Comparing calcite and phosphate oxygen isotope paleothermometers - d18O of Silurian brachiopods and conodonts

Journal article
(Original article)


Publication Details

Author(s): Joachimski M
Journal: Geochimica Et Cosmochimica Acta
Publisher: Meteoritical Society
Publication year: 2000
Volume: 64
Journal issue: 11
Pages range: 1859-1872
ISSN: 0016-7037


Abstract


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 δO(phosphate) 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 δO(phosphate) values with variations close to the analytical precision (±0.2‰). Together with a significant correlation of conodont δO(phosphate) and articulate brachiopod shell δO(carbonate) 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 δO(carbonate) values, the δO(phosphate) 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 δO because both organisms were thriving on a broad shallow marine carbonate platform. Whereas δO(phosphate) values of Silurian conodonts are close to δO(phosphate) values of modern and Mesozoic tropical biogenic apatites, most Silurian calcitic brachiopod shells from Gotland are depleted in O when compared to modern or Mesozoic brachiopods. We therefore suggest that Silurian conodonts from Gotland record paleotemperature and δO of Silurian sea water more faithfully than coeval calcitic brachiopod shells. Copyright (C) 2000 Elsevier Science Ltd.



FAU Authors / FAU Editors

Joachimski, Michael Prof. Dr.
Lehrstuhl für Geologie (Exogene Dynamik)

Last updated on 2018-26-12 at 20:50