| Horseshoe Canyon Formation | |
|---|---|
| Stratigraphic range:Campanian-Maastrichtian ~73.1–68 Ma[1] | |
 Horseshoe Canyon Formation atHorsethief Canyon, nearDrumheller. The dark bands are coal seams. | |
| Type | Geological formation |
| Unit of | Edmonton Group |
| Sub-units | Strathmore Member, Drumheller Member, Horsethief Member, Morrin Member, Tolman Member, Carbon Member, Whitemud Member |
| Underlies | Battle Formation,Scollard Formation |
| Overlies | Bearpaw Formation |
| Lithology | |
| Primary | Sandstone |
| Other | Shale,coal |
| Location | |
| Coordinates | 51°25′24″N112°53′18″W / 51.42333°N 112.88833°W /51.42333; -112.88833 (Horseshoe Canyon) |
| Region |  AlbertaWestern Canadian Sedimentary Basin |
| Country |  Canada |
| Type section | |
| Named for | Horseshoe Canyon |
| Named by | E.J.W. Irish, 1970 |
TheHorseshoe Canyon Formation is astratigraphic unit of theWestern Canada Sedimentary Basin in southwesternAlberta.[2][3] It takes its name fromHorseshoe Canyon, an area ofbadlands nearDrumheller.
The Horseshoe Canyon Formation is part of theEdmonton Group. In its type section (Red Deer River Valley atDrumheller), it is ~250 metres (820 ft) thick, but further west the formation is older and thicker, exceeding 500 metres (1,600 ft) nearCalgary.[4] It is of LateCretaceous age,Campanian to earlyMaastrichtian stage (EdmontonianLand-Mammal Age), and is composed ofmudstone,sandstone,carbonaceousshales, andcoal seams. A variety of depositional environments are represented in the succession, includingfloodplains,estuarine channels, and coal swamps, which have yielded a diversity of fossil material. Tidally-influenced estuarine point bar deposits are easily recognizable as Inclined Heterolithic Stratification (IHS). Brackish-water trace fossil assemblages occur within these bar deposits and demonstrate periodic incursion of marine waters into the estuaries.
The Horseshoe Canyon Formation crops out extensively in the area around Drumheller, as well as farther north along theRed Deer River nearTrochu and along theNorth Saskatchewan River inEdmonton.[2] It is overlain by the Battle andScollard formations.[4] The Drumheller Coal Zone, located in the lower part of the Horseshoe Canyon Formation, was mined forsub-bituminous coal in the Drumheller area from 1911 to 1979, and theAtlas Coal Mine in Drumheller has been preserved as a National Historic Site.[5] In more recent times, the Horseshoe Canyon Formation has become a major target forcoalbed methane (CBM) production.
Dinosaurs found in the Horseshoe Canyon Formation includeAlbertavenator,Albertosaurus,Anchiceratops,Anodontosaurus,Arrhinoceratops,Atrociraptor,Epichirostenotes,Edmontonia,Edmontosaurus,Hypacrosaurus,Ornithomimus,Pachyrhinosaurus,Parksosaurus,Saurolophus, andStruthiomimus. Other finds have includedmammals such asDidelphodon coyi, non-dinosaurreptiles,amphibians,fish, marine and terrestrialinvertebrates and plant fossils. Reptiles such as turtles and crocodilians are rare in the Horseshoe Canyon Formation, and this was thought to reflect the relatively cool climate which prevailed at the time. A study by Quinney et al. (2013) however, showed that the decline in turtle diversity, which was previously attributed to climate, coincided instead with changes in soil drainage conditions, and was limited by aridity, landscape instability, and migratory barriers.[6]
The Drumheller Coal Zone has been a primary coalbed methane target for industry. In the area between Bashaw and Rockyford, the Coal Zone lies at relatively shallow depths (about 300 metres) and is about 70 to 120 metres thick. It contains 10 to 20 metres of cumulative coal, in up to 20 or more individual thin seams interbedded with sandstone and shale, which combine to make an attractive multi-completion CBM drilling target. In total, it is estimated there are 14 trillