Geology Reference
In-Depth Information
Fig. 17.25
A ca 17 km NW-SE transect along part of the Topic
Cliffs of Western Colorado from Kirschbaum and Hettinger
2004
. Notice how the architecture of the 'anomalous' clastic
wedge (Aschoff
2008
) (complex lower half of diagram) con-
trasts with that of the wedge above (containing Rollins Sandstone
shorelines). This anomalous wedge has stacked, thin, extensively
progradational shorelines (
yellow
) that are frequently incised by
channels and valleys containing estuarine (
pink
) and coastal plain
(
green
) deposits. This architectural complexity, probably refl ec-
ting irregular coastline morphology compared to the straight
shorelines of the overlying Rollins Sandstone, also contains an
unusual degree of tidal infl uence
Table 17.3
Thick, transgressive non-valleyed tidal accumulations
Depositional
environment
Example
Location
Setting
Thickness
References
Uppermost Chimney
Rock Sandstone
of Rock Springs Fm
NE Utah/SW
Wyoming
Uppermost transgressive part
of a regressive-transgressive
fourth-order sequence
60 m
Four vertically
stacked tide-dominated
estuarine accumulations
Plink-
Björklund
(
2008
)
Formation that correlate basinwards to multiple
marine shorelines of the Sego, Corcoran and Cozzette
Sandstones and their coeval Mancos Shale basinal
equivalents. To the north, along southern Wyoming
and northern Colorado, the time interval includes the
alluvial-estuarine Trail and Rusty Members of the
Ericson Formation that correlate basinwards to about
12 marine shoreline tongues of the Iles Formation and
their coeval Mancos Shale equivalents. The characteristic
features of this anomalous stratigraphic interval that
contrast with the underlying (Blackhawk Formation in
Utah; Rock Springs Formation in Wyoming) and over-
lying (Rollins Sandstone, Trout Creek and Twenty-
Mile Sandstones in Colorado) successions are:
1. A relatively slow, average sediment accumulation
rate of 42 m/My - less than half the rate seen in the
underlying Rock Springs Formation in S. Wyoming,
and in the Blackhawk Formation in Utah, as well
as a fast rate of overall shoreline progradation
(~208 km/My) relative to underlying and overlying
