THE FRASNIAN-FAMENNIAN BOUNDARY IN THE SOUTHERN URALS

Abstract

On the western slope of the Southern Urals, a continuous conodont zone sequence within different facies of the Frasnian-Famennian (F-F) boundary beds is documented. In all the sections the boundary between both stages runs within lithologically uniform successions and can be determined only by a sharp faunal change. In brachiopod facies, it is placed within brachiopod shell beds and relates to the base of the Barma Beds, i.e., the level marked by a simultaneous appearance of the index brachiopod species Pugnoides(?) markovskii and the zonal conodont species Palmatolepis triangularis. In goniatite facies, the F-F boundary can be traced by the disappearance of diverse Frasnian conodonts and goniatites of the genus Manticoceras, coupled with the first occurrence of the conodont Pa. triangularis; the sequence shows also the well-known icriodid blooms in the earliest Famennian. Finds of Famennian goniatites (representatives of the genus Cheiloceras) are confined to the crepida zones. In the sections of the West-Zilair, where the F-F boundary passage consists of siliceous-terrigenous deposits, the boundary can be established only by a change in conodont assemblages. In all the sections under investigation the F-F boundary level shows a drastic faunal change that corresponds to the global Kellwasser Event.