Research Training Program

Jocelynn Johnson
University of Manitoba
Winnipeg, Manitoba, CANADA

Ed Vicenzi, Ph.D.
Supervising Scientist
Department of Mineral Sciences

"This program was one of the most educational experiences I have had the privilege to be part of."

A Microchemical Investigation of Fossilized Wood: Biological Preservation and the Influence of Mineralization

The degree of structural change in fossilized wood may be directly linked to the minerals that replace the cellular structure. With improved knowledge of the amount of biological structure that can be preserved in the process of petrifaction of easily recognized organisms, the chances of identifying microorganisms in other geological samples, such as meteorites, increase. As the project deals with both biological organisms and minerals; four things were taken into consideration: species of plant, amount of decay, and minerals present, as well as the most suitable imaging technique(s) for each specimen. Six fossil wood specimens were analyzed in this study; of these samples, two were identified to their species. One specimen was identified as Callixylon sp., an extinct tree, another was a remarkably well-preserved member of the genus Salix sp. (willow). The remaining four specimens were unidentifiable as decay was too far progressed prior to mineralization. The ages of the specimens ranged from Miocene-Pliocene (1.8-23.8 million years) to Devonian (417-354 million years). Nine minerals were identified in the six specimens. The specimens have one dominant mineral, and may have up to four additional accessory minerals. The dominant minerals were chalcedony (SiO2), opal (SiO2•nH2O), hematite (FeO2), dolomite (CaMg(CO3)2), limonite (FeOH• nH2O), and apatite (Ca5(PO4)3(OH,F,Cl), and may also occur as accessory minerals. The remaining three minerals occurring only as accessory minerals were pyrite (FeS2), calcite (CaCO3), and barite (BaSO4). Determination of the amount of structure preserved and by which minerals, was accomplished through the use of imaging techniques such as: light microscopy, polarized light microscopy, back scattered electron imaging and x-ray mapping using the scanning electron microscope, charge-contrast imaging using the environmental scanning electron microscope, and catholuminescence imaging.

This research was supported by a grant from the Smithsonian Women's Committee Internship Endowment.

Letter of gratitude