Stratigraphy, Structural Geology, and Hydrocarbon Habitat in the Southern Canadian Rocky Mountain Foothills Belt
TIPPETT, CLINTON R., and ROBERT D. McMECHAN, Shell Canada Limited, Calgary, Alberta, Canada
The Southern Canadian Rocky Mountain Foothills belt of southwestern Alberta forms the easternmost subdivision of the Cordilleran region at this latitude. This structural zone is approximately 40 km wide and extends 440 km north-northwest from the U.S. border to the North Saskatchewan River. It is characterized at the surface by deformed Mesozoic strata with isolated inliers of Paleozoic carbonates. The Foothills belt and adjacent plains and Front Ranges structural provinces share a common Phanerozoic stratigraphy. This is comprised of 1 to 2 km of platformal Paleozoic carbonates and minor clastics which are blanketed by predominantly clastic Mesozoic and earliest Tertiary strata of a comparable to somewhat greater thickness that are related to Cordilleran orogenesis and erosion. These units are carried in northeast-directed thrust plates with progressively deeper stratigraphic levels involved toward the west. The Precambrian crystalline basement of Hudsonian age extends beneath all three provinces and is not involved in either thin-skinned or thick-skinned foreland-style deformation. Middle Proterozoic sedimentary rocks are carried in Front Range structures such as the Lewis thrust sheet, but only close to the U.S. border.
The major reservoirs in the Foothills belt occur in the Mississippian Turner Valley and Livingstone Formations and in the upper Devonian Palliser Formation. Traps are formed within structural imbrications by juxtaposition of reservoir units against tight footwall strata with lateral spillpoints controlling the extent of hydrocarbon accumulations. Producing fields are characterized by multipool structural stacks and are well illustrated by the Waterton and Jumping Pound West fields. The basal Mississippian Exshaw Formation is believed to be the source for oil and gas in the region. Recoverable sales gas reserves in producing fields range over several orders of magnitude from 3.0 tcf down to 50 bcf. Considerable condensate, NGLs and sulfur complement their sales gas streams.
AAPG Search and Discovery Article #91010©1991 AAPG Rocky Mountain Section Meeting, Billings, Montana, July 28-31, 1991 (2009)