Quick Search:    advanced search

GSW Home   GeoRef Home   My GSW Alerts   Contact GSW   About GSW   Journals List   Help

This Article Résumé Figures Only Full Text Full Text (PDF) Submit a response Alert me when this article is cited Alert me when eLetters are posted Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in ISI Web of Science Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Nielsen, K. S. Articles by Leckie, D. A. Search for Related Content GeoRef GeoRef Citation

A new stratigraphic framework for the Upper Colorado Group (Cretaceous) in southern Alberta and southwestern Saskatchewan, Canada

Nexen Inc., 801 – 7th Ave. SW, Calgary, AB T2P 3P7

Claudia J. Schröder-Adams

Department of Earth Sciences, Carleton University, 1125 Colonel By Drive, Ottawa, ON K1S 5B6

Dale A. Leckie

Nexen Inc., 801 – 7th Ave. SW, Calgary, AB T2P 3P7

Extensive marine shales and shallow-marine sandstones of the Cretaceous Upper Colorado Group represent one of the last thick, informally named, stratigraphic intervals in the southern part of the Western Canada Sedimentary Basin. Two regionally-mappable formations in southern Alberta and southwestern Saskatchewan are introduced: The Carlile Formation (Turonian) overlying the Second White Specks Formation, and the Niobrara Formation (Coniacian–Santonian) underlying the Milk River Formation. Both names are extensions of lithologically-similar and laterally-equivalent strata in adjacent parts of the Interior Seaway in Canada and the United States. The boundary between the Carlile and Niobrara formations is recognized at a distinct zone (3 to 15 m thick) of 17 bentonites in the lower part of the Niobrara Formation, whereof two are argon-argon dated to 89.19 (± 0.51) and 89.40 (± 0.31).

Regional variations in lithology, petrophysics and geochemistry of the two new formations make it possible to further subdivide these into formal subunits. The Carlile Formation is subdivided into the informal lower, middle and upper units. The Niobrara Formation is formally subdivided into three mappable members in ascending order: the shaly, non-calcareous Verger Member, the sandstone-rich Medicine Hat Member, and the shaly calcareous First White Specks Member.

An outcrop reference section of the Carlile Formation is designated at Deer Creek (east of West Butte) in the Sweetgrass Hills of north-central Montana. The single core cut from the Carlile Formation in southern Alberta and southwestern Saskatchewan is located at 13-20-17-7W4 and includes twelve metres of the upper part of the formation. It is used as a reference section for the boundary between the Carlile and Niobrara formations. A reference core of the Niobrara Formation is located at 4-16-22-15W4, which also is designated as the type section of the Verger, Medicine Hat and First White Specks members. An outcrop section at the Ghost River Dam Spillway, west of Calgary, serves as the outcrop reference section for the Medicine Hat Member and is correlated to the subsurface using wireline logs and foraminiferal biostratigraphy.

This article has been cited by other articles:

				Y. Yang and A. D. Miall Marine transgressions in the mid-Cretaceous of the Cordilleran foreland basin re-interpreted as orogenic unloading deposits Bulletin of Canadian Petroleum Geology, September 1, 2008; 56(3): 179 - 198. [Abstract] [Full Text] [PDF]

				B. L. Varban and A. G. Plint Allostratigraphy of the Kaskapau Formation (Cenomanian-Turonian) in the subsurface and outcrop: NE British Columbia and NW Alberta, Western Canada Foreland Basin Bulletin of Canadian Petroleum Geology, December 1, 2005; 53(4): 357 - 389. [Abstract] [PDF]