218-4 Trace Element Geochemistry of Ordovician Microfossils from Baffin Island, Canada: Revisiting a Museum Archive

Abstract:

The Ordovician was characterized by large shallow seas and a warmer climate for most of its approximately 40 million year duration. This environment allowed for massive diversification of marine invertebrates, ones who left their fossilized remains behind to record the chemical composition of their environment. A sample of these fossils were collected from a site known as Silliman’s Fossil mount on Baffin Island, Canada, in the summer of 1947 by paleontologist A.K. Miller and geologist Walter Youngquist. A portion of these samples were given to their contemporary A. Scott Warthin, a professor at Vassar College, for microfossil analysis, particularly on ostracods. However, these samples were never published upon and became part of his museum collection. Walter and Youngquist dated these samples to the Upper Ordovician using species identification, millions of years before the anoxia of the End Ordovician Mass extinction. We revisited these samples using modern geochemical tools to investigate whether they could provide new insight into the conditions of the marginal marine environment of Laurentia in the Ordovician. SEM/EDS analysis revealed concentrated zones of mercury, cerium, lanthanum, molybdenum, and neodymium, among other rare earth elements. Bulk analysis via Direct Mercury Analyzer indicated Hg levels above values that have been recorded for Ordovician limestones and shales. These rare earth elements, as well as the levels of mercury that we measured, likely indicate that an anoxic event is preserved at Silliman’s fossil mount  . Further chemical analysis of these samples, alongside a comparison study with fossil samples from the Trenton and Richmond formations of New York from the same time period will allow us to ascertain the nature of the anoxia recorded in the microfossils of Baffin Island.

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