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    Wyświetlanie 1-4 z 4
    Tytuł:
    Anomalous Upper Devonian mercury enrichments : comparison of Inductively Coupled Plasma – Mass Spectrometry (ICP-MS) and Atomic Absorption Spectrometry (AAS) analytical data
    Autorzy:
    Racki, G.
    Rakociński, M.
    Marynowski, L.
    Powiązania:
    https://bibliotekanauki.pl/articles/2060451.pdf
    Data publikacji:
    2018
    Wydawca:
    Państwowy Instytut Geologiczny – Państwowy Instytut Badawczy
    Tematy:
    Mercury anomalies
    analytical methods
    geochemistry
    Frasnian-Famennian boundary
    Devonian-Carboniferous boundary
    volcanism
    Opis:
    Mercury geochemistry is emerging recently as a hot topic in chemostratigraphical and facies research, owing to the diagnostic character of Hg enrichments as a proxy of volcanic activity (crucial in the context of assumed causal links between volcanic cataclysms and mass extinctions). Thus, as a prerequisite to such far-reaching interpretations, reliable analytical determinations of Hg concentrations are necessary. In conventionally performed analyses in sedimentary geochemistry, Inductively Coupled Plasma – Mass Spectrometry (ICP-MS) is usually applied, as an analytical standard for trace elements, including Hg. However, with a detection limit (DL) of 10 ppb, such measured values have been questioned as a conclusive geochemical indicator of Hg anomalies, and, instead, far more accurate techniques, such as Atomic Absorption Spectrometry (AAS; DL = 0.2 ppb), are requested. As a preliminary test of this view, we present comparative analysis of 91 samples from three sections encompassing the key Frasnian-Famennian and Famennian-Tournaisian boundary intervals in Morocco (Lahmida), Germany (Kahlleite) and Uzbekistan (Novchomok), for which Hg concentrations were determined by both methods in the same samples. Despite some differences, especially at low Hg concentrations, both analytical methods reveal the same 12 extraordinarily enriched samples in excess of 1 ppm (with one exception, the determination error is <20%), as well as similar overall chemostratigraphic patterns characterized by a few prominent Hg spikes, with a top value of 5.8 ppm. The Hg concentrations determined by ICP-MS and AAS are significantly correlated, as high as r = 0.98 (Novchomok), even if the first method reveals a general tendency toward slightly heightened values (by ~15 to 30% for medians). Therefore, ICP-MS results can conclusively be used in mercury chemostratigraphy in order to recognize extraordinary volcanic (or other) signals, at least in the Devonian geological record. False Hg anomalies were not generated by these conventional ICP-MS determinations.
    Źródło:
    Geological Quarterly; 2018, 62, 3; 487--495
    1641-7291
    Pojawia się w:
    Geological Quarterly
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    The Frasnian-Famennian events in a deep-shelf succession, Subpolar Urals: biotic, depositional, and geochemical records
    Autorzy:
    Yudina, A B
    Racki, G.
    Savage, N.M.
    Racka, M.
    Malkowski, K.
    Powiązania:
    https://bibliotekanauki.pl/articles/21692.pdf
    Data publikacji:
    2002
    Wydawca:
    Polska Akademia Nauk. Instytut Paleobiologii PAN
    Tematy:
    Famennian
    biotic record
    Frasnian
    geochemical record
    depositional record
    geochemistry
    Kellwasser crisis
    conodont
    biostratigraphy
    paleontology
    lithostratigraphy
    carbon isotope
    Opis:
    The Frasnian–Famennian (F–F) boundary is well biostratigraphically documented in the Palmatolepis−rich deposits exposed along the Syv’yu River in the lower slopes of the Subpolar Urals. The thin−bedded calcareous−clayey−siliceous deep−slope succession of the Vorota Formation appears to represent continuous Domanic−type deposition throughout the world−wide carbonate crisis time, without evidence for the basal Famennian hiatus or a large−scale sedimentary perturbation within a regressive setting. The northernmost Laurussian sequence exhibits many well known signatures throughout the broad F–F timespan: the appearance of organicand clay−rich deposits, icriodontid and radiolarian blooms, and a correlative shift of several geochemical proxies towards hypoxic and high−productivity regimes, perfectly recorded by positive 13Ccarb excursions of +3.5‰. Integrative biotic, microfacies and geochemical data substantiate a longer−term oceanographic destabilization, attributable to multiple Earth−bound triggering factors in (episodically enhanced?) greenhouse climate and punctuated eustatic sea−level highstands, superimposed on the elevated deposition of organic carbon−rich sediments during the Upper Kellwasser Event. Unsteady eutrophicated, and oxygen−depleted ecosystems during the F–F biotic crisis interval could be assumed, especially when intensified by various spasmodic tectono−volcanic phenomena in the incipiently closing Ural Ocean.
    Źródło:
    Acta Palaeontologica Polonica; 2002, 47, 2
    0567-7920
    Pojawia się w:
    Acta Palaeontologica Polonica
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    The weathering-modified iridium record of a new Cretaceous–Palaeogene site at Lechowka near Chelm, SE Poland, and its palaeobiologic implications
    Autorzy:
    Racki, G.
    Michalski, M.
