Dear Margo
You Might also want to have a look at papers by John Kingston and those 
by Nancy Sikes,  these tend to be based on african sites but they have 
good methodologies which may be useful to you.
It sounds like the real problem is weather these carbonates are 
pedogenic or ground water derived. There should be plenty of textural 
differences to help sort this out. The Retallack soils of the past book 
(blackwell 2001) may be of some use there for some of the macroscopic 
textures but you may well want to look at microscopic scales as well. 
As for ground water carbonate textures there is a lot of information 
available try searching the meteoric diagenesis literature (although it 
is getting a bit old now SEPM special pub. no. 36 might be a good place 
to start).
Good luck

Dr. Peter Ditchfield
Stable Isotope Laboratory Manager
Research Laboratory for Archaeology and the History of Art
University of Oxford
Dyson Perrins Building, South Parks Road
Oxford, UK
OX1 3QY
tel:01865-285210
fax:01865-285220
On 27 Feb 2006, at 21:36, Margo Schwadron wrote:

> 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
>