Geology Reference
In-Depth Information
Fig. 17.21
A tendency to
misinterpret transgressive
tidal deposits on the tops of
regressive shorelines as
distributary channels or
upper shoreface units in the
Cretaceous Western Interior
Seaway was highlighted by
Devine (
1991
) . He empha-
sized the common regressive
(R)-transgressive (T) nature
of sequences, the tide-infl u-
enced or tide-dominated
nature of the transgressive
deposits, and the presence of
transgressive ravinement
surfaces (TD)at the regres-
sive-transgressive turn-
arounds. (Modifi ed from
Devine
1991
)
erosion surfaces (e.g. Van Wagoner et al.
1990
; Van
Wagoner
1991
; Plink-Bjorklund
2008
) (Fig.
17.24
),
refl ect an initial signifi cant seaward shift of facies,
where fl uvial deposits occur above the valley base (e.g.
Hampson et al.
2008a,
b
) , have adjacent interfl uve sur-
faces (e.g., O'Byrne and Flint
1995
) and show onlap of
infi ll strata onto the valley walls (e.g. Plink-Bjorklund
2008
; Charvin et al.
2010
) . The valleys were incised
during times of sea-level fall and lowstand, and are
interpreted to have been fi lled mainly during lowstand
and transgression (eg., Kenilworth Member of Blackhawk
Fm and Chimney Rock Sandstone), or primarily during
transgression (Desert, Grassy and Sunnyside Members
of Blackhawk Fm). Valley incisions were particularly
common during the 77.5-75 Myear interval as discussed
below, and an example of the detail within a 20 m-thick
valley-fi ll from Iles 3 sandstone tongue (Crabaugh
2001
) is shown in Fig.
17.24
.
The Campanian WIS valley fi lls occur as wave-dom-
inated, mixed-energy or tide-dominated estuary depos-
its (
sensu
Dalrymple et al.
1992
) . The wave-dominated
estuarine fi lls are similar to those in thin, non-valley-
confi ned tidal accumulations and consist of tide-infl u-
enced fl uvial, bayhead delta, central basin (lagoonal)
and outer-estuarine wave-dominated barrier, tidal inlet,
fl ood-tidal delta deposits (e.g. Yoshida
2000
) . The only
mixed-energy estuary fi ll is that reported from the
Chimney Rock Sandstone, which is similar to a wave-
dominated estuary, except for the occurrence of inner-
estuarine tidal bars in association with bayhead deltas
(Plink-Bjorklund
2008
; Fig.
17.23
). The tide-dominated
estuarine accumulations consist of tide-infl uenced fl u-
vial, tidal channel, outer-estuarine tidal bar and marginal
tidal fl at deposits (e.g. Fitzsimmons
1994
) .
Two of the tidal accumulations included here with
incised valley fi lls are associated with basal fl uvial
