Comparing oxygen isotope records of silurian calcite and phosphate—δ18O compositions of brachiopods and conodonts

Details Comparing oxygen isotope records of silurian calcite and phosphate—δ18O compositions of brachiopods and conodonts Comparing oxygen isotope records of silurian calcite and phosphate—δ18O compositions of brachiopods and conodonts

Jun 2000

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2000gecoa..64.1859w&link_type=abstract

Geochimica et Cosmochimica Acta, Volume 64, Issue 11, p. 1859-1872.

Computer Science

5

Scientific paper

Oxygen isotope compositions of Silurian calcitic brachiopod shells from Gotland are compared with those of phosphatic inarticulate brachiopod shells and conodonts from identical stratigraphic horizons. The δ18Ophosphate values of inarticulate brachiopod shells vary widely (13.0 to 17.5‰ V-SMOW) and are significantly lower than those of coeval conodont samples (17.5 to 19.5‰ V-SMOW). Conodont samples from individual beds have homogenous δ18Ophosphate values with variations close to the analytical precision (±0.2‰). Together with a significant correlation of conodont δ18Ophosphate and articulate brachiopod shell δ18Ocarbonate values (r = 0.85), this observation suggests that primary marine oxygen isotope compositions are better preserved in conodont apatite than in inarticulate brachiopod shell apatite. However, with decreasing δ18Ocarbonate values, the δ18Ophosphate values of conodonts are higher than expected for theoretical isotopic equilibrium with brachiopod calcite. Different habitats of conodonts and brachiopods cannot account for the observed offset in δ18O because both organisms were thriving on a broad shallow marine carbonate platform. Whereas δ18Ophosphate values of Silurian conodonts are close to δ18Ophosphate values of modern and Mesozoic tropical biogenic apatites, most Silurian calcitic brachiopod shells from Gotland are depleted in 18O when compared to modern or Mesozoic brachiopods. We therefore suggest that Silurian conodonts from Gotland record paleotemperature and δ18O of Silurian sea water more faithfully than coeval calcitic brachiopod shells.

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