Graduate Thesis Or Dissertation
 

Bedrock geology and stratigraphy of the Late Cretaceous Nanaimo Group of the Maple Bay-Cowichan Bay area, British Columbia

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  • Regionally preserved in a structural basin, rocks of the Cretaceous Nanaimo Group nonconformably overlie metavolcanic and metasedimentary rocks of the Permian and older Sicker Group. Cretaceous rocks of the thesis area occur in three formations, the Comox, Extension-Protection, and Cedar Dist; and, during two cycles, were deposited in environments which, as a result of transgressions and regressions, ranged from fluvial to marine. Paleocurrent and rock analyses indicate that sediments were derived from an uplifted volcanic and metamorphic terrane southwest of the study area, suggesting a possible Sicker Group source. The Benson Number of the Comox Formation is the basal unit of the Nanaimo Group and consists of gravels, cobbles, and boulders deposited by highly competent streams during the initial phase of the first depositional cycle. Detritus was rapidly transported from a nearby source and quickly buried as channel lag deposits in alluvial fans. After an erosional episode and/or a period of non-deposition, sands and gravels of the Extension-Protection Formation were transported by high velocity, low sinuosity streams and deposited on nonmarine delta plains and marine delta fronts. Grading laterally, seaward of the sands and gravels, the silt- and mud-sized particles of the Cedar District Formation, the youngest Mesozoic sediments to be preserved in the thesis area, were transported to a prodelta environment where they then settled from suspension or were deposited by turbidity currents. Existing Cretaceous deposits were preserved in large blocks tilted by post-Crectaceous faulting.
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