Stratigraphy and architecture of shallow-marine strata on an active margin, lower Nanaimo Group, Vancouver Island, BC

摘要

An outcrop-based study of the Late Cretaceous Lower Nanaimo Group in the Nanaimo Basin was conducted to assess depositional architectures in a forearc basin and refine its stratigraphic relationships. Unlike foreland basins and on passive margins, transgressive shoreline successions are commonly observed in the Nanaimo Basin and developed in response to tectonically induced base-level changes and high sedimentation rates. Through a comparison of my results to previously studied transgressive succession and process-response relationships, a conceptual model is developed for predicting transgressive shallow-marine shoreline architectures in sedimentary basins. From a stratigraphic perspective, analysis of key measured sections shows that lower Nanaimo Group strata represent four facies associations: FA1, FA2, FA3, and FA4. The existing lithostratigraphic framework does not consider these depositional architectures, and this work demonstrates that a sequence stratigraphic framework is needed for the lower Nanaimo Group.