Paper No. 123-1
Presentation Time: 9:00 AM-6:30 PM
A REEXAMINATION OF THE DIVERSITY AND STRATIGRAPHIC DISTRIBUTION OF THE EARLY TONIAN APATITE SCALE MICROFOSSILS, FIFTEENMILE GROUP, YUKON
COHEN, Phoebe, Geosciences, Williams College, 947 Main Street, Williamstown, MA 01267 and
BARKER, Henry Cleave, Williams College, Williamstown, MA 01267, hcb1@williams.edu
Binding together biotic and abiotic systems, the evolution of biomineralization is one of the most pivotal events in the history of life on earth. The origins of primary, controlled eukaryotic biomineralization are not entirely clear, but Apatitic Scale Microfossils (ASMs) from the early Neoproterozoic (Tonian Period, 1000 – 717 Ma) Fifteenmile Group of Yukon, Canada, may represent the oldest evidence of eukaryotic biomineralization in the fossil record. These microfossils are constructed of nanoscale crystallite networks comprised of calcium phosphate minerals and organic carbon, and are interpreted as cell coverings similar to those found in modern coccolithophores. Cohen and Knoll (2012) documented the diversity of ASMs macerated from carbonates at the single known ASM locality at Mount Slipper. Here, we examine new specimens collected in 2014 from Mount Slipper. We document new species, reveal new detail of existing taxa, and provide a higher-resolution look at the stratigraphic distribution of ASMs at Mount Slipper.
Cohen and Knoll described fossils from 5 horizons; here we expand that to 23 horizons, spread out over 38 meters of section. In addition to several new taxa, we found well-preserved specimens with intricate, fragile structures still left intact—likely examples of previously described taxa, which lacked these structures due to poor preservation. We found several previously described taxa, such as Characodictyon skolopium, in new horizons, extending the range of those taxa. In addition, we examine the relationship between a local dolomitization front at Mount Slipper and the preservation of ASMs, revealing more information about why these unique fossils appear to be so rare. A clearer understanding of the preservation, stratigraphic distribution, and morphology of ASMs may help us make inferences about Neoproterozoic ocean chemistry and marine ecological dynamics.
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