Early Llandovery crinoids and stelleroids from the Cataract Group (Lower Silurian) in southern Ontario, Canada /

Sedimentology of an Early Silurian carbonate ramp: the Manitoulin Formation, southern Ontario

Canadian Journal of Earth Sciences ◽

10.1139/e93-212 ◽

1993 ◽

Vol 30 (12) ◽

pp. 2453-2464 ◽

Cited By ~ 5

Author(s):

A. S. Anastas ◽

M. Coniglio

Keyword(s):

Carbonate Ramp ◽

Michigan Basin ◽

Storm Events ◽

Fair Weather ◽

Continuous Transition ◽

Southern Ontario ◽

Sediment Reworking ◽

Lower Silurian ◽

Shallow Basin ◽

Water Facies

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.

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Lithofacies and age variation in the Fossil Hill Formation (Lower Silurian), southern Georgian Bay region, Ontario

Canadian Journal of Earth Sciences ◽

10.1139/e99-081 ◽

1999 ◽

Vol 36 (10) ◽

pp. 1743-1762

Author(s):

Christopher A Stott ◽

Peter H von Bitter

Keyword(s):

Apparent Absence ◽

Southern Ontario ◽

Georgian Bay ◽

Tectonic Model ◽

Lower Silurian ◽

Bedded Chert ◽

Age Variation

The Fossil Hill Formation in the southern Georgian Bay region demonstrates considerable faunal and lithological variation. Well-defined distinctions exist between bedded chert-bearing, sparsely fossiliferous, argillaceous dolostones of the formation in the eastern Beaver Valley and relatively pure, fossiliferous, non-chert-bearing dolostones observed on the nearby southern Bruce Peninsula and Cape Rich Steps. Biostratigraphic studies and lithostratigraphic tracing through the intervening Bighead Valley suggest that the Fossil Hill Formation of the eastern Beaver Valley is correlative with the typical lower Pentamerus bank and the overlying coral-stromatoporoid biostrome of late Aeronian (Llandovery C1-C2) age observed on the southern Bruce Peninsula and Cape Rich Steps. Regionally, the Fossil Hill Formation exhibits significant age variation; biostratigraphically diagnostic brachiopods (Pentamerus oblongus, Pentameroides subrectus, and Plicostricklandia castellana) from the formation near Walters Falls indicate Telychian (Llandovery C4-C6) to early Wenlock age for part of the unit there. The highly localized preservation of Fossil Hill Formation strata of Telychian age in the Walters Falls area, along with contemporaneous facies changes noted in strata of Aeronian age and the apparent absence of Fossil Hill Formation strata at other localities, suggests that the paleotopography of the southern Georgian Bay region varied markedly during the mid to late Llandovery. A tectonic model that relates epeirogenic uplift associated with the Algonquin Arch in southern Ontario to the vertical rotation of fault-bounded lithospheric blocks, and additions to the model suggested herein, may explain the observed variations.

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