The ordovician history of the Iapetus Ocean in Britain: New palaeomagnetic constraints

New late Tremadoc-edy Arenig palaeomagnetic results from SW Wales imply that S Britain (part of Eastern Avalonia) occupied a southerly latitude of c. 60s in early Ordovician times. When combined with Scottish Ordoviaan pdneomagnetic data, which indicate a 150s latitude, the results indicate that the British sector of the Iapetus Ocean reached n latitudinal width of c. 5OOO km in Tremadoc-Arenig times, which was reduced to c. 3Wkm by Llanvirn-Llandeilo (mid-Ordovician) times. 'Lbe new data resolve two previous controversies in Palaeozoic palaeogeography. First, the high southerly palaeolatitude links Avdonia to Gondwana, marginal to W Africa, thus reconciling codlicting reconstructions based upon either pdaeomagnetic or fnundlfaaes evidence done. Second, reliable LIanvirn pdaeomagnetic data imply that Avdonia had rifted northwards by Arenig time, whereas Armorica remained proximal to northern Africa throughout the Ordovician. The combined data therefore establish that Avdonia and Armoricn formed separate micro-continents when rifting from Gondwana.