Articoli di riviste: "Euxinie"

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Grice, K., R. E. Summons, E. Grosjean, R. J. Twitchett, W. Dunning, S. X. Wang e M. E. Bottcher. "DEPOSITIONAL CONDITIONS OF THE NORTHERN ONSHORE PERTH BASIN (BASAL TRIASSIC)". APPEA Journal 45, n. 1 (2005): 262. http://dx.doi.org/10.1071/aj04023.

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An oil-source rock correlation has been established for the northern onshore Perth Basin (Western Australia) based on unusual aromatic and polar biomarkers attributed ultimately to a green sulphur bacterial source. Several of these biomarkers have been identified throughout the entire Sapropelic Interval of a proven petroleum source rock intersected within a recently discovered marine Permian- Triassic Perth Basin borehole (Hovea–3) and several Perth Basin crude oils. Today, green sulphur bacteria live in the anaerobic zones of stratified lakes or in marine environments with restricted water circulation, where the upper sulphide limit coincides with the lower limit of oxygen. The presence of photosynthetic pigments and carotenoids of green sulphur bacteria, or their diagenetic alteration products in sediments provide unequivocal evidence for photic zone euxinic conditions in the paleowater column. Multiple lines of evidence for photic zone euxinia and euxinic depositional conditions for the Hovea–3 source rock have been obtained from biomarker analyses. Photic zone euxinia is usually associated with the widespread deposition of organic-matter-rich sediments that constitute important source rocks for petroleum deposits that are being exploited today. With the exception of the Perth Basin, such organic-matter-rich sediments are virtually absent from Upper Permian and Lower Triassic sediments globally. Several lines of evidence indicate localised surface ocean productivity may have played a key role in the deposition of a petroleum source rock at this location, although photic zone euxinia was globally more widespread during the Permian-Triassic Superanoxic Event.

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WIGNALL, PAUL B., DAVID P. G. BOND, YADONG SUN, STEPHEN E. GRASBY, BENOIT BEAUCHAMP, MICHAEL M. JOACHIMSKI e DIERK P. G. BLOMEIER. "Ultra-shallow-marine anoxia in an Early Triassic shallow-marine clastic ramp (Spitsbergen) and the suppression of benthic radiation". Geological Magazine 153, n. 2 (1 ottobre 2015): 316–31. http://dx.doi.org/10.1017/s0016756815000588.

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AbstractLower Triassic marine strata in Spitsbergen accumulated on a mid-to-high latitude ramp in which high-energy foreshore and shoreface facies passed offshore into sheet sandstones of probable hyperpycnite origin. More distal facies include siltstones, shales and dolomitic limestones. Carbon isotope chemostratigraphy comparison allows improved age dating of the Boreal sections and shows a significant hiatus in the upper Spathian. Two major deepening events, in earliest Griesbachian and late Smithian time, are separated by shallowing-upwards trends that culminated in the Dienerian and Spathian substages. The redox record, revealed by changes in bioturbation, palaeoecology, pyrite framboid content and trace metal concentrations, shows anoxic phases alternating with intervals of better ventilation. Only Dienerian–early Smithian time witnessed persistent oxygenation that was sufficient to support a diverse benthic community. The most intensely anoxic, usually euxinic, conditions are best developed in offshore settings, but at times euxinia also developed in upper offshore settings where it is even recorded in hyperpycnite and storm-origin sandstone beds: an extraordinary facet of Spitsbergen's record. The euxinic phases do not track relative water depth changes. For example, the continuous shallowing upwards from the Griesbachian to lower Dienerian was witness to several euxinic phases separated by intervals of more oxic, bioturbated sediments. It is likely that the euxinia was controlled by climatic oscillations rather than intra-basinal factors. It remains to be seen if all the anoxic phases found in Spitsbergen are seen elsewhere, although the wide spread of anoxic facies in the Smithian/Spathian boundary interval is clearly a global event.

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Hutchings, Alec M., e Alexandra V. Turchyn. "A quantification of the effect of diagenesis on the paleoredox record in mid-Proterozoic sedimentary rocks". Geology 49, n. 9 (24 giugno 2021): 1143–47. http://dx.doi.org/10.1130/g48774.1.

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Abstract Iron speciation in ancient sedimentary rocks is widely used to reconstruct oceanic redox conditions over geological time, specifically to assess the extent of oxic, euxinic (anoxic containing sulfide), and ferruginous (anoxic containing iron) conditions. We explore how post-depositional sedimentary processes can skew particular geochemical signals in the rock record. One such process is when aqueous sulfide—including that produced in the sediment column—reacts with sedimentary iron, converting non-sulfide, highly reactive iron minerals to iron-sulfide minerals; this can lead to increased preservation of iron as pyrite and an overestimation of seafloor euxinia. We show that sedimentary rocks with higher (>5 wt%) total iron content are more buffered to this effect and thus are a more reliable indicator of true water-column euxinia. When considering this effect in the geological past, we estimate that true euxinia in the mid-Proterozoic may have been as much as fourfold less than previously thought—more in line with other recent paleoredox proxies not based on iron minerals. Marine iron and sulfate concentrations were more equivalent in Proterozoic–Neoproterozoic oceans, suggesting this time period was particularly susceptible to this post-depositional alteration, explaining the extent of euxinia suggested for this geological interval.

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Mitchell, Ross N., Uwe Kirscher, Marcus Kunzmann, Yebo Liu e Grant M. Cox. "Gulf of Nuna: Astrochronologic correlation of a Mesoproterozoic oceanic euxinic event". Geology 49, n. 1 (25 agosto 2020): 25–29. http://dx.doi.org/10.1130/g47587.1.

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Abstract The ca. 1.4 Ga Velkerri and Xiamaling Formations, in Australia and the north China craton, respectively, are both carbonaceous shale deposits that record a prominent euxinic interval and were intruded by ca. 1.3 Ga dolerite sills. These similarities raise the possibility that these two units correlate, which would suggest the occurrence of widespread euxinia, organic carbon burial, and source rock deposition. Paleomagnetic data are consistent with Australia and the north China craton being neighbors in the supercontinent Nuna and thus permit deposition in a single large basin, and the putative stratigraphic correlation. However, lack of geochronological data has precluded definitive testing. The Xiamaling Formation has been shown to exhibit depositional control by orbital cycles. Here, we tested the putative correlation with the Velkerri Formation by cyclostratigraphic analysis. The Velkerri Formation exhibits sedimentological cycles that can be interpreted to represent the entire hierarchy of orbital cycles, according to a sedimentation rate that is consistent with Re-Os ages. Comparison of the inferred durations of the euxinic intervals preserved in both the Xiamaling and Velkerri Formations reveals a nearly identical ∼10-m.y.-long oceanic euxinic event. This permits the interpretation that the two hydrocarbon-rich units were deposited and matured in the same basin of Nuna, similar to the Gulf of Mexico during the breakup of Pangea.

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Shopov, Vladimir, e Maria Stancheva. "Correlation of the zonal schemes in the Quaternary sediments of the Bulgarian Black Sea shelf according to molluscs and ostracods". Geologica Balcanica 24, n. 3 (30 giugno 1994): 77–82. http://dx.doi.org/10.52321/geolbalc.24.3.77.

