Sequence Stratigraphy - Trace Fossils as Indicators of Sedimentary Environments - page 177

presence of ichnogenera characteristic of unstressed, normal-marine conditions
(e.g., Helminthorhaphe , Phycosiphon , Zoophycos , Asterosoma , and Scolicia ;
MacEachern and Gingras, 2007; MacEachern and Pemberton, 1994 ). Sedimen-
tologically, these parasequences show distinct coarsening-upward successions
of consistent thickness. The parasequences are stacked into a progradational
parasequence set, typical of HNR (e.g., Pattison, 1991 ).
By contrast, the estuarine valley fill successions are characterized by highly
complex facies architectures that record incremental transgressive fill, variable
estuarine subenvironments, periods of valley reincision, and the presence of
internal erosional discontinuities. Ichnological suites within the estuary con-
form well to the brackish-water (i.e., salinity reduced) ichnological model
(e.g., Beynon et al., 1988; Gingras et al., 1999, 2012; MacEachern and Gingras,
2007; MacEachern and Pemberton, 1994; Pemberton et al., 1982 ).
Bay-head delta lobes occur in the landward zones of the valley and form
intervals dominated by sandy successions that coarsen upward in the short term
(at the scale of individual lobes), but fine upward in the long term as a result of
backstepping. Intervals consist of both wave- and current-generated sedimen-
tary structures, are markedly heterolithic, and display low bioturbation intensi-
ties (BI

0-3) that vary spatially at the bed and bedset scale ( Fig. 10 ;
MacEachern and Pemberton, 1994; Pattison and Walker, 1994 ). Suites are of
low diversity and dominated by facies-crossing elements that commonly occur
in sandy intervals (e.g., Ophiomorpha irregulaire , Cylindrichnus , Rosselia ,
Planolites , and Teichichnus ; MacEachern and Gingras, 2007 ).
Central-basin deposits are generally more mudstone dominated, but also
coarsen upward, commonly due to the backstepping of the estuary mouth com-
plex ( Fig. 11 A-C). Most central-basin successions form composite bedsets
attributable to wavy and lenticular bedding, but are dominated by wave-
generated sedimentary structures (e.g., Boreen and Walker, 1991; MacEachern
and Pemberton, 1994; Pattison and Walker, 1994 ). These bays vary widely in
character depending upon the salinity gradient within the bay, the position of the
deposits with respect to the mouth of the estuary, and the overall sedimentation
rate. Most central-basin successions show moderate intensities of bioturbation
(BI

¼

1-3) with localized bands of BI 0 (typically associated with storm beds)

¼ ¼

and BI 4. The resulting facies shows the highest ichnological diversities of the

valley, locally displaying 9-11 ichnogenera. Nevertheless, elements typical of
more normal-marine settings, which are common in the underlying highstand
parasequences, are notably absent. Common trace fossils in the central-basin
deposits include Planolites , Thalassinoides , Schaubcylindrichnus freyi , Chon-
drites , Teichichnus , Rosselia , Cylindrichnus , Palaeophycus , Diplocraterion ,
and Ophiomorpha irregulaire ( MacEachern and Gingras, 2007; MacEachern
and Pemberton, 1994 ).
The estuary mouth complex is sandstone-dominated and consists mainly of
bioturbated muddy sandstones ( Fig. 9 A and B) or current-generated cross-
stratified sandstones. Tidal-inlet and tidal-channel deposits are dominated by

¼