Differential Compaction Within the Woodbend Group of Central Alberta

Abstract

ABSTRACT Upper Devonian Leduc reefs found in the subsurface of central Alberta are generally buried by more compactable shales of the Ireton Formation. The compactability contrast between the shales and the carbonates is sufficient to produce significant structural deformation of the overlying horizons. Overburden pressures can also result in differential collapse and/or compaction of the reef itself. These reductions in bulk volume can be analysed by several different methods: constructing a compaction curve; measuring the amount of pressure solution that has taken place; or preparing isopach and structure-contour maps. Application of the above methods and comparison with model studies carried out on similar sediments leads to the conclusion that differential compaction within the Woodbend Group of central Alberta has affected the structure of all but the shallowest of beds. There is also strong evidence that collapse of the reef core itself has been an important mechanism in the development of reef morphology, and that rebound and undercompaction may have been active in the past. These studies indicate that approximately 2000 ft of sediment have been eroded at the Paleozoic unconformity.