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The Candona Ostracod Zone corresponds the Upper Chaudinian where the Dreissena rostriformis tschaudae Molluscan Zone is indicated. The Didacna crassa pontocaspia – Dreissena euxinica and Didacna crassa pontocaspia – Alba ovata Molluscan Concurrent-range-zones corresponding to the Cryptocyprideis bogatschovi Ostracod Zone are interpreted respectively in the Middle Pleistocene, Old Euxinian and Uzunlarian Stages. The section of the Upper Pleistocenian (Karangatian) molluscan zones has not been presented for analysis of the Ostracod sequences. The sequence of the molluscan and ostracod zones in the inner shelf has been broken by a barren zone which corresponds to the continental sediments, deposited in the Early New Euxinian. The Loxoconcha lepida Ostracod Zone corresponds to the following in superposition Upper Euxinian Dreissena polymorpha – Dreissena rostriformis distincta Molluscan Concurrent-rage-zone. The Hydrobia ventrosa – Monodacna caspia Molluscan Zone together with the following in superposition Mytilus galloprovincialis Zone comprise the sediments of the Old Chernomorian. The intervals occupied by the Cyprideis torosa Ostracod Zone correspond to these molluscan zones. The Falunia rubra – Loxoncha granulata Osatracod Zone comprises the area occupied by the Spisula subtruncata triangula Molluscan zone including also the upper parts of the Mytilus galloprovincialis Molluscan Zone.

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JIN, CHENGSHENG, CHAO LI, THOMAS J. ALGEO, MENG CHENG, LIDAN LEI, ZIHU ZHANG e WEI SHI. "Evidence for marine redox control on spatial colonization of early animals during Cambrian Age 3 (c. 521–514 Ma) in South China". Geological Magazine 154, n. 6 (29 dicembre 2016): 1360–70. http://dx.doi.org/10.1017/s0016756816001138.

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AbstractThe early Cambrian Period was a key interval in Earth history with regard to changes in both ocean chemistry and animal evolution. Although increasing ocean ventilation has been widely assumed to have played a key role in the rapid appearance, diversification and spatial colonization of early animals, this relationship is in fact not firmly established. Here, we report a high-resolution Fe-C-S-Al-Ti geochemical study of the lower Cambrian Wangjiaping section from an outer-shelf setting of the Yangtze Sea of South China. Iron speciation data document a redox transition from dominantly euxinic to ferruginous conditions during Cambrian Age 3 (c. 521–514 Ma). Interpretation of coexisting pyrite sulphur isotope (δ34Spy) records from Wangjiaping reveals relatively high marine sulphate availability at Wangjiaping. Furthermore, Wangjiaping section shows lower δ34Spy (‒2.1±5.3‰) and lower TOC (2.4±1.1%) values but higher positive correlation (R2 = 0.66, p < 0.01) between TOC and Fepy/FeHR relative to deeper sections reported previously, suggesting that euxinia developed at Wangjiaping in response to increasing marine productivity and organic matter-sinking fluxes. Our reconstructed redox conditions and fossils at Wangjiaping in comparison with previously well-studied strata in the inner-shelf Xiaotan and Shatan sections suggest that planktonic and benthic planktonic trilobites with bioturbation appeared in the oxic water columns, whereas only planktonic trilobites without bioturbation occurred within the anoxic (even euxinic) water columns during Cambrian Age 3. This finding indicates that spatial heterogeneity of redox conditions in the shelves had an important effect on early animal distribution in the Yangtze Block.

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Wendt, Anna K., Mike A. Arthur, Rudy Slingerland, Daniel Kohl, Reed Bracht e Terry Engelder. "Geochemistry and depositional history of the Union Springs Member, Marcellus Formation in central Pennsylvania". Interpretation 3, n. 3 (1 agosto 2015): SV17—SV33. http://dx.doi.org/10.1190/int-2014-0228.1.

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Debate continues over paleoenvironmental conditions that prevail during deposition of organic-carbon (C)-rich marine source rocks in foreland basins and epicontinental seas. The focus of disagreement centers largely on paleowater depth and the prevalence of anoxia/euxinia. The issues of paleodepth and water column conditions are important for prediction of lateral variations in source quality within a basin because the viability of a hydrocarbon play depends on a thorough understanding of the distribution of source rock quality and depositional environments. We used inorganic geochemical data from the Middle Devonian Marcellus Shale in the Appalachian Basin to illustrate interpretive strategies that provided constraints on conditions during deposition. Source evaluation typically relies on the analysis and interpretation of organic geochemical indicators, potentially also providing evidence of the degree of thermal maturity and conditions of the preservation of the organic matter. The Marcellus Formation is thermally mature, making the evaluation of the organic-carbon fraction for geologic interpretation inadequate. Because most labile organic matter has largely been destroyed in the Marcellus Formation, analysis of inorganic elements may be used as an alternative interpretative technique. Several inorganic elements have been correlated to varying depositional settings, allowing for their use as proxies for understanding the paleodepositional environments of formations. A high-resolution geochemical data set has been constructed for the Union Springs Member along a transect of cores from proximal to distal in the Appalachian Basin in central Pennsylvania using major, minor, and trace elemental data. Our results suggested that during deposition, the sediment-water interface, and a portion of the water column, was anoxic to euxinic. As deposition continued, euxinia was periodically interrupted by dysoxia and even oxic conditions, and a greater influx of clastic material occurred. Such variations were likely related to fluctuations in water depth and progradation of deltaic complexes from the eastern margin of the Appalachian Basin.

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МЕРЕНКОВА, С. И., Г. А. КАЛМЫКОВ, А. Ю. ПУЗИК, Р. Р. ГАБДУЛЛИН, И. В. БАДЬЯНОВА, М. А. ВОЛКОВА, К. П. КАЗЫМОВ e М. М. ШИРОЯН. "GEOCHEMICAL FACETS OF THE INIKAN FORMATION AS INDICATORS OF STRATIFICATION AND HYDROCHEMISTRY OF THE CAMBRIAN PALEOBASIN". Геология и геофизика 65, n. 2 (29 febbraio 2024): 265–87. http://dx.doi.org/10.15372/gig2023140.

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Выполнены геохимические исследования пород иниканской свиты из береговых обнажений р. Юдома. Для всех проанализированных литологических разностей характерно значительное обогащение B, Ni, Mo, Ag, Sb, U, т. е. редокс-чувствительными элементами, а также элементами, способными к биоосаждению. Источником элементов являлась морская вода, выщелачивающая их из эолового материала. Установлено, что отложения накапливались в аноксических условиях с периодами возникновения как эвксинных (по-видимому, в придонном слое), так и субоксических условий. Развитие таких аноксических и эвксинных условий вызвано устойчивой стратификацией океана, существовавшей в раннесреднекембрийское время в данной части бассейна. Помимо этого, длительное накопление богатых ОВ осадков в условиях аноксии, периодической эвксинии и устойчивой стратификации указывает на возможное наличие в данной части бассейна геоморфологически обособленной впадины. CIA—Кcorr варьируется от 68 до 95. Невысокие значения индекса могут быть связаны со значительной высотой в области денудации. Geochemical studies of Inikan Formation rocks from the coastal outcrops of the Yudoma River were carried out. All analyzed lithological varieties are characterized by significant enrichment in B, Ni, Mo, Ag, Sb, U (redox-sensitive trace metals and elements associated with biodeposition). The source of the elements was sea water that leached them from the eolian material. It was found that the deposits accumulated in anoxic environments with periods of both euxinic (probably, in the bottom water mass) and suboxic conditions. Such anoxic and euxinic conditions developed due to the stable stratification of the ocean that existed in the early–middle Cambrian in this part of the basin. In addition, the long-term accumulation of organic-rich sediment under conditions of anoxia, periodic euxinia, and stable stratification indicates the presence of a geomorphologically isolated depression in this part of the basin. CIA-Kcorr ranges from 68 to 95. The low values of the CIA may be related to the height of the relief in the sedimentary source area.