    Koeberl, C.
    Harasimiuk, M.
    Powiązania:
    https://bibliotekanauki.pl/articles/20009.pdf
    Data publikacji:
    2011
    Wydawca:
    Polska Akademia Nauk. Instytut Paleobiologii PAN
    Tematy:
    Cretaceous
    geochemical anomaly
    Lechowka n.Chelm
    Paleogene
    Polska
    anomaly
    biostratigraphy
    extinction
    geochemistry
    geological setting
    iridium
    lithology
    paleobiology
    paleontology
    weathering-modified iridium
    Opis:
    In the light of integrated biostratigraphic and geochemical data, a complete shallow−marine succession across the Cretaceous–Palaeogene (K–Pg) boundary, with the critical boundary clay coupled with a burrowed siliceous chalk (“opoka” in Polish geological literature), possibly equivalent of the basal Danian Cerithium Limestone in Denmark, has been discovered at Lechówka near Chełm, SE Poland. An extraterrestrial signature marking the K–Pg boundary is confirmed by anomalously high amounts of iridium (up to 9.8 ppb) and other siderophile elements (especially Au and Ni), as well as by an elevated Ir/Au ratio consistent with a chondrite meteoritic composition. The major positive iridium spike surprisingly occurs in Maastrichtian marls, 10 cm below the boundary clay interval, which can be explained by diagenetic mobilisation and re−concentration of the impact−derived components. Thus, intensively infiltrating, humic acid−rich ground waters during the long−lasting Palaeogene weathering in tropical humid regimes were probably responsible not only for the large−scale decalcification of the Lechówka section, but also for both downward displaced position of the iridium enrichment, a dispersed profile of this anomaly and its significantly lessened value, but still approaching an increase by a factor of 100. This modified record of the K–Pg boundary event points to a careful reconsideration of the iridium anomaly as a trustworthy marker for studying the extinction patterns across the K–Pg boundary, as supported by the recent data from New Jersey, USA.
    Źródło:
    Acta Palaeontologica Polonica; 2011, 56, 1
    0567-7920
    Pojawia się w:
    Acta Palaeontologica Polonica
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Faunal dynamics across the Silurian-Devonian positive isotope excursions (delta13C, delta18O) in Podolia, Ukraine: Comparative analysis of the Ireviken and Klonk events
    Autorzy:
    Racki, G.
    Balinski, A.
    Wrona, R.
    Malkowski, K.
    Drygant, D.
    Szaniawski, H.
    Powiązania:
    https://bibliotekanauki.pl/articles/20924.pdf
    Data publikacji:
    2012
    Wydawca:
    Polska Akademia Nauk. Instytut Paleobiologii PAN
    Tematy:
    fauna dynamics
    Silurian
    Devonian
    isotope excursion
    Podolia
    Ukraine
    comparative analysis
    Ireviken event
    Klonk event
    Brachiopoda
    Conodonta
    Chitinozoa
    carbon isotope
    oxygen isotope
    geochemistry
    Opis:
    Two global isotopic events, the early Sheinwoodian (early Wenlock) and that at the Silurian–Devonian transition, have been comprehensively studied in representative carbonate successions at Kytayhorod and Dnistrove, respectively, in Podolia, Ukraine, to compare geochemistry and biotic changes related correspondingly to the Ireviken and Klonk events. These two large−scale isotope excursions reveal different regional ecosystem tendencies. The well−defined increasing trend across the Llandovery–Wenlock boundary in siliciclastic input, redox states and, supposedly, bioproductivity, was without strict correlative relations to the major ¹³C enrichment event. The environmental and biotic evolution was forced by eustatic sea−level fluctuations and two−step climate change toward a glaciation episode, but strongly modified by regional epeirogeny movements due to location near the mobile Teisseyre−Törnquist Fault Zone. Thus, the global early Sheinwoodian biogeochemical perturbation was of minor depositional significance in this epeiric sea, as in many other Laurussian domains. Conversely, the Podolian sedimentary record of the Klonk Event exhibits temporal links to the abrupt δ¹³C anomaly, overprinted by a tectonically driven deepening pulse in the crucial S–D boundary interval. This carbon cycling turnover was reflected in the regional carbonate crisis and cooling episodes, paired with a tendency towards eutrophication and recurrent oxygen deficiency, but also with major storms and possible upwelling. Faunal responses in both Podolian sections follow some characters of the Silurian pattern worldwide, as manifested by conodont changeover prior to the major early Sheinwoodian isotopic/climatic anomaly. This contrasts with the relative brachiopod and chitinozoan resistances in the course of the Ireviken Event. Also, during the Klonk Event, a moderate faunal turnover, both in benthic and pelagic groups, occurred only near the very beginning of the prolonged ¹³C−enriched timespan across the system boundary, possibly due to progressive dysoxia and temperature drop. The characters point to a peculiarity of the Klonk Event by comparison with the Silurian global events, and some similarity already to the succeeding Devonian transgressive/anoxic episodes.
    Źródło:
    Acta Palaeontologica Polonica; 2012, 57, 4
    0567-7920
    Pojawia się w:
    Acta Palaeontologica Polonica
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
      Wyświetlanie 1-4 z 4

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