Age and correlation of the Middle Ordovician bentonites on Bornholm

A restudy of fossils from the lowermost part of the Dicellograptus Shale on Bornholm shows that they provide no reliable evidence that the lowermost part of the bentonite-bearing succession in that unit, including the thickest bentonite bed, belongs in the Nemagraptus gracilis Zone. Comparison with Scanian successions in the Fågelsång area and at Tommarp indicates that this portion of the Dicellograptus Shale on Bornholm is more probably coeval with a part of the Diplograptus multidens Zone. Regional comparisons between the bentonite-bed successions of the Fågelsång area, Kinnekulle, and the Sinsen section in Norway suggest that at least some bentonite beds can be traced over very long distances in southern Baltoscandia.