Regional Tectonic Controls on Sedimentation during the Cenomanian-Turonian Time in the Western Interior Basin (WIB), Canada

Mapping by potential field methods suggested that the crystalline basement beneath the WIB, Canada is a mosaic of Archean and Proterozoic tectonic domains bounded by regional faults and shear zones. Further, integration of potential field data with the Lithoprobe seismic data suggested that the basement beneath the major part of central and southern Alberta is dominated by flexural effects related to formation and evolution of the foreland basin. The reason for dominance of flexural effects is that owing to its old thermal age, lithosphere in Canada is close to its maximum strength and therefore less susceptible to failure by reactivation of shear zones.

The term ‘basement control' is invoked if sedimentation in the Phanerozoic section is influenced by the reactivation of faults and shear zones in the crystalline basement. High-resolution stratigraphic study of the Blackstone Formation (Cenomanian-Turonian), WIB, Canada provides evidence for lack of reactivation of basement shear zones in ~200,000 Km² study area that is underlain by 8 basement tectonic domains. There are no thickness anomalies across domain boundaries on well log correlations, lithoprobe Central Alberta Seismic transect, and on isopach maps that can be ascribed to reactivation of basement shear zones. Temporal and spatial thickness changes in measured sections and on isopach maps are instead related to subsidence induced by migrating thrust and sediment loads. The middle Cenomanian (post ‘X' bentonite) erosional unconformity at the base of the Second White Specks Formation in the area close to Alberta-Saskatchewan border has often been ascribed to reactivation of several inferred basement faults. However, this unconformity has no relation to the basement structure and represents forebulge unconformity that resulted due to flexural response of the lithosphere to uniform thrust loading along the strike of the Cordillera, and submarine erosion during the middle Cenomanian time.