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Abstract

In marine settings seven recurring ichnofacies are recognized, each named for a representative ichnogenus: Trypanites, Teredolites, Glossifungites, Skolithos, Cruiziana, Zoophycos and Nereites. These trace fossil associations reflect adaptations of benthic trace-makers to such environmental parameters as substrate consistency, hydrodynamic energy level, depositional processes, hydrography and food supply. The traces in the marine softground ichnofacies (i.e., Skolithos, Cruziana, Zoophycos and Nereites) are distributed according to numerous environmental factors, including especially bathymetry; the traces in the hardground (Trypanites), firmground (Glossifungites) and woodground (Teredolites) ichnofacies are distributed on the basis of substrate type and consistency (Fig. 15-1).

The bathymetric zonation of softground ichnofacies is imperfect. Particular combinations of trace fossils vary according to local conditions and age relationships, and there are numerous examples of bathymetric displacement of many of supposed facies-characteristic ichnotaxa (e.g., shallow-water occurrences of Zoophycos and deep-water examples of Skolithos). Therefore, extreme caution must be exercised when applying bathymetric generalizations to rock sequences based solely on individual trace fossils. However, as Howard (1978) has pointed out, in spite of these limitations, zonations based on the energy-depth ichnofacies model (Fig. 15-2) are real. Seilacher's (1967a) model continues to stand as an excellent indicator of general depositional conditions.

One of the best examples of the energy-depth zonation of trace fossils is the classic beach-to-offshore sequence, which is characterized by a relatively simple energy gradient. Shallow, nearshore zones are typified by high-energy conditions and are dominated by physical sedimentary structures. Deeper, lower-energy, offshore environments display increasing biogenic influence (e.g., see Howard and Reineck, 1972

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