Unit Name: Poplar Beds
Unit Type: Lithostratigraphic
Usage: Currently in use
Age Interval: Meramecian (340 - 333 ma)
Age Justification: Brindle (1960) reports the presence of a coral-brachiopod-molluscan fauna in the Poplar Beds, dominated by brachiopods that he recognized as Meramecian in age.
Originator: Saskatchewan Geological Society, 1956.
Named for the Poplar field, Montana which produces oil from several relatively thin carbonate beds in the section. A characteristic development is illustrated in Murphy East Poplar Unit No. 1 borehole in Sec. 2, Twp. 28N, Rge. 51E, Montana, between 1,611.8 and 1,769 m (5,288 and 5,809 ft). Fuzesy (1960) proposed a standard reference section for the Saskatchewan subsurface in Lake Alma 8-22-2-17W2M, between 1,812 and 1,937 m (5,945 and 6,356 ft).
The Poplar is widespread in the interior of the Williston basin and in the central Montana trough. The beds cover some 12950 km2 (5059 mi2) in southeastern and southcentral Saskatchewan, with their average maximum extending about 58 km (36 mi) north of the U.S. border. In Saskatchewan the Poplar Beds have a minimum thickness of about 117 m (384 ft) and attain a maximum thickness in the central part of the Williston Basin of about 152 m (500 ft).
Fuzesy (1960) described the Poplar Beds as consisting of limestones, argillaceous dolomites and evaporites. The evaporites are primarily anhydrite and evaporitic dolomite, but Fuzesy reported that two halite intervals exist in a small region in the vicinity of the standard reference well. These halites range from 4.6 to 12 m (15 to 89 ft) thick.
The Saskatchewan Geological Society (1956) placed the lower contact of the Poplar at the base of an anhydrite underlying a 30 m (98 ft) thick interval of anhydrites and mudstone immediately above the Ratcliffe Beds. Fuzesy (1960) found that the basal evaporite is not always present and a more consistent marker bed for recognition of the base of the Poplar is a 6 to 10 m (20 to 33 ft) thick zone of argillaceous dolomitic limestone or argillaceous dolomite that produces a markedly low resistivity response. The Poplar Beds may be recognized as well by a pronounced positive deflection of the spontaneous potential log. The top of the unit is a matter of some controversy as well; Fuzesy (1960) recommended that it be placed some 30 m (98 ft) below the base of the Kibbey Limestone, which was proposed as the top by the Saskatchewan Geological Society.
Brindle, 1960; Fuzesy, 1960; Saskatchewan Geological Society, 1956.
Source: CSPG Lexicon of Canadian Stratigraphy, Volume 4, western Canada, including eastern British Columbia, Alberta, Saskatchewan and southern Manitoba; D.J. Glass (editor)
Contributor: D.M. Kent
Entry Reviewed: Yes
Name Set: Lithostratigraphic Lexicon
LastChange: 29 Apr 2003