| Abstract: | One-hundred fluid inclusions in Silurian marine halite were analyzed in order to determine the major-ion composition of Silurian seawater. The samples analyzed were from three formations in the Late Silurian Michigan Basin, the A-1, A-2, and B Evaporites of the Salina Group, and one formation in the Early Silurian Canning Basin (Australia), the Mallowa Salt of the Carribuddy Group. The results indicate that the major-ion composition of Silurian seawater was not the same as present-day seawater. The Silurian ocean had lower concentrations of Mg2+, Na+, and SO2-4, and much higher concentrations of Ca2+ relative to the ocean‘s present-day composition. Furthermore, Silurian seawater had Ca2+ in excess of SO2-4. Evaporation of Silurian seawater of the composition determined in this study produces KC1-type potash minerals that lack the MgSO4-type late stage salts formed during the evaporation of present-day seawater. The relatively low Na+ concentrations in Silurian seawater support the hypothesis that oscillations in the major-ion composition of the oceans are primarily controlled by changes in the flux of mid-ocean ridge brine and riverine inputs and not global or basin-scale, seawater-driven dolomitization. The Mg2+/Ca2+ ratio of Silurian seawater was ~1.4, and the K+/Ca2+ ratio was ~0.3, both of which differ from the present-day counterparts of 5 and 1, respectively. Seawaters with Mg2+/Ca2+ <2 facilitate the precipitation of low-magnesian calcite (mol % Mg < 4) marine ooids and submarine carbonate cements whereas seawater with Mg2+/Ca2+ >2 (e.g., modern seawater) facilitate the precipitation of aragonite and high-magnesian calcite. Therefore, the early Paleozoic calcite seas were likely due to the low Mg2+/Ca2+ ratio of seawater, not the pCO2 of the Silurian atmosphere. Copyright ?? 2002 Elsevier Science Ltd. |
| Genre: | Article |
| ProdID: | 70024584 |
| Citation Author: | Brennan, S. T.; Lowenstein, T. K. |
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| Citation End Page: | 2700 |
| Citation Issue: | 15 |
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| Citation Language: | English |
| Citation Larger Work Title: | Geochimica et Cosmochimica Acta |
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| Citation Number Of Pages: | 18 |
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| Citation Search Results Text: | The major-ion composition of Silurian seawater; 2002; Article; Journal; Geochimica et Cosmochimica Acta; Brennan, S. T.; Lowenstein, T. K. |
| Citation Start Page: | 2683 |
| Citation Volume: | 66 |
| Citation Year: | 2002 |
| Type: | citation/reference |
| Text: | The major-ion composition of Silurian seawater; 2002; Article; Journal; Geochimica et Cosmochimica Acta; Brennan, S. T.; Lowenstein, T. K. |
| URL (THUMBNAIL): | http://pubs.er.usgs.gov/thumbnails/outside_thumb.jpg |
| URL (DIGITAL OBJECT IDENTIFIER): | http://dx.doi.org/10.1016/S0016-7037(02)00870-0 |
| Date Other: | Tue, 1 Jan 2002 00:00 -0600 |
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