Benthic faunal associations in the Lower Silurian Solvik Formation of the Oslo‐Asker Districts, Norway

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Abstract
In the Asker District of the Oslo Region there occurs an unusually complete and fossiliferous transition between the uppermost Ordovician and lowermost Silurian, which gives a unique opportunity to assess changes in benthic community structure across the boundary. Seven associations of benthic invertebrates are described from the Solvik Formation (Lower Silurian) of the Oslo Region, Norway. Three of these can be subordinated to a Clorinda and four to a Stricklandia equivalent paleocommunity. These early Silurian paleocommunities succeeded the late Ordovician Onniella paleocommunity, although some associations bearing Stricklandia probably took over the niche of the Nicolella paleocommunity. The faunal associations are subcategories primarily related to lithofacies, while the larger-scale paleocommunities are primarily related to distance from shore. This difference is caused by very eurytopic key-members defining the paleocommunities. These key-members can live in most types of lithofacies, but are otherwise dependent on factors more directly related to depth. The dominance of eurytopic key-members in Early Silurian time was affected by the Ordovician-Silurian extinction period, when a eurytopic life style was a great advantage.