Sequence Stratigraphy - Trace Fossils as Indicators of Sedimentary Environments - page 153

sedimentology. The strong facies control on the character and distribution of
trace-fossil suites allows this data to be integrated with physical sedimentology
to yield more precise depositional interpretations of the sedimentary units. Like
sedimentology, ichnology has been employed, for the most part, to assist in the
identification and interpretation of bounding surfaces separating different stra-
tal units (e.g., Ainsworth, 1994; Bann et al., 2004; Dam, 1990; Hillg¨rtner,
1998; MacEachern et al., 1992a,b, 1999a, 2007a,b; Pemberton et al., 1992a;
Savrda, 1991a,b; Savrda et al., 2001a,b; Taylor and Gawthorpe, 1993 ).
The ichnological identification and interpretation of key bounding surfaces
has rested on the recognition of (1) ichnologic omission suites, and (2) the
juxtaposition of softground trace-fossil suites (cf. MacEachern et al., 1992b,
2007a,b; Pemberton and MacEachern, 1995; Pemberton et al., 2004 ). Ichnolo-
gical omission focuses on substrate-controlled ichnofacies and palimpsest
suites and has a long history of application to sedimentary successions (e.g.,
Bromley, 1975; Bromley and Goldring, 1992; Bromley et al., 1984; Dam,
1990; de Gibert and Robles, 2005; F¨rsich et al., 1981; Hayward, 1976; Jones
and Pemberton, 1989; Kobluk et al., 1977; Miller and Rehmer, 1982; Pember-
ton and Frey, 1985; Pemberton et al., 1980; Savrda, 1991a,b; Vossler and
Pemberton, 1988 ). The latter approach addresses vertically and laterally juxta-
posed trace-fossil associations that contravene Walther's Law and is best
achieved through the integration with physical sedimentological facies analysis
(e.g., Bann et al., 2004; Bhattacharya, 1993; Fielding et al., 2006, 2008;
Ghibaudo et al., 1996; Hampson and Howell, 2005; Hampson and Storms,
2003; Hillg¨rtner, 1998; MacEachern and Pemberton, 1994; MacEachern
et al., 1998, 1999a,b, 2007a,b; McIlroy, 2004, 2008; Mellere and Steel, 1995;
Pattison and Walker, 1994, 1998; Pemberton and MacEachern, 1995, 2005;
Pemberton et al., 1992a, 2001, 2004; Rodr´guez-Tovar et al., 2007; Savrda,
1995; Savrda et al., 2001b; Taylor and Gawthorpe, 1993; Taylor et al., 2003 ).
Research continues to expand and refine the role of trace-fossil analysis in
the sequence-stratigraphic evaluation of siliciclastic and carbonate successions.
This chapter summarizes the ichnological signal of the key bounding surfaces of
sequence-stratigraphic relevance. Three case studies are presented that show-
case some of the ways in which ichnology can assist in the identification of
these bounding surfaces and the interpretation of the successions.
1.1 Nomenclature, Key Bounding Surfaces, and Systems Tracts
The working group on sequence stratigraphy, appointed in 2008 by the Inter-
national Subcommission on Stratigraphic Classification, provides guidelines
concerning sequence-stratigraphic nomenclature and key bounding surfaces
( Catuneanu et al., 2011 ).
The subaerial unconformity (SU; Sloss et al., 1949 ) is an unconformity that
forms under subaerial conditions as a result of fluvial erosion or bypass, pedo-
genesis, wind degradation, or dissolution and karstification. This is considered
the sequence boundary within the context of the “depositional sequence” model.