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Geochemical and ecological aspects of lower Frasnian pyrite-ammonoid level at Kostomłoty (Holy Cross Mountains, Poland)

By G. Racki, A. Piechota, D.P.G. Bond and P.B. Wignall


The lower Frasnian (transitans Zone with Ancyrodella priamosica = MN 4 Zone) rhythmic basin succession of marly limestones and\ud shales (upper Szydlówek Beds) at Kostomloty, western Holy CrossMts., Central Poland, contains a record of the transgressive-hypoxic\ud Timan Event in this drowned part of southern Laurussian shelf. The unique facies consists of organic-rich marly shales and a distinctive\ud pyritic, goniatite level, 1.6m thick. The faunal assemblage is dominated by pyritized shells of diminutivemollusks with cephalopods (including\ud goniatites Epitornoceras and Acanthoclymenia), buchioline bivalves (Glyptohallicardia) and styliolinids. This interval is\ud marked by moderately low Th/U ratios and pyrite framboid size distributions suggestive of dysoxic rather than permanent euxinic conditions.\ud The scarcity of infauna and bioturbation resulted in finely laminated sedimentary fabrics, as well as the low diversity of the presumed\ud pioneer benthos (mostly brachiopods). In the topmost part of the Szydlówek Beds, distinguished by the Styliolina coquina\ud interbedded between limestone-biodetrital layers, the above geochemical proxies and C-isotope positive shift indicate a tendency to\ud somewhat increased bottom oxygen deficiency and higher carbon burial rate linked with a bloom of pelagic biota during high-productivity\ud pulse. The geochemical and community changes are a complex regional record of the initial phase of a major perturbation in the\ud earth-ocean system during a phase of intermittently rising sea level in the early to middle Frasnian, and associated with the highest positive\ud C-isotope ratios of the Devonian

Year: 2004
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