Fault - Controlled Dissolution of Bedded Rock Salt

Analyses of well log and seismic data suggest that about 40 m of Famennian-age bedded rock salt was uniformly deposited within the Wabamun Group in the Stettler area, southeastern Alberta, Canada. Subsequent to deposition, this original rock salt was leached to the extent that it is preserved now only as isolated-tocontiguous bodies of irregular shape and variable thickness. In the immediate study area, dissolution appears to have been initiated by regional faulting and/or fracturing during the mid-Late Cretaceous, and accentuated thereafter by various large-scale mechanisms including glaciation. In this paper, seismic data across a _prominent NNE trending salt-dissolution feature in the Stettler area are presented. In short cross-section, this subsidence feature IS manifested as an upward-expanding zone of "measurable" subsidence, characterized by increased structural relief at greater depths, and small-amplitude nearvertical offsets. This subsidence feature is consistent with: 1) the onset of salt dissolution as a result of regional faulting and/or fracturing during mid-Late Cretaceous time; 2) the plastic deformation of rock salt (creep); 3) the gradual (as opposed to catastrophic) subsidence of the post-salt strata; and 4) accelerated rates of leachinJ durinJ the Pleistocene and Holocene in response to glacial loading and unloading.