Electronic Thesis and Dissertation Repository


Doctor of Philosophy




Corcoran, Patricia L.


The Gordon Lake Formation of the Paleoproterozoic Huronian Supergroup is a primarily-siliciclastic succession ranging from 300 to 1100 m thick. Lithostratigraphic and sedimentological analysis of the formation in the Bruce Mines and Flack Lake areas, and Killarney and Lady Evelyn-Smoothwater provincial parks revealed 7 lithofacies, which comprise 3 distinct lithofacies associations. The lithofacies associations are subtidal nearshore, subtidal to shallow shelf, and mixed intertidal flat. Microbially-induced sedimentary structures (MISS) related to microbial mat destruction and decay were recognized in the Flack Lake area. The preserved MISS include sand cracks, mat chips, remnant gas domes, and pyrite patches, and iron laminae. A biological origin for the fossil structures is supported by their similarities to modern and ancient documented examples of MISS, the sand-dominated nature of the substrate in which they are preserved, and key microtextures identified in thin section. The identified MISS support the interpretation of a tidal flat depositional environment. The Gordon Lake Formation contains soft-sediment deformation structures (SSDS) in all four study areas. Identified SSDS include load casts, convolute bedding, pseudonodules, ball-and-pillow structures, flame structures, syn-sedimentary faults, and one dewatering pipe. The primary trigger mechanism is interpreted to be storm or tsunami activity, however seismic shock, overloading brought about by density inversions, or a combination of these processes, may have influenced the development of the structures to a lesser degree. Microbial mats may have played a minor role in the formation of the SSDS, but do not appear to have been a prominent driving mechanism. Detrital zircon U-Pb ages from a sandstone provide new evidence for the maximum depositional age of the formation and reinterpretation of the depositional history of the upper Huronian Supergroup. The average age of the youngest zircon grains constrains the age of deposition to sometime after 2315 ± 5 Ma, but prior to intrusion of gabbro (Nipissing) approximately 95 m.y. later.

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