Lower Cambrian acritarchs and the Proterozoic-Cambrian boundary in southern Norway

Acritarchs are reported from Lower Cambrian sections in the area of Lake Mjøsa in southern Norway that previously yielded poor skeletal faunas. These skeletal faunas constitute in part the grounds for the fauna! biozonation of the Lower Cambrian in Baltoscandia. Compared with other previously investigated sections in Baltoscandia and Greenland, the Lake Mjøsa sections produced numerically sparse assemblages of acritarchs. Taxonomically, they are readily comparable to assemblages from the platform areas of eastern Europe in the USSR and Poland which establish the basis for previously detined 'stages' and acritarch biozones. They can also be compared to assemblages from sequences in the remaining fragments of shelf areas of the early Palaeozoic Iapetus Ocean bordering the present-day North Atlantic (e.g. the Scandinavian Caledonides, Spitsbergen, East and North Greenland, and Scotland). In southern Baltoscandia acritarch assemblages comparable to the Talsy 'stage' ( = Skiagia ornata acritarch zone) were recovered only from Lower Cambrian sequences in areas that during early Cambrian times presumably underwent considerable subsidence along the Teisseyre/Tornquist Lineament. In other areas, including southern Norway, the earliest recovered diagnostic assemblage is consistent with a Vergale 'stage' age ( = Micrhystridium dissimilare zone). Acritarch evidence from the Vardal Sandstone Member and the Ringsaker Quartzite Member is poor. However, the virtually barren quartzarenites of the Hardeberga Sandstone in southern Sweden, which are correlated with the Ringsaker Quartzite Member on lithological and ichnofaunal grounds, yielded abundant Talsy 'stage' age-diagnostic acritarchs. A new acritarch species (Celtiberium ? quadratum n.sp.) is described from the Bråstad shale