Synthesis of late Paleozoic and Mesozoic eolian deposits of the ...

quartzose composition of the rock. The quartzite
of McGery Canyon in the Paradise Range (sect.
33, T12N, R37E, Nye County, Nevada), currently
being mapped by N.J. Silberling of the U.S. Geo-
logical Survey, consists of similar lithologies and
has similarly poor but suggestive evidence of an
eolian origin. The thickness of these units is un-
known but each is at least 100 m thick and the
quartzite of McGery Canyon may be considerably
thicker.
Isolated outcrops of clean quartz sandstone and
quartzite near Currie in northeastern Nevada that
are interpreted by some workers as a marine facies
of the Aztec Sandstone have added more confu-
sion than resolution to interpretations of late Early
Jurassic eolianites. The beds are flat laminated or
contain scarce thin tabular-planar crossbed sets
(most of which are less than 15 cm thick) that do
not appear to be eolian in origin. Orange quartz
sandstone beds less than 2 km south of Currie
may well correlate with the Aztec but they are
largely flat laminated and do not represent dune
deposits. They could have been deposited on eolian
flats adjacent to the main body of an erg or they
may have been deposited in subaqueous environ-
ments. Red quartz sandstones or quartzites about
10 km north and northwest of Currie are almost
entirely flat laminated and may have been de-
posited in environments similar to the beds just
south of Currie. These beds are better cemented
(with silica) and a different color (red rather than
orange) than the beds south of Currie. The stratal
relationships of these beds are questionable and it
is conceivable that they might be Paleozoic in age.
In summary, none of the beds around Currie
appear to have been deposited in eolian dune
fields and for that reason they were not included
in this study.
Stratigraphic relationships at the base of the
isopach interval are poorly understood in north-
western Colorado and northeastern Utah. Poole
and Stewart (1964) suggested that much of the
Glen Canyon Sandstone in this area may be
equivalent to the Lukachukai Member of the
Wingate Sandstone and Kayenta Formation
farther southwest in southeastern Utah and south-
western Colorado. On the other hand, we feel that
the regional stratigraphic relationships (for exam-
ple, see Pipiringos and O'Sullivan, 1978, pl. 1,
section B-B' between U12 and W59-W60) point
toward a correlation in which only the lower 15-30
m of flat-bedded strata in the Glen Canyon Sand-
stone correlate with the Lukachukai Member and
Kayenta Formation. If correct, this yields a corre-
lation of the upper or predominantly eolian part
of the Glen Canyon Sandstone with the Navajo
and Aztec Sandstones and with the eolian upper
part of the Nugget Sandstone. We recognize inter-
fingering at the base of eolian strata that comprise
the upper Nugget, upper Glen Canyon, Navajo
and Aztec Sandstones. However, we do not feel
that the interfingering is of sufficient magnitude
to make the upper Glen Canyon equivalent to the
Lukachukai Member of the Wingate Sandstone or
to any significant part of the Kayenta Formation,
nor do we think that the upper Glen Canyon
correlates with any appreciable part of the lower
or Bell Springs Member of the Nugget Sandstone.
The isopach interval on Fig. 18 reflects these
correlations.
The late Early Jurassic erg deposits attain a
maximum thickness of 677 m in the central Utah
part of the Utah-Idaho trough; they thin and
pinch out eastward owing to eastward beveling
beneath the J-2 unconformity (Fig. 19). The origi-
nal eastward extent of the erg is unknown, but to
our knowledge there are no sedimentologic hints
that the sandstone grades eastward into a non-
eolian facies a short distance east of the outcrop
limits of these beds. Thus, the erg could well have
extended some considerable distance farther east
than its present extent suggests. The erg deposits
tend to thicken westward into the Utah-Idaho
trough and, in southeastern Idaho and southeast-
ern California, they appear to thin west of the
trough. However, the data are unreliable in these
areas and one cannot be assured that the west-
ward thinning is real and not a reflection of
scarcity of measurements and poor quality of the
data (owing to cover, estimated thicknesses rather
than measurements, and to structural or strati-
graphic complexities). Most time-stratigraphic
units of late Paleozoic and Mesozoic age in the
Western Interior thin eastward onto the craton by
depositional processes. Judging from this, it would
seem as though the late Early Jurassic erg units
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