Sequence Stratigraphy - Trace Fossils as Indicators of Sedimentary Environments - page 164

3. ICHNOLOGICAL APPLICATIONS TO
SEQUENCE STRATIGRAPHY (CASE STUDIES)
The applications of ichnology to sequence stratigraphy are best illustrated through
case studies. The first two case studies come fromthe extensively studied EarlyCre-
taceous Viking Formation of the Western Canada Sedimentary Basin of Alberta,
Canada. Discontinuities in this interval are widespread and abundant. They are
interpreted to have resulted from a combination of tectonic and eustatic processes
operating in the foreland basin, as well as deposition associated with a period of low
accommodation. The third case study comes from the Middle Permian-Early
Triassic Khuff Formation, offshore Iran. This carbonate succession accumulated
on a carbonate platform subject of repeated regression and transgression.
3.1 Incised Shorefaces, Viking Formation, Alberta, Canada
The Viking Formation of Alberta contains a number of sharp-based sand bodies
of shallow-marine origin, which overlie widespread erosional discontinuities
(e.g., Downing andWalker, 1988; MacEachern et al., 1998, 1999a,b; Posamentier
et al., 1992; Walker and Wiseman, 1995 ). These sand bodies are interpreted as
incised shorefaces. Incised shorefaces can be generated during the FSST or the
TST. The FSST occurrences overlie the RSME and are genetically linked to
the Viking valley incisions lying further landward (e.g., Pattison and Walker,
1994; Posamentier et al., 1992; Walker and Wiseman, 1995 ;see Section 3.2 ).
The LST example directly overlies the FSST at Judy Creek, resting on a CC.
The LST displays progradation as well as aggradation. The TST examples are
associated with the WRS excavated during erosive shoreface retreat across the
SU, to produce a composite surface (WRS/SU; Fig. 3 ). The incised shorefaces
of the FSST and TST are excavated into shallow-marine parasequences that
reflect normal regression associated with the HST. These parasequences consist
of facies broadly similar to those of the incised shorefaces, making recognition
of the FSST, LST, and retrogradationally stacked TST shoreline deposits chal-
lenging. Recognition of the presence of a stratigraphic discontinuity, therefore,
is critical. Ichnologically, these discontinuities are commonly demarcated by
firm-ground and palimpsest softground omission suites.
3.1.1 Shorefaces of the FSST and LST
The FSST shoreface overlies the RSME (cf. Helland-Hansen and Gjelberg,
1994; Hunt and Tucker, 1992, 1995; Mellere and Steel, 1995 ; Figs. 4 and 5 ).
The RSME is ideally suited to omission suite colonization, as the discontinuity
is cut in a subaqueous marine setting, allowing the dewatered, firm, or cemented
substrate to become colonized by infauna prior to its burial during forced regres-
sive shoreface progradation. The RSME is considered to be excavated and
available for omission colonization only in positions above fair-weather wave
base. Certainly, erosion may persist as far seaward as the storm-wave base, but