2008 Joint Meeting of The Geological Society of America, Soil Science Society of America, American Society of Agronomy, Crop Science Society of America, Gulf Coast Association of Geological Societies with the Gulf Coast Section of SEPM
Paper No. 141-5
Presentation Time: 8:00 AM-4:45 PM

Incremental Trace Element and Stable Isotopic Analysis of Modern Bahamian Ooids

DUGUID, Sarah M.A., Geological Sciences and Geological Engineering, Queen's University, Kingston, ON K7L3N6, Canada, duguid@geoladm.geol.queensu.ca, KYSER, Kurt, Geological Sciences and Geological Engineering, Queen's Univ, Kingston, ON K7L 3N6, JAMES, Noel P., Department of Geological Science and Geological Engineering, Queen's University, Kingston, ON K7L 3N6, Canada, and RANKEY, Eugene, Marine Geology and Geophysics, Rosenstiel School of Marine and Atmospheric Sciences, 4600 Rickenbacker Causeway, Miami, FL 33149

Ooids are ubiquitous carbonate particles in the geological record, but their specific mechanism of formation continues to be controversial. To delineate the processes responsible for modern ooid formation, the outer and inner cortices and nuclei from six Bahamian localities representing a spectrum of environments were incrementally dissolved. At each step, ooid surfaces were examined using SEM, evolved gas was analyzed for carbon and oxygen stable isotopes, and trace element compositions were determined using continuous leach techniques. SEM observations reveal that the outer cortex is punctuated by unfilled microborings while the inner cortex contains microborings filled with aragonite cement such as that associated with the microbe Solentia sp. Outer and inner cortices have a remarkably similar covarying d18O and d13C trend having a slope near 1, with low values in the outermost cortex, and high values nearest the nucleus. Continuous leaching reveals a corresponding change in composition, with the outer cortex having a high Mg/Ca ratio and a variable Sr/Ca ratio whereas the inner cortex has a low Mg/Ca ratio but constant Sr/Ca ratio indicating Sr contents near 5000ppm. This change in cortex chemistry is interpreted to reflect rapid precipitation of the outer cortex but diagenetic alteration by microbes and associated cements in the inner cortex. High d13C values near 5 in the inner cortex further indicate that 12C fixation occurs in the microenvironment of the borings in the ooid cortex, perhaps associated with the microborers themselves. Thus, Bahamian ooids are grains that have been altered by microbial processes that can be distinguished through incremental analysis.

2008 Joint Meeting of The Geological Society of America, Soil Science Society of America, American Society of Agronomy, Crop Science Society of America, Gulf Coast Association of Geological Societies with the Gulf Coast Section of SEPM
General Information for this Meeting
Session No. 141--Booth# 5
Geochemistry; Geochemistry, Organic (Posters)
George R. Brown Convention Center: Exhibit Hall E
8:00 AM-4:45 PM, Sunday, 5 October 2008

Geological Society of America Abstracts with Programs, Vol. 40, No. 6, p. 131

© Copyright 2008 The Geological Society of America (GSA), all rights reserved. Permission is hereby granted to the author(s) of this abstract to reproduce and distribute it freely, for noncommercial purposes. Permission is hereby granted to any individual scientist to download a single copy of this electronic file and reproduce up to 20 paper copies for noncommercial purposes advancing science and education, including classroom use, providing all reproductions include the complete content shown here, including the author information. All other forms of reproduction and/or transmittal are prohibited without written permission from GSA Copyright Permissions.