Abstract
The position of the Iapetus Ocean suture can be traced between Ordovician fossil localities in the Southern Uplands and the Lake District which contain, respectively, distinct North American and European faunas. The Southern Uplands contains North American Caradoc faunas in the Northern Belt, and is considered to have been accreted onto the Laurentian (North American) margin between the Llandeilo and the end of the Wenlock. Deep seismic reflection profiling shows that a surface, probably parallel to the suture zone, dips down to the northwest from the Solway Line. In eastern Ireland, the surface trace of the suture coincides with the Navan Fault, which separates the Longford-Down massif from Ordovician sediments containing European faunas. The Navan–Silvermines Fault may represent the surface expression of the suture, but it is masked by Wenlock turbidites, which appear to have crossed over the plate boundary. Northward subduction of continental crust below the margin of Laurentia during the late Silurian may explain the influx of turbidite fans from the north or north west onto depressed crust to the south of the suture. Termination of subduction coincides with the widespread Acadian Orogeny in the Emsian (at 395±5 Ma).