Skip navigation
Please use this identifier to cite or link to this item:
Title: Fluid Inclusions in Marine Halite as a Window into the MG Isotopic Composition of Past Oceans
Authors: Beale, Andrea
Advisors: Higgins, John
Contributors: Bender, Michael
Department: Geosciences
Class Year: 2014
Abstract: Evidence from marine carbonates, evaporites, and fossil echinoderms has conclusively shown that seawater composition varied considerably during the Phanerozoic. Seawater has oscillated on 100- to 200-million-year cycles between “calcite seas,” periods with predominant carbonate formation of low-Mg calcite and Mg/Ca ratios as low as 1, and “aragonite seas,” periods with predominantly aragonite formation and Mg/Ca ratios of up to 5. Proposed explanations for the oscillations between calcite and aragonite seas include changes in the rate of Mg uptake at mid-ocean ridges and variations in shallow-water dolomitization rates. This study is the first to analyze the validity of these proposed explanations using direct measurements of seawater magnesium isotope ratios within evaporites. δ26Mg values of Phanerozoic seawater were obtained by developing a new method for analysis of brine inclusions trapped within ancient marine halite. Dissolution of fluid-inclusion-rich halite followed by magnesium separation using ion chromatography and isotope ratio analysis using an MC-ICP MS led to highly reproducible δ26Mg values for modern, Messinian, and Silurian-age seawater samples. Silurian and modern samples showed similar δ26Mg values, suggesting that similar processes may drive seawater composition during the two time periods. Further adjustments to the methodology and additional sample analysis can achieve a more complete dataset for seawater δ26Mg values and a better understanding of the processes that have controlled the chemistry of seawater throughout the Phanerozoic.
Extent: 47 pages
Type of Material: Princeton University Senior Theses
Language: en_US
Appears in Collections:Geosciences, 1929-2016

Files in This Item:
File SizeFormat 
Beale_Andrea.pdf8.7 MBAdobe PDF    Request a copy

Items in Dataspace are protected by copyright, with all rights reserved, unless otherwise indicated.