The Frasnian-Famennian (F-F) boundary is well biostratigraphically documented in the Palmatolepis-rich deposits exposed along the Sywiu 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 organic- and 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 d13Ccarb excursions of +3.5 o/oo. 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.

Key words: Frasnian; Famennian; Kellwasser Crisis; conodonts, microfacies, carbon isotopes; geochemistry; Timan− Pechora Basin.

Alexandra B. Yudina [alexa_geo@yahoo.com], Institut Geologii, Komi Nauchnyj Tsentr, Uralskoye Otdeleniye, Syktyvkar, Russia; Grzegorz Racki [racki@us.edu.pl], Maria Racka [racka@ultra.cto.us.edu.pl], Wydział Nauk o Ziemi, Uniwersytet Śląski, ul. Będzińska 60, PL−41−200 Sosnowiec, Poland; Norman M. Savage [nmsavage@oregon.uoregon.edu], Department of Geological Sciences, University of Oregon, Eugene, OR 97403, USA; Krzysztof Małkowski [malk@twarda.pan.pl], Instytut Paleobiologii PAN, ul. Twarda 51/53, PL−02−089Warszawa, Poland.