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Oxygen and carbon isotopes of Early Permian cold-water carbonates, Tasmania, Australia

C. Prasada Rao and D. C. Green
Oxygen and carbon isotopes of Early Permian cold-water carbonates, Tasmania, Australia
Journal of Sedimentary Petrology (December 1982) 52 (4): 1111-1125

Abstract

Formed at a paleolatitude near 80 degrees S during the Gondwanan ice age, and associated with glaciomarine sediments. A shallow-marine carbonate depositional model has been proposed. Australian Permian brachiopods and molluscs have unusually light delta O (super 18) PDB values and heavier delta C (super 13) PDB values than modern cold-water carbonates. Tasmanian-Permian whole-rock delta O (super 18) PDB values fall at the edge of the "Normal Marine Limestone" and range towards lighter values (-16.9% PDB). The delta O (super 18) values of cements (-7.6 to -25.6% PDB) partly overlap with those delta O (super 18) values obtained for fresh-water cements in the Early Permian continental tillites from Antarctica and South Africa (Gondwanaland), indicating that the Early Permian sea was diluted by isotopically light melt waters. The delta O (super 18) values of fauna give unrealistic paleotemperatures because of melt-water dilution of the sea. However, calculated delta O (super 18) values, corresponding to marine delta C (super 13) values of brachiopods and Eurydesma and extrapolated from a model of the linear trend of delta C (super 13) -delta O (super 18) in modern and last-glacial cold-water carbonates, give reasonable estimates of Australian Permian temperatures of up to 15 degrees C with the coldest waters of less than 4 degrees C around Tasmania. The sequential deviation lines of delta O (super 18) -.C (super 13) of both cements and the fauna indicate that the original delta O (super 18) value of fauna was as high as +6% PDB. This indicates an average seawater temperature for Tasmania in the Early Permian of -1.8 degrees C, similar to the present average -1.9 degrees C water temperature near ice shelves around Antarctica. The delta O (super 18) of the Early Permian sea is inferred to have been about +1.2% PDB, similar to that observed during the Pleistocene glaciations, and was diluted by melt water as light as delta O (super 18) SMOW = -31% at 5 degrees C (-26% PDB). It is unlikely that the delta O (super 18) composition of the well-mixed open Permian sea ever reached a value as light as delta O (super 18) PDB = -6%. It is suggested that the Permian sea delta C (super 13) value was about +2% PDB, heavier than that of modern and Pleistocene seawater.--Modified journal abstract.


ISSN: 0022-4472
Coden: JSEPAK
Serial Title: Journal of Sedimentary Petrology
Serial Volume: 52
Serial Issue: 4
Title: Oxygen and carbon isotopes of Early Permian cold-water carbonates, Tasmania, Australia
Affiliation: Univ. Tasmania, Dep. Geol., Hobart, Australia
Pages: 1111-1125
Published: 198212
Text Language: English
Publisher: Society of Economic Paleontologists and Mineralogists, Tulsa, OK, United States
References: 67
Accession Number: 1983-037466
Categories: Isotope geochemistry
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. 1 table, geol. sketch map
S43°40'00" - S39°30'00", E143°49'60" - E148°30'00"
Secondary Affiliation: Dep. Mines, AUS, Australia
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2017, American Geosciences Institute.
Update Code: 1983
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