Hi,
> I'm an archeologist trying to identify/interpret the nature
> and formation
> of an unusual indurated carbonate layer
Regarding the different structures of various types of calcretes you may refer to:
Freytet, P., and Plaziat, J.-C., 1982, Continental carbonate sedimentation and pedogenesis-Late Cretaceous and early Tertiary of southern France, in Purser, B.H., ed., Contributions to Sedimentology 12: Stuttgart, E. Schweizerbart'che Verlags-buchhandlung (Nägele u. Obermiller), 213 p.
Retallack, G.J. 1997. A colour guide to paleosols. John Wiley and Sons, Chichester, 175 p. (ISBN 0-471-96711-4).
A good place to start for stable isotopes may be:
Ekart, D.D., Cerling, T.E., Montaņez, I.P. & Tabor, N.J. (1999): A 400 million year carbon isotope record of pedogenic carbonate: implications for paleoatmospheric carbon dioxide. - American Journal of Science, 299, 805-827.
regards
Robert
--
Dr. Robert van Geldern
Leibniz Institute for Applied Geosciences (GGA)
S3: Geochronology and Isotopehydrology
Stilleweg 2, 30655 Hannover, Germany
phone: +49-(0)511-643-2313 (office), -2539 (lab)
fax: +49-(0)511-643-3665
mailto:[log in to unmask]
> -----Original Message-----
> From: Stable Isotope Geochemistry
> [mailto:[log in to unmask]] On Behalf Of Margo Schwadron
> Sent: Monday, February 27, 2006 10:37 PM
> To: [log in to unmask]
> Subject: [ISOGEOCHEM] Help Interpret Carbonate/Calcrete Isotope Values
>
>
> 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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