Sequence Stratigraphy - Trace Fossils as Indicators of Sedimentary Environments - page 175

FIGURE 10 TS/SU of a wave-dominated estuarine valley. Core box photo (A) and close-up photo
(B) showing fully marine offshore mudstones erosionally overlain by brackish-water heterolithic
facies of the estuary central-basin complex. The stratigraphic discontinuity (arrow) represents
the transgressive surface associated with bay-line flooding, overlying the subaerial unconformity
(TS/SU). The surface is demarcated by granules of chert and firmground Gastrochaenolites ( Ga )
of the Glossifungites Ichnofacies. Crystal Field, Alberta. See Fig. 3 for sequence-stratigraphic
surface names. Scale bar ¼ 15 cm (A).
buried beneath fluvial deposits. Omission suites associated with ravinement
generally record ethologies consistent with high-energy conditions, typified
by permanent vertical dwellings consistent with filter-feeding organisms
(e.g., firmground Skolithos and Diplocraterion ; cf. MacEachern et al., 1992a,
b, 1999b ). Omission suites do not generally accompany the TS unless it directly
overlies the SU (e.g., TS/SU). These occurrences typically record ethological
groupings more consistent with low-energy conditions, as colonization of the
TS/SU occurs in sheltered and/or distal positions during transgression
(cf. MacEachern and Burton, 2000; Savrda et al., 2001a ).
3.2.2 Juxtaposed Facies of the Viking Incised Estuarine Valleys
Recognition of estuarine incised-valley fills is also facilitated by the contrast
between the facies into which the valley is incised and the brackish-water
deposits of the valley itself. In the case of the Viking Formation at Crystal
and Willesden Green, the facies of the estuarine valley complexes are readily
identified ichnologically, as the SU is incised into open-marine parasequences
that record shelf to distal lower shoreface settings ( MacEachern and Pemberton,
1994; Pemberton et al., 1992b ). Regionally, the SU is identified by truncation of
the underlying parasequences that record normal regression. The underlying
parasequences are typified by high bioturbation intensities (BI ¼ 4-5), uni-
formly distributed bioturbation, a high ichnological diversity, and the common