Geology Reference
In-Depth Information
Fig. 17.3
Stratigraphic data across N. Utah, S. Wyoming and N.
Colorado showing clastic wedges prograding progressively basin-
wards through Lower to Upper Campanian. The settings discussed
in this paper where there are well-developed tidal deposits (see
also Fig .
17.18
) are (1) many of the most basinal, regressive sands,
on the distal fringes of clastic wedges (e.g., Haystack Mountains
tongues in Hanna Basin; Morapos and Mancos sandstones in Sand
Wash Basin; Kremmling, Muddy Buttes, Hygiene and Carter
sandstones in Middle Park Basin), (2) the transgressive systems
tracts capping almost all the marine shoreline sands. In addition,
there is an unusual degree of tidal infl uence throughout the 77.5-
75 Ma low-accommodation interval (see LAR interval marked on
chart). The Iles sandstones associate with both marine shales and
with coaly coastal plain deposits in the Sand Wash Basin column
(Diagram modifi ed from Gomez-Veroiza and Steel
2010
) .
LAR
(low-aspect ratio) is terminology of Aschoff and Steel (
in press
)
The treatment of tidal records is not exhaustive, but
is rather problem-oriented, emphasizing that there
are two main categories of tidal deposits, regressive
(mainly in a lowstand position in the basin) and
transgressive, and there is a generally strong tidal infl u-
ence (all sea level stands) within the time interval
77.5-75 Ma. We organize the discussion of tidal
deposits as follows:
1. Tidal sandbodies of
Setting 1
, representing
regres-
sive
, distally situated, tide-dominated, subaqueous
marine deltas, or deltas variably reworked by tidal
currents in the seaway. These regressive occurrences
occur at or near the progradational limits of many
clastic wedges that built from the Sevier fold-and-
thrust belt into the Western Interior Seaway (Fig.
17.3
).
Because of their spatial position, far into the basin
at the extremities of 80-100 km shoreline transits,
they are likely to be falling-stage and lowstand sand-
bodies, occurring near the regressive-transgressive
turnaround of the wedges or sub-wedges.
