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track preservation (fwd)



Forwarded with the permission of David Gillette to answer part of the 
track preservation problem. 

Sally Shelton
Director, Collections Care and Conservation


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---------- Forwarded message ----------
Date: Tue, 26 Sep 1995 11:28:05 -0600
>From: David Gillette <NRDOMAIN.NRUGS.DGILLETTE@email.state.ut.us>
To: jaeger@isem.univ-montp2.fr
Cc: libsdnhm@CLASS.ORG
Subject: track preservation

Dear Professor Jaeger:
     I have just received a message from Sally Shelton with a copy of
the letter she sent to you regarding preservation of Permian tracks
in redbeds. I have not conducted controlled experiments, nor do I
have reliable first-hand knowledge concerning chemical preservatives.
     However, from observation of others' attempts to preserve tracks
in situ, I have concluded that there are two main hazards that
accelerate erosion of tracks: human activities and weathering. People
walking in the tracks or nearby is certainly destructive. Attempting
to stabilize tracks in situ by application of chemicals is usually or
always destructive, too. 
     Weathering is also destructive, especially when tracks are
alternately wet and dry, and even more especially when tracks are
subjected to freezing. I have concluded that the single most
important measure for preservation and stabilation is keeping tracks
dry. The best way to keep them dry is to place a shelter over them
with a roof and walls, which can also control visitor access.
Chemical hardeners have the long term effect of causing spalling; the
surface remains intact, but beneath the surface, moisture collects
and cannot escape the rock; minerals will precipitate from the
moisture if the rock dries out, and if the rock is moist during a
freeze, the saturated level will expand, causing deterioration from
the inside. 
     I observed that effect on two tracks preserved in Dallas, Texas
at Southern Methodist University, one preserved with a chemical
hardener, the other untreated. After twenty years of neglect in the
campus flower garden, the one with hardener was no longer
recognizable, the untreated one was still relatively clear.
Fortunately, Dallas seldom has freezing temperatures so the effect of
freeze-thaw was not pronounced. 
     If your concern is preservation in perpetuity, I recommend
burial of the rocks with natural sand and clay to a depth below
freeze level. Covering them with plastic has the effect of drawing
water, clearly defeating your purpose. Whatever you do, I recommend
first and most importantly (1) keep the tracks dry; and (2) keep them
from freezing. As an alternative, they could be collected and placed
in a museum, but that's a huge job if the trackway is extensive.     
     Also, natural weathering can sometimes help expose tracks; in
some cases you can enhance the clarity of tracks in this fashion, but
they should be monitored so that the natural enhancement does not go
too far. 
     If you wish to send specific details about your concern, please
feel free to respond. I hope this helps. /// Sincerely yours, David
D. Gillette, State Paleontologist of Utah, Utah Geological Survey,
2363 S. Foothill Drive, Salt Lake City, Utah 84109.