Re: Plants for Navajo Sandstone food

Arthur V. Chadwick (
Sat, 07 Feb 1998 19:17:49 -0800

My friend Glenn writes:

>I have found in the literature plant impressions from unit 6 of a carbonate
>lens in the lower Navajo.
> "Two plant impressions were found in rocks of unit 6. the better
>preserved is most likely an early reed-like form comparable to the
>present-day Equisetum. it is 14.5 cm long and 0.9 cm wide at the bottom and
>decreases to approximately 0.7 cm wide toward the top. The oil-like top is
>not well defined, but small ridges on the outside wall of the stem are
>preserved. The other impression, less well preserved, is thought to
>represent a similar plant. it measures approximately 32 cm long, is 3.2 cem
>wide and 1 cm deep, but has no distinctive detailed structure."~James K.
>Gilland, "Paleoenvironment of a Carbonate Lens in the Lower Navajo Sandstone
>Near Moab, Utah" Utah Geology 6(1979):1:29-38, p. 36

Two plant impressions! Now I am impressed. The question is why they were
there. With all those hungry animals around, you would think the two
remaining plants would have been wasted long before they got buried! Two
plants do not a garden make!

>Well, if there are leaf impressions in the Navajo, one would presume that
>the leaves would need roots. And if there were plants having roots, then
>rhizoliths are not to be unexpected. The intepretation is internally

TWO impressions, neither of which was a leaf. You are jumping the data,
Glenn! How many roots do you think those two stem fragments represent???
Enough to explain all the "root casts" in the Navajo? Could they feed all
the animals represented by the Navajo trackways and fossils? Remember the
ratio of plants to animals in any conceivable ecosystem to be functional
requires biomass of plants to be many times the biomass of the animals.
>I might point out that the geochemistry of this carbonate lens is such that
>it precludes this being a marine deposit.
> "The carbonate lens is interpreted to be a fresh water lake deposit.
> Boron values are so low as to preclude possibility of marine deposition."
>~James K. Gilland, "Paleoenvironment of a Carbonate Lens in the Lower Navajo
>Sandstone Near Moab, Utah" Utah Geology 6(1979):1:29-38, p. 37

Yeah, well, even if that did truely obviate a saline marine origin, I don't
really need it to be saline, just water will do for me.

>Also pollen and spores are quite abundant in some layers suggesting local
>"Pollen and spores are well preserved in some layers of unit 6. A major
>percentage of the specimens are of one type and give strong support to local
>floral development near shore."~James K. Gilland, "Paleoenvironment of a
>Carbonate Lens in the Lower Navajo Sandstone Near Moab, Utah" Utah Geology
>6(1979):1:29-38, p. 36

Good! Now all we need to do is find the plant remains to go with the
pollen and we will be set! Except that one kind of plant, especially if it
is equisetum-like, is not going to satisfy a very broad ecology (ever tried
chewing on an equisetum stem? They are about 95% silica... maybe we should
check the teeth of the fossils for wear:-)). I can just see their
statement if they had found a lot of different pollen types: " ...The wide
variety of pollen types represented in the sample gives strong support to
local floral development near shore...".

>>But did these "interdune" deposits have plant fossils in them???
>At least one did!!!! Gotcha :-)

One out of seven. Must have been some pretty hungry animals out there in
those dunes, Glenn :-).