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Rood, Tim. "Black Sea variations: Arrian's Periplus". Cambridge Classical Journal 57 (dicembre 2011): 137–63. http://dx.doi.org/10.1017/s1750270500001305.

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Comme tous les Grecs, il n'a pas pu ne pas embellir ce qu'il a touché. On retrouve en lui cet éminent esprit d'une race privilégiée qui dans les sujets les plus arides fait pénétrer l'art et même la poésie. … même en quittant … le Périple d'Arrien, nous pouvons dire comme Fuséli en quittant les marbres du Parthénon: ‘Ah! les Grecs, les Grecs, c'étaient des dieux.’ H. Chotard, Le Périple de la Mer Noire par ArrienArrian's Periplus maris Euxini (Circumnavigation of the Euxine) is an ambitious and unusual work. Written in the 130s AD in the form of a letter to the emperor Hadrian, who had himself visited the Black Sea a few years earlier, it was a literary complement to a report Arrian made in Latin, as governor of Cappadocia, on Rome's military position in the Black Sea. It is also unusual in its form: unlike most periploi, which are marked by continuity of movement and by a highly repetitive style, it is discontinuous both in its spatial movement and in its narrative style.

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Grice, Kliti, Alex I. Holman, Chloe Plet e Madison Tripp. "Fossilised Biomolecules and Biomarkers in Carbonate Concretions from Konservat-Lagerstätten". Minerals 9, n. 3 (6 marzo 2019): 158. http://dx.doi.org/10.3390/min9030158.

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In the vast majority of fossils, the organic matter is degraded with only an impression or cast of the organism remaining. In rare cases, ideal burial conditions result in a rapid fossilisation with an exceptional preservation of soft tissues and occasionally organic matter. Such deposits are known as Lagerstätten and have been found throughout the geological record. Exceptional preservation is often associated with finely crystalline quartz (e.g., cherts), fine sediments (e.g., muds) or volcanic ashes. Other mechanisms include burial in anoxic/euxinic sediments and in the absence of turbidity or scavenging. Exceptional preservation can also occur when an organism is encapsulated in carbonate cement, forming a concretion. This mechanism involves complex microbial processes, resulting in a supersaturation in carbonate, with microbial sulfate reduction and methane cycling the most commonly suggested processes. In addition, conditions of photic zone euxinia are often found to occur during concretion formation in marine environments. Concretions are ideal for the study of ancient and long-extinct organisms, through both imaging techniques and biomolecular approaches. These studies have provided valuable insights into the evolution of organisms and their environments through the Phanerozoic and have contributed to increasing interest in fields including chemotaxonomy, palaeobiology, palaeoecology and palaeophysiology.

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Gomes, Maya L., e David T. Johnston. "Oxygen and sulfur isotopes in sulfate in modern euxinic systems with implications for evaluating the extent of euxinia in ancient oceans". Geochimica et Cosmochimica Acta 205 (maggio 2017): 331–59. http://dx.doi.org/10.1016/j.gca.2017.02.020.

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Raiswell, R., e R. A. Berner. "Pyrite formation in euxinic and semi-euxinic sediments". American Journal of Science 285, n. 8 (1 ottobre 1985): 710–24. http://dx.doi.org/10.2475/ajs.285.8.710.

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Zheng, Wang, Geoffrey J. Gilleaudeau, Linda C. Kah e Ariel D. Anbar. "Mercury isotope signatures record photic zone euxinia in the Mesoproterozoic ocean". Proceedings of the National Academy of Sciences 115, n. 42 (1 ottobre 2018): 10594–99. http://dx.doi.org/10.1073/pnas.1721733115.

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Photic zone euxinia (PZE) is a condition where anoxic, H2S-rich waters occur in the photic zone (PZ). PZE has been invoked as an impediment to the evolution of complex life on early Earth and as a kill mechanism for Phanerozoic mass extinctions. Here, we investigate the potential application of mercury (Hg) stable isotopes in marine sedimentary rocks as a proxy for PZE by measuring Hg isotope compositions in late Mesoproterozoic (∼1.1 Ga) shales that have independent evidence of PZE during discrete intervals. Strikingly, a significantly negative shift of Hg mass-independent isotope fractionation (MIF) was observed during euxinic intervals, suggesting changes in Hg sources or transformations in oceans coincident with the development of PZE. We propose that the negative shift of Hg MIF was most likely caused by (i) photoreduction of Hg(II) complexed by reduced sulfur ligands in a sulfide-rich PZ, and (ii) enhanced sequestration of atmospheric Hg(0) to the sediments by thiols and sulfide that were enriched in the surface ocean as a result of PZE. This study thus demonstrates that Hg isotope compositions in ancient marine sedimentary rocks can be a promising proxy for PZE and therefore may provide valuable insights into changes in ocean chemistry and its impact on the evolution of life.

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Cheng, Keyi, Maya Elrick e Stephen J. Romaniello. "Early Mississippian ocean anoxia triggered organic carbon burial and late Paleozoic cooling: Evidence from uranium isotopes recorded in marine limestone". Geology 48, n. 4 (31 gennaio 2020): 363–67. http://dx.doi.org/10.1130/g46950.1.

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Abstract The Early Mississippian (Tournaisian) positive δ13C excursion (mid-Tournaisian carbon isotope excursion [TICE]) was one of the largest in the Phanerozoic, and the organic carbon (OC) burial associated with its development is hypothesized to have enhanced late Paleozoic cooling and glaciation. We tested the hypothesis that expanded ocean anoxia drove widespread OC burial using uranium isotopes (δ238U) of Lower Mississippian marine limestone as a global seawater redox proxy. The δ238U trends record a large Tournaisian negative excursion lasting ∼1 m.y. The lack of covariation between δ238U values and facies changes and proxies for local depositional and diagenetic influences suggests that the δ238U trends represent a global seawater redox signal. The negative δ238U excursion is coincident with the first TICE positive excursion, supporting the hypothesis that an expanded ocean anoxic event controlled OC burial. These results provide the first evidence from a global seawater redox proxy that an ocean anoxic event drove Tournaisian OC burial and controlled Early Mississippian cooling and glaciation. Uranium and carbon modeling results indicate that (1) there was an ∼6× increase in euxinic seafloor area, (2) OC burial was initially driven by expanded euxinia followed by expanded anoxic/suboxic conditions, and (3) OC burial mass was ∼4–17× larger than that sequestered during other major ocean anoxic events.

