Biozonation of the Furongian (upper Cambrian) Alum Shale Formation at Hunneberg, Sweden

Abstract

The Furongian Alum Shale at Nygård, Hunneberg, Sweden, has been sampled for trilobites. The section is ≥12.20 m thick and comprises a relatively thick Olenus superzone, overlain by more condensed Parabolina, Leptoplastus, Protopeltura and Peltura superzones. The section is truncated low in the Peltura superzone, presumably due to late Furongian uplift. The internal zonation of the sparsely fossiliferous Olenus superzone is unsettled. Above that level, the Parabolina spinulosa, Leptoplastus crassicornis–Leptoplastus angustatus, Sphaerophthalmus flagellifer, Ctenopyge similis, Ctenopyge spectabilis, Ctenopyge tumida and Ctenopyge bisulcata zones are documented. The C. similis–C. spectabilis zonal interval yielded a lower faunal assemblage with Ctenopyge (Mesoctenopyge) erecta, Sphaeropthalmus modestus and Ctenopyge (M.) spectabilis and an upper assemblage with Ctenopyge (M.) similis, Sphaeropthalmus angustus and Protopeltura planicauda. Hence, the FAD’s of C. (M.) similis and C. (M.) spectabilis are opposite of the previously described pattern. We informally refer to the lower assemblage as the S. modestus biozone and to the upper assemblage as the S. angustus biozone (believed to be equivalent to the C. similis and C. spectabilis chronozones, respectively). It is possible that the true range of the rare species C. (M.) similis has to date escaped recognition. Alternatively, if the existing chronozonation is correct, this implies reworking and the discussed interval at Nygård must in that case represent the C. spectabilis Zone. Ctenopyge (Ctenopyge) bisulcata, C. (M.) similis, C. (M.) spectabilis, L. angustatus, L. crassicornis, Leptoplastus paucisegmentatus?, Peltura scarabaeoides scarabaeoides, Peltura planicauda, Sphaerophthalmus alatus, Sphaerophthalmus drytonensis, S. modestus, Triangulopyge humilis and Triangulopyge majusculus have not previously been reported from the locality.