Faunal Provinces and Possible Planetary Reconstruction of the Middle Cambrian

After a world-wide correlation of Middle Cambrian biostratigraphic units the epoch is divided into three periods of time that may be approximately equal and perhaps be of 10 m.y. duration. Trilobite occurrences for each of these periods for different parts of the world have been recorded. The smallest faunally homogeneous areas with a sufficiently large list of generic occurrences are compared both at the family and generic levels. This comparison, based on Simpson's coefficient, employs cluster, principal component and discriminative analyses. The groups so produced are interpreted as indicating provinciality. Three provinces-Columban (Americas), Viking (Europe, northwestern Africa, and maritime North America), and Tollchuticook (Asia, Australia, and Antarctica)-are denned as being distinct through the Middle Cambrian. It is stressed that although the data analysis provides fairly concrete evidence for faunal similarity the planetary reconstructions are an attempt to express these results within the context of the most reliable palaeomagnetic data available. As the number and reliability of Cambrian palaeomagnetic determinations increases and as more geotectonic data from critical areas become available these reconstructions may be confirmed or modified.