Ordovician limestone in Halsingland, Sweden

摘要

Limestone boulders of Early and Middle Ordovician age occur along the Baltic coast of Sweden from c. 59 degrees N to c. 62.5 degrees N, apparently at a considerable distance from any known source rocks on land. We have investigated a limestone block from Lake Kultebo, at 61 degrees N, not far inland. The conodont elements enclosed in the rock are of Mid-Ordovician age and show that the block could not have been transported any considerable distance from the west, as has previously been suggested. The new finds of presumed glacially transported boulders of Early Ordovician age confirm earlier reports of such rocks in the area. The conodont faunas here indicate that the boulders could well have been derived locally, e.g., from the floor of the SW Gulf of Bothnia, the northern part of the Baltic Sea. We conclude that at least as far as 61 degrees N, there are probably larger areas of parautochtonous Lower and Middle Ordovician rocks than was earlier assumed.