LE3 .A278 2009

2009

Pufahl, Peir

Acadia University

Bachelor of Science

Honours

Physics

Physics

Brachiopods are bivalve invertebrates that are routinely used by Earth scientists to understand the chemistry of ancient oceans. Because brachiopod shells are thought to precipitate in chemical equilibrium with seawater, their shell chemistry reflects ocean composition at the time of precipitation. What is not clear is how shell chemistry is altered during burial once the brachiopod dies and is exported into the geological record. Although Earth scientists use an array of techniques to assess changes in shell microstructure during burial, they often lack the resolution necessary to adequately determine whether shells are altered. Such analysis is paramount when establishing what brachiopods should be used for paleoenvironmental interpretation. Techniques commonly employed in the material sciences to understand microstructure include scanning electron microscopy coupled with a dedicated cathodoluminescence system (SEM-CL) and transmission electron microscopy (TEM). These techniques, however, are not widely used in the Earth sciences. For the first time the microstructure of unaltered and altered brachiopod shells from a range of geological ages are analyzed using these techniques to better understand alteration. Based on CL microfabrics, four categories of increasing shell alteration are observed. Cursory TEM analysis indicates that differences in shell chemistry are related to changes in shell microstructure during alteration. Such changes in microfabric include dislocations and stacking faults within the low Mg calcite. Further TEM work is necessary to confirm these relationships.

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https://scholar.acadiau.ca/islandora/object/theses:598