GRANT 216. THE DEPOSITIONAL ENVIRONMENT FOR THE BLACK SHALES OF THE UPPER DEVONIAN LONG RAPIDS FORMATION, NORTHERN ONTARIO.

The Upper Devonian Long Rapids Formation in northern Ontario was deposited in a warm, tropical environment which experienced periodic fluctuations in oxygen content of the water column. The black shales were deposited under anoxic water conditions, and other sedimentary components, such as green-grey mudstones and carbonates, were deposited under oxygenated water conditions. The deposition of these units can best be explained with a model using a stratified water column, where a pycnocline separates anoxic and oxic waters. Periodic movements of this pycnocline to the sediment-water interface, or the disappearance of it altogether, would determine the type of sediment deposited. Movement of the pycnocline may be due to surface plankton blooms, tectonic readjustments along the craton's marginal edge, or climatic variance.