Calcite overgrowths were precipitated from artificial seawater at 25$ sp circ$C on synthetic calcite seeds using a chemo-stat precipitation technique to investigate the influence of the $P sb{CO sb2}$ on magnesium incorporation. Powder X-ray diffraction (APXRD) analyses of the overgrowths indicate that the amount of MgCO$ sb3$ incorporated during precipitation is independent of the $P sb{CO sb2}$ over 4 orders of magnitude (10$ sp{-0.5}$ to 10$ sp{-4.6}$atm). The magnesium content of the overgrowths estimated from mass balance calculations of carbonate alkalinity of the reacting solutions ($ Delta$Ac) and flame spectrophotometric (AAS) analyses of the reacted solids yield similar results away from the extremes of $P sb{CO sb2}$ investigated in this study. These results contrast with those obtained from previous investigations and indicate that variations in the composition of magnesium calcite cements during the Phanerozoic cannot be explained solely on the basis of atmospheric $P sb{CO sb2}$ excursions. The concentration of sulfate and sodium in the overgrowths, however, appears to correlate with variations in $P sb{CO sb2}$. / In a separate set of experiments, using the same precipitation technique, the influence of a biogenic seed material on the composition and mineralogy of overgrowths was investigated. The mineralogy of these precipitates was characterized by APXRD and Guinier-Hagg film x-ray diffraction. Overgrowths of aragonite and a high Mg-calcite (16.7 mole % MgCO$ sb3$) were precipitated from artificial seawater on crushed interambulacral shells of the sea urchin Diadema at a $P sb{CO sb2}$ of 10$ sp{-2.5}$ atm over a range of saturation states ($ Omega sb{ rm calcite}$ = 6.0 to 11.6). When compared to results of the previous study, it was not possible to determine unequivocally if the difference in composition and mineralogy of the overgrowths resulted from the influence of either the structure of the seed material or residual skeletal matrix organic manner. / Transmission and scanning electron micrographs of solid overgrowths and substrates from the two series of experiments provide physical evidence of the existence and morphology of the precipitates.
| Identifer | oai:union.ndltd.org:LACETR/oai:collectionscanada.gc.ca:QMM.68181 |
| Date | January 1993 |
| Creators | Hartley, George |
| Contributors | Mucci, Alfonso (advisor) |
| Publisher | McGill University |
| Source Sets | Library and Archives Canada ETDs Repository / Centre d'archives des thèses électroniques de Bibliothèque et Archives Canada |
| Language | English |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Format | application/pdf |
| Coverage | Master of Science (Department of Earth and Planetary Sciences.) |
| Rights | All items in eScholarship@McGill are protected by copyright with all rights reserved unless otherwise indicated. |
| Relation | alephsysno: 001397043, proquestno: AAIMM94439, Theses scanned by UMI/ProQuest. |
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