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17. INYERTEBRATE ICHNOLOGY OF CONTINENTAL FRESHWATER EN VIRONMENTS

assemblages that do not exhibit recurrence in the stratigraphic record under a similar set of environ-mental conditions do not qualify as ichnofacies. Any potential ichnofacies should be based on a senes of examples carefuUy selected from the ichno-logic record, rather than a mere list of theoretical assemblages or documentation of local examples. Seilacherian archetypal ichnofacies should not be confused with ichnocoenoses. An ichnocoenosis refers to a group of biogenic structures that results from the work of a single community and, therefore, is a very different concept than ichnofacies and is applicable to different scalę analysis (Bromley, 1990). Some authors (e.g., Hasiotis, 2004) have criticized the ichnofacies concept on these grounds, but the ichnofacies model is based upon recurring ichnocoenoses and tracę fossil assemblages (Bromley et al., in press). A common misunderstanding is the assertion that if a particular tracę fossil assemblage or ichnocoenosis cannot readily be ascribed to one ichnofacies, then the ichnofacies model is not valid. As noted by Pemberton et al. (1992), the ichnofacies model is analogous to facies models and, accordingly, archetypal ichnofacies are produced through a 'distillation' process that concentrates the diagnostic features of various ichno-faunas and eliminates the local peculiarities or the 'noise' of the particular examples. As in the case of facies models, an ichnofacies serves as a norm for purposes of comparison, framework, and guide for futurę observations, predictor in new situations, and basis for interpretation. Of course, at a local scalę, discrete ichnofacies may be subdivided into different assemblages with paleoecological and paleoenviron-mental implications, integrating sedimentologic and ichnologic datasets (MacEachem et al., 1999; McDroy, 2004). In shallow marinę clastic successions, this approach has resulted in models of onshore-offshore ichnofacies gradients that have been extremely useful in refining environmental zonations (e.g., MacEachem et al., 1999). Additionally, the addition of concepts and methods derived from the ichnofabric approach, such as the recognition of the taphonomic factors involved in the shaping of particular ichnofacies (Bromley and Asgaard, 1991), should be taken into account to produce morę robust models.

The ichnofacies model has been expanded into the Continental realm in recent years. In his original model, Seilacher (1967) recognized only one ichnofacies for Continental environments, the Scoyenia ichnofacies. He proposed the Scoyenia ichnofacies for 'nonmarinę sands and shales, often red beds, with a distinctive association of tracę fossils' and referred to a previous schematic illustration of this ichnofauna (Seilacher, 1.963, Fig. 17.7), whlch included meniscate

burrows, arthropod trackways, and bilobed traces, as well as several physical sedimentary structures (e.g,, desiccation cracks). Frey et al. (1984) noted that the Scoyenia ichnofacies subsequently was used as a catchall for all assemblages of Continental tracę fossils. However, the Scoyenia ichnofacies has precise environmental implications because it occurs in low-energy Continental deposits periodically exposed to air or inundated, intermediate between aąuatic and nonaquatic (Frey et al., 1984; Frey and Pemberton, 1984,1987). The fact that the Scoyenia ichnofacies was only one of the recurrent tracę fossil assemblage of Continental environments and that Continental environments are as diverse as marinę settings has been acknowledged by ichnologists long ago. However, it was not until recently that studies addressing the problem of recognizing additional Continental ichnofacies were published (e.g., Smith et al., 1993; Buatois and Mangano, 1995a; Bromley, 1996; Genise et al., 2000). At present, three Continental archetypal (i.e., Seilacherian) ichnofacies are accepted: the Scoyenia, Mermia, and Coprinisphaera ichnofacies (Fig. 17.1 and Table 17.1). The former two occur in fluvio-Iacustrine environments and are, therefore, discussed herein. The latter is present in palaeosois and its analysis is beyond the scope of this paper (seę Genise et al., 2000 and Genise, 2004). In addition, the marinę Skolithos ichnofacies may occur also in high-energy Continental environments (Buatois and Mangano, 1995a, 1998; Melchor et al., 2003). Continental ichnofacies have been addressed in morę detail in a series of chapters (e.g., Buatois and Mangano, 1995a, 1998, 2002, 2004; Genise et al., 2000; Genise, 2004; McDroy, 2004).

A common misconception is to assume a direct correlation between ichnofacies and depositional environments. Ichnofacies are not indicators of sedimentary environments but reflect sets of environ-mental factors. As Frey et al. (1990) put it, ichnofacies are not intended to be paleobathymeters. A well-known example is the occurrence of the Skoiilhos ichnofacies, typical of foreshore to upper-foreshore settings, in lower-shoreface to offshore tempestites and deep-marine turbidites (e.g., Crimes, 1977; Pemberton and Frey, 1984; Pemberton and MacEachem, 1997). The Cruziana ichnofacies, though typical of lower-shoreface to offshore deposits. may be present in shallower settings, commonly intertidal flats of tide-influenced shorelinos (e.g., Mangano et al., 2002; Mringano and Buatois, 2004a,b). Rega rd less of the depositional environment involved, it is a precise set of eiwironniental conditions that is indicated by a specifłc ichnofacies. This situntion is also the rule rather than the e\ception for Continental ichnofacies.