Sedimentology and stratigraphy of the Cenomanian-Turonian Kaskapau Formation, northeast British Columbia and northwest Alberta.

摘要

The Cenomanian-Turonian Kaskapau Formation is part of the Upper Cretaceous Smoky Group that was deposited within the Canadian sector of the Western Interior Seaway. The Kaskapau Formation has a thickness of ∼700 m in the west and thins dramatically eastwards to ∼70m, over a distance of ∼200 km. The thickness of the Kaskapau Formation, the prominent eastward tapering and the dominance of mudstones suggest that this formation accumulated during a time of high accommodation. The study interval, allostratigraphically defined between two regional markers (K1 and GS surfaces) spans about 3--3.5 Ma.; On the basis of flooding surfaces, 28 allomembers were recognized and correlated within a subsurface grid that consists of 753 wire line logs (gamma ray and resistivity) and 14 major outcrop sections. For each allomember two isopach maps showing the total thickness and the sand content have been produced. Based on the depositional history interpreted for each allomember, between five to seven allomembers were grouped into major subdivisions (Units I to V) that each, reflects a general subsidence pattern at the basin scale.; Within Unit I (allomembers 1 to 6) uplift and subsidence on the order of 20 to 40 m observed along a linear zone of warping trending N-S in the central part of the study area, suggests the presence of a zone of mechanical weakness within the Precambrian basement along the boundary between the Kiskatinaw low and Ksituan high domains. The vertical movements (uplift/subsidence) were interpreted in terms of different responses to changing in-plane stress.; The total isopach maps suggest that the boundary between units I and II (which almost coincides with the Cenomanian-Turonian boundary) marks an important change in the stress field that rotates from W-E to SW-NE. This rotation is interpreted to correspond to a major change in the tectonic regime within the Canadian Cordillera during the Mid-Cretaceous.