Arenig conodont successions from central Sweden

Abstract

Abstract Samples from three localities in central Sweden, Gymninge in Närke, Nusnäs in Dalarna (drill core) and Sommartjärnen in the Lockne area of southern Jämtland, represent stratigraphical intervals from the upper part of the Paroistodus proteus Zone to the top of the Baltoniodus navis Zone. It was shown that the Megistaspis (Varvaspis) planilimbata trilobite Zone is connected with the upper Paroistodus proteus Zone, that an interval with M. (V.) aff. estonica, the socalled ‘Transition Beds’, together with the Megalaspides (M.) dalecarlicus trilobite Zone is equivalent to the lower Oepikodus evae Zone, and that the Megistaspis (Varvaspis) estonica Zone corresponds to the upper O. evae Zone. Ties between the Megistaspis (M.) lata Zone and the Baltoniodus triangularis and the B. navis Zones were confirmed. Graptolites of the Phyllograptus densus Zone were found below the O. evae Zone. The investigated samples could in addition be attributed to specific intervals within the conodont Zones, using presence/absence and frequency data. Seven samples from the Oepikodus evae Zone of Gymninge and Sommartjärnen were compared with 37 samples from the same Zone in eight other sections, from Öland in the south to northern Jämtland in the north. Thus it was possible to piece together a succession of four subunits within the O. evae Zone. Six samples from Sommartjärnen, Gymninge and Nusnäs, representing the Baltoniodus triangularis and B. navis Zones were compared with 36 samples from 10 other sections including these two Zones. In this interval it seems possible to subdivide the B. triangularis Zone into a lower and an upper part, and to distinguish three successive units within the B. navis Zone. It is concluded that with detailed stratigraphical work it is possible to claim that different parts of conodont zones are represented or preserved in different areas.