Geology Reference
In-Depth Information
Fig. 17.23
Correlation panel across Chimney Rock Sandstone
near Minnies Gap, Wyoming-Utah border. Note the great thick-
ness of the backstepping tide-dominated estuarine sandstones
stacked on four tidal ravinement surfaces (uppermost Chimney
Rock Sandstone), accumulated above an incised valley fi ll with
a mixed-energy estuary fi ll (middle part of the Chimney Rock
Sandstone), incised into a set of regressive, river- and wave-
dominated deltaic units (lowermost Chimney Rock Sandstone)
(From Plink-Björklund 2008)
open-mouth estuarine deposits (
sensu
Dalrymple et al.
1992
) with tide-infl uenced fl uvial, tidal channel, upper-
fl ow-regime tidal fl at, outer-estuarine tidal bar and
marginal tidal fl at deposits.
than their regressive counterparts. The tendency for the
increased abundance of tidal deposits in transgres-
sive tracts may be simply due to the shelf coming into
tidal resonance as it widens during transgression.
The thinness of most of these transgressive intervals
(typically <5 m) probably refl ects a lack of signifi cant
relief during rapid transgressive drowning or a low
sediment supply, whereas thicker transgressive accu-
mulations (9-15 m thick) refl ect a higher sediment
supply and a steeper transgressive trajectory.
In contrast, the transgressive tidal accumulations in
incised valleys commonly reach signifi cant thicknesses
(up to 40 m). This happens preferentially within low-
accommodation settings where valley abundance and
depth of incision are preferentially increased. Valley
17.4.4 Causes of Increased Tidal Infl uence
in Transgressive Settings
Thin tidal accumulations indicate drowning and
cannibalization of strandplains and formation of back-
barrier lagoons, or drowning of delta plains and river
mouths and formation of wave-dominated estuaries or
back-barrier lagoons. These transgressive accumu-
lations often display a greater degree of tidal infl uence
