Re: preserving raindrops and mats
Arthur V. Chadwick (chadwicka@swac.edu)
Thu, 15 Jan 1998 21:49:45 -0800>>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
Sure, but my point was nobody bothered to look for a playa lake fabric.
Just as you did they probably assumed that was the explanation for the
dewatering structures. Cleaarly if someone had found evidence for a playa
lake (salt accumulation, flat-lying fine grained sediment) in the midst of
the massively cross-bedded Navajo sands and then found associated with it
dewatering structures in the aoppropriate relationship, that would be one
thing. But no such relationship is evident in the picture in question, and
it was dismissed at least by you, and possibly by the editors as well, as
explanable in terms of a playa lake. Here the model is determining the
data, and the cart is before the horse.
Art
http://chadwicka.swau.edu