HR: 08:00h
AN: PP41E-01 INVITED    [Abstracts]
TI: Secondary Ion Mass Spectrometry as a Tool for Measuring Mg/Ca in Small, Rare and Altered Foraminifera
AU: * Bice, K L
EM: kbice@whoi.edu
AF: Department of Geology and Geophysics, Woods Hole Oceanographic Institution, Woods Hole, NA 02543, United States
AU: Shimizu, N
EM: nshimizu@whoi.edu
AF: Department of Geology and Geophysics, Woods Hole Oceanographic Institution, Woods Hole, NA 02543, United States
AU: Layne, G
EM: gdlayne@mun.ca
AF: Department of Earth Sciences, Memorial University of Newfoundland, St. John's, NL A1B 3X5, Canada
AB: Secondary ion mass spectrometry (SIMS) is useful for measuring the molar ratio of magnesium (Mg) to calcium (Ca) in both primary calcite and diagenetic minerals in foraminifera. The spatial resolution of standard SIMS (10 microns or less) and small amount of material removed (less than 2 ng) makes it possible to avoid targets that include embedding material and encrusting or infilling minerals such as secondary calcite and authigenic clays in diagenetically altered samples. Because analyses are performed on individuals, SIMS is also a viable technique for generating Mg/Ca values from sediment samples in which foraminifera are rare or have low mass. For clean primary calcite samples, Mg/Ca ratios from SIMS compare well to those obtained using inductively coupled plasma mass spectrometry (ICP-MS), while maintaining information regarding the variability of elemental ratios within individual tests. For samples with secondary calcite or stubbornly adhering clays, SIMS enables us to accurately measure primary calcite compositions and to assess and reconcile contamination problems in bulk samples analyzed by the more common solution-based ICP-MS technique. SIMS and NanoSIMS (with resolution of 1 micron) are valuable methods for the identification and avoidance of problems of diagenesis and the analysis of rare or delicate foraminifera. However, because of operator time required to properly target delicate (thin-walled) or contaminated foraminifera, SIMS may not be feasible for Mg/Ca studies where large numbers (hundreds) of samples must be processed and where bulk measurements on multiple individuals will suffice. The presentation will include examples of attempts to use combined Mg/Ca (from SIMS and ICP-MS) and oxygen isotope ratios to quantify upper ocean temperature change in the late Cretaceous.
DE: 0473 Paleoclimatology and paleoceanography (3344, 4900)
DE: 1065 Major and trace element geochemistry
DE: 4924 Geochemical tracers
DE: 4954 Sea surface temperature
DE: 9610 Cretaceous
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2007 Fall Meeting