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Archibald, Zofia Halina. "EUXINE SITES". Classical Review 52, n. 1 (marzo 2002): 142–44. http://dx.doi.org/10.1093/cr/52.1.142.

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WOTTE, THOMAS, e HARALD STRAUSS. "Questioning a widespread euxinia for the Furongian (Late Cambrian) SPICE event: indications from δ13C, δ18O, δ34S and biostratigraphic constraints". Geological Magazine 152, n. 6 (20 maggio 2015): 1085–103. http://dx.doi.org/10.1017/s0016756815000187.

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AbstractResults from a high-resolution study of δ13Ccarb, δ18Ocarb, δ34SCAS, δ34SCRSand elemental concentrations (Ca, Fe, Mg, Mn and Sr) in the Furongian Kyrshabakty section, southern Kazakhstan, are reported here. The investigated interval covers the Drumian to Jiangshanian stages of the Cambrian Period, respectively the regionalPtychagnostus atavustoIvshinagnostus ivshini-Irvingella majortrilobite zones. δ13Ccarbdata include the Steptoean positive carbon isotope excursion (SPICE) with a local peak value of +5‰. The onset of SPICE corresponds to theKormagnostus simplex–Glyptagnostus stolidotuszones and pre-dates the base of the Paibian Stage/Furongian Series. δ34SCASdata already increase during theLejopyge armatabiozone culminating in three positive excursions prior and after the SPICE maximum. Differences in onset, peak values and shape of the δ13Ccarband/or δ34SCASexcursions at Kyrshabakty, but also in almost all sections characterized by the SPICE, are pointing towards Furongian seawater that was low in sulphate concentration and heterogeneous in its carbonate carbon and sulphate sulphur isotopic composition. The occurrence of benthic faunal elements in almost all SPICE-related sections strongly supports oxygenated conditions at the seafloor, therefore excluding widespread anoxia or euxinia. Regional anoxic conditions are most probable. A positive δ18Ocarbexcursion parallel to the SPICE could probably be explained by a decline in seawater pH associated with a sea-level rise. Again, no euxinic conditions would be mandatory for explaining the SPICE event.

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Seitaj, Dorina, Regina Schauer, Fatimah Sulu-Gambari, Silvia Hidalgo-Martinez, Sairah Y. Malkin, Laurine D. W. Burdorf, Caroline P. Slomp e Filip J. R. Meysman. "Cable bacteria generate a firewall against euxinia in seasonally hypoxic basins". Proceedings of the National Academy of Sciences 112, n. 43 (7 ottobre 2015): 13278–83. http://dx.doi.org/10.1073/pnas.1510152112.

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Seasonal oxygen depletion (hypoxia) in coastal bottom waters can lead to the release and persistence of free sulfide (euxinia), which is highly detrimental to marine life. Although coastal hypoxia is relatively common, reports of euxinia are less frequent, which suggests that certain environmental controls can delay the onset of euxinia. However, these controls and their prevalence are poorly understood. Here we present field observations from a seasonally hypoxic marine basin (Grevelingen, The Netherlands), which suggest that the activity of cable bacteria, a recently discovered group of sulfur-oxidizing microorganisms inducing long-distance electron transport, can delay the onset of euxinia in coastal waters. Our results reveal a remarkable seasonal succession of sulfur cycling pathways, which was observed over multiple years. Cable bacteria dominate the sediment geochemistry in winter, whereas, after the summer hypoxia,Beggiatoaceaemats colonize the sediment. The specific electrogenic metabolism of cable bacteria generates a large buffer of sedimentary iron oxides before the onset of summer hypoxia, which captures free sulfide in the surface sediment, thus likely preventing the development of bottom water euxinia. As cable bacteria are present in many seasonally hypoxic systems, this euxinia-preventing firewall mechanism could be widely active, and may explain why euxinia is relatively infrequently observed in the coastal ocean.

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Sokolovskaya, Yu G., E. D. Krasnova, D. A. Voronov, D. N. Matorin, A. A. Zhiltsova e S. V. Patsaeva. "Optical Proxies of Euxinia: Spectroscopic Studies of CDOM, Chlorophyll, and Bacteriochlorophylls in the Lagoon on Zeleny Cape (the White Sea)". Photonics 10, n. 6 (9 giugno 2023): 672. http://dx.doi.org/10.3390/photonics10060672.

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Along the shoreline of the White Sea, due to the post-glacial uplift of the coast, some water bodies with stable stratification have been formed. They have been classified as meromictic as they are at different stages of isolation from the Sea. As separation progresses, significant changes occur in the water column, including the composition of chromophoric dissolved organic matter (CDOM) and the structure of the aquatic microbial community. In this work, we searched for optical proxies of euxinia (anoxic conditions with accumulated hydrogen sulfide) in the water column of the meromictic lagoon on Zeleny Cape. The lagoon is separated from the White Sea basin by a shallow threshold that completely isolates the lagoon during low tide, but marine water enters the lagoon during high tide. The ecosystem in the lagoon is characterized by the marine salinity of water and a high organic matter content in the bottom water and sediments. In this study, spectral methods were used to obtain the depth distribution of CDOM, chlorophyll, and bacteriochlorophyll in the lagoon with strong water stratification and euxinic conditions in the bottom water. The measured optical CDOM characteristics were compared with hydrochemical data (water salinity, Eh, pH, dissolved oxygen), phytoplankton (oxygenic phototrophs), and green sulfur bacteria (anoxygenic phototrophs) distribution along the water column. The spectroscopic methods showed to have the advantages of not requiring water sample pre-treatment and allowing rapid sensing of CDOM and photosynthetic pigments at each horizon.

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Archibald, Zofia Halina. "THE EUXINE SEA". Classical Review 50, n. 1 (aprile 2000): 237–39. http://dx.doi.org/10.1093/cr/50.1.237.

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Kunert, Alexandra, Johnathan Clarke e Brian Kendall. "Molybdenum Isotope Constraints on the Origin of Vanadium Hyper-Enrichments in Ediacaran–Phanerozoic Marine Mudrocks". Minerals 10, n. 12 (30 novembre 2020): 1075. http://dx.doi.org/10.3390/min10121075.

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Vanadium is an important redox-sensitive trace metal for paleoenvironmental reconstructions. Modern organic-rich sediments persistently contain sediment V enrichments <500 μg/g, but many ancient marine organic-rich mudrocks record enrichments >500 μg/g. Previous studies propose that ancient V enrichments of these magnitudes (“V hyper-enrichments”) were deposited from hyper-sulfidic bottom-waters with higher H2S levels (≥10 mM) than observed in modern euxinic basins. To test the importance of hyper-sulfidic conditions for generating V hyper-enrichments, we compare V concentrations with Mo isotope (δ98Mo) compositions from mudrock samples ranging in age from Ediacaran to Pleistocene. In the modern ocean, sediments deposited from strongly euxinic bottom waters ([H2S]aq > 11 μM) closely record global seawater δ98Mo because conversion of molybdate to tri- and tetra-thiomolybdate is quantitative. By contrast, large Mo isotope fractionations occur during Mo adsorption to Fe-Mn particulates or because of incomplete formation of the most sulfidic thiomolybdates in weakly euxinic settings ([H2S]aq < 11 μM), which both favor removal of lighter-mass Mo isotopes to sediments. We find multiple examples when mudrocks with V hyper-enrichments are associated with a wide range of δ98Mo for a single time interval, including values at or below oceanic input δ98Mo (0.3–0.7‰). This observation suggests significant isotopic offset from reasonable seawater values (typically ≥1.0‰). Thus, we conclude that hyper-sulfidic conditions were not responsible for many V hyper-enrichments in Ediacaran–Phanerozoic mudrocks. Instead, sediment V hyper-enrichments can be explained by high Fe-Mn particulate fluxes to weakly euxinic sediments or by moderately restricted euxinic settings with strongly euxinic ([H2S]aq > 11 μM but not necessarily > 10 mM) or weakly euxinic (with slow clastic sedimentation rates and high organic carbon fluxes) bottom waters where vigorous water exchange provides a continuous V supply from the open ocean.

