnail.jp

    Литосфера. 2023. № 2

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    Biostratigraphic and structural research in the Guedelhinha–Lançadoiras–Algaré sector in the context of the geology of the Neves–Corvo mine region, Iberian Pyrite Belt

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    ABSTRACT: Based on drill hole sampling and sedimentary rock dating by palynology, the present research focuses on the palynostratigraphic events established in the key geological section of Guedelhinha–Lançadoiras–Algaré located in the Portuguese Neves–Corvo mine region, Iberian Pyrite Belt. The age data allow detailing the lithostratigraphic sequence and further understanding the complex structural setting, representing an important contribution to the geological knowledge of this sector located to the immediate WNW of the Neves–Corvo VMS deposit. The combination of the studied events allows the reconstruction of the Devonian-Carboniferous sedimentation and paleoenvironments along the Iberian Pyrite Belt. Several stratigraphic hiatuses identified in the Neves–Corvo region by the palynological record are confirmed, mainly occurring from the mid Frasnian to mid Famennian, from the early and mid Strunian, and from the early to late Tournaisian, which were mainly coincident with the worldwide extinction events, in particular during Frasnian–Famennian and Late Devonian times. Extensional tectonics and related gravitational faults, local uplift mechanisms and intense volcanic activity could also explain the lack of palynological data and sedimentary hiatus. In this research, the importance of the late Strunian times in the Iberian Pyrite Belt (Miospore Biozone LN of the Neves Formation) is highlighted, confirming the contemporaneity of felsic volcanism, hydrothermalism, sulphide mineralization precipitation and black shale anoxic sedimentation.info:eu-repo/semantics/acceptedVersio

    Macroevolution and adaptive processes of the Leptocoeliidae family (Brachiopoda) throughout the Silurian and Devonian. e2321742

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    The Leptocoeliidae family (genera Anabaia, Australocoelia, Eocoelia, Leptocoelia, Leptocoelina and Pacificocoelia) has an important place in the global paleobiogeography, during the Silurian and Devonian. During these periods, global climate changes impacted a lot of invertebrate faunas in the epicontinental seas of Gondwana. In the Silurian, the genus Eocoelia reached a cosmopolitan behavior, while Leptocoeliaemerged by adaptive sympatric processes and Anabaia became extinct. After that, during the Devonian, the genus Australocoelia emerged and reached cosmopolitan levels while Leptocoelina and Pacificocoelia emerged by sympatries in the equatorial regions. Australocoelia, during the Devonian, occupied the same ecological niches that were previously occupied by Anabaia in the Silurian. It can be said that the same occurred with Pacificocoelia and Eocoloelia in the seas of Laurentia, configuring a process of succession of fauna

    New constraints for the western Paleotethys paleogeography-paleotectonics derived from detrital signatures: Malaguide Carboniferous Culm Cycle (Betic Cordillera, S Spain)

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    Carboniferous sandstone within the Paleo-Mesomediterranean Domain (Malaguide Subdomain), in southern Spain, represents a key detrital mode within the sedimentary budget of convergent plate boundaries during the Variscan s.s. to Paleotethysian orogenic time span (≈ 420–300 Ma). This Carboniferous detritus corresponds with Culm lithostratigraphic depositional unit, and it covers an important gap of information (paleogeographic, paleotectonic, source areas) to the area located between the Iberian-French massifs and the African Paleo-Atlas, in the western Paleotethys. Sandstone composition is quartzolithic and records an important high-to-medium-low grade metamorphic content. The source area was a lithic and transitional recycled orogen with a signature of volcanic and ophiolitic detritus (≈ 330 Ma and/or older). These supplies seem to be derived from a mid-crustal deformed and thrusted Cambrian to lower Carboniferous terrane, involved in the plate convergence (the southern Europe Iberian-French massifs overriding the north African area) of the Variscan s.s. orogenic system, rapidly exhumed and uplifted. Consequently, in the overriding hinterland (southern Europe: Iberian-French massifs), a Pre-middle Carboniferous metamorphic basement should be already structured during middle Carboniferous when thrusting took place, suggesting Proterozoic-Early Carboniferous (most probably, ≈ 420 to 330 Ma) metamorphic highlands. The presence of serpentinite-like detritus (≈ 330 Ma and/or older) seems to indicate a metamorphosed oceanic crust being dismantled at that time, thus, ophiolitic sutures (most probably developed at ≈ 420–330 Ma) zones are tentatively proposed at the northern Gondwana. The occurrence of a synsedimentary volcanic activity (andesitic) should be related to a lost magmatic arc (most probably developed at ≈ 360–330 Ma), reinforcing the idea of a nearby subduction area. Therefore, the thick terrigenous Culm deposits (≈ 330–300 Ma) from the Malaguide Subdomain could be deposited in a complex foreland system basin connected northward with carbonate platforms and with a crystalline highland uplifted domain from the southern Europe Iberian-French massifs and southward with the African Paleo-Atlas Domain. The studied middle-late Carboniferous sandstone petrofacies deeply contributes to paleogeographic reconstructions since blocks fragmentation and spreading, during the Paleotethysian and Alpine orogenies, rearranged the Paleozoic paleogeography now part of the Cenozoic Perimediterranean Chains. After the correlation with the Carboniferous from other western Paleotethys domains, new paleogeographic-paleotectonic constraints are proposed for the transitional area between the Iberian-French massifs and the African Paleo-Atlas Domain.Research Project PID2020-114381GB-I00 to M. Martín-Martín, Spanish Ministry of Education and Science; Research Groups and Projects of the Generalitat Valenciana, Alicante University (CTMA-IGA) are acknowledged. Support from Ministero Italiano dell'Università e della Ricerca Scientifica to S. Criniti, is also acknowledged

    Ichnological analysis of the Messinian-Zanclean (Miocene-Pliocene) transition at Eraclea Minoa (Sicily): Tracemaker response to the Terminal Messinian Flood

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    A detailed ichnological analysis has been conducted, for the first time, of the Arenazzolo and Trubi formations of the Caltanissetta Basin in Sicily. Aim of this analysis is to evaluate paleoenvironmental changes affecting macrobenthic tracemaker communities during the re-flooding of the Mediterranean at the end of the Messinian Salinity Crisis. The uppermost Messinian Arenazzolo Formation is characterized by a scarcity of trace fossils, probably related to high energy depositional conditions, and perhaps no fully normal salinity level yet, resulting in an unfavourable habitat for macrobenthic tracemaker communities. The exclusive presence of small traces (Chondrites) sparsely distributed in several horizons is associated to intermittent phases of lower energy conditions facilitating colonization by opportunistic tracemakers. A significant change in trace fossil assemblages is observed at the transition to the Zanclean Trubi Formation. Here the ichnofossil assemblage consists of?Arenicolites, Chondrites, Halimedides, Palaeophycus, Planolites, Thalassinoides, Trichichnus and Zoophycos, assigned to the Zoophycos ichnofacies, revealing an abundant, diverse, well-developed, multi-tiered, tracemaker community. This change observed at the Messsinian/Zanclean boundary is related to the rapid establishment of normal, full-marine, conditions with well oxygenated bottom- and pore-waters, and food availability in a deep marine environment. Comparison with previous micropaleontological studies supports the magnitude of the paleoenvironmental change affecting both pelagic and benthic environments
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