Secular changes in ocean chemistry are
related to the mineralogy of carbonate precipitates, and had been predicted by
global ocean models. Ten years ago, Dickson described the Mg content of Cambrian
to Eocene echinoderm ossicles and compared the data to other first-order
geochemical cycles and proxies. The data revealed systematic changes coincident
with previous interpretations of ocean Mg/Ca ratios, with high mole% MgCO3
in Early Cambrian and late Carboniferous to Triassic samples, and low values in
Silurian and Jurassic to Cretaceous echinoderms. The paper suggested that the
data “add another independent line of
evidence that collectively can leave little doubt that major changes in the seawater
Mg/Ca ratio have occurred,” but noted other short-term changes.
EchinodermSkeletal Preservation: Calcite-Aragonite Seas and the Mg/Ca Ratio ofPhanerozoic Oceans by J.A.D. (Tony)
Dickson, Journal of Sedimentary Research, v. 74, p. 355-365.
No comments:
Post a Comment