Regarding oxygen isotopes in carbonates, extreme heavy values are
characteristic of tropical lakes, but values we obtained in Proterozoic
saline lake carbonates (dolomite) seem to be heavier than anything I've
seen published on pre-Holocene material. Values ranged up to +10 PDB as
quoted in the publications below, but more recently I've been working
with Christoph Spoetl at Innsbruck on a finer spatial resolution and
mm-scale laminae are heavier than that, with values up to +14.9. The
carbonates formed in a hyper-arid climate like that of the Antarctic Dry
Valley lakes.
Fairchild, I.J. & Spiro, B., 1990. Carbonate minerals in glacial
sediments: geochemical clues to palaeoenvironment. In: Glacimarine
Environments: Processes and Sediments (Ed. J.D. Scourse & J.A.
Dowdeswell). Geological Society of London Special Publication, 53,
241-256.
34.
Fairchild, I.J., Hambrey, M.J., Jefferson, T.H. and Spiro, B. 1989. Late
Proterozoic glacial carbonates in NE Spitsbergen: new insights into the
carbonate-tillite association. Geological Magazine, 126, 469-490.
Ian J. Fairchild
Professor of Physical Geography
GEES (School of Geography, Earth and Environmental Sciences)
University of Birmingham,
Edgbaston, Birmingham B15 2TT, UK
Telephone: (+44)(0)121 414 4181 (Fax ...5528)
e-mail: [log in to unmask]
-----Original Message-----
From: Stable Isotope Geochemistry [mailto:[log in to unmask]] On
Behalf Of Matt Kohn
Sent: 24 March 2005 12:51
To: [log in to unmask]
Subject: [ISOGEOCHEM] Positive extremes for d13C and d18O
Hi,
An idle question: What are the extreme positive values for
terrestrial d13C and d18O? I know marine diatom d18O can reach c. +40
permil, and lacustrine carbonate d13C can reach c. +5 permil. But I
also know several years ago that someone on the list reported d13C
values >+10 permil, for lacustrine carbonate (I think: I haven't
found the published reference yet). Are there higher values, and if
so in what environments do they occur?
Thanks,
Matt
--
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Dr. Matthew J. Kohn, Associate Professor
Director, Undergraduate studies
Department of Geological Sciences
701 Sumter St., Room EWS 617
University of South Carolina
Columbia, SC 29208
phone: (803)-777-5565 fax:(803)-777-6610
http://urania.geol.sc.edu/~golab/vita.htm
articles: http://urania.geol.sc.edu/~golab/GOpdfs.htm
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