The Porcupine Hills Formation is a

stratigraphic Stratigraphy is a branch of geology concerned with the study of rock layers (strata) and layering (stratification). It is primarily used in the study of sedimentary and layered volcanic rocks. Stratigraphy has three related subfields: lithost ...

unit of middle to late

Paleocene The Paleocene ( ), or Palaeocene, is a geological epoch (geology), epoch that lasted from about 66 to 56 mya (unit), million years ago (mya). It is the first epoch of the Paleogene Period (geology), Period in the modern Cenozoic Era (geology), ...

age Age or AGE may refer to: Time and its effects * Age, the amount of time someone has been alive or something has existed ** East Asian age reckoning, an Asian system of marking age starting at 1 * Ageing or aging, the process of becoming older ...

in the

Western Canada Sedimentary Basin The Western Canada Sedimentary Basin (WCSB) underlies of Western Canada including southwestern Manitoba, southern Saskatchewan, Alberta, northeastern British Columbia and the southwest corner of the Northwest Territories. This vast sedimentary ba ...

. It takes its name from the

Porcupine Hills The Porcupine Hills refer to various groups of hills and uplands located in the prairie provinces of Canada, specifically the provinces of Saskatchewan and Manitoba. They are part of the Manitoba Escarpment, which was the shoreline of the anc ...

of southwestern

Alberta Alberta is a Provinces and territories of Canada, province in Canada. It is a part of Western Canada and is one of the three Canadian Prairies, prairie provinces. Alberta is bordered by British Columbia to its west, Saskatchewan to its east, t ...

, and was first described in

outcrop An outcrop or rocky outcrop is a visible exposure of bedrock or ancient superficial deposits on the surface of the Earth and other terrestrial planets. Features Outcrops do not cover the majority of the Earth's land surface because in most p ...

George Mercer Dawson George Mercer Dawson (August 1, 1849 – March 2, 1901) was a Canadian geologist and surveyor. He performed many early explorations in western North America and compiled numerous records of the native peoples. Biography He was born in ...

in 1883.

Lithology

The Porcupine Hills Formation is composed primarily of

mudstones Mudstone, a type of mudrock, is a fine-grained sedimentary rock whose original constituents were clays or muds. Mudstone is distinguished from ''shale'' by its lack of fissility.Blatt, H., and R.J. Tracy, 1996, ''Petrology.'' New York, New York ...

siltstone Siltstone, also known as aleurolite, is a clastic sedimentary rock that is composed mostly of silt. It is a form of mudrock with a low clay mineral content, which can be distinguished from shale by its lack of fissility. Although its permeabil ...

s and

sandstone Sandstone is a Clastic rock#Sedimentary clastic rocks, clastic sedimentary rock composed mainly of grain size, sand-sized (0.0625 to 2 mm) silicate mineral, silicate grains, Cementation (geology), cemented together by another mineral. Sand ...

s. The sediments were derived from the

Canadian Cordillera The Pacific Cordillera, also known as the Western Cordillera or simply The Cordillera, is a top-level physiographic region of Canada, referring mainly to the extensive cordillera system in Western and Northwestern Canada that constitutes the northe ...

during tectonic uplift and erosion in the late stages of the

Laramide Orogeny The Laramide orogeny was a time period of mountain building in western North America, which started in the Late Cretaceous, 80 to 70 million years ago, and ended 55 to 35 million years ago. The exact duration and ages of beginning and end of the o ...

, and were transported eastward by river systems and deposited in fluvial and

floodplain A floodplain or flood plain or bottomlands is an area of land adjacent to a river. Floodplains stretch from the banks of a river channel to the base of the enclosing valley, and experience flooding during periods of high Discharge (hydrolog ...

environments. The mudstones are characterized by well-developed

paleosol In Earth science, geoscience, paleosol (''palaeosol'' in Great Britain and Australia) is an ancient soil that formed in the past. The definition of the term in geology and paleontology is slightly different from its use in soil science. In geo ...

s and

caliche Caliche () is a soil accumulation of soluble calcium carbonate at depth, where it precipitates and binds other materials—such as gravel, sand, clay, and silt. It occurs worldwide, in aridisol and mollisol soil orders—generally in arid or se ...

nodules, and the sandstones are

cross-bedded In geology, cross-bedding, also known as cross-stratification, is layering within a stratum and at an angle to the main bedding plane. The sedimentary structures which result are roughly horizontal units composed of inclined layers. The original ...

and cemented with

calcite Calcite is a Carbonate minerals, carbonate mineral and the most stable Polymorphism (materials science), polymorph of calcium carbonate (CaCO3). It is a very common mineral, particularly as a component of limestone. Calcite defines hardness 3 on ...

. In contrast to the

Paskapoo Formation The Paskapoo Formation is a stratigraphic unit of Middle to Late Paleocene age in the Western Canada Sedimentary Basin. The Paskapoo underlies much of southwestern Alberta, and takes the name from the Blindman River ( means 'He is blind' in Cr ...

, 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 A semi-arid climate, semi-desert climate, or steppe climate is a aridity, dry climate sub-type. It is located on regions that receive precipitation below Evapotranspiration#Potential evapotranspiration, potential evapotranspiration, but not as l ...

, while the climate farther north was more humid.

Distribution

The Porcupine Hills Formation is present in southwestern Alberta, from the

Waterton River Waterton Lake () is a mountain lake in southern Alberta, Canada, and northern Montana, United States. The lake is composed of two bodies of water, connected by a shallow channel known locally as the Bosporus. The two parts are referred to as Middl ...

near the Canada–US border in the south to the

Bow River The headwaters of the Bow River in Alberta, Canada, start at the Bow Glacier and Bow Lake (Alberta), Bow Lake in Banff National Park in the Canadian Rockies, Canadian Rocky Mountains. The glacial stream that feeds Bow Lake (Alberta), Bow Lake ...

near

Calgary Calgary () is a major city in the Canadian province of Alberta. As of 2021, the city proper had a population of 1,306,784 and a metropolitan population of 1,481,806 making it the third-largest city and fifth-largest metropolitan area in C ...

in the north. The upper limit is the present day erosional surface, so its original thickness can not be determined; however, the maximum recorded thickness is in the Porcupine Hills.

Relationship to other units

The Porcupine Hills Formation is exposed at surface or is overlain by

Quaternary The Quaternary ( ) is the current and most recent of the three periods of the Cenozoic Era in the geologic time scale of the International Commission on Stratigraphy (ICS), as well as the current and most recent of the twelve periods of the ...

sediments. Its base is a thick sandstone that rests disconformably on a paleosol horizon of the underlying

Willow Creek Formation The Willow Creek Formation is a stratigraphic unit of Late Cretaceous to Early Paleocene age in the Western Canada Sedimentary Basin of southwestern Alberta. It was first described by George Mercer Dawson in 1883 along the Willow Creek, a tribu ...

. 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 The Ravenscrag Formation is a stratigraphic unit of early Paleocene Geochronology, age in the Western Canadian Sedimentary Basin, Western Canada Sedimentary Basin. It was named for the settlement of Ravenscrag, Saskatchewan, and was first describ ...

of southern

Saskatchewan Saskatchewan is a Provinces and territories of Canada, province in Western Canada. It is bordered on the west by Alberta, on the north by the Northwest Territories, on the east by Manitoba, to the northeast by Nunavut, and to the south by the ...

and the

Fort Union Formation The Fort Union Formation is a geologic unit containing sandstones, shales, and coal beds in Wyoming, Montana, and parts of adjacent states. In the Powder River Basin, it contains important economic deposits of coal, uranium, and coalbed methane. ...

of Montana and North Dakota, which are not contiguous with it but are of similar age.

References

{{Authority control Geologic formations of Alberta Western Canadian Sedimentary Basin Paleogene Alberta Hills of Alberta Mudstone formations of Canada Siltstone formations of Canada Sandstone formations of Canada Shale formations of Canada