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Pre-Arenig Activity in the Caledonian-Appalachian Orogen |
Department of Earth Sciences, University of Cambridge, Downing Street, Cambridge CB2 3EQ, UK
British Geological Survey, Keyworth, Nottingham NG12 5GG, UK
The early Phanerozoic faunas of the Caledonides (late Precambrian to Tremadoc) are reviewed; they reflect the early history of the Iapetus Ocean. The long-established distinction between ‘Pacific’ and ‘Atlantic’ faunas is justified, but the latter are divisible into Avalonian and Baltic sub-faunas. Putative deep-water faunas have a more cosmopolitan distribution. Five time segments are considered: late Precambrian (Vendian), early, middle and late Cambrian, and Tremadoc. In the late Precambrian, consideration is given to the distribution of soft-bodied Ediacaran faunas. In the Cambrian and Tremadoc, interpretations are based primarily on trilobite distributions, although other fossils have biogeographical importance. Supposed transgressive-regressive cycles, which are connected with eustatic sea-level changes, influence faunal distributions. The perturbations giving rise to the biomeres recognized around the N American craton also appear to be recognizable elsewhere in the Caledonides; they may reflect eustatic changes of sea level.
