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Mon, 27 Feb 2006 16:36:45 -0500 |
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Hi all,
I’m an archeologist trying to identify/interpret the nature and formation
of an unusual indurated carbonate layer (Calcrete? Caliche? Duricrust?
Marl?) found between two distinct prehistoric Indian occupations on
several freshwater tree island in Everglades National Park, Florida. This
was found at many sites, and there is a temporal correlation, that based
on c14 dates, suggests the layer formed sometime between 3800 BP and 2700
BP. There seems to be potential for data suggesting paleoenvironmental
change, and abandonment of the site during a possible wetter hydrological
regime.
Nevertheless, I’m having extreme difficulty in trying to interpret this
layer. I do not have the background in geochemistry, and most geologists I
consult have never seen anything like it and don’t know what to call it,
or how it formed. I had isotopic analysis done for inorganic carbon and
oxygen:
d13C-cal. d18O-cal.
MS-EU-1 -1.6 -3.4
MS-EU-2 -1.7 -1.2
MS-EU-3 -5.9 -2.1
MS-EU-4 -0.9 -1.0
The geologist who ran them said that "the data show that they were not
formed in a soil dominated by trees. If they were pedogenic carbonates,
the soil would have supported more grasses than trees during the period
when these carbonates were formed. It's also possible they are groundwater
carbonate or pond/lake carbonate. We could do some calculation to
estimate the temperatures of their formation. "
I was hoping to find a “database” of known isotopic values that would help
us interpret this data. Does anyone on this listserve have any suggestions
for what these isoptopic values indicate? Any additional research avenues
I should take, and any references I should look at? Any help is GREATLY
appreciated!
Sincererly,
Margo Schwadron, M.A., RPA
Archeologist, National Park Service
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