Supervisors: Nick Butterfield (Earth Sciences) and Sasha Turchyn (Earth Sciences)
Importance of the area of research:
Diagenetic replacement of shelly fossils with pyrite is a widespread phenomenon in the geological record, but the processes by which it occurs are poorly understood. Unlike the replacement of non-mineralized anatomy, pyritization of hard-tissue requires a precise correspondence between sulphide precipitation and dissolution of the original carbonate/phosphate/silica phases. Palaeontological data reveal that some biominerals and microstructures are conspicuously more susceptible to pyritization than others, though the fidelity and degree of replacement is sensitive to local diagenetic conditions. The aim of this study is to reconstruct the taphonomic pathways responsible for such fossils, and to consider their palaeobiological implications.
The project will focus on a comparative analysis of pyritized fossils from the Middle Cambrian Mount Cap Formation (Canada), Middle Devonian Silica Shale Formation (USA), and the Jurassic of Dorset Kimmeridge Clay (Lias and UK).
What the student will do:
Partially and fully pyritized sponge spicules, brachiopods, bivalves and ammonites will be studied using optical petrography and SEM to resolve diagenetic fabrics, and geochemically to determine the timing of the secondary sulphides and availability of iron. The bacterial sulphate reduction responsible for supplying sulphide ions for pyrite precipitation can potentially be tracked using high-resolution sulphur isotope analysis of the pyrite. Sulphur isotope data will be used to derive a general model for substrate-specific pyritization, including the differential effects of histology, depositional environment and time.
Please contact the lead supervisor directly for further information relating to what the successful applicant will be expected to do, training to be provided, and any specific educational background requirements.
Butterfield, N. J. 2003. Exceptional fossil preservation and the Cambrian Explosion. Integrative and Comparative Biology 43:166–177.
Raiswell, R. 1997. A geochemical framework for the application of stable sulphur isotopes to fossil pyritization. Journal of the Geological Society, London 154:343–356.
Sommerfield, C. K., Aller, R. C., & Nittrouer, C. A. 2001. Sedimentary carbon, sulfur, and iron relationships in modern and ancient diagenetic environments of the Eel River Basin (U.S.A.). Journal of Sedimentary Research 71:335–345.