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21

Porter, Susannah M., e Leigh Anne Riedman. "Systematics of organic-walled microfossils from the ca. 780–740 Ma Chuar Group, Grand Canyon, Arizona". Journal of Paleontology 90, n. 5 (settembre 2016): 815–53. http://dx.doi.org/10.1017/jpa.2016.57.

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AbstractThe ca. 780–740 Ma Chuar Group, Grand Canyon, Arizona, provides an exceptional record of life during the diversification of crown-group eukaryotes, just prior to the first Cryogenian glaciation. We document in detail the assemblage of organic-walled microfossils preserved in fine-grained siliciclastics throughout the unit. In contrast with earlier studies, we primarily used SEM to document fossil morphologies, augmented by transmitted light microscopy, FIB-SEM, and TEM. This resulted in the discovery of new species and the recognition of broad-ranging, intraspecific biological and taphonomic variation in other species. Twenty-two species and five unnamed morphotypes are described, including three new species:Kaibabia gemmulella,Microlepidopalla mira, andVolleyballia dehlerae; two new combinations:Galerosphaera walcottiiandLanulatisphaera laufeldii; and 17 previously described forms. The possible colonial green algaPalaeastrum dyptocranumButterfield in Butterfield, Knoll, and Swett, 1994 and the index fossilCerebrosphaera globosa(Ogurtsova and Sergeev, 1989) Sergeev and Schopf, 2010 (=C. buickiiButterfield, 1994) are described for the first time from Chuar rocks.Lanulatisphaera laufeldii, a locally abundant and globally widespread species characterized by submicrometer filamentous processes that form a reticulate network, may be a useful marker for the time interval just before the appearance of vase-shaped microfossils (VSMs) ca. 740 Ma.Organic-walled microfossil assemblages decline in diversity upsection, coincident with the appearance of VSMs and intermittent euxinia within the basin. Whether this pattern is due to preservational bias related to greater water depth or the higher TOC of upper Chuar rocks or instead reflects biotic turnover related to the spread of euxinic water masses in the basin is unknown.

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22

Sokolova, T. A., e O. Yu Ermolaeva. "Environmental assessment of vegetation of the spit and Tuzla island (Krasnodar Territory, Republic of the Crimea)". Plant Biology and Horticulture: theory, innovation, n. 149 (10 dicembre 2019): 165–76. http://dx.doi.org/10.36305/0201-7997-2019-149-165-176.

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In order to classify the vegetation, as well as its sozological assessment, based on the Brown-Blancke method, geobotanical descriptions of the vegetation of the spit and Tuzla island were carried out, rare species were noted, and a cartographic survey of the territory was carried out. As a result of five-year studies, the classification of vegetation of the spit and Tuzla island was made. 22 associations (2 new - Lactuco tataricae-Elaeagnetum angustifoliae and Gypsophiletum perfoliatae), 8 subassociations (6 new - Lactuco tataricae-Elaeagnetum angustifoliae juncetosum maritimae, L. t.-E. a.) are described. Artemisetosum arenariae, Phragmito-Juncetum maritimi puccinelietisum distantis, Cakilo euxinae-Crambetum artemisetosum arenariae, Cakilo euxinae-Lactucetum tataricae typicum, C. e.-L. t. gypsophiletosum perfoliatae, basal 2 community and 7 out of 13 classes and 14 unions. A geobotanical map of the spit and Tuzla island has been compiled. The high estimates of the environmental significance of observed association: Cakilo euxinae-Lactucetum tataricae, Eryngio maritimi-Cakiletum euxinae, Gypsophiletum perfoliatae and Elaeagnetum angustifoliae-Lactucetum tataricae. The necessary establishment of protected areas for the protection of some plant communities in the vegetation and the islands.

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23

Lenz, C., T. Jilbert, D. J. Conley, M. Wolthers e C. P. Slomp. "Are recent changes in sediment manganese sequestration in the euxinic basins of the Baltic Sea linked to the expansion of hypoxia?" Biogeosciences 12, n. 16 (19 agosto 2015): 4875–94. http://dx.doi.org/10.5194/bg-12-4875-2015.

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Abstract. Expanding hypoxia in the Baltic Sea over the past century has led to the development of anoxic and sulfidic (euxinic) deep basins that are only periodically ventilated by inflows of oxygenated waters from the North Sea. In this study, we investigate the potential consequences of the expanding hypoxia for manganese (Mn) burial in the Baltic Sea using a combination of pore water and sediment analyses of dated sediment cores from eight locations. Diffusive fluxes of dissolved Mn from sediments to overlying waters at oxic, hypoxic and euxinic sites are consistent with an active release of Mn from these areas. Although the present-day fluxes are significant (ranging up to ca. 240 μmol m−2 d−1), comparison to published water column data suggests that the current benthic release of Mn is small when compared to the large pool of Mn already present in the hypoxic and anoxic water column. Our results highlight two modes of Mn carbonate formation in sediments of the deep basins. In the Gotland Deep area, Mn carbonates likely form from Mn oxides that are precipitated from the water column directly following North Sea inflows. In the Landsort Deep, in contrast, Mn carbonate and Mn sulfide layers appear to form independently of inflow events, and are possibly related to the much larger and continuous input of Mn oxides linked to sediment focusing. Whereas Mn-enriched sediments continue to accumulate in the Landsort Deep, this does not hold for the Gotland Deep area. Here, a recent increase in euxinia, as evident from measured bottom water sulfide concentrations and elevated sediment molybdenum (Mo), coincides with a decline in sediment Mn content. Sediment analyses also reveal that recent inflows of oxygenated water (since ca. 1995) are no longer consistently recorded as Mn carbonate layers. Our data suggest that eutrophication has not only led to a recent rise in sulfate reduction rates but also to a decline in reactive Fe input to these basins. We hypothesize that these factors have jointly led to higher sulfide availability near the sediment–water interface after inflow events. As a consequence, the Mn oxides may be reductively dissolved more rapidly than in the past and Mn carbonates may no longer form. Using a simple diagenetic model for Mn dynamics in the surface sediment, we demonstrate that an enhancement of the rate of reduction of Mn oxides is consistent with such a scenario. Our results have important implications for the use of Mn carbonate enrichments as a redox proxy in marine systems.

