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

Many eofian sandstones have one or more
margins that were removed by later erosion or are
covered by younger strata and no subsurface data
is available. This is most common along the west-
ern and southern margins of the region of study.
Late Paleozoic eolian deposits
Introduction
The late Paleozoic eolian sandstones range in
age from Atokan to late Leonardian and possibly
Guadalupian (Fig. 2). They are divided here into
five erg-bearing sequences: Pennsylvanian, Wolf-
campian, Leonardian I, Leonardian II and
Leonardian III. Each sequence is intercalated with
or bracketed by fossil-bearing rocks. Penn-
sylvanian eolian deposits are primarily distributed
north of the Ancestral Rockies, whereas Permian
ergs are extensively distributed to the southwest of
these major barriers. Figure 4 shows the distribu-
tion of late Paleozoic tectonic elements that af-
fected Pennsylvanian and Permian deposition.
Pennsylvanian eolian deposits
Pennsylvanian eolian deposition is widespread
and has been documented from the lower Casper
Formation (Steidtmann, 1974), lower Tensleep
Sandstone (Mankiewicz and Steidtmann, 1979;
Kerr, this volume) and Quadrant Sandstone
(Saperstone and Ethridge, 1984) in Wyoming and
adjacent Montana and Colorado, in the lower
Weber Sandstone of Utah, Wyoming and Col-
orado (Bissell and Childs, 1958; Driese and Dott,
1984), and from the Honaker Trail Formation of
the Hermosa Group of southeastern Utah (Loope,
1984). In addition, eolian sandstone is present in
the Manakacha and Wescogame Formations of
the Supai Group in northern Arizona but has yet
to be documented in the literature. The Pennsyl-
vanian age of each of the above is well docu-
mented by intercalated fossil-beating marine rocks.
Figure 5 and Table 2 present the data base for
Pennsylvanian and Permian eolian deposits.
The Pennsylvanian deposits, although almost
certainly a series of separate ergs ranging from
Atokan to Virgilian in age, are herein isopached
on a single map. Eolian-bearing units consist of
several stratigraphic units across Wyoming, south-
ern Montana, northern Utah and northern Col-
orado (Fig. 6). The lack of detailed stratigraphic
and sedimentologic data prevent further subdivi-
sion. The eolian deposits in southeastern Utah and
the Grand Canyon region do not have sufficient
data available to construct isopachs; only their
known and inferred lateral distribution are shown.
For simplicity, the northern sand body will be
referred to as the Tensleep complex and it also
includes part of the Weber, Quadrant and Casper
stratigraphic units. The Tensleep forms a broad
sheet across the Central and Northern Rocky
Mountain region that generally ranges to 100 m
thick but the erg-bearing interval locally exceeds
300 m in northern Utah and 500 m in southwest-
ern Montana (Bissell and Childs, 1958; Mallory,
1967; Saperstone and Ethridge, 1984). Figure 7A,
B and C shows the Tensleep and related units in
cross-section. Although the unit is renowned for
exposures of large-scale, high-angle sand-flow
strata that dip to the south and southeast (Steidt-
mann, 1974; Mankiewicz and Steidtmann, 1979),
detailed sedimentologic studies have documented
a broad variety of eolian stratification styles in-
cluding small-scale trough and planar-tabular
wind-ripple cross strata, horizontal to gently in-
clined wind-ripple strata, and wet and dry inter-
dune deposits (Mankiewicz and Steidtmann, 1979;
Driese and Dott, 1984; Saperstone and Ethridge,
1984; Kerr, this volume; J. Haslett, pets. commun.,
1986). In addition, each of the above authors have
noted interbedding of eolian and marine-sabkha
strata within the Tensleep Sandstone, especially
near erg-deposit margins.
The Tensleep complex is a north-northwest-
trending sandstone body (Fig. 6) bordered by
marine clastic and carbonate rocks to the west
(Oquirrh and Wood River Groups and related
rocks), marine carbonate to the east (lower Min-
nelusa Formation and related rocks), and fluvial
clastic rocks to the south (Maroon Formation and
Fountain Arkose; Maughan and Wilson, 1960).
Little is known about the erg margins to the north,
although Stewart and Walker (1980) reported Pen-
nsylvanian eolian deposits in the Rockies of
southern Canada.