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Anomalous Upper Devonian mercury enrichments : comparison of Inductively Coupled Plasma – Mass Spectrometry (ICP-MS) and Atomic Absorption Spectrometry (AAS) analytical data

Racki G., Rakociński M., Marynowski L.

Geological Quarterly

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2018

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Vol. 62, No. 3

487--495

EN

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.

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Conodont biostratigraphy of the Frasnian-Famennian boundary in the Esfahan and Tabas areas, Central Iran

Gholamalian H.

Geological Quarterly

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2007

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Vol. 51, No 4

453-476

EN

The Frasnian-Famennian (F-F) boundary in Central Iran has been investigated on the basis of conodont faunas (34 species and subspecies) from four sections: Chahriseh near Esfahan, and Kal-e-Sardar, Howz-e-Dorah and Ghale-Kalaghu near Tabas. The F-F boundary in the Chahriseh section is located in a one-metre interval between beds EX1 and F-F9 whereas in the Kal-e-Sardar section it is at the base of bed Cly1. The F-F boundary can not be recognized in the Howz-e-Dorah and Ghale-Kalaghu sections be cause of uncon form able relation ships and erosion of the upper most late Frasnian beds indicated incidentally by reworked boulders (indicating con temporaneous tectonic activity) and by the abrupt appearance of contrasting environments, including tempestites at the base of the lower Famennian. The best conodont and palaeoenvironmental data were obtained from the Kal-e-Sardar section where a deeper marine environment prevailed during the late Frasnian, be coming shallower in the early Famennian; the Chahriseh section displays small fluctuations in sea level during the early Famennian. The conodont faunas display the inception of the Polygnathus communis group in the late Frasnian (rhenana-linguiformis zones) and the appearance of Icriodus alternatus mawsonae in the Late rhenana Zone. A new age-range is suggested for Polygnathus aequalis Klapper and Lane, from the transitans to the linguiformis zones. Three conodont biozones are represented in the late Frasnian to early Famennian of the Chahriseh section, two late Frasnian and one early Famennian in the Kal-e-Sardar section and two biozones in the late Frasnian and early Famennian of both the Howz-e-Dorah and Ghale-Kalaghu sections. Two new species are described: Polygnathus tabasianus (Early to Late crepida zones) and Polygnathus vachiki (Late rhenana-linguiformis zones).

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Stratigraphy and geological events at the Frasnian-Famennian boundary in the Southern Urals

Veimarn A. B., Puchkov V. N., Abramova A. N., Artyushkova O. V., Baryshev V. N., Degtyaryov K. E., Kononova L. I., Maslov V. A, Mosejchuk V. M., Pazukhin V. N., Pravikova N. V., Tevelev A. V., Yarkova A. V.

Geological Quarterly

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2004

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Vol. 48, No 3

233--244

EN

Detailed biostratigraphic correlation of late Frasnian and Famennian sections in the Southern Urals shows that the key global scale events near the boundary of Frasnian and Famennian are clearly expressed in combination with important regional scale tectonic events. The maximum regression occured during triangularis zones time, being recorded as common hiatuses. The beginning of specific ultra- potassic mantle volcanism took place during the linguiformis Zone. Processes of olistostrome deposition, uplift of the Uraltau zone, the start of flysch deposition, and exhumation of the high pressure-low temperature Maksiutovo metamorphic complex also took place very close to the Frasnian-Famennian boundary, as the general regression coincided with active local tectonic movements as the Magnitogorsk island arc collised with the East European continent. The global scale events at the F-F boundary are connected with activity of the Late Devonian superplume, which encompassed a vast area of the Kazakhstanian, East European, Siberian, Gondwana and South Chinese plates.

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Late Devonian facies variety in Iran: volcanism as a possible trigger of the environmental perturbation near the Frasnian-Famennian boundary

Mahmudy Gharaie M. H., Matsumoto R., Kakuwa Y., Milroy P. G.

Geological Quarterly

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2004

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Vol. 48, No 4

323-332

EN

Upper Devonian successions surrounding the Frasnian-Famennian (F-F) boundary in Iran consist of mixed carbonate/silisiclastic deposits. The successions are characterized by conspicuous ferruginous limestones, clay-rich units, black shales, and mafic volcanic rocks that provide important insights into palaeoenvironmental conditions during this interval of Earth’s history. An increase of kaolinite/illite ratio in clays associated with the F-F boundary suggests that increased chemical weathering was facilitated by warm and humid climatic conditions. Distinctive ferruginous-oolite deposits overlying the crucial Frasnian-Famennian boundary interval indicate a high supply rate of Fe-bearing clay originated during enhanced weathering under such climatic conditions. Black shales associated with the F-F boundary are interpreted to be the result of a high primary productivity caused by an increased influx of land-derived nutrients and regional volcanic activity. Widespread rift-related, basaltic activity along eastern Laurussia and northern Gondwana during the mid-Late Devonian is believed to have contribution to this global warming surrounding the F-F boundary.

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Gamma-ray spectrometry across the Upper Devonian basin succession at Kowala in the Holy Cross Mountains (Poland)

Bond D., Zatoń M.

Acta Geologica Polonica

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2003

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Vol. 53, nr 2

93-99

EN

The Upper Devonian sequence at Kowala in the Holy Cross Mountains was logged using gamma-ray spectrometry, for investigating the changes of oxygenation level in the Late Devonian basin. The Th/U ratio indicates that oxygen levels were low throughout the Late Frasnian interval, with low peaks during the Kellwasser Events showing anoxic conditions in the basin. The F-F boundary interval was also oxygen deficient, but there may have been a brief reoxygenation at the boundary itself. By the Famennian crepida Zone, the basin gradually began to reoxygenate, but in the trachytera Zone another anoxic event, the Annulata Event occurred, causing a bloom rather than extinction of specially adapted taxa such as Guerichia. Thus the gamma-ray spectrometry data suggests that basinal anoxia prevailed through much of the Late Frasnian. The F-F extinction might have been the result of prolonged stresses imposed on the ecosystem, particularly during the euxinic Upper Kellwasser Event.