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Abstract
Journal of Sedimentary Research, Section
A: Sedimentary Petrology and Processes
Vol. 67 (1997)No.
3. (May), Pages 531-535
Assessing Mineralogical and Geochemical Heterogeneity in the Sub 63 Micron
Size Fraction of Holocene Lime Muds
Julian E. Andrews, Socrates Christidis (1), Paul F. Dennis
ABSTRACT
Silt- and clay-size material (<= 63 µm) of Holocene lime muds
from south Florida and south Australia were subdivided into five fractions
(<= 10 µm, >10-20 µm, >20-30 µm, >30-45 µm,
and >45-63 µm) by wet sieving. Carbonate mineralogy, elemental chemistry
(Mg, Sr, Fe, and Mn), and stable carbon and oxygen isotopic compositions
were determined for each size fraction. The only statistically significant
variation in carbonate mineralogy with size was enrichment in aragonite
in the south Florida <= 10 µm fraction, by up to 10% relative
to other size classes. This aragonite enrichment causes increase in Sr
concentration and increase in d13C
and d18O values (on average by up
to 1.0% and 0.8% respectively, relative to means of other size classes).
In south Florida, this very fine-grained, high Sr, isotopically enriched
aragonite probably has a calcareous algal source. Overall, within-sample
mineralogical and geochemical variation is probably not large enough to
invalidate use of the <= 63 µm fraction as a comparator for ancient
micrites. However, local and regional-scale facies variation does cause
significant change in mineralogy and geochemistry. Carbon isotope compositions,
in particular, show marked variation that might survive burial diagenetic
stabilization.
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