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Chemostratigraphy of the Devonian-Carboniferous boundary sections in central, western and southern Europe

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KUMPAN Tomáš BÁBEK Ondřej KALVODA Jiří FRÝDA Jiří MATYS GRYRGAR Tomáš

Rok publikování 2013
Druh Článek v odborném periodiku
Časopis / Zdroj Schriftenreihe der Deutschen Gesellschaft für Geowissenschaften
Fakulta / Pracoviště MU

Přírodovědecká fakulta

Citace
Obor Geologie a mineralogie
Klíčová slova geochemistry of sedimentary carbonate rocks;chemostratigraphy;Famennian;Tournaisian
Popis The GSSP of the Devonian-Carboniferous (D-C) boundary is currently subject of extensive criticism due to the problems with the first appearance datum of the conodont Siphonodella sulcata. The multiphase Hangenberg Event (HBE), a sedimentary record of environmental perturbations at the end of the Famennian was proposed as an alternative solution (Walliser, 1986). However, multi-proxy approach is necessary for understanding which of the event phases is really of global importance and hence useful for correlations and new definition. Carbon and oxygen isotope chemostratigraphic studies have been carried out in the European and North American sections recently (e.g. Kaiser et al. 2008). At present, the positive shift of carbon isotopes at the base or within the HBE interval is the most distinct correlative feature. This contribution presents new results of high-resolution element (EDXRF) and bulk stable carbon isotope geochemistry survey of the D-C boundary sections from the Moravian Karst (Czech Republic), Carnic Alps (Austria), Dinant Synclinorium (Belgium and N. France), Pyrenees and Montagne Noire (S. France). The general trends of element concentrations and their ratios are follows: elemental proxies indicate low rates of terrigenous input (e.g. Al, Zr/Al, K/Al) and higher paleoproductivity (e.g. Sr/Al, Mn/Fe) proxies in the Famennian below the HBE. This record is interpreted as indicating a prolific bioproduction period. Culmination of these values together with still enigmatic Mn/Al proxy was documented in the sections where limestones persist at the HBE base. Low values of Mn/Al and increase of the Sr/Ca and terrigenous input proxies take place where shales occur at the HBE base. It demonstrates the supposed eutrophication that caused mass extinction at the base of the HBE (Kaiser et al. 2008). An increase in the terrigenous input proxies, which occurs at the top of the HBE, could be interpreted as progradation of siliciclastics during a sea-level fall. The d13C excursion to values around 4 %. in the Moravian Karst (Lesní lom section) occurs at the HBE base and is regarded as synchronous with the other European and American HBE d13C shifts (Kumpan et al. in press). A sharp positive d13C excursion at the boundary between the Strunian and Hastarian facies (Dinant Synclinorium) reflects a stratigraphic gap at the D-C boundary, which is probably linked to the HBE sea-level fall. The positive shifts of d13C values cannot be regarded as the HBE equivalent but rather as a record of the Early Tournaisian isotopically heavier carbon system.
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