Tectono-stratigraphic model for the early evolution of the Late Cretaceous Nanaimo Group: Georgia Basin, British Columbia, Canada

The Late Cretaceous Nanaimo Group is a siliciclastic succession deposited into the Georgia Basin, that is exposed in BC, Canada. The Nanaimo Group records the initiation and evolution of a forearc basin and is separated into two dominant outcrop regions, the Comox and Nanaimo sub-basins. The traditional lithostratigraphic framework used to describe the Nanaimo Group employs a single-basin layer-cake model and does not consider the effects of paleotopography on the basal nonconformity. As a result, lithoformations comprise strata that are not temporally nor genetically related. This outcrop-based study assesses the depositional architecture, facies relationships, and temporal/stratigraphic equivalency of lower Nanaimo Group strata between the Comox and Nanaimo sub-basins, establishing a new framework for the lower Nanaimo Group. Two spatially and chronologically distinct coal-bearing fields, separated by a regional transgression are identified and a pair of long-lived submarine canyons systems are proposed to have routed sediment into the Paleo-Pacific.