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24

Lenz, C., T. Jilbert, D. J. Conley, M. Wolthers e C. P. Slomp. "Are recent changes in sediment manganese sequestration in the euxinic basins of the Baltic Sea linked to the expansion of hypoxia?" Biogeosciences Discussions 11, n. 6 (25 giugno 2014): 9889–918. http://dx.doi.org/10.5194/bgd-11-9889-2014.

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Abstract (sommario):

Abstract. Expanding hypoxia in the Baltic Sea over the past century has led to anoxic and sulfidic (euxinic) deep basins that are only periodically ventilated by inflows of oxygenated waters from the North Sea. In this study, we investigate the consequences of the expanding hypoxia for manganese (Mn) burial in the Baltic Sea using a combination of pore water and sediment analyses of well-dated sediment cores from 8 locations. Diffusive fluxes of dissolved Mn from sediments to overlying waters at oxic and hypoxic sites are in line with an active release of Mn from these areas. However, this flux of Mn is only small when compared to the large pool of Mn already present in the hypoxic and anoxic water column. Our results highlight two modes of Mn carbonate formation in sediments of the deep basins. In the Gotland Deep area, Mn carbonates likely form from Mn oxides that are precipitated from the water column directly following North Sea inflows. In the Landsort Deep, in contrast, Mn carbonate and Mn sulfide layers form independent of inflow events, with pore water Mn produced in deeper layers of the sediment acting as a key Mn source. While formation of Mn enrichments in the Landsort Deep continues to the present, this does not hold for the Gotland Deep area. Here, increased euxinia, as evident from measured bottom water sulfide concentrations and elevated sediment molybdenum (Mo), goes hand in hand with a decline in sediment Mn and recent inflows of oxygenated water (since ca. 1995) are no longer consistently recorded as Mn carbonate layers. We postulate that the reduction of Mn oxides by hydrogen sulfide following inflows has become so rapid that Mn2+ is released to the water column before Mn carbonates can form. Our results have important implications for the use of Mn carbonate enrichments as a redox proxy in marine systems.

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25

Helz, George R., e Marvourneen K. Dolor. "What regulates rhenium deposition in euxinic basins?" Chemical Geology 304-305 (aprile 2012): 131–41. http://dx.doi.org/10.1016/j.chemgeo.2012.02.011.

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26

Scott, Clint, e Timothy W. Lyons. "Contrasting molybdenum cycling and isotopic properties in euxinic versus non-euxinic sediments and sedimentary rocks: Refining the paleoproxies". Chemical Geology 324-325 (settembre 2012): 19–27. http://dx.doi.org/10.1016/j.chemgeo.2012.05.012.

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27

Bura-Nakić, Elvira, Morten B. Andersen, Corey Archer, Gregory F. de Souza, Marija Marguš e Derek Vance. "Coupled Mo-U abundances and isotopes in a small marine euxinic basin: Constraints on processes in euxinic basins". Geochimica et Cosmochimica Acta 222 (febbraio 2018): 212–29. http://dx.doi.org/10.1016/j.gca.2017.10.023.

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28

Olteanu, Radu. "The “Cimpia Moment” (late Miocene, Romania) and the Pannonian-Pontian boundary, defined by ostracods". Journal of Micropalaeontology 8, n. 2 (1 dicembre 1989): 239–47. http://dx.doi.org/10.1144/jm.8.2.239.

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Abstract. The boundary between the Pannonian and Pontian (late Miocene) of the Pannonian area is recognised on the basis of ostracod faunas. A comparison is made between the faunas of the Pannonian Basin and the Dacic-Euxine Basin. A transitional fauna with Pannonian elements, but a stronger Pontian component, is described from Cimpia (Romania). This indicates a more gradual transition between the two stages in the Pannonian Basin than in the Dacic-Euxine Basin, where there is a sharp faunal break indicating a period of non-deposition or erosion.

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29

Filatova, N. I. "Jurassic anoxic event in the Pacific (on the West Kamchatka-Asia data)". Доклады Академии наук 487, n. 5 (2 settembre 2019): 543–46. http://dx.doi.org/10.31857/s0869-56524875543-546.

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The correlation of allochthonous lithotectonic complexes of the Pacific allows to establish Early Jurassic (Sinemurian-Toarcian) anoxic event (J1-OAE) for time in the Asia-West Kamchatka region. This event is characterized by organic-riched black cherts and shales bearing pyrite that accumulated in the euxinic oceanic deep water basins of the Pacific. Later anoxic regime gradually weakened that was reflected in dominating of Midle-Upper Jurassic red gematite jaspers. J1-OAE in the Pacific was synchronous to global warming induced by planetary magmatic activity. Volcanic gases and hydroterms stimulated euxinic conditions in the deep water basins. The Sinemurian-Toarcian interval of the OAE in the Pacific Ocean is confirmed by data of the numerous World basins.

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30

Abraham, Mohd Al Farid, Bernhard David A. Naafs, Vittoria Lauretano, Fotis Sgouridis e Richard D. Pancost. "Warming drove the expansion of marine anoxia in the equatorial Atlantic during the Cenomanian leading up to Oceanic Anoxic Event 2". Climate of the Past 19, n. 12 (20 dicembre 2023): 2569–80. http://dx.doi.org/10.5194/cp-19-2569-2023.

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Abstract. Oceanic Anoxic Event 2 (OAE 2) (∼ 93.5 Ma) is characterized by widespread marine anoxia and elevated burial rates of organic matter. However, the factors that led to this widespread marine deoxygenation and the possible link with climatic change remain debated. Here, we report long-term biomarker records of water-column anoxia, water-column and photic zone euxinia (PZE), and sea surface temperature (SST) from Demerara Rise in the equatorial Atlantic that span 3.8 Myr of the late Cenomanian to Turonian, including OAE 2. We find that total organic carbon (TOC) content is high but variable (0.41 wt %–17 wt %) across the Cenomanian and increases with time. This long-term TOC increase coincides with a TEX86-derived SST increase from ∼ 35 to 40 ∘C as well as the episodic occurrence of 28,30-dinorhopane (DNH) and lycopane, indicating warming and expansion of the oxygen minimum zone (OMZ) predating OAE 2. Water-column euxinia persisted through much of the late Cenomanian, as indicated by the presence of C35 hopanoid thiophene but only reached the photic zone during OAE 2, as indicated by the presence of isorenieratane. Using these biomarker records, we suggest that water-column anoxia and euxinia in the equatorial Atlantic preceded OAE 2 and this deoxygenation was driven by global warming.

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31

Scholz, Florian, James McManus e Stefan Sommer. "The manganese and iron shuttle in a modern euxinic basin and implications for molybdenum cycling at euxinic ocean margins". Chemical Geology 355 (settembre 2013): 56–68. http://dx.doi.org/10.1016/j.chemgeo.2013.07.006.

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32

Hedreen, Guy. "The Cult of Achilles in the Euxine". Hesperia 60, n. 3 (luglio 1991): 313. http://dx.doi.org/10.2307/148068.

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33

KLEPAC-CERAJ, V., C. A. HAYES, W. P. GILHOOLY, T. W. LYONS, R. KOLTER e A. PEARSON. "Microbial diversity under extreme euxinia: Mahoney Lake, Canada". Geobiology 10, n. 3 (13 febbraio 2012): 223–35. http://dx.doi.org/10.1111/j.1472-4669.2012.00317.x.

