Porcupine Hills Formation

The Porcupine Hills Formation is a stratigraphic unit of middle to late Paleocene age in the Western Canada Sedimentary Basin. It takes its name from the Porcupine Hills of southwestern Alberta, and was first described in outcrop by George Mercer Dawson in 1883.[2]

Porcupine Hills Formation Stratigraphic range: Paleocene PreꞒ Ꞓ O S D C P T J K Pg N
Type	Geological formation
Underlies	erosional surface
Overlies	Willow Creek Formation
Thickness	up to 1,200 metres (3,940 ft)[1]
Lithology
Primary	Shale
Other	Sandstone, shale
Location
Coordinates	49.78753°N 113.88020°W / 49.78753; -113.88020 (Porcupine Hills Formation)
Region	Alberta
Country	Canada
Type section
Named for	Porcupine Hills (Alberta)
Named by	G.M. Dawson, 1883

Lithology

The Porcupine Hills Formation is composed primarily of mudstones, siltstones and sandstones. The sediments were derived from the Canadian Cordillera during tectonic uplift and erosion in the late stages of the Laramide Orogeny, and were transported eastward by river systems and deposited in fluvial and floodplain environments.[3]

The mudstones are characterized by well-developed paleosols and caliche nodules, and the sandstones are cross-bedded and cemented with calcite. In contrast to the Paskapoo Formation, an equivalent formation farther to the north, there are no coaly beds. This has given rise to the hypothesis that during the deposition of the Porcupine Hills Formation the climate was semi-arid, while the climate farther north was more humid.[3]

Distribution

The Porcupine Hills Formation is present in southwestern Alberta, from the Waterton River near the Canada–US border in the south to the Bow River near Calgary in the north.[4] The upper limit is the present day erosional surface, so its original thickness can not be determined; however, the maximum recorded thickness is 1,200 metres (3,940 ft) in the Porcupine Hills.[1]

Relationship to other units

The Porcupine Hills Formation is exposed at surface or is overlain by Quaternary sediments. Its base is a thick sandstone that rests disconformably on a paleosol horizon of the underlying Willow Creek Formation.[3]

In the north near the Bow River, the Porcupine Hills Formation grades into the equivalent Paskapoo Formation. It is correlated with upper part of the Ravenscrag Formation of southern Saskatchewan and the Fort Union Formation of Montana and North Dakota, which are not contiguous with it but are of similar age.[5][6]

References

1. Lexicon of Canadian Geologic Units. "Porcupine Hills Formation". Retrieved 2010-01-01.
2. Dawson, G.M., 1883. Preliminary report on the geology of the Bow and Belly river region, Northwest Territory, with special reference to the coal deposits. Geological Survey of Canada, Report of Progress for 1880-81-82, Part B.
3. Hamblin, A.P. (2004). "Paskapoo-Porcupine Hills Formation in western Alberta: Synthesis of regional geology and resource potential. Geological Survey of Canada, Open File 4679". Retrieved 2013-08-01.
4. Prior, G. J., Hathaway, B., Glombick, P.M., Pana, D.I., Banks, C.J., Hay, D.C., Schneider, C.L., Grobe, M., Elgr, R., and Weiss, J.A. (2013). "Bedrock Geology of Alberta. Alberta Geological Survey, Map 600". Archived from the original on 2013-09-25. Retrieved 2013-08-13.CS1 maint: multiple names: authors list (link)
5. Mossop, G.D. and Shetsen, I., (compilers), Canadian Society of Petroleum Geologists (1994). "The Geological Atlas of the Western Canada Sedimentary Basin, Chapter 24: Upper Cretaceous and Tertiary strata of the Western Canada Sedimentary Basin". Archived from the original on 2013-07-21. Retrieved 2013-08-01.CS1 maint: multiple names: authors list (link)
6. Alberta Geological Survey, 2013. "Alberta Table of Formations; Alberta Energy Regulator" (PDF). Archived from the original (PDF) on 2015-09-25. Retrieved 2016-06-20.