Map 573

Map 573

MAP 573

Paleotopography of the Sub-Cretaceous Unconformity Surface, West Central Alberta

Author(s) Peterson, J. MacCormack, K. Date 2014-06-27

The sub-Cretaceous unconformity is an important regional surface across the Alberta Basin, and represents a significant period of non-deposition and erosion initiated after the deposition of Upper Jurassic/Lower Cretaceous sediments of the first foreland basin clastic wedge. With the exception of the upper Fernie and Nikanassin formations, this major unconformity surface separates the basin into two distinct depositional settings; a lower passive margin and an upper foreland basin.

The study area covers NTS map sheets 83G, 83J, 83K, and part of 83F. The southwest limit of the study area is defined by the approximate limit of the main Cordilleran deformation.

Geophysical wireline logs were reviewed to identify the depth of the unconformity and the corresponding subcropping stratigraphic units. Cores from various subcropping areas were reviewed to validate log responses at the unconformity surface.

ArcGIS Geostatistical Analyst was used to model the unconformity surface data using a 500 metre grid cell spacing. The dominant southwest dipping trend was removed from the modelled surface to provide residual values representing the paleotopography. Underlying stratigraphic units were modelled independently and then integrated into a 3D geocellular model using Petrel 2013. The geocellular model was then truncated by the sub-Cretaceous unconformity surface to identify the subcrop geometry of each stratigraphic unit. Model results were cross-validated with well control data and subcrop edges were adjusted where required.