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34

Meyer, Katja M., e Lee R. Kump. "Oceanic Euxinia in Earth History: Causes and Consequences". Annual Review of Earth and Planetary Sciences 36, n. 1 (maggio 2008): 251–88. http://dx.doi.org/10.1146/annurev.earth.36.031207.124256.

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35

Helz, George R., Elvira Bura-Nakić, Nevenka Mikac e Irena Ciglenečki. "New model for molybdenum behavior in euxinic waters". Chemical Geology 284, n. 3-4 (maggio 2011): 323–32. http://dx.doi.org/10.1016/j.chemgeo.2011.03.012.

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36

Stacey, Jack, Ashleigh v. S. Hood e Malcolm W. Wallace. "Persistent late Tonian shallow marine anoxia and euxinia". Precambrian Research 397 (ottobre 2023): 107207. http://dx.doi.org/10.1016/j.precamres.2023.107207.

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37

Rddad, Larbi. "Fixation and redistribution of arsenic during early and late diagenesis in the organic matter-rich members of the Lockatong Formation, Newark basin, USA: implication for the quality of groundwater". Atlantic Geology 53 (28 giugno 2017): 253–68. http://dx.doi.org/10.4138/atlgeol.2017.010.

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Abstract (sommario):

The Byram and Walls Island members in the lower and upper sections, respectively, of the Lockatong Formation in the Newark basin near the border between Pennsylvania and New Jersey were chosen to assess (i) the role of euxinic/anoxic conditions in sequestering arsenic (As) and other trace elements and (ii) the redistribution of these elements during catagenetic transformations. ἀese members are rich in organic matter and host pyrite which occurs as disseminations, small patches, and subparallel veins. ἀe sulfur isotope values of pyrite samples range between -7.5 and 0.5 ‰CDT (average = -3.5‰CDT). ἀe negative δ34S values are indicative of Bacterial Sulfate Reduction (BSR) under low temperature and euxinic/anoxic conditions. ἀe total organic carbon (TOC) values in this member ᴀuctuate between 0.5 and 2.1%. ἀese euxinic/anoxic conditions enhanced the incorporation of As and other trace elements in both organic matter and pyrite. ἀe As concentrations range from 13 to 800 mg/kg and from 1.4 to 34 mg/kg in pyrite and black shale samples, respectively. Rock Eval analyses reveal that organic matter is over-mature which altered the correlation between TOC and As. ἀe thermal cracking of organic matter resulted in the removal of these elements from organic matter and their subsequent incorporation in pyrite and bitumen. Organic matter- and pyrite-rich anoxic black shale layers and bitumen veins are potential sources of arsenic in groundwater in the Newark basin, with arsenic values that reach up to 215 μg/L.

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38

Staubwasser, M., R. Schoenberg, F. von Blanckenburg, S. Krüger e C. Pohl. "Isotope fractionation between dissolved and suspended particulate Fe in the oxic and anoxic water column of the Baltic Sea". Biogeosciences Discussions 9, n. 4 (19 aprile 2012): 4793–817. http://dx.doi.org/10.5194/bgd-9-4793-2012.

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Abstract. Fe isotope ratios and concentrations of dissolved Fe (Fedis, < 0.45 μm) and of suspended particulate Fe (FeSPM) from a depth profile in the Eastern Gotland Basin, Baltic Sea, show a sharp gradient in δ56Fedis across the suboxic interface with δ56Fedis = −0.4 ‰ in the euxinic deep basin and δ56Fedis = +0.3 ‰ in the oxic upper water column. The isotopic gradient overlaps with a strong concentration gradient of Fedis, a concentration maximum in FeSPM and lower δ56FeSPM values than δ56Fedis. These features indicate preferential loss of light Fe isotopes into suspended iron-oxyhydroxides (FeIOH) during typical oxidative precipitation across the redox interface in the marine environment. The sign of the fractionation, Δ56FeFe_IOH–Fe(II)(aq) < 0 ‰, is in contrast to similar, mostly non-marine redox environments, where Δ56FeFe_IOH–Fe(II)(aq) > 0 ‰. The difference appears to be the result of isotope exchange dominated by reaction kinetics in the marine water column, rather than equilibrium fractionation generally inferred for oxidative Fe precipitation elsewhere. High residual δ56Fedis immediately above the suboxic interface and throughout the oxic water column suggest that any potential Fe export from reducing waters or sediments into the open water column is enriched in the heavy isotopes. Within the suboxic to euxinic deep basin the decreasing δ56FeSPM trend with depth and a generally low δ56Fedis are comparable to trends in marine anoxic sediment profiles indicative of microbial reductive Fe dissolution. This confirms supply of dissolved Fe to the euxinic water column mainly from reductive dissolution of settling particles.

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39

ARSLAN, Murat. "Arrianus un Karadeniz Seyahati (Arriani Periplus Ponti Euxini)". LIBRI Kitap Tanitimi, Elestiri ve Ceviri Dergisi 1, n. 1 (23 dicembre 2015): 93. http://dx.doi.org/10.20480/lbr.2015115472.

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40

Nadel, Benjamin. "The Euxine Pontos as seen by the Greeks". Dialogues d'histoire ancienne 17, n. 2 (1991): 115–26. http://dx.doi.org/10.3406/dha.1991.1940.

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41

Fox, Calum P., Jessica H. Whiteside, Paul E. Olsen, Xingqian Cui, Roger E. Summons, Erdem Idiz e Kliti Grice. "Two-pronged kill mechanism at the end-Triassic mass extinction". Geology 50, n. 4 (5 gennaio 2022): 448–53. http://dx.doi.org/10.1130/g49560.1.

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Abstract (sommario):

Abstract High-resolution biomarker and compound-specific isotope distributions coupled with the degradation of calcareous fossil remnants reveal that intensive euxinia and decalcification (acidification) driven by Central Atlantic magmatic province (CAMP) activity formed a two-pronged kill mechanism at the end-Triassic mass extinction. In a newly proposed extinction interval for the basal Blue Lias Formation (Bristol Channel Basin, UK), biomarker distributions reveal an episode of persistent photic zone euxinia (PZE) that extended further upward into the surface waters. In the same interval, shelly taxa almost completely disappear. Beginning in the basal paper shales of the Blue Lias Formation, a Lilliput assemblage is preserved consisting of only rare calcitic oysters (Liostrea) and ghost fossils of decalcified aragonitic bivalves. The stressors of PZE and decalcification parsimoniously explain the extinction event and inform possible combined causes of other biotic crises linked to emplacement of large igneous provinces, notably the end-Permian mass extinction, when PZE occurred on a broad and perhaps global scale.

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42

Loevezijn, Gerard B. S. van, e J. G. M. Raven. "From carbonate platform to euxinic sea – the collapse of an Early/Middle Devonian reef, Cantabrian Mountains (Spain)". Geologos 23, n. 3 (20 dicembre 2017): 143–61. http://dx.doi.org/10.1515/logos-2017-0018.

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AbstractThe Santa Lucía Formation represents the major phase in Devonian reef development of the Cantabrian Zone (Cantabrian Mountains, northwest Spain). In the present study the transition from the carbonate platform deposits of the Santa Lucía Formation to the overlying euxinic basinal deposits of the Huergas Formation is described. These transitional strata are connected to the Basal Choteč Event and represent a condensed sedimentation of micritic dark-grey and black limestones with an upward increase of dark shale intercalations with iron mineralisation surfaces and storm-induced brachiopod coquinas. The transitional beds are grouped into a new unit, the Cabornera Bed, which consists of limestone, limestone-shale and shale facies associations, representing a sediment-starved euxinic offshore area just below the storm wave base. Four stages in reef decline can be recognised: a reef stage, an oxygen-depleted, nutrient-rich stage, a siliciclastic-influx stage and a pelagic-siliciclastic stage. Additional geochemical and geophysical investigations are needed to verify the results presented herein.

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43

Slomp, Caroline P. "Reconstructing the history of euxinia in a coastal sea". Geology 41, n. 4 (aprile 2013): 523–24. http://dx.doi.org/10.1130/focus0420131.1.

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44

Grice, K. "Photic Zone Euxinia During the Permian-Triassic Superanoxic Event". Science 307, n. 5710 (4 febbraio 2005): 706–9. http://dx.doi.org/10.1126/science.1104323.

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45

Barberán, Albert, e Emilio O. Casamayor. "Euxinic Freshwater Hypolimnia Promote Bacterial Endemicity in Continental Areas". Microbial Ecology 61, n. 2 (24 novembre 2010): 465–72. http://dx.doi.org/10.1007/s00248-010-9775-6.

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46

Wu, C., T. Yang, G. A. Shields, X. Bian, B. Gao, H. Ye e W. Li. "Termination of Cryogenian ironstone deposition by deep ocean euxinia". Geochemical Perspectives Letters 15 (luglio 2020): 1–5. http://dx.doi.org/10.7185/geochemlet.2025.

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47

Eckert, Sebastian, Hans-Jürgen Brumsack, Silke Severmann, Bernhard Schnetger, Christian März e Henning Fröllje. "Establishment of euxinic conditions in the Holocene Black Sea". Geology 41, n. 4 (aprile 2013): 431–34. http://dx.doi.org/10.1130/g33826.1.

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48

Fulton, J. M., M. A. Arthur, B. Thomas e K. H. Freeman. "Pigment carbon and nitrogen isotopic signatures in euxinic basins". Geobiology 16, n. 4 (25 marzo 2018): 429–45. http://dx.doi.org/10.1111/gbi.12285.

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49

SMOLAREK, JUSTYNA, WIESŁAW TRELA, DAVID P. G. BOND e LESZEK MARYNOWSKI. "Lower Wenlock black shales in the northern Holy Cross Mountains, Poland: sedimentary and geochemical controls on the Ireviken Event in a deep marine setting". Geological Magazine 154, n. 2 (4 febbraio 2016): 247–64. http://dx.doi.org/10.1017/s0016756815001065.

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Abstract (sommario):

AbstractThe stratigraphic variability and geochemistry of Llandovery/Wenlock (L/W) Series boundary sediments in Poland reveals that hemipelagic sedimentation under an anoxic/euxinic water column was interrupted by low-density bottom currents or detached diluted turbid layers that resulted in intermittent seafloor oxygenation. Total organic carbon values and inorganic proxies throughout the Wilków 1 borehole section suggest variable redox conditions. U/Mo ratios > 1 throughout much of the Aeronian and Telychian stages, together with an absence of pyrite framboids, suggest oxygenated conditions prevailed. However, elevated total organic carbon near the Aeronian/Telychian boundary, together with increased U/Th and V/(V + Ni) ratios and populations of small pyrite framboids are consistent with the development of dysoxic/anoxic conditions at that time. U/Th, V/Cr and V/(V + Ni) ratios, as well as Uauthig and Mo concentrations, suggest that during the Ireviken black shale deposition, bottom-water conditions deteriorated from oxic during Telychian time to mostly suboxic/anoxic immediately prior to the L/W boundary, before a brief reoxygenation at the end of the Ireviken black shale sedimentation in the Sheinwoodian Stage. Rapid fluctuations in U/Mo during the Ireviken Event are characteristic of fluctuating redox conditions that culminated in an anoxic/euxinic seafloor in Sheinwoodian time. Following Ireviken black shale deposition, conditions once again became oxygen deficient with the development of a euxinic zone in the water column. The Aeronian to Sheinwoodian deep-water redox history was unstable, and rapid fluctuations of the chemocline across the L/W Series boundary probably contributed to the Ireviken Event extinctions, which affected mainly pelagic and hemipelagic fauna.

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50

Shopov, Vladimir. "Local mollusc standard zones of Quaternary sediments from the Bulgarian Black Sea shelf". Geologica Balcanica 23, n. 6 (30 dicembre 1993): 25–32. http://dx.doi.org/10.52321/geolbalc.23.6.25.

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Abstract (sommario):

The only boundary which can be used to differentiate the Bulgarian Black Sea shelf into stratigraphic zones is the spatial distribution of mollusc fauna. This boundary is bathymetrically determined and divides the central morphological shelf zone into two uneven parts given inner and outer shelf. Another boundary is drawn which follows roughly the parallel of Cape Kaliakra and divides it into two uneven parts. The sediments of Low Pleistocene series were not deposited in the inner shelf zone and here a stratigraphic gap is established there which coincides with Chaudian Age. A similar gap at the time of Early Chaudinian Subage is established in the outer zone of the shelf where the Dreissena rostriformis tschaudae local mollusc Range-zone is indicated. In both shelf zones the sedimentation continues by formation of the Middle Pleistocene Old Euxinian and Uzunlarian Regional Stage in whose sediments the corresponding are Didacna crassa pontocaspia – Dreissena euxinica and Didacna crassa pontocaspia – Abra ovatа local mollusc Parallel Range-zones. The Upper Pleistocene (Karangatian) mollusc zones are established only at the inner parts of the Bourgas Bay and there three: Corbula gibba – Rissoa parva, Paphia senescens – Cardium tuberculatum and Cardium edule – Bittium reticulatum local mollusc Parallel Range-zone are found out which correspond to the three Substages of the Karangatian Regional Stage. The succession of the mollusc zones from the inner shelf is interrupted by a barren zone which corresponds to the continental deposits sedimented at the time of the Early New Euxinian Substage. During the greater part of the Late Pleistocene Subepoch in the zone of the outer shelf a stratigraphic gap is established. In the composition of the zone community of the next in superposition Dreissena polymorpha – Dreissena rostriformis distincta local mollusc Parallel Range-zone two associations are established – one in the inner and another in the outer shelf. The climatic changes which took place after the Würm glaciation restored the connection of the Black Sea with the World Ocean. In the Black Sea basin this Holocene transgression causes uplift of the sea level and increasing of the salinity to its recent values. The latter determines the successional changes of the mollusc communities which from the beginning of the Holocene became more halophilic. The community of Hydrobia ventrosa – Monodacna caspia caspia local mollusc Parallel Range-zone and Mytilus galloprovincialis local mollusc Range-zone comprise the sediments of Old Chernomorian Substage. The two New Chernomorian Spisula subtruncata triangula and Modiolus phaseolinus local mollusc Range-zone are fingering spatially in the zone of the outer shelf together with increase of the bottom at practically one and same composition of the zonal community.

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