chacha333
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chacha333
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| 10 Jul 2008 1:48 AM |
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Here's an exchange between me and Dr. Virginia Steen-McIntyre (USGS-Retired), that I think sheds more light on the geology of this central Texas site:
quote:
Charlie,
Your images 6 and 7 of the "Cementations (Bed Ice) from Unit Lima" (posted April 5) look interesting. Are the coarse gravelly "lumps" part of an underlying layer or are they actually previously-cemented fragments of a coarser, older gravel incorporated in a younger gravel (still older than your gravel with in situ artifacts)?
Virginia
Afternoon, Virginia.
Some dislodged boulders of the cemented gravel cobbles were discovered on top of the gravel cap when I first discovered the site:
I assume these were eroded off the bedrock, upstream, and deposited on top of the gravel cap during heavy rain events. I've found no loose boulders or cobbles of the cemented gravels within secure strata, which I've tentatively defined as gravel in a hard matrix of silt, clay and limestone sand.
I think the cementations, which are adhered to the bedrock, once underlay the gravel cap that contains the artifacts that are being recovered. Some of the cementations still have gravel, in matrix, covering them (or at least in close proximity):
http://cayman.globat.com/~bandstexas.com/site18.jpg
http://cayman.globat.com/~bandstexas.com/site19.jpg
http://cayman.globat.com/~bandstexas.com/site20.jpg
http://cayman.globat.com/~bandstexas.com/site21.jpg
http://cayman.globat.com/~bandstexas.com/site22.jpg
http://cayman.globat.com/~bandstexas.com/site25.jpg
Whereas others are completely exposed, because the previously existing gravel cap, overlaying the cementations, has been swept downstream:
It appears these cementations were formed prior to, or in the early stages of the gravel deposition, unless carbonate concentrated at the bottom of the already deposited gravel cap, and created cementations only at the bottom of the cap.
I've found what might be artifacts within the cementations:
http://cayman.globat.com/~bandstexas.com/afw201.jpg
http://cayman.globat.com/~bandstexas.com/afw202.jpg
http://cayman.globat.com/~bandstexas.com/afw203.jpg
I'm going to have to find better specimens to make a solid argument for artifacts existing in this particular stratum. It would be ideal to find a "no-brainer" artifact in the cementations, still attached to the bedrock. I'm looking. 
What's your take on the cementations?
Respectfully,
Charlie
Charlie Hatchett
Charlie@preclovis.com
www.preclovis.com
http://forum.preclovis.com/
20 May 2007 |
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chacha333
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