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Fossil Echinoderms As Monitor of the Mg/Ca Ratio of Phanerozoic Oceans
J. A. D. Dickson
Opinion has long been divided as to whether the Mg/Ca ratio of
seawater remained constant during the Phanerozoic or underwentsubstantial secular change. Existing empirical evidence for theMg/Ca
of ancient seawater provides a poorly resolved and oftencontroversial
signal. Echinoderm fossils that have retained theirbulk original
chemistry, despite micrometer-scale changes, preservea record of
seawater Mg/Ca and confirm that major changes in Mg/Caoccurred during
the Phanerozoic. Echinoderms from the Cambrianand from the
Carboniferous to the Triassic indicate a seawaterMg/Ca of ~3.3,
whereas echinoderms from the Jurassic to the Cretaceousindicate a
Mg/Ca of ~1.4. The present seawater Mg/Ca is ~5.
Department of Earth Sciences, University of Cambridge, Downing
Street, Cambridge, CB2 3EQ, UK. E-mail: jadd1{at}esc.cam.ac.uk
Marine Sepiolite in Middle Permian Carbonates of South China: Implications for Secular Variation of Phanerozoic Seawater Chemistry.
J. Yan, A. Munnecke, T. Steuber, E. H. Carlson, and Y. Xiao (2005)
Journal of Sedimentary Research
75, 328-338
|Abstract »|Full Text »|PDF »
Origin of Meter-Scale Submarine Cavities and Herringbone Calcite Cement in a Cambrian Microbial Reef, Ledger Formation (U.S.A.).
C. B. de Wet, H. M. Frey, S. B. Gaswirth, C. I. Mora, M. Rahnis, and C. R. Bruno (2004)
Journal of Sedimentary Research
74, 914-923
|Abstract »|Full Text »|PDF »
Effect of ambient Mg/Ca ratio on Mg fractionation in calcareous marine invertebrates: A record of the oceanic Mg/Ca ratio over the Phanerozoic.
(2004)
Geology
32, 981-984
A model for calcium, magnesium and sulfate in seawater over Phanerozoic time.