Re: preserving raindrops and mats

Glenn Morton (grmorton@waymark.net)
Thu, 15 Jan 1998 20:05:20 -0600

At 09:50 AM 1/15/98 -0800, Arthur V. Chadwick wrote:
>At 08:55 PM 1/14/98 -0600, Glenn Morton wrote:
>>Unfortunately, I quit saving the AAPG explorer about 2 years ago. Now I
>>regret it. I remember that photo but a water escape structure might not be
>>unexpected given certain environments which are found in the Navajo.
>>
>> "Recent work shows that the Navajo is indeed a classic
>>desert sand dune deposit. Locally, however, can be found
>>evidence for small oases or playa lakes represented by
>>distinctive thin layers of grayish limestone that often contain
>>reveal tracks. Although rare, the Navajo has also yielded
>>skeletal remains of crocodilians (a small primitive Protosuchus-
>>like crocodilian), mammal-like reptiles known as trytylodonts,
>>and dinosaurs including the chicken-sized theropod Segisaurus and
>>the small prosauropod Ammosaurus."~Martin Lockley and Adrian P.
>>Hunt, Dinosaur Tracks, (New York: Columbia University Press,
>>1995), p. 130
>>
>>Escape structures in the playa deposits would not be unexpected.
>
>Yes, but it is tautologic to assume a playa lake to explain the
>deformations then to say there was a playa lake and that explains the
>deformations. Let's look for independent evidence for a playa lake at the
>locality in question that is not based on the presence of dewatering
>structures.

I don't think it is tautological because there would be a difference in the
sedimentologic fabric. The cross-beds of the eolian dunes would be onlapped
by horizontal playa deposits, looking like:
\\\\\\\\\\\\\\\\ ////////////////
\\\\\\\\\\\\\\\\\-------------////////////////
\\\\\\\\\\\\\\\\\\-----------/////////////////

.....dune...........Playa.........dune

glenn

Adam, Apes, and Anthropology: Finding the Soul of Fossil Man

and

Foundation, Fall and Flood
http://www.isource.net/~grmorton/dmd.htm