The Ichnofacies Paradigm - Trace Fossils as Indicators of Sedimentary Environments - page 121

ichnotaxonomic entities. Although various ichnogenera may come and go
throughout the geological record and trace-fossil suites as well as “ichnofabrics”
may differ in time and space, the “essence” of the behavioral and trophic groupings
that define the ichnofacies remains consistent. In thisway, the temporal limitations
of individual ichnogenera and ichnospecies have less importance, and ichnological
suites and ichnofabrics consisting of different ichnotaxa can be compared and con-
trasted ethologicallywith one another. This truth lies at the heart of the ichnofacies
paradigm and explains the enduring strength of the concept.
Ichnological suites constitute part of the total aspect of the rock interval and
consist of the primary biogenic structures created by organisms that inhabited the
depositional environment. Insights into the depositional environment are derived
from the fact that organisms respond in predictable ways to variations in environ-
mental conditions (see Section 2 ). Although in the marine realm many of these
conditions change progressively with increasing water depth, ichnogenera dis-
play only a passive relationship to bathymetry ( Frey et al., 1990 ). This passive
relationship does tend to lead to predictable proximal-distal trends in many suc-
cessions, but there are numerous exceptions, particularly those associated with
dynamic depositional regimes (e.g., submarine fans, fan deltas, sandy tide-
dominated shelves, etc.). The resulting ichnological suites and ichnofabrics tend
to vary spatially, so much so that they are not readily mappable at the scale of
depositional facies (for an exception, see Bockelie, 1991 ). Ichnofacies serve
as the conceptual basis for grouping these spatially variable suites and ichnofab-
rics, allowing them to be employed to interpret the depositional environment. In
this way, ichnofacies, like lithofacies, are subject toWalther's Law. The utility of
ichnofacies to paleoenvironmental reconstruction lies in their lateral continuity
and predictable vertical succession, which leads to mappable units. Accurate
interpretations of depositional environments favor reliable predictions of later-
ally adjacent settings and their associated ichnofacies. Like all facies analyses,
interpretations of ichnofaunas are improved substantially when they are evalu-
ated in the context of their sedimentological (i.e., lithofacies) and stratigraphic
context (e.g., Bann et al., 2004, 2008; Buatois et al., 2012; Crimes et al., 1981;
Dam, 1990; Ekdale et al., 1984; Frey, 1990; Genise et al., 2004; Gingras et al.,
2001 ;M ´ ngano and Buatois, 2004; MacEachern et al., 2007a,c, 2010; McIlroy,
2004a, 2008; Melchor, 2004; Pemberton and Frey, 1984; Pickerill, 1992; Savrda
et al., 2001a,b; Smith, 1993; Smith et al., 1993; Taylor and Goldring, 1993 ).
Ichnological suites that showdepartures from the archetypal Seilacherian ichno-
facies are also common, but their recognition and interpretation are possible only by
comparison with these established norms (e.g., Bann et al., 2004; Buatois and M ´ n-
gano, 2011; Gingras et al., 2012; MacEachern et al., 2007b, 2010 ;cf. Section 4 ). By
their very nature, anomalous ichnological suites yield important insights into the spe-
cific characteristics of the depositional setting, highlighting animal/sediment inter-
actions in response to imposed environmental stresses. In this way, brackish-water
environments, anoxic to dysaerobic settings, and areas of fluvio-deltaic deposition
can be readily recognized (e.g., Bann et al., 2004, 2008 ; Buatois et al., 2012 ;