|
|
 |
|||||||||||||||||
|
|||||||||||||||||
 |
|||||||||||||||||
| JOURNAL HOME | HELP | CONTACT PUBLISHER | SUBSCRIBE | ARCHIVE | SEARCH | TABLE OF CONTENTS |
1 Morton K. Blaustein Department of Earth and Planetary Sciences, Johns Hopkins University, Baltimore, Maryland 21218, USA
The Mg/Ca ratio of seawater has changed significantly over the Phanerozoic, primarily as a function of the rate of ocean-crust production. Echinoids, crabs, shrimps, and calcareous serpulid worms grown in artificial seawaters encompassing the range of Mg/Ca ratios that existed throughout the Phanerozoic exhibit a direct nonlinear relationship between skeletal and ambient Mg/Ca. Specimens grown in seawater with the lowest Mg/Ca (
1) changed their mineralogy to low-Mg calcite (<4 mol% MgCO3), suggesting that these high-Mg calcareous organisms would have produced low-Mg calcite in the Cretaceous, when oceanic Mg/Ca was lowest (1). These results support the empirical evidence that the skeletal chemistry of calcareous organisms has varied significantly over the Phanerozoic as a function of the Mg/Ca of seawater, and that the Mg/Ca of unaltered fossils of such organisms may be a record of oceanic Mg/Ca throughout the Phanerozoic. Mg fractionation algorithms, which relate skeletal Mg/Ca, seawater Mg/Ca, and temperature, were derived from these and other experiments. They can be used to estimate paleoceanic Mg/ Ca ratios and temperatures from fossil skeletal Mg/Ca of the organisms evaluated. Pale oceanic Mg/Ca ratios, recalculated by using the echinoderm Mg fractionation algorithm from published fossil echinoid Mg/Ca, crinoid Mg/Ca, and paleotemperature data, are consistent with other estimates and models of oceanic Mg/Ca over the Phanerozoic.
Key Words: seawater Mg/Ca ratio • echinoderms • calcite • Cretaceous • Mg fractionation • paleotemperature
This article has been cited by other articles:
|
|
 |
|
  V. De Choudens-Sanchez and L. A. Gonzalez Calcite and Aragonite Precipitation Under Controlled Instantaneous Supersaturation: Elucidating the Role of CaCO3 Saturation State and Mg/Ca Ratio on Calcium Carbonate Polymorphism Journal of Sedimentary Research, June 1, 2009; 79(6): 363 - 376. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 C. Borremans, J. Hermans, S. Baillon, L. Andre, and P. Dubois Salinity effects on the Mg/Ca and Sr/Ca in starfish skeletons and the echinoderm relevance for paleoenvironmental reconstructions Geology, April 1, 2009; 37(4): 351 - 354. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
J.A.D. Dickson Mississippian Paleocean Chemistry from Biotic and Abiotic Carbonate, Muleshoe Mound, Lake Valley Formation, New Mexico, U.S.A.--Discussion Journal of Sedimentary Research, January 1, 2009; 79(1): 40 - 41. [Full Text] [PDF]
|
|
|
|
|
|
F.J. Hasiuk and K.C. Lohmann Mississippian Paleocean Chemistry from Biotic and Abiotic Carbonate, Muleshoe Mound, Lake Valley Formation, New Mexico, U.S.A.--Reply Journal of Sedimentary Research, January 1, 2009; 79(1): 42 - 43. [Full Text] [PDF]
|
|
|
|
|
|
J. B. Ries, S. M. Stanley, and L. A. Hardie Scleractinian corals produce calcite, and grow more slowly, in artificial Cretaceous seawater Geology, July 1, 2006; 34(7): 525 - 528. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
J. B. Ries Aragonitic Algae in Calcite Seas: Effect of Seawater Mg/Ca Ratio on Algal Sediment Production Journal of Sedimentary Research, March 1, 2006; 76(3): 515 - 523. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 J. B. Ries Aragonite production in calcite seas: effect of seawater Mg/Ca ratio on the calcification and growth of the calcareous alga Penicillus capitatus Paleobiology, September 1, 2005; 31(3): 445 - 458. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
S. M. Stanley, J. B. Ries, and L. A. Hardie Seawater chemistry, coccolithophore population growth, and the origin of Cretaceous chalk Geology, July 1, 2005; 33(7): 593 - 596. [Abstract] [Full Text] [PDF]
|
|
| JOURNAL HOME | HELP | CONTACT PUBLISHER | SUBSCRIBE | ARCHIVE | SEARCH | TABLE OF CONTENTS |
