The Ichnofacies Paradigm - Trace Fossils as Indicators of Sedimentary Environments - page 122

Dashtgard, 2011a; Gingras et al., 1999, 2001;MacEachern andBann, 2008 ;MacEa-
chern and Gingras, 2007; MacEachern et al., 2005, 2007b; McIlroy, 2004a, 2007;
Savrda, 2007; Savrda et al., 2001a,b ).
4. THE ROLE OF SEILACHERIAN ICHNOFACIES
The Seilacherian ichnofacies operate as facies models , addressing animal/sedi-
ment responses in the depositional environment ( MacEachern et al., 2010 ).
They have been built through the distillation of recurring characteristics of
trace-fossil suites from numerous case studies ( Fig. 8 ). The distillation of obser-
vations from these case studies allows the ichnofacies to retain the recurring
characteristics of the attributable suites (e.g., diversities, ethological groupings,
responses to substrate consistency), independent of their case-specific charac-
teristics and minimizes the impact of changes in suites owing to evolution.
Ichnogenera may differ, but their ethological and trophic affinities are equi-
valent, and hence, their significance to the interpretation of the depositional
environment is comparable. The unique characteristics of the suites are retained
in order to evaluate the details of the specific case study. Ichnofacies have also
been validated and refined via neoichnological studies (see Section 2 ). This
“process ichnology” (e.g., Dashtgard, 2011a,b; Gingras et al., 2007a,b, 2011 )
underpins the ichnofacies concept just as process sedimentology underpins
lithofacies-based facies models.
Ichnofacies models serve the same five functions ( Fig. 8 ) as do lithofacies
models (e.g., Walker, 1992 ; see also Dalrymple, 2010; MacEachern et al.,
2010 ). First, an archetypal ichnofacies acts as a norm for the purposes of com-
parison. Archetypal ichnofacies, by acting as norms for comparison, allow
one to determine whether a new example meets the criteria for inclusion
within a specific ichnofacies. Without a norm, it cannot be determined
whether a new example contains unusual or anomalous characteristics. If it
conforms to an archetypal ichnofacies, it strengthens the concept, and inter-
pretation of the new example is simplified. If it differs from the established
norm, then the worker can specify precisely how it differs and refine its
interpretation.
The second role of the ichnofacies concept is to act as a framework or guide
for future observations . When one is working in particular bioturbated units,
mental search criteria are erected. Certain ichnofacies have commonly associ-
ated trace-fossil elements. Knowing these affinities helps to guide the worker
and focuses the worker's eye to search out outcrop or core orientations that dis-
play the entire suite.
The third role of the ichnofacies concept is that it serves as a predictor in
new situations . The Seilacherian ichnofacies paradigm demonstrates that the
various archetypal ichnofacies correspond to predictable combinations of envi-
ronmental conditions. Seilacherian ichnofacies show a close relationship with