Early Cambrian provincialism and biogeographic boundaries in the North Atlantic region



Early Cambrian lithofacies and their stratigraphic context, characteristic of a number of tectonic elements within the North Atlantic region, are interpreted with respect to depositional environment and related trilobite provincialism. Faunas of the North American province are typically indigenous to shallow, warm water on a sand-carbonate shelf on the North American craton; those of the Scandian province to shallow cold water with predominantly clastic deposition on the European platform; those of the Avalonian province to shallow cold water with predominantly clastic deposition fringing islands and rises on the Iapetus Ocean floor; Intermediate zone faunas, consisting of North American, Avalonian and endemic elements, to the slope or margin of the North American shelf; faunas of the Tethyan province to a shelf bordering Gondwanaland ranging from warm to cold at different times and different places, and under some Avalonian influence in the later Early Cambrian; and a pelagic realm characterized by agnostids. Biogeographic boundaries are related to the position of the thermocline and to light regimen, which determines the biogeography of autotrophs and hence of provincial niche structure. Provincialism is determined by gross environmental differences reinforced by biotic factors.