Paleocurrents and depositional environments of deep water conglomerates in the Cambro-Ordovician Cap Enragé Formation, Quebec Appalachians
Journal Articles
Overview
Research
Identity
Additional Document Info
View All
Overview
abstract
The Cap Enragé conglomerates are deep water, resedimented types associated with pebbly and massive sandstones. They resemble other deep water conglomerates in Quebec, especially those at Lévis-Lauzon, L'Islet Wharf, and Grosses Roches. All of these conglomerates were derived from a carbonate shelf to the northwest, and flow directions at Lévis and L'Islet are dominantly southward. By contrast, flow directions at Grosses Roches are to the west and southwest, suggesting deflection of conglomeratic flows by a topographic obstruction.In the Cap Enragé, only published flow directions from sandstones suggest flow toward south and southeast. One published conglomeratic flow direction indicates southwestward flow. Our paleoflow work on the entire outcrop length of the Cap Enragé conglomerates demonstrates dominantly westward and southwestward flow, reinforcing the idea of a topographic obstruction deflecting flows.We have demonstrated some consistent horizontally-fining facies relationships in the conglomerates. Beginning with massive, coarse cobble–boulder conglomerates, there are horizontal passages into finer conglomerates with crude stratification shown up by rows of cobbles and then pebbles, and finally into well stratified coarse sandstones with layers of granules and pebbles. Compared with local flow directions, these horizontally-fining relationships occur in upstream, downstream, and lateral directions.We suggest that southeastward, downslope-flowing currents were forced to swing southwestward by an obstruction, and hence the entire Cap Enragé Formation was deposited in a broad depression or channel trending parallel to the base of slope. Within this overall interpretation, we suggest that the conglomerate members of the Cap Enragé were deposited in meandering talweg channels, similar to those of the modern La Jolla submarine fan channel. Upstream-, downstream-, and laterally-fining facies sequences may be related to the filling of large scours within the talweg, or to facies changes from the talweg to adjacent terraces.
