More and More Navajo sandstone plants

Glenn Morton (
Thu, 12 Feb 1998 21:08:37 -0600

For your consideration, Art,

"Silicified wood has been reported previously from the Navajo Sandstone
(Triassic-Jurassic) near Moab, Utah; additional information is now at hand.
At least five individual trees represented by stumps standing in place of
growth, eroded to within about .7 m of the root bases, and surrounded by much
shattered material including sections of branches are seen in a clean exposure
in the northeast corner of T. 20S, R. 17E. All trees are small, diameter 40-60
cm, are conifers (taxonomy not yet determined), and were apparently buried
completely or nearly completely by wind-blown sand in position of growth.
"From drill-hole data the level of growth is very near 65 m from the base
of the Navajo Sandstone which is about 170 m thick in the vicinity. a
limestone lens ranging up to 72 cm thick lies about 3.2 m above the root bases.
The connection between trees and a small water body may be that both were
dependant on artesian flow through deep-seated fractures. A strong set of
joints trending about N.15W cuts through the fossil-=bearing area and may be
the present day expression of such fractures."
"This and similar fossil 'forests' must be taken into account in
reconstructing the paleoecology of the Navajo. it is possible the scattered
ponds and small groves of trees provided food and perches for the pterosaurs
known to have left trackways in nearby localities."~William Lee Stokes,
"Silicified Trees in the Navajo Sandstone, East Central Utah," 36th Ann. GSA
Rocky Mtn Section and 79th Ann. GSA Cordilleran Section Meeting, Abstracts with
Programs, 1983,15:5 p. 286

"Silicified wood fragments as much as 20 cm. in diameter are widespread in
outcrops of the Triassic-Juraswsic Navajo Sandstone near Moab, Utah. The wood
is typically found in indistinctly crossbedded sandstone peripheral to thin,
discontinuous carbonate beds. some trunks are in nearly vertical position
suggesting in situ preservation. Smooth, fluted surfaces on some fragments
indicate abrasion before burial.
"Diverse tubular and cylindrical structures, typically in diameter are
also abundant in the Navajo. They occur just below horizontal truncation
planes which separate sets of crossbeds. Crossbedding is indistinct below the
truncation planes, and distinct and undisturbed above. Tubes are composed of
an outer sheath of well-cemented sand surrounding a core of calcite spar;
cylindrical features consist entirely of sand. These structures have many
similarities with root casts in Holocene dunes at Arches National Park, near
Moab, and have important implications concerning depositional environments of
the Navajo Sandstone."~David B. Loope, "Fossil Wood and Probable Root Casts in
the Navajo Sandstone," 32th Ann. GSA Rocky Mtn Section Meeting, Abstracts with
Programs, 1979, 11:6 p. 286


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