Unearthing the Past: Concretions of the Jurassic Fernie Formation

• Main Author: Käch, Fiona
• Format: Others
• Published: Scholarship @ Claremont 2018
• Subjects: Jurassic; siliceous; concretion; pyrite; geochemistry.; Geochemistry; Geology; Sedimentology
• Online Access: http://scholarship.claremont.edu/cmc_theses/1833; http://scholarship.claremont.edu/cgi/viewcontent.cgi?article=3049&context=cmc_theses

The organic-rich mudrocks of the Jurassic Fernie Formation in British Columbia, Canada contain unusual silica concretions. The silica originated from dissolved volcanic ashes found in the Highwood Member. A lack of radial trends in d13C and internal zonation demonstrate that these concretions grew pervasively. Stable isotope data from calcite inter-grown within the silica matrix (d13C and d18O) indicate that the concretions formed during sulfate reduction and methanogenesis. The d34S revealed a suppressed sulfur fractionation and suggest that they formed in a system that became progressively closed. The Fernie concretions offer insight into the formation of siliceous concretions in marine environments.