Re: Plants for Navajo Sandstone food

Glenn Morton (
Sat, 07 Feb 1998 21:23:09 -0600

At 07:17 PM 2/7/98 -0800, Arthur V. Chadwick wrote:
>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!

You have been boxing me about the head and shoulders because I couldn't find
plants in the Navajo. Now I have found them and they aren't good enough? I
am disappointed. Those plants lay in the Navajo for several million years
just for you. :-)

>>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.

But given the fact that the Navajo occupied about 5 million years of time
there don't need to be that many animals alive at any one time to account
for the number of footprints(~William L. Bilodeau and Stanley B. Keith,
"Lower Jurassic Navajo-Aztec-Equivalent Sandstones in Southern Arizona and
Their Paleogeographci Significance," Bulletin of the American Association of
Petroleum Geologists, 70(1986):6:690-701, p. 699)

>>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.

Why? Was the flood made up of fresh water rather than brackish?

>>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 :-).

Now that we know there are plants in the Navajo, those rhizoliths make a
little more sense. They are the evidence of the other plant flora.


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