IDENTIFICATION AND CHARACTERIZATION OF STROMATOLITES FROM GRAND RAPIDS, MANITOBA, CANADA USING SPECTROSCOPIC TECHNIQUES

Stromatolites are a distinct organo-sedimentary deposit that are termed microbialites due to their laminated internal fabric. Stromatolites are a result of benthic microbial communities that trap and bind sediments or mineral precipitates. The stromatolites collected from Grand Rapids are small (~10-20 cm diameter) bun-shaped structures with thin (mm-scale) laminations recognized by slight changes in colour. Deposition occurred during the Silurian period within the Moose Lake Formation strata between 419.2 to 443.8 million years ago. Stromatolites can give us insights into how life developed due to their presence on early Earth.

The Grand Rapids stromatolites underwent spectroscopic laboratory analysis to determine their composition which is useful to provide insights into their preservation over time. An ASD LabSpec 4 Hi-Res spectrometer was used to identify the stromatolite material as carbonate. Absorption band positions and Bruker D8 Advance diffractometer XRD data showed that the carbonate was dolomite. Many stromatolites have been found to be predominantly composed of carbonate materials so this determination supports previous findings. Unlike many older stromatolites, the samples from Grand Rapids are well preserved and have likely not undergone any metamorphic changes or recrystallization. This would have resulted in the carbonate materials to be replaced by microcrystalline quartz or destruction of their laminated structure. Our instruments detected no traces of quartz. The BWTek i-Raman-532-S which was utilized to potentially indicate biological signatures, however any mineralogical or organic signatures were masked by strong fluorescence resulting in uninformative data. The composition of the individual laminations has not been discriminated by the Raman or reflectance due to the likelihood of being too similar in composition to be discriminated. We are continuing our examination of the causes of the tonal differences among the laminae.

This study was supported by grants and contracts from the Canadian Space Agency (CSA), MRIF, CFI, UWinnipeg, and NSERC. NNT thanks the Geological Society of America for supporting this study through a GSA Student Research Grant.