SEDIMENTOLOGY OF AN EARLY SILURIAN CARBONATE RAMP - THE MANITOULIN FORMATION, SOUTHERN ONTARIO

The Manitoulin Formation is a pervasively dolomitized Lower Silurian carbonate unit that was deposited in the Michigan Basin and locally in the Appalachian Basin. The formation reaches a maximum thickness of 11.1 m in southern Ontario and can be subdivided into eight facies and four regionally correlatable facies assemblages. Owing to the relatively continuous transition of shallow to deeper water facies from the northern to southern portions of the study area, the Manitoulin Formation is interpreted as having formed on a carbonate ramp with a southerly component of dip. Our study suggests that the Algonquin Arch, which is transected by the outcrop belt, did not significantly influence deposition or separate the Michigan and Appalachian basins. Depending on its location on the ramp, the Manitoulin Formation shows evidence of varying degrees of episodic storm events alternating with fair-weather processes such as wave shoaling, sediment reworking, and bioturbation. Apart from bioturbation, these fair-weather processes became less prevalent to the south. The gently dipping antecedent topography, the temporary lack of frame-builders, and a shallow basin setting led to the creation of a carbonate ramp rather than a rimmed shelf.