From Proterozoic strata to a synthesized seismic reflection trace: implications for regional seismic reflection patterns in northwestern Canada

Abstract

Calculation of a synthetic seismic reflection trace from detailed descriptions of exposed Proterozoic strata in northwestern Canada permits correlation of reflections on regional seismic profiles to surface outcrop. Approximately 5.4 km (composite thickness) of Paleo- and Mesoproterozoic strata are exposed in the Muskwa anticlinorium that is located within the foreland of the Cordillera in northeastern British Columbia. The Tuchodi anticline is the easternmost structure of the Muskwa anticlinorium and has the deepest levels of Proterozoic strata exposed. At this location, prominent seismic reflection layering rises toward the surface and is easily correlated to the deeper formations of the Muskwa assemblage stratigraphy. These layers are followed westward into the middle crust, where they are overlain by dramatically thickened (by about five times) strata, primarily of the Tuchodi Formation. Along the same line of section, the Muskwa assemblage reflections overlie additional subparallel layered reflections at depth whose lithology and origin are unknown. However, coupled with other observations, including regional refraction results that indicate the crustal layers have both low seismic p-wave velocities and low ratios of p- and s-velocities, regional gravity observations that indicate the layers are low density, and correlation to similar layers on other seismic profiles that exhibit characteristic seismic stratigraphic features, the subparallel layers that are present beneath the known Muskwa assemblage are most easily interpreted as layered Proterozoic (meta-) sedimentary rocks. These results provide the basis for interpreting the Muskwa anticlinorium as a crustal-scale structure that formed when a deep basin of Proterozoic strata was inverted and thrust over an ~20 km high footwall ramp during Cordilleran orogenesis.