Trilobites and intercontinental tie points in the Upper Cambrian of Scandinavia

Abstract

The Upper Cambrian faunas of Scandinavia are generally dominated by olenid trilobites, which provide a firm basis for the biostratigraphic classification. The olenids tend, however, to be provincial and facies controlled. By contrast, many agnostoid genera and species have a nearly worldwide distribution and are excellent biostratigraphic indices in Middle and Upper Cambrian strata. Three distinctive and geographically widely distributed agnostoid species are known from the lower part of the Upper Cambrian in Scandinavia: Linguagnostus reconditus POLETAEVA and ROMANENKO, 1970, Aspidagnostus lunulosus (KRYSKOV in Borovikov and Kryskov, 1963), and Glyptagnostus reticulatus (ANGELIN, 1851). They are the most valuable species available for correlations with Upper Cambrian deposits outside Baltica. L. reconditus is seemingly confined to the Agnostus pisiformis Zone and provides strong evidence for correlation of that zone with the recently defined L. reconditus Zone of Peng and Robison. G. reticulatus appears in the Olenus gibbosus Subzone and ranges up into the O. wahlenbergi Subzone, suggesting that the lower part of the Olenus/Agnostus (Homagnostus) obesus Zone correlates with the G. reticulatus Zone in, e.g., Australia, China, and Kazakhstan. The presence of A. lunulosus in the O. gibbosus Subzone provides additional evidence for this correlation. Higher in the sequence agnostoids become rare, and the species recorded from the medial and upper Upper Cambrian of Baltica permit only broad correlations with other continents.