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

Page Sandstone-filled depressions up to 10 m thick
on the J-2 surface are composed of coarser-gained,
flat to low-inclined cross-strata of wind-ripple
origin (Knight, 1986). Western outcrops of Page
Sandstone commonly are deformed, probably the
result of evaporite dissolution in the underlying
Carmel Formation.
The Page Sandstone is interpreted as a coastal
erg system that paralleled the Carmel sabkha and
shallow marine embayment to the west; the east-
ern inland limits were largely defined by the
Monument bench (Fig. 20) (Peterson and
Pipiringos, 1979; Caputo, 1980; Blakey et al., 1983;
Knight, 1986; Peterson, 1986; Kocurek and
Hunter, 1986). Eastward of the Page Sandstone,
potentially equivalent units (lower Dewey Bridge
Member of the Entrada Sandstone, lower part of
the Upper Member of the Carmel Formation) are
largely sabkha in origin. The Page Sandstone was
deposited over the irregular, eroded J-2 surface
that is commonly marked by thin-granule lag de-
posits and polygonal fractures (Peterson and
Pipiringos, 1979), the latter interpreted by Kocurek
and Hunter (1986) as forming in an evaporite-en-
crusted surface. Knight (1986) has interpreted the
coarser-grained basal deposits of the Page Sand-
stone that fill depressions on the J-2 surface as
probably predating the Page erg system per se,
and representing sand deposit over the J-2 surface
in an overall sand-undersaturated environment in
which deposition occurred only in depressions.
Middle Jurassic 111, IV, V eolian deposits
Introduction
The Middle Jurassic (Bathonian-Callovian)
Entrada Sandstone system and directly equivalent
units (Fig. 2) form perhaps the most complex
eolian system in the western United States, and
are present in nine states extending from Utah to
the Texas and Oklahoma panhandles, and from
Arizona and New Mexico to the Black Hills of
South Dakota. This erg system, composed of
numerous units, is illustrated here as three units
on three maps. Our three units do not necessarily
coincide with previous subdivisions of the Entrada
as explained below. Because of stratigraphic com-
plexities and uncertainties and despite our at-
tempts to not do so, part of the three intervals
possibly overlap in time and all are likely strongly
diachronous.
Figure 27 shows the most extensive and oldest
parts of the Entrada system consisting of: lower
and middle members of the Entrada Sandstone in
west-central Utah; Entrada Sandstone of southern
Utah, northern Arizona, southwestern and south-
eastern Colorado, and northern Utah; Slick Rock
Member of the Entrada Sandstone in east-central
Utah and west-central Colorado; Canyon Springs
Member of the Sundance Formation in Wyoming,
South Dakota, and northwestern Colorado;
Iyanbito, medial silty and upper sandy members
of the Entrada Sandstone in northwestern New
Mexico; and Entrada Sandstone and Exeter Mem-
ber of the Entrada Sandstone in east-central and
eastern New Mexico, Texas, and Oklahoma. The
Dewey Bridge Member of the Entrada Sandstone
in east-central Utah is not included on Fig. 27
because this unit generally lacks eolian deposits
and because it correlates with the older Carmel
Formation (see Page Sandstone discussion).
Figure 28 shows the Upper Member of the
Entrada Sandstone of west-central Utah, the pos-
sibly somewhat older Cow Springs Member of the
Entrada Sandstone in northeastern Arizona and
the Cow Springs Member and overlying lower
part of the sandstone at Mesita in New Mexico. It
should be noted that the Exeter Member of the
Entrada Sandstone (included in Fig. 27) in north-
eastern New Mexico may be time-equivalent to
the Cow Springs member (Lucas et al., 1985).
Restored cross-sections are shown on Fig. 29 and
Table 7 lists Entrada Sandstone data points. Fig-
ure 30 shows what may be the youngest part of
the Entrada erg systems, the Moab Tongue of the
Entrada Sandstone in east-central Utah.
Middle Jurassic 111
Overall, the Entrada Sandstone conformably
overlies the Carmel Formation. Progressing east-
ward to the pinch-out of that unit, the Entrada
Sandstone rests directly on the J-2 unconformity
that is underlain by progressively older rocks to
the east.
Across Wyoming the Canyon Springs Member
of the Sundance Formation rests on the J-2 surface
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