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

The presentation of each eolian-bearing se-
quence will follow the same format. Description in
the text will be brief, especially in cases where the
rocks are well described in previous literature.
Emphasis will be placed on facies and geometric
relations of the eolian units, especially lateral con-
figurations. We will show that few eolian deposits
are simple layer-cake sand bodies, and rather that
most are complex units that change vertically and
laterally and show strong diachronous characteris-
tics. Preliminary and general interpretations of erg
geometry will be offered, although this topic is
more completely discussed in other papers in this
volume.
Isopachs alone are insufficient for interpreta-
tion of complex sandstone-body geometry. Most
of the isopach maps have additional symbols for
interpretation of eolian sandstone-body geometry.
The lines that show percentage of eolian deposits
document trends of increasing or decreasing eolian
sediment within an interval. The bounding lines of
the eolian interval also aid interpretation of the
maps. Zero lines indicate wedge-out of an eolian
I. Pinch-out by truncation beneath
unconformity (e.g. east edge Navajo SS)
2. Vertically stacked facies change
(e.g. west edge Cedar Mesa SS)
~ ' ~ ~ i
3. Facies change, eolian climb
(e.g. southeast edge Schnebly Hill Fro)
4. Facies change, non-eolian climb
(e.g. south edge Wingate SSI
body, either by pinch-out of the entire interval as
in the case of the De Chelly-Schnebly Hill Forma-
tion and eastern edge of the Page Sandstone, or
pinch-out of eolian sandstone into other facies of
the interval as in the case of the western edge of
the Page Sandstone. The latter may be accompa-
nied by facies change as well as pinch-out. The
narrow saw-toothed lines indicate major facies
change throughout the entire erg-beafing interval.
Cross-sections aid in the interpretation of eolian
geometry. One or more are presented for each
interval discussed in the text.
Another situation that is not clearly shown on
the maps is the pinch-out of a major eolian tongue
with the continuation in the direction of pinch-out
of the main eolian body. This can be shown
clearly only in cross-section. An example is the
Navajo-Kayenta intertonguing across southwest-
ern Utah and north-central Arizona; the main
body of the Navajo continues well southwest of
the area of major intertonguing. Figure 3 diagram-
matically shows various types of eolian sandstone
margins and refers to a real example of each.
5. Simple pinch-out (lap out)
(e.g. east edge Page SS)
6. Simple pinch-out of single tongue
(e.g. east edge White Rim SS )
.... ..... "... : . ~. "/'."..'. : .'"... ~ ".' : :.;~i :': .".
'~\'"' .... "' ' " ' i'.-..:~::'::':?.""'..
7. Facies change, single eolian tongue
(e.g. Lamb Point Tongue, Navajo SS]
B. Split by non-eolian tongue
(e.g. west edge Page SS)
EOLIAN ROCKS
I I NON-EOLIAN ROCKS
Fig. 3. Simple cross-sections depicting geometry of various margins of ergs. An example from eolian sandstones of the Western
Interior is given for each. Compare with actual isopach maps and cross sections for true scale and geometry.