HR: 1340h
AN: B53B-1000    [Abstracts]
TI: Variations in Organic $\delta ^{13}$C and Radiolarian Population Dynamics in the Silurian Cape Phillips Formation, Cornwallis Island, Canadian Arctic
AU: Noble, P J
EM: noblepj@unr.edu
AF: University of Nevada, Reno, Mailstop 172, Reno, NV 89557 United States
AU: * Jones, M K
EM: jonesm6@unr.nevada.edu
AF: University of Nevada, Reno, Mailstop 172, Reno, NV 89557 United States
AB: Samples of graptolitic calcareous shale from the Silurian Cape Phillips Formation, located on Cornwallis Island, Canadian Arctic were collected for geochemical and paleontological study. Radiolarians were recovered and identified from 16 sample horizons from a 21 meter section. This section encompasses most of the \textit{perneri} Graptolite Zone. Calcareous shale from 16 horizons was analyzed for $\delta ^{13}$C$_{organic}$ and $\delta ^{13}$C$_{carbonate}$. At the base of the section there is a baseline shift in $\delta ^{13}$C$_{organic}$ of -2.5\permil\ over 4.5 meters. The $\delta ^{13}$C$_{organic}$ curve then stabilizes at about 6 meters until the top of the section with the exception of two excursions: a -1\permil\ excursion at 11 m; and a -2\permil\ excursion at 20m. $\delta ^{13}$C$_{carbonate}$ shows a similar baseline shift and prominent excursions versus section height. However, the $\delta ^{13}$C$_{carbonate}$ excursions occur approximately 1m higher in the section than the $\delta ^{13}$C$_{organic}$ excursions. Radiolarians recovered from this section exhibit changes in relative abundance that correlate closely to the $\delta ^{13}$C$_{organic}$ 11m and 20m excursions. Inaniguttidae, Palaeoscenidiidae, and a new species, \textit{taxon 4} are observed to increase in relative abundance at the negative $\delta ^{13}$C$_{organic}$ excursions. In contrast, a second new species, \textit{taxon 6}, was observed to decrease in relative abundance at the negative excursions. The increase in palaeoscenidiids is most conspicuous with numbers exceeding 50{%} of the population at the 11.5 m horizon. The coincidence of fluctuations in the relative abundances of the radiolarian species and shifts in the values of $\delta ^{13}$C$_{organic}$ and $\delta ^{13}$C$_{carbonate}$ suggest an environmental control. Modern radiolarians exhibit similar fluctuations in relation to changes in eutrophication, surface circulation patterns, or watermass structure. Likewise, changes in productivity or surface water characteristics may be factors that drive the relative abundance fluctuations in the Cape Phillips Formation.
DE: 4267 Paleoceanography
DE: 3030 Micropaleontology
SC: Biogeosciences [B]
MN: 2004 AGU Fall Meeting