Date of Award


Degree Type


Degree Name

Master of Science




Dr. Fred J. Longstaffe

Second Advisor

Dr. Jisuo Jin


The δ13C and δ180 values and elemental compositions of 29 Late Ordovician (Hirnantian Stage) shells from eight different brachiopod species from the Ellis Bay Formation, Anticosti Island, Quebec, were measured to evaluate their fidelity of chemical and isotopic preservation. Three groups of Mendacella shells from three separate Hirnantian time periods were also analyzed to provide δ C and δ O curves for this time interval. Significant differences in δ C and δ 0 values among species, shells of the same species, and within individual shells from early to late growth stages suggest that original isotopic compositions were retained. Differences in chemical compositions between shell-matrix and shell-cement boundaries also suggest minimal alteration. These brachiopods are therefore deemed suitable proxies for the δ C and δ 0 values of Hirnantian seawater. The carbon and oxygen isotope compositions of Mendacella are consistent with previous studies. A large, positive excursion at the end-Hirnantian is suggestive of a cooling event.



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