The Trouble with Ichnofacies

For about 60 years, the ichnofacies model has been used to identify trace fossil assemblages associated with sedimentary environments. However, the ichnofacies model faces many problems, including: (1) how ichnofacies are defined; (2) non-environmental controls of trace fossil distribution; (3) trace fossil homeomorphy; (4) lack of autecology; (5) facies-crossing ichnotaxa; (6) non-uniformitarian aspects of trace fossil history; (7) monotaxial and other low-diversity ichnoassemblages; (8) ichnoassemblages that do not fit into established ichnofacies; and (9) taphonomic biases. Because of these problems, ichnofacies have become an over-generalized, assumption-ridden, exception-laden model that relies on diverse ad hocisms to explain away many of its shortfalls. Ichnofacies should be abandoned, and the relationship of trace fossils to sedimentary environments should be analyzed in a more granular and precise manner, focused on individual trace fossils or ichnoassemblages in conjunction with analysis of lithofacies and other biofacies data. Fossilized behavior is the conceptual paradigm of ichnology, not ichnofacies.