Cambrian-Ordovician Deep Marine Channel-Fill Successions in Eastern Canada: Outcrop Analogues to Deep Marine Offshore Fields Western Africa
Denis Lavoie1, Pamela A. Reynolds2, and Donald K. Sickafoose2
1Quebec Division, Geological Survey of Canada, Quebec City, QC, Canada
2Sub-Saharan Africa, ExxonMobil Exploration Company, Houston, TX
Cambrian to Ordovician slope to toe-of-slope successions in eastern Quebec are exposed laterally for over 600 km. These deposits were accumulated after the Ediacaran rifting of Rodinia, on the “passive” continental margin of Laurentia. The mudstone-dominated succession reaches up to 5 km in thickness. Three sandstone and conglomerate intervals are recognized and can be linked with either eustatic events or tectonic readjustment of failed Proterozoic rift arm.
The first deep-marine coarse-grained deposit is late Early Cambrian and coincides with a global sea level lowstand. These deposits consist of sandstone and conglomerate arranged in thickening and coarsening-upward decametre-thick intervals. This succession ranges between 500 to 600 meters in thickness.
The second event occurred at the end of the Cambrian Grand Cycle B, the facies architecture and nature of the deposits suggest tectonic activity along a failed rift graben as the primary control on deposition. The succession fills metre- to decametre-deep channels with abandonment mud facies and lateral switching; a common fining-upward trend is present within individual channel. The sediment consists of Cambrian limestone and sandstone, Proterozoic rift basalt and metamorphic fragments.
The last event is latest Cambrian to earliest Ordovician and coincides with the end of the Cambrian Grand Cycle C at a time of a major sea level lowstand. The deposits consist of well sorted, medium-grained quartz arenite with rare graded bedding and few current ripples on the top of some beds. These discontinuous deposits can reach thickness of 200 meters.
This constrained chronostratigraphic framework demonstrates depositional variability on the scale of a passive margin. Using these outcrop analogues can help in predicting lateral extent, thickness and facies distribution of deep-water deposits in the sub-surface.
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