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 quantified. Assemblages of Cambrian age are distinctive: their diversity is lower, pascichnia and agrichnia relatively unimportant, and ‘shallow‐marine’ ichnotaxa more common, than in subsequent periods. There appear to be no environmental reasons that would have precluded more extensive colonization of the deep‐marine environment during the Cambrian. The significant restructuring of deep‐marine communities at, or near, the Cambrian–Ordovician boundary is therefore attributed to competition for ecospace and/or resources within shallow‐marine environments during the early Phanerozoic, as a result of which ichnotaxa, including examples of pascichnia and agrichnia, were displaced offshore. The Nereites ichnofacies, as traditionally understood, is thus characteristic of only deep‐marine environments younger than the Cambrian. Copyright © 2001 John Wiley & Sons, Ltd.