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

horseshoe-shaped eolian body that wraps around
the northern edge of the Holbrook Basin in east-
ern Arizona and related negative areas of western
New Mexico (Fig. 9). Sandstones thicken towards
the basin from a probable depositional edge along
the Sedona Arch (Fig. 4) and a zone of facies
change to Cutler Formation in the Four comers
region and rapidly changes facies to marine and
sabkha carbonate and redbed deposits in basinal
areas. The erg deposits are thickset, about 180 m
thick, near the sharp facies change toward the
basin. The rocks are firmly dated by the inter-
bedded Fort Apache Member of the Schnebly Hill
Formation (Blakey and K.nepp, in press) although
exact temporal correlations within this complex
body, especially with the Mesita Blanca Sandstone
Member of the Yeso Formation in New Mexico
are yet to be solved. It is suggested here that the
oldest eolian deposits in this sequence are con-
tained in the Mesita Blanca Sandstone of New
Mexico and lower Schnebly Hill Formation of the
western Mogollon Rim, and that the youngest
eolian deposits are in the upper part of the De
Chelly Sandstone in northeast Arizona and upper
Schnebly Hill formation in the Mogollon Rim. We
also suggest, based on physical stratigraphy and
cursory sedimentologic observations, that a thin
eolian tongue near the top of the Organ Rock
Formation in the upper Lake Powell region of
southeastern Utah may be a northward extension
of the De Chelly Sandstone.
The De CheUy and related formations were
deposited during a period of erosion to the north
and abrupt subsidence along the southern Col-
orado Plateau. It appears that the period of ero-
sion to the north saw the mobilization of large
amounts of sand from older Pennsylvanian and
Permian ergs and that the sand was fed southward
until it crossed the Sedona Arch and encountered
rapid subsidence along the Holbrook basin. Here
the sand was trapped between a broad slightly
positive region to the north and marine and sahkha
conditions in the negative area to the south (Blakey
and Middleton, 1983). During periods of low sea
level and/or extensive influx of sand from the
north, the erg prograded southward across the
coastal plain. Rises in sea level caused transgres-
sion and destruction of the ergs, which resulted in
an unconformity overlain by sabkha and marine
redbeds and carbonate.
Leonardian H eolian deposits
The middle Leonardian eolian complex is like-
wise restricted to the southern Colorado Plateau
and includes the bulk of the Coconino Sandstone
and coeval Glorieta Sandstone (Fig. 10). The
Coconino has long been considered eolian (Mc-
Kee, 1933) but details concerning eolian sedi-
mentology remain largely unpublished. The
Coconino perhaps most closely approaches the
stereotype of the layer-cake, monotonous quartz-
arenite eolian deposit. The unit displays less inter-
tonguing and facies changes than most other late
Paleozoic erg deposits and, in many places, is
chiefly large-scale, cross-stratified sandstone;
however, as will be discussed, there are exceptions
to the above. The age of the Coconino and Glorieta
is based on stratigraphic position; it overlies and
intertongues with the De Chelly Sandstone of
Yeso age and underlies the upper Coconino and
White Rim Sandstones which intertongue with the
marine Toroweap Formation. The above strati-
graphic relations are best exposed along the west
side of the Sedona Arch and are thoroughly docu-
mented by Rawson and Turner-Peterson (1980).
The Coconino thickens from a feather edge
along the Utah-Arizona border to nearly 300 m in
the central Mogollon Rim (Figs. 7E and 10). East
of the Sedona Arch, the lower and upper Coconino
are inseparable and isopachs are combined. The
north feather edge is probably depositional; it was
modified by post-Coconino erosion especially in
northeastern Arizona across the Defiance Plateau.
The erg-bearing sequence is exposed across much
of central and northern New Mexico in the
Glorieta Sandstone but south and east of the
Colorado Plateau little sedimentological data is
available and it is uncertain how much of the
formation is eolian.
In the central and eastern MogoUon Rim, the
typical Coconino grades into alternating small- to
medium-scale cross-stratified sandstone and inter-
calated wavy bedded to horizontally stratified
sandstone. Though this eastern facies has been
considered to be of marine origin by some workers,
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