The Ma Butte Formation is a stratigraphic unit of

Early Cretaceous The Early Cretaceous ( geochronological name) or the Lower Cretaceous (chronostratigraphic name), is the earlier or lower of the two major divisions of the Cretaceous. It is usually considered to stretch from 145 Ma to 100.5 Ma. Geology Pro ...

( Albian) age in the

Western Canada Sedimentary Basin The Western Canadian 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 ...

. It was named for Ma Butte, a mountain north of Coleman, Alberta, by J.R. McLean in 1980. It is present in the foothills of southwestern Alberta and it contains plant fossils.Glass, D.J. (editor) 1997. Lexicon of Canadian Stratigraphy, vol. 4, Western Canada including eastern British Columbia, Alberta, Saskatchewan and southern Manitoba. Canadian Society of Petroleum Geologists, Calgary, 1423 p. on CD-ROM. .

Stratigraphy and lithology

The Ma Butte Formation is a unit of the

Blairmore Group The Blairmore Group, originally named the Blairmore Formation, is a geologic unit of Early Cretaceous age in the Western Canada Sedimentary Basin that is present in southwestern Alberta and southeastern British Columbia. It is subdivided into ...

. It consists primarily of fine-grained

sandstone Sandstone is a clastic sedimentary rock composed mainly of sand-sized (0.0625 to 2 mm) silicate grains. Sandstones comprise about 20–25% of all sedimentary rocks. Most sandstone is composed of quartz or feldspar (both silicates) ...

s interbedded with

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.Blatt ''et al.'' 1980, p ...

s and

mudstone 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 (parallel layering).Blatt, H., and R.J. Tracy, 1996, ''Petrology. ...

s. Some coarser grained sandstones and

conglomerate Conglomerate or conglomeration may refer to: * Conglomerate (company) * Conglomerate (geology) * Conglomerate (mathematics) In popular culture: * The Conglomerate (American group), a production crew and musical group founded by Busta Rhymes ** Co ...

beds are also present. Beds of bentonite and

tuff Tuff is a type of rock made of volcanic ash ejected from a vent during a volcanic eruption. Following ejection and deposition, the ash is lithified into a solid rock. Rock that contains greater than 75% ash is considered tuff, while rock cont ...

increase upward toward the contact with the overlying Crowsnest Formation. The sandstones of the Ma Butte Formation are

quartzose Silicon dioxide, also known as silica, is an oxide of silicon with the chemical formula , most commonly found in nature as quartz and in various living organisms. In many parts of the world, silica is the major constituent of sand. Silica is one ...

, in contrast with the feldspathic sandstones of the underlying

Beaver Mines Formation The Beaver Mines Formation is a stratigraphic unit of Early Cretaceous ( Albian) age in the Western Canada Sedimentary Basin that is present in southwestern Alberta and southeastern British Columbia, Canada. It was established by G.B. Mellon in 1 ...

Distribution and thickness

The Ma Butte Formation is present in the southern foothills of Alberta as far north as the Red Deer River. It has a maximum reported thickness of near the Bow River.

Depositional environment and paleontology

The sediments of the Ma Butte Formation were derived from erosion of mountain ranges to the west, transported eastward by river systems, and deposited in a variety of floodplain environments. They include angiosperm (flowering plant)

fossils A fossil (from Classical Latin , ) is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserved in ...

, in contrast to the underlying Beaver Mines Formation. This marks the first appearance of angiosperms in this area.

Relationship to other units

The Ma Butte Formation is also known as the Mill Creek Formation. It disconformably overlies the Beaver Mines Formation. It is conformably overlain by the Crowsnest Formation in the south and the contact between the two is gradational. It is disconformably overlain by the Blackstone Formation in the north, and it is correlative with the Bow Island Formation to the east.

References

{{reflist Geologic formations of Alberta Cretaceous Alberta Albian Stage Sandstone formations of Canada Siltstone formations Mudstone formations Tuff formations Western Canadian Sedimentary Basin