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UBC Theses and Dissertations

The effect of deformational mechanisms on the permeability of Upper Paleozoic limestone, dolostone and sandstone near Overfold Mountain, 55 kilometres southeast of Fernie, British Columbia Hammack, Janet L.


Overfold Mountain is located approximately 55 km southeast of Fernie British Columbia in the MacDonald Range of the Rocky Mountains. In the area, limestones, dolostones and sandstones of the Upper Carboniferous Rundle Group and Rocky Mountain Group have been thrown into a series of northwesterly trending folds on the hanging wall of the Lewis Thrust sheet. This study focuses on the deformational mechanisms which have led to the development of one of these megascopic structures, with an emphasis on the role of permeability before, during and after deformation. Deformational mechanisms which have been active near Overfold Mountain include solution processes (pressure solution and hydraulic fracturing), shear fracturing, and intragranular mechanisms (mechanical twinning, dislocation glide, and microfracturing). How strain is partitioned between these mechanisms is largely governed by the permeability of the unit. Permeability is of primary importance in the determination of how a rock will respond in a nonhydrostatic stress field at low temperatures (<0.5 Tm). In the study area, carbonate rocks with a high initial permeability have accommodated strain by pressure solution. Carbonates and sandstones of low initial permeability have accommodated strain by shear fracturing and intragranular mechanisms. Finite permeability in the carbonates and sandstones of the study area, has been altered as a result of these deformational mechanisms. Units which had a high permeability prior to deformation have had their permeability blocked by pressure solution. Units which had a low permeability prior to deformation, have developed microfractures which have increased the finite permeability. This latter phenomenon is well illustrated in the dolostone units studied, both of which have a very well developed fracture porosity.

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