Colonization of the deep-marine environment during the early Phanerozoic: the ichnofaunal record

Temporal changes in the ichnogeneric diversity and ethological structure of 50 Cambrian to Carboniferous deep-marine ichnofaunal assemblages were quan tified. Assemblages of Cambrian age are distinctive: their diversity is low er, pascichnia and agrichnia relatively unimportant, and 'shallow-marine' i chnotaxa more common, than in subsequent periods. There appear to be no env ironmental reasons that would have precluded more extensive colonization of the deep-marine environment during the Cambrian. The significant restructu ring of deep-marine communities at, or near, the Cambrian-Ordovician bounda ry is therefore attributed to competition for ecospace and/or resources wit hin shallow-marine environments during the early Phanerozoic, as a result o f which ichnotaxa, including examples of pascichnia and agrichnia, were dis placed offshore. The Nereites ichnofacies, as traditionally understood, is thus characteristic of only deep-marine environments younger than the Cambr ian. Copyright (C) 2001 John Wiley & Sons, Ltd.