The St. Mary River Formation is a geologic

formation Formation may refer to: Linguistics * Back-formation, the process of creating a new lexeme by removing or affixes * Word formation, the creation of a new word by adding affixes Mathematics and science * Cave formation or speleothem, a secondar ...

Late Cretaceous The Late Cretaceous (100.5–66 Ma) is the younger of two epochs into which the Cretaceous Period is divided in the geologic time scale. Rock strata from this epoch form the Upper Cretaceous Series. The Cretaceous is named after ''creta'', ...

(71.9-67 Ma) age of 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 sedimen ...

in southwestern

Alberta Alberta ( ) is one of the thirteen provinces and territories of Canada. It is part of Western Canada and is one of the three prairie provinces. Alberta is bordered by British Columbia to the west, Saskatchewan to the east, the Northwest T ...

and northwesternmost

Montana Montana () is a state in the Mountain West division of the Western United States. It is bordered by Idaho to the west, North Dakota and South Dakota to the east, Wyoming to the south, and the Canadian provinces of Alberta, British Columb ...

. It was first described from

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

s along the St. Mary River by

George Mercer Dawson George Mercer Dawson (August 1, 1849 – March 2, 1901) was a Canadian geologist and surveyor. Biography He was born in Pictou, Nova Scotia, the eldest son of Sir John William Dawson, Principal of McGill University and a noted geologis ...

in 1883, and it takes its name from the river. Fossils from the formation include remains of dinosaurs,Weishampel, David B; et al. (2004). "Dinosaur distribution (Late Cretaceous, North America)." In: Weishampel, David B.; Dodson, Peter; and Osmólska, Halszka (eds.): The Dinosauria, 2nd, Berkeley: University of California Press, pp. 574-588. . as well as

bivalve shell A bivalve shell is part of the body, the exoskeleton or shell, of a bivalve mollusk. In life, the shell of this class of mollusks is composed of two hinged parts or ''valves''. Bivalves are very common in essentially all aquatic locales, includi ...

s, plant fossils, and

trace fossil A trace fossil, also known as an ichnofossil (; from el, ἴχνος ''ikhnos'' "trace, track"), is a fossil record of biological activity but not the preserved remains of the plant or animal itself. Trace fossils contrast with body fossils, ...

Lithology

The St. Mary River Formation is generally considered to consist of two units. The lower of the formation was deposited in brackish water environments, and is characterized by 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 silicat ...

s, grey

shale Shale is a fine-grained, clastic sedimentary rock formed from mud that is a mix of flakes of clay minerals (hydrous aluminium phyllosilicates, e.g. kaolin, Al2 Si2 O5( OH)4) and tiny fragments (silt-sized particles) of other minerals, especiall ...

s, coquinoid beds, carbonaceous

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 and

coal Coal is a combustible black or brownish-black sedimentary rock, formed as rock strata called coal seams. Coal is mostly carbon with variable amounts of other elements, chiefly hydrogen, sulfur, oxygen, and nitrogen. Coal is formed when ...

beds. The remainder of the formation was deposited in freshwater fluvial and floodplain environments and is characterized by interbedded sandstone and siltstone, with minor occurrences of carbonaceous shale and coal.

Thickness and distribution

The St. Mary River Formation is part of an eastward-thinning wedge of sediments derived from the erosion of the mountains to the west. It is about thick in the exposures along the Crowsnest and Castle Rivers, and about thick along the

Oldman River The Oldman River is a river in southern Alberta, Canada. It flows roughly west to east from the Rocky Mountains, through the communities of Fort Macleod, Lethbridge, and on to Grassy Lake, where it joins the Bow River to form the South Saskatchew ...

Relationship to other units

The St. Mary River Formation conformably overlies the Blood Reserve Sandstone, or the

Bearpaw Formation The Bearpaw Formation, also called the Bearpaw Shale, is a geologic formation of Late Cretaceous (Campanian) age. It outcrops in the U.S. state of Montana, as well as the Canadian provinces of Alberta and Saskatchewan, and was named for the Bear ...

where the Blood Reserve Sandstone is absent, and it is conformably overlain by the

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 trib ...

. It extends from

Glacier County, Montana Glacier County is located in the U.S. state of Montana. As of the 2020 census, the population was 13,778. The county is located in northwestern Montana between the Great Plains and the Rocky Mountains, known to the Blackfeet as the "Backbone o ...

to as far north as the Little Bow River in Alberta, where it grades into and intertongues with the contemporaneous strata of the

Horseshoe Canyon Formation The Horseshoe Canyon Formation is a stratigraphic unit of the Western Canada Sedimentary Basin in southwestern Alberta. It takes its name from Horseshoe Canyon, an area of badlands near Drumheller. The Horseshoe Canyon Formation is part of th ...

Fossil content

Flora

Eighteen species of plant leaves were described from the St. Mary River Formation in 1949.Bell, W.A. 1949. Uppermost Cretaceous and Paleocene floras of western Canada. Geological Survey of Canada, Bulletin 13, 231 p. More recent work downstream from the St. Mary Reservoir increased the total to at least 32 species. The assemblage includes remains of

fern A fern (Polypodiopsida or Polypodiophyta ) is a member of a group of vascular plants (plants with xylem and phloem) that reproduce via spores and have neither seeds nor flowers. The polypodiophytes include all living pteridophytes exce ...

s, ''

Ginkgo ''Ginkgo'' is a genus of non-flowering seed plants. The scientific name is also used as the English name. The order to which it belongs, Ginkgoales, first appeared in the Permian, 270 million years ago, and is now the only living genus with ...

'',

conifer Conifers are a group of cone-bearing seed plants, a subset of gymnosperms. Scientifically, they make up the division Pinophyta (), also known as Coniferophyta () or Coniferae. The division contains a single extant class, Pinopsida. All ext ...

s, a ''

Trapa The water caltrop is any of three extant species of the genus ''Trapa'': ''Trapa natans'', ''Trapa bicornis'' and the endangered ''Trapa rossica''. It is also known as buffalo nut, bat nut, devil pod, ling gok ( Chinese: 菱角), ling nut, lin ko ...

''-like plant,Stockey, R.A. and Rothwell, G.W. (1997)
The aquatic angiosperm ''Trapago angulata'' from the Upper Cretaceous (Maastrictian) St. Mary River Formation of southern Alberta
International Journal of Plant Sciences 158(1): 83-94, and at least six types of large

monocot Monocotyledons (), commonly referred to as monocots, (Lilianae '' sensu'' Chase & Reveal) are grass and grass-like flowering plants (angiosperms), the seeds of which typically contain only one embryonic leaf, or cotyledon. They constitute one ...

leaves in addition to a

sabal ''Sabal'' is a genus of palms (or fan-palms) endemic to the New World. Currently, there are 17 recognized species of ''Sabal'', including one hybrid species. The species are native to the subtropical and tropical regions of the Americas, from th ...

oid palm.Riley, M.G. and Stockey, R.A.(2004)
''Cardstonia tolmanii'' gen. et sp. nov (Limnocharitaceae) from the Upper Cretaceous of Alberta, Canada
International Journal of Plant Sciences 165(5): 897-916.

Molluscs

Beds of ''

Ostrea ''Ostrea'' is a genus of edible oysters, marine bivalve mollusks in the family Ostreidae, the oysters. Fossil records This genus is very ancient. It is known in the fossil records from the Permian to the Quaternary (age range: from 259 to 0. ...

'' and ''

Corbicula ''Corbicula'' is a genus of freshwater and brackish water clams, aquatic bivalve mollusks in the family Cyrenidae, the basket clams.Gofas, S. (2015). Cyrenidae Gray, 1847. In: MolluscaBase (2015). Accessed through: World Register of Marine Sp ...

'' shells are common in the basal, brackish water portion of the formation. The overlying freshwater beds include shells of freshwater and terrestrial

molluscs Mollusca is the second-largest phylum of invertebrate animals after the Arthropoda, the members of which are known as molluscs or mollusks (). Around 85,000 extant species of molluscs are recognized. The number of fossil species is estim ...

. Shells of

unionid The Unionidae are a family of freshwater mussels, the largest in the order Unionida, the bivalve molluscs sometimes known as river mussels, or simply as unionids. The range of distribution for this family is world-wide. It is at its most diverse ...

freshwater

mussel Mussel () is the common name used for members of several families of bivalve molluscs, from saltwater and freshwater habitats. These groups have in common a shell whose outline is elongated and asymmetrical compared with other edible clams, which ...

s are common in the fluvial sandstones.

Mammals

The mammals of the St. Mary River Formation were described by Sloan and Russell in 1974.Sloan, R.E. and Russell, L.S. 1974. Mammals of the St. Mary River Formation (Cretaceous) of southwestern Alberta. Life Sciences Contributions, Royal Ontario Museum, Number 95.

Dinosaurs

Dinosaur tracks

The St. Mary River Formation has produced relatively few dinosaur fossils from its outcrops in southwestern Alberta.Ryan, M. J., and Russell, A. P., 2001. Dinosaurs of Alberta (exclusive of Aves): In: Mesozoic Vertebrate Life, edited by Tanke, D. H., and Carpenter, K., Indiana University Press, Introduction, page 281. However, footprints and trackways have been found along the St. Mary and Oldman Rivers. More than 100 track-bearing stratigraphic units were documented in one section thick, which is one of the highest densities of track-bearing layers reported from any succession. One footprint from the formation includes the first record of skin impressions from the bottom of a

hadrosaur Hadrosaurids (), or duck-billed dinosaurs, are members of the ornithischian family Hadrosauridae. This group is known as the duck-billed dinosaurs for the flat duck-bill appearance of the bones in their snouts. The ornithopod family, which includ ...

foot.

Ornithischians

Theropods

References

{{Western Canadian Sedimentary Basin, South AB=yes Stratigraphy of Alberta Cretaceous Montana Cretaceous Alberta Campanian Stage Maastrichtian Stage of North America Sandstone formations of Canada Sandstone formations of the United States Ichnofossiliferous formations