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

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member is unconformably overlain by marine de-
posits of the Curtis or SummerviUe Formations or
the Romana Sandstone, and may be at least equiv-
alent to the upper part of the middle member of
the Entrada Sandstone elsewhere. The upper
member of the Entrada Sandstone largely oc-
cupies the Circle Cliffs basin or trough, with an
isopach pattern similar to that of the underlying
lower and middle members. Lateral relationships
of the upper member are poorly understood,
largely because much of the unit was removed
prior to deposition of overlying rocks but also
because many critical areas are concealed or were
removed by erosion (Fig. 28).
The Cow Springs Member of the Entrada has
been recognized as a distinct unit within the En-
trada (Peterson, in press). The unit retains forma-
tion status in the southern San Juan basin pending
additional studies. As seen in Fig. 29E, the Cow
Springs forms a northwest-southeast elongate
body. Progressing northwestward the member ap-
parently grades into the upper part of the middle
member of the Entrada Sandstone in north-central
Arizona. The northeastern boundary of the Cow
Springs is a facies change primarily into silty
mudstones of the Wanakah Formation. The Cow
Springs is broadly interpreted as a later-phase erg
of the Entrada Sandstone that existed inland from
sabkha or restricted marine deposits represented
by the Wanakah Formation or middle member of
the Entrada. Its distribution may partly reflect the
nature of preservation beneath the J-5 uncon-
formity. Facies patterns within the Cow Springs
show a clear northeastward decrease in the per-
centage of cross-stratified sandstone toward facies
change into the Wanakah Formation.
The sandstone at Mesita (Condon, 1985a, b;
Condon and Peterson, 1986) is a predominantly
eolian unit in the southeastern San Juan basin of
northwestern New Mexico that was formerly as-
signed to the Bluff Sandstone (Rapaport et al.,
1952) or to the Bluff and Zuni Sandstones
(Maxwell, 1976, 1982). The Mesita is divided into
lower and upper parts (Condon, 1985a, b) that we
here tentatively correlate with the Cow Springs
Sandstone and the Recapture Member of the
Morrison Formation, respectively; this relation is
reflected in the isopach map (Fig. 28).
Middle Jurassic V
Following O'Sullivan (1980a, b, 1981a, b) and
O'Sullivan and Pierce (1983), the Moab Tongue of
the Entrada Sandstone is distinguished by bedding
style from the underlying and laterally adjacent
Slick Rock Member. The Moab Tongue consists
of one to a few large sets of cross-strata, and the
Slick Rock Member consists of interbedded thin
sets of cross-strata and silty, red, flat-bedded units.
Using this criterion, the Moab Tongue is restricted
to a fairly small part of southeastern Utah. Earlier,
Wright et al. (1962) used different, but now con-
sidered unreliable, criteria to trace the Moab
Tongue into southwestern Colorado.
The Moab Tongue reaches a maximum thick-
ness of about 34 m along the northeast side of the
Monument uplift (Fig. 30). To the northwest, the
tongue is replaced laterally by red beds in the
lower part of the lower Summerville Formation of
McKnight (1940), now the Curtis Formation (Fig.
29C). Here the Moab Tongue is overlain by the
restricted marine Summerville Formation, and
separated from the Slick Rock Member by the
lowermost lower Summerville Formation of Mc-
Knight (1940). This lower tongue of Summerville
pinches out eastward so that the Moab Tongue
directly overlies the Slick Rock Member.
Southeastward, most of the Summerville that lies
above the Moab is truncated by the J-5 unconfor-
mity. O'Sullivan (1980b) showed that Summerville
redbeds overlying the Moab are truncated east-
ward by the sub-Morrison unconformity. How-
ever, more recent but as yet unpublished work by
R.B. O'Sullivan (pers. commun., 1986) indicates
that a thin part of the Summerville does continue
eastward to merge with similar redbeds at the top
of the Wanakah Formation in southeastern Utah.
Hence, the Moab is succeeded by restricted marine,
sabkha, or tidal-flat(?) deposits.
In the northeastern portion of the outcrops, the
Moab Tongue grades into the Stick Rock Member
(Fig. 29C). Similarly, to the south the tongue
breaks into numerous cross-stratified and flat-bed-
ded units included in the Stick Rock Member. At
the southern localities, a thin wedge of the
Wanakah Formation lies on the Moab Tongue
and separates it from the overlying J-5 unconfor-
mity.