Senior Theses 2007
Jan Trienekens (2007). Geochemical evidence for the formation of marine ooids: a microbial mediated process
Faculty Advisor: Joel Thompson
Through the multiproxy analysis of both modern Great Bahaman Bank ooids and ancient Miami Oolite a definitive link occurs between the microbes and the precipitated carbonate of the ooids. The determination was conducted utilizing light and epifluoresecence microscopy to view the surface bacterial colonies in addition to petrographic microscopy to view the internal structure. The associated biological pigments were extracted and analyzed using HPLC and the primary pigments were found to be 19' butanoyloxyfucoxanthin, diatoxanthin, chlorophyll A and phaeophytin A. The presence of these pigments indicates both pigmented heterotrophic and autotrophic bacteria may occur on and within the ooids. XRD analysis showed a recrystalization has occurred between the ancient and modern ooid samples and revealed a 6 to 1 calcite to aragonite ratio for the ancient ooids vs. pure aragonite for the modem ooids. Evidence of microbial interaction is further illustrated by stable carbon isotopes, which reveal a 12C enrichment in the inorganic carbon samples, which most likely is the result of a microbially mediated source in the form of respired organic carbon. Based on a simple mixing model it can be estimated that 10% of the inorganic carbon is from a respired source. Additionally both the bulk and intracrystalline organic matter were analyzed for carbon and nitrogen isotopes. Little difference was noted between the bulk and intracrystalline isotopic carbon values in modem samples and showed an overall δ l3C fractionation of approximately -20‰ between the dissolved inorganic carbon source and the associated organic matter, consistent with a marine microbial signature. The ancient Miami oolite sample was found to have a δ l3C organic value of -26‰. This change may be attributed to a change in the primary microbes associated with the production of ooids. Nitrogen isotopic values showed a discrepancy between bulk and intracrystalline isotopic values. This may be attributed to surface degradation or the presence of nitrogen fixing cyanobacteria. The intracrystalline nitrogen values were found to be between 2.25‰ and 1.34‰, which is likely a more representative value to the bulk values of 1.96‰ to 0.67‰. The offset between bulk and intracrystalline sample may be due to nitrogen fixing cyanobacteria, which show this sample to be in line with a base nitrogen signature of a mixed cyanobacterial and autotrophic or heterotrophic biomass. The amino acid results yielded the presence of the following amino. acids, alanine, valine, glycine, serine, isoleucine, leucine, aspartic acid/asparagines, glutamic acid/glutamine, phenylalanine, tyrosine and lysine. Ultimately the combined effect of these analytical tests demonstrates a logical argument for the codependence of microbes in the formation of ooids.