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The AAPG/Datapages Combined Publications Database

Utah Geological Association

Abstract


Proceedings of the First International Conference on the New Basement Tectonics, 1974
Pages 142-152

Chapter 4. Great Plains & Central United States: Bedrock Jointing on the Alberta Plains

Elkanah A. Babcock

Abstract

Regional joints in the southern and central Alberta plains form patterns which persist over an area extending from the Rocky Mountain foothills to the Saskatchewan border (approximately 200,000 km2). These patterns persist vertically through a section of rocks ranging in age from Late Cretaceous to Late Paleocene.

The basic unit of jointing is an orthogonal system consisting of two sets of extension fractures. Two or more orthogonal systems may be present at a given locality creating a complex pattern of joints. System I predominates and has sets trending approximately normal and parallel to the Rocky Mountains, about 55 to 65° and 140 to 155°. System II joints trend approximately 5° and 95°, but swing about 15° clockwise in the Drumheller area. A system having sets trending 45° and 135° is present near Medicine Hat.

System I joints roughly parallel intermediate width (32–64 km) subsurface structural undulations described by Robinson and others (1969). System II joints trend parallel and normal to the crest of the Sweetgrass arch in southern Alberta. Further study is needed to determine the age and origin of jointing.

Regional joints of the Alberta plains show similarities with regional joints in similar structural settings on the Appalachian Plateau and on the Central Oklahoma Plains. Within these areas orthogonal systems of regional joints trend normal and parallel to the adjacent fold belt over vast areas, and the strike patterns persist through great thicknesses of sedimentary rock.


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