A borehole drilled within the Rathkenny Tract, southwest of Navan, eastern Ireland, yielded a rich graptolite fauna, including three excellent basal Silurian graptolite assemblages, from a deep-water, pelagic and hemipelagic sequence, ranging in age from uppermost Caradocian to middle Wenlockian, from immediately below Carboniferous strata. Biostratigraphic analysis of the graptolites shows that there are eight, discrete faunal (biostratigraphic) units, and these, together with the lithology, indicate the graptolite-bearing sequence is mostly inverted and faulted at several levels.Biogeographic affinities of several of the Llandoverian and of the Wenlockian graptolite species, as well as some lithological data, suggest that the Rathkenny Tract lay on the southeast side of the Iapetus Ocean. The presence of the youngest graptolites further suggests that some element, at least, of the Iapetus Ocean, though probably narrow by this time, was clearly still in existence until at least middle Wenlockian.

You do not currently have access to this article.