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2 Cambrian palaeogeography
Cambrian continents are thought to have resulted from the breakup of a neoproterozoic supercontinent called Rodinia. The waters of the Cambrian period appear to have been widespread and shallow. It is thought that Cambrian climates were significantly warmer than those of preceding times that experienced extensive ice ages discussed as the Varanger glaciation. Continental drift rates in the Cambrian may have been anomalously high. Because of their complexity, it is difficult to describe continental motions in text. Time-sequenced maps of paleo-continents and other major geologic features are called paleomaps and are available at several Internet sites (see below).
3 Cambrian fauna
Aside from a few enigmatic forms that may or may not represent animals, all modern animal phyla except bryozoa appear to have representatives in the Cambrian, and most except sponges seem to have originated just after or just before the start of the period. Many extinct phyla and odd animals that have unclear relationships to other animals also appear in the Cambrian. The apparent "sudden" appearance of very diverse faunas over a period of no more than a few tens of millions of years is referred to as the "Cambrian Explosion".
The best studied sites where soft parts of organisms have fossilized are in the Burgess shale of British Columbia. They represent strata from the middle Cambrian and provide us with a wealth of information on early animal diversity. Similar faunas have subsequently been found in a number of other places -- most importantly in very early Cambrian shales in China's Yunnan Province (see Maotianshan shales). Fairly extensive pre-Cambrian Ediacarian faunas have been identified in the past 50 years, but their relationships to Cambrian forms are quite obscure.
4 External links and references
Geologic timescale
