A seismic case study of salt dissolution and subsidence in response to regional deformation, south-central Alberta

Abstract

Bedded rock salt with a net thickness of about 40 m was deposited uniformly within the Famennian Wabamun Group in the Stettler South study area (T33–34, R18–21W4M) of south-central Alberta. Subsequent to deposition, this original rock salt was leached to the extent that it is preserved now as irregular-shaped bodies of widely differing areal extent and thickness. In the immediate study area, dissolution was initiated by regional deformation during the mid-Late Cretaceous, and accentuated thereafter by various large-scale processes including glaciation. Seismic data illustrate that at least some salt-dissolution features in the Stettler South area retain a marked linear orientation (SSW-NNE). In cross section (on west-east oriented seismic lines), these structures are manifested as upward-expanding zones of observable subsidence. These zones of subsidence are characterized by increased structural relief at greater depth (resulting principally to the timing of the leaching, stoping, and lateral strain within post-salt strata), and small-amplitude near-vertical offsets. The character of these subsidence features is consistent with: (1) the onset of dissolution as a result of regional deformation during mid-Late Cretaceous; (2) the plastic deformation (creep) of rock salt; (3) the plastic deformation (on a large scale) and relatively gradual subsidence of the post-salt strata; and (4) accelerated rates of leaching in response to glacial loading and unloading.