Lowenstein, T. K. (2001) Oscillations in Phanerozoic Seawater Chemistry: Evidence from Fluid Inclusions. Science, 294 (5544). 1086-1088 doi:10.1126/science.1064280
| Reference Type | Journal (article/letter/editorial) | ||
|---|---|---|---|
| Title | Oscillations in Phanerozoic Seawater Chemistry: Evidence from Fluid Inclusions | ||
| Journal | Science | ||
| Authors | Lowenstein, T. K. | Author | |
| Year | 2001 (November 2) | Volume | 294 |
| Page(s) | 1086-1088 | Issue | 5544 |
| Publisher | American Association for the Advancement of Science (AAAS) | ||
| DOI | doi:10.1126/science.1064280Search in ResearchGate | ||
| Mindat Ref. ID | 2529478 | Long-form Identifier | mindat:1:5:2529478:5 |
| GUID | bad1edc5-324f-4aa3-8415-93ee510c4119 | ||
| Full Reference | Lowenstein, T. K. (2001) Oscillations in Phanerozoic Seawater Chemistry: Evidence from Fluid Inclusions. Science, 294 (5544). 1086-1088 doi:10.1126/science.1064280 | ||
| Plain Text | Lowenstein, T. K. (2001) Oscillations in Phanerozoic Seawater Chemistry: Evidence from Fluid Inclusions. Science, 294 (5544). 1086-1088 doi:10.1126/science.1064280 | ||
| In | (2001, November) Science Vol. 294 (5544) American Association for the Advancement of Science (AAAS) | ||
References Listed
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 | Ayora, Carlos, Garcia-Veigas, Javier, Pueyo, Juan-Jose (1994) The chemical and hydrological evolution of an ancient potash-forming evaporite basin as constrained by mineral sequence, fluid inclusion composition, and numerical simulation. Geochimica et Cosmochimica Acta, 58 (16) 3379-3394 doi:10.1016/0016-7037(94)90093-0 |
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| Samples analyzed by ESEM-EDS: Late Precambrian (543 to 544 Ma) Ara Group Oman; Early Cambrian (520 to 540 Ma) Angarskaya Formation (Fm.) Siberia; Silurian (418 to 440 Ma) Salina Group Michigan USA and Carribuddy Group Western Australia; Permian (251 to 258 Ma) Salado Fm. New Mexico USA; Early Cretaceous (112 to 124 Ma) Muribeca Fm. Brazil and Loeme Fm. Congo; Late Cretaceous (94 to 112 Ma) Maha Sarakham Fm. Laos-Thailand; modern halite Baja California Mexico. | |
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| Peryt T. M., Kovalevich V. M., Zbl. Geol. Palaont. Teil I 1995, 337 (1996). | |
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| Maximum paleoseawater Mg 2+ /Ca 2+ ratios for the Cambrian Silurian and Cretaceous (Fig. 2 top of vertical bars) were found directly by ESEM-EDS measurement of Mg 2+ and Ca 2+ in fluid inclusions [analytical accuracy (mean – expected)/expected is better than 7%; precision (relative standard deviation) is 6% for Ca 2+ and 16% for Mg 2+ ]. Measured Mg 2+ /Ca 2+ ratios are maxima because they do not account for the Ca 2+ lost from seawater during earlier precipitation of CaCO 3 and CaSO 4 formed before halite. Mg 2+ /Ca 2+ ratios in Cambrian Silurian and Cretaceous paleoseawater were also modeled using the Harvie-Møller-Weare (HMW) computer program (18) (bottom of vertical bars). Because the analyzed fluids are concentrated brines we used the following backtracking procedure to estimate the compositions of the parent seawaters. Measured concentrations of the individual major ions in the inclusion fluids were plotted against the conservative ion Mg 2+ the progress variable of evaporative concentration which does not partition into solid phases until the late “bittern” stages. We then used the HMW computer program to determine for each evaporite deposit examined the paleoseawater with the major-ion composition that provided the best fit to the full set of Na + K + Ca 2+ and Cl – versus Mg 2+ plots using trial-and-error fitting. A requirement of the modeling procedure was that the succession of salts formed from evaporation of modeled paleoseawater of a given age exactly match the observed sequence of evaporites. All modeling was done using a present-day Cl – of 548 mmol and assuming that SO 4 2– was 14 mmol; present-day SO 4 2– is 28 mmol. | |
| Mg 2+ /Ca 2+ ratios in Precambrian and Permian seawater could not be obtained directly from fluid inclusions because they contained no measurable Ca 2+ and therefore fell on the SO 4 2– side of the Ca-SO 4 chemical divide as does modern seawater. In these waters evaporation and precipitation of CaCO 3 and CaSO 4 consumes virtually all Ca 2+ from the brines leaving SO 4 2– in excess during later brine evolution. For these geological periods we estimated the seawater Mg 2+ /Ca 2+ ratios by the modeling procedures outlined in (12) assuming Ca 2+ of 10 mmol (Ca 2+ concentration in modern seawater giving the maximum Mg 2+ /Ca 2+ on vertical bars) and a Ca 2+ of 15 mmol 1.5 times modern seawater (minimum Mg 2+ /Ca 2+ on vertical bars). The three Tertiary Mg 2+ /Ca 2+ ratios were calculated from the Mg 2+ concentrations of (11) for Eocene (37 Ma) Middle Miocene (14 Ma) and Late Miocene (5 Ma) paleoseawater and Ca 2+ concentrations of 10 and 15 mmol. | |
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| One limitation of the seawater secular variation hypothesis is the incomplete knowledge of ancient mid-ocean ridge hydrothermal brine fluxes. | |
| A. G. Fischer in Climate in Earth History (National Academy Press Washington DC 1982) pp. 97–104. | |
| S. M. Stanley L. A. Hardie GSA Today 9 (no. 2) 1 (1999). | |
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| . The HMW computer program calculates at each evaporation step concentrations (in molalities) of all the major ions and moles of salts precipitated. | |
 | Timofeeff, M.N, Lowenstein, T.K, Brennan, S.T, Demicco, R.V, Zimmermann, H, Horita, J, von Borstel, L.E (2001) Evaluating seawater chemistry from fluid inclusions in halite: examples from modern marine and nonmarine environments. Geochimica et Cosmochimica Acta, 65 (14) 2293-2300 doi:10.1016/s0016-7037(01)00591-9 |
| We thank W. Blackburn for laboratory assistance and N. Harris R. Hite J. Horita V. Kovalevich M. A. da Silva M. El Tabakh and H. Zimmermann for samples and discussions. Supported by NSF grant EAR-9725740. |
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