Cambrian to basal Ordovician lithostratigraphy in southern Scandinavia

The lithostratigraphic subdivision of the Cambrian successions in Scania-Bornholm, Ostergotland, Vastergotland, Narke, Oland-Gotland, the southern Bothnian Sea and the Mjosa District is reviewed and revised. The review includes the Tremadocian part of the Alum Shale Formation. The Cambrian of Scania-Bornholm comprises the Nexo, Hardeberga, Laesa, Gislov and Alum Shale formations. The Nexo Formation of Bornholm is subdivided into the new Gadeby and Langeskanse members, which are c. 40 and 50 m thick, respectively. The 1–15 m thick arkosic basal part of the sandstone succession in Scania, previously treated as part of the Hardeberga Sandstone, is allocated to the Nexo Formation. The ‘Balka Sandstone’ of Bornholm is considered an integrated part of the Hardeberga Formation and the designation Balka Sandstone Formation is abandoned. The Hardeberga Formation, which is 109 m thick on Bornholm and c. 105–110 m in Scania, comprises the Hadeborg (new), Lunkaberg (Scania only), Vik, Brantevik and Tobisvik members. The overlying Laesa Formation contains the Norretorp and Rispebjerg members; the former is regarded a senior synonym of the Broens Odde member of Bornholm. The Norretorp Member is thicker in Scania than previously estimated (> 25 m, rather likely even > 30 m); on Bornholm it is 103 m thick. The Rispebjerg Member is 1–3.7 m thick. The Cambrian of the Oland-Gotland area, the southern Bothnian Sea and the districts of south central Sweden comprises the File Haidar, Borgholm and Alum Shale formations. The File Haidar Formation of the Oland-Gotland area, which is up to 127 m thick, includes the Viklau, Nar Shale and Nar Sandstone members; the Grotlingbo Member is transferred to the Borgholm Formation. The validity of the Kalmarsund Member is questioned; its lithological characteristics probably reflect diagenesis. The Lingulid and Mickwitzia sandstone members constitute the File Haidar Formation in south central Sweden, where the unit is up to 37 m thick. New names and to some extent new definitions are introduced for the members of the Borgholm Formation, viz. Kvarntorp Member (new name for the thin glauconitic sandstone overlying the Lingulid Sandstone Member in central Sweden), Mossberga Member (new name for the coarse part of the Eccaparadoxides oelandicus Shale sensu Hagenfeldt 1994), Barstad Member (new name for the fine-grained part of the Eccaparadoxides oelandicus Shale), Aleklinta Member (new name for the Paradoxides paradoxissimus Siltstone) and Tornby Member (new name for the Paradoxides paradoxissimus Shale). The Granulata Conglomerate (= Acrothele Conglomerate of previous literature) is formally ranked as a bed at the base of the Aleklinta Member. The informal designation Soderfjarden formation is abandoned. The Borgholm Formation locally exceeds 150 m in the OlandGotland area; it is significantly thinner in south central Sweden. The Cambrian of the Mjosa District comprises the Vangsas, Ringstrand and Alum Shale formations. Of these, the new Ringstrand Formation encompasses the strata between the Vangsas and Alum Shale formations, previously referred to as the ‘Holmia Series’. The Ringstrand Formation includes the Brennsaetersag (new), Redalen (new), Tomten (new), Evjevik and Skyberg (new) members. Thickness estimates are rendered difficult due to tectonic overprinting, but the Ringstrand Formation is probably about 50-60 m thick in the Lower Allochthon around Lake Mjosa. The Scandinavian Alum Shale Formation, which is up to 100 m thick in Scania and even thicker subsurface of Kattegat, is restricted to encompass only kerogeneous mudstones/shales with subordinate limestones and very rare sandstone beds. It is proposed abandoning the Klappe Shale and Fjallbranna Formation of the Lower Allochthon of Jamtland and to regard these units as part of the Alum Shale Formation. Several widespread thin units are formally ranked as beds within the Alum Shale Formation, including the Forsemolla Limestone Bed (new name for the ‘fragment limestone’ at or near the base of the Alum Shale Formation in Scania; this unit is also developed in Ostergotland