The Silurian is an interesting time in earth's history. Following the end-Ordovician crisis, benthic marine faunas underwent a period of community restructuring and diversification. Plankton likewise underwent faunal turnovers and diversification, yet there has been little work on the plankton community as a whole and their relationship to changes in the physical environment. One of the least understood groups of Silurian plankton are radiolarians. They are exclusively marine organisms whose highest abundance and diversity is usually associated with ocean settings and complex watermass structure. In cherts, they commonly are the bulk constituents in the rock, and in distal shelf settings, they can be found intermittently in great abundance. Radiolarians are a potentially valuable resource for understanding the paleoceanographic history of early Paleozoic marine basins providing their range and distribution can be closely constrained and calibrated with better studied fossil groups.
This study proposes to examine radiolarians and siliceous sponge spicules from the Cape Phillips Fm., Canadian Arctic, and to integrate these data with graptolite biostratigraphy and geochemistry in order to get a better picture of the dynamics of Silurian plankton communities. This work may eventually feed into research proposed by Canadian colleagues on the organic-walled microfossils and conodonts. Three specific problems will be addressed: 1. Biostratigraphic tool development - The investigator has been working towards developing a biostratigraphic scheme for the Ordovician-Silurian, but lacks independent age control on Late Silurian sections. The Cape Phillips Fm., has the best preserved Silurian radiolarians in the world, its age is well constrained by graptolites, and has the best possibility of providing the age control needed. 2. Extinction/diversification events - Radiolarian response will be examined across two mid Silurian graptolite extinctions and subsequent diversification. Carbon isotope analysis of the non-carbonate fraction will be conducted across the extinctions to look for related geochemical signatures. 3. Siliceous spicules in paleoecology - The percentage of lithistid to hexactinellid spicules has previously been observed to vary with sea level rise in Late Ordovician sections. Spicules will be examined in conjunction with the physical stratigraphy in order to test their sensitivity to local sea-level fluctuation. These data will be tied into changes observed in the plankton community and the basin history.
