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

Introduction
The most voluminous expanse of eolian deposi-
tional systems in the geological record occurs
across the Western Interior of the United States.
The area stretches from southern Nevada and
adjacent California across the Mogollon Rim of
Arizona across the northern half of New Mexico
into the Texas and Oklahoma panhandles, north-
ward through eastern Utah and western Colorado,
eastward into north-central Colorado, northward
into Wyoming and the Black Hills of South
Dakota, west into southwestern Montana, and full
circle south along the Cordilleran Hinge Line
through southwest Utah to southern Nevada (Fig.
1 * ). Within this vast area, the greatest concentra-
tion of eolian-beating formations occurs on the
Colorado Plateau in south-central Utah and adjac-
ent Arizona (Blakey, this volume). Eolian deposi-
tion began in the Early and Middle Pennsylvanian
(Atokan, Desmoinesian), reached an initial climax
during the early Permian (Wolfcampian,
Leonardian), waned during the Triassic, and
reached a second climax during the Middle
Jurassic; eolian deposition declined during the
Late Jurassic and is absent in the Cretaceous (Fig.
2). Thus eolian deposits are distributed throughout
160 m.y. of time and dominated deposition in
some areas.
Purpose and scope
The chief purpose of this paper is to describe
the geometry of the late Paleozoic and Mesozoic
eolian deposits of the Western Interior. We are
presenting an atlas that documents geometry,
stratigraphy, and facies relations of the eolian-
bearing intervals. The information is presented in
a series of maps and cross sections, each of which
is carefully documented by maps and tables to the
source of the original data.
Methods
Field-based observations and studies of the
authors, both published and unpublished, form
* Due to their large size Figs, 1, 4, 5, 6, 8, 9, 10, 11, 12, 13, 15,
17, 18, 20, 21, 22, 24, 25, 27, 28, 30, 31, 33 and 34 are placed
together on the foldouts in this article.
the foundation of this paper; however, most of the
basic data has been collected from the literature.
The isopachs were constructed from data points
that were carefully plotted by township and range,
numbered, listed with author, their section desig-
nation, interval of study, and thickness of eolian
interval. Because much of the information in the
literature does not specify the environment of
deposition of the rocks of interest or misinterpre-
ted the origin of the rocks, or contains outdated
stratigraphic terminology, we used our collective
experience to define the eolian intervals within the
original authors' section. Thus it is possible for
subsequent workers to take our data back to the
original source and see how our interpretations fit
within the framework of the original authors' work.
Space limitations and tremendous breadth of sub-
ject demanded that our conclusions be arrived at
directly without much discussion or debate of
numerous hypotheses.
It should be noted that the isopachs show the
thickness of the eolian-bearing interval and not
necessarily the thickness of a formal rock-strati-
graphic interval or rocks of a particular age (Table
1). In general the isopachs show the thickness of
erg or dune deposits from the base of the oldest
eolian sandstone to the top of the youngest one. In
some instances the thickness of simple, thick,
non-eolian tongues is subtracted from the iso-
pached interval. Because many geologic units con-
tain mixtures of eolian and non-eolian rocks, the
isopachs may vary considerably from previously
published maps of a given formation; or where
specified, they may include parts of more than one
formation or stratigraphic unit. Most of the maps
have patterns that show approximate percentages
of eolian rocks within the overall eolian-bearing
sequence. If a given eolian interval shows an iso-
pach of 100 m and a percentage of 50, this means
that the thickness of the eolian-beating rocks of a
given interval is 100 m and that approximately
half of that interval contains eolian-deposited
rocks.
We caution the reader that because the maps
vary slightly in method of construction, Table 1
must be consulted when examining our presenta-
tion of a given eolian sequence; be aware of what
the data mean! We found it necessary to vary the