St. Mary River Formation

The St. Mary River Formation is a geologic formation of Late Cretaceous (Campanian to Maastrichtian) age of the Western Canada Sedimentary Basin in southwestern Alberta and northwesternmost Montana.[3][4] It was first described from outcrops along the St. Mary River by George Mercer Dawson in 1883, and it takes its name from the river.

St. Mary River Formation
Stratigraphic range: Early Maastrichtian
↓
Strata of the St. Mary River Formation at the St. Mary Reservoir spillway.
TypeGeological formation
UnderliesWillow Creek Formation
OverliesBearpaw Formation
Thicknessup to 762 metres (2,500 ft)
Lithology
PrimarySandstone, shale[1]
OtherMudstone, coal
Location
Coordinates49.6°N 114.1°W / 49.6; -114.1
Approximate paleocoordinates49.6°N 86.5°W / 49.6; -86.5
Region Alberta,
 Montana
Country Canada,
 USA
Type section
Named forSt. Mary River
Named byGeorge Mercer Dawson[2]
Year defined1883
St. Mary River Formation (Canada)
St. Mary River Formation (Alberta)

Fossils from the formation include remains of dinosaurs,[5] as well as bivalve shells, plant fossils, and trace fossils.[6]

Lithology

The St. Mary River Formation is generally considered to consist of two units. The lower 30–60 meters (98–197 ft) of the formation was deposited in brackish water environments, and is characterized by fine-grained sandstones, grey shales, coquinoid beds, carbonaceous mudstones and coal 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 762 metres (2,500 ft) thick in the exposures along the Crowsnest and Castle Rivers, and about 457 metres (1,500 ft) thick along the Oldman River.

Relationship to other units

The St. Mary River Formation conformably overlies the Blood Reserve Sandstone, or the Bearpaw Formation where the Blood Reserve Sandstone is absent, and it is conformably overlain by the Willow Creek Formation. It extends from Glacier County, Montana 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.[3][4]

Fossil content

Molluscs

Beds of Ostrea and Corbicula shells are common in the basal, brackish water portion of the formation. The overlying freshwater beds include shells of freshwater and terrestrial molluscs. Shells of unionid freshwater mussels are common in the fluvial sandstones.[6]

Flora

Eighteen species of plant leaves were described from the St. Mary River Formation in 1949.[7] More recent work downstream from the St. Mary Reservoir increased the total to at least 32 species. The assemblage includes remains of ferns, Ginkgo, conifers,[8] a Trapa-like plant,[9] and at least six types of large monocot leaves in addition to a sabaloid palm.[8]

Mammals

The mammals of the St. Mary River Formation were described by Sloan and Russell in 1974.[10]

Dinosaur tracks

The St. Mary River Formation has produced relatively few dinosaur fossils from its outcrops in southwestern Alberta.[11] 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 177 metres (580 ft) 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 foot.[12]

Ornithischians
Ornithischians
Genus Species Location Stratigraphic position Material Notes Images

Anchiceratops[13]

A. ornatus[14]

Remains later found to be referrable to Anchiceratops, but it's not known what species.[13]
Montanoceratops
Pachyrhinosaurus

Edmontonia[15]

E. longiceps[15]

Montanoceratops[16]

M. cerorhynchus[16]

Pachyrhinosaurus[13]

P. canadensis[13]

Regaliceratops[17]

R. peterhewsi
  • Alberta

Theropods
Theropods
Genus Species Location Stratigraphic position Material Notes Images

Albertosaurus[13]

[13]

Saurornitholestes[18]

cf. Saurornitholestes sp.[18]

Troodon[19]

Troodon sp."[19]
Color key
Taxon Reclassified taxon Taxon falsely reported as present Dubious taxon or junior synonym Ichnotaxon Ootaxon Morphotaxon
 Notes
Uncertain or tentative taxa are in small text; crossed out taxa are discredited.

See also
  • List of dinosaur-bearing rock formations

References
  1. Lexicon of Canadian Geologic Units. "St. Mary River 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. 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)
  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 2013-07-05. Retrieved 2013-08-13.CS1 maint: multiple names: authors list (link)
  5. 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. ISBN 0-520-24209-2.
  6. Hamblin, A. P. (1998). "Edmonton Group/St Mary River Formation: Summary of Literature and Concepts. Geological Survey of Canada, Open File 3578" (PDF). Retrieved 2014-01-31.
  7. Bell, W.A. 1949. Uppermost Cretaceous and Paleocene floras of western Canada. Geological Survey of Canada, Bulletin 13, 231 p.
  8. 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.
  9. 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,
  10. 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.
  11. 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.
  12. Currie, P.J., Nadon, G.C. and Lockley, M.G. (1991). "Dinosaur footprints with skin impressions from the Cretaceous of Alberta and Colorado. Can. J. Earth Sci. 28: 102-115". doi:10.1139/e91-009. Cite journal requires |journal= (help)CS1 maint: multiple names: authors list (link)
  13. "1.4 Alberta, Canada; 13. St. Mary River Formation," in Weishampel, et al. (2004). Pages 577-578.
  14. Listed as "? A. ornatus" in "1.4 Alberta, Canada; 13. St. Mary River Formation," in Weishampel, et al. (2004). Pages 577-578.
  15. Listed as "Edmontonia cf. longiceps" in "1.4 Alberta, Canada; 13. St. Mary River Formation," in Weishampel, et al. (2004). Pages 577-578.
  16. "3.11 Montana, United States; 11. St. Mary River Formation," in Weishampel, et al. (2004). Pages 583-584.
  17. Brown, Caleb M.; Henderson, Donald M. (June 4, 2015). "A new horned dinosaur reveals convergent evolution in cranial ornamentation in ceratopsidae". Current Biology (online). doi:10.1016/j.cub.2015.04.041.
  18. Listed as "cf. Saurornitholestes sp." in "1.4 Alberta, Canada; 13. St. Mary River Formation," in Weishampel, et al. (2004). Pages 577-578.
  19. Listed as "? Troodon sp." in "1.4 Alberta, Canada; 13. St. Mary River Formation," in Weishampel, et al. (2004). Pages 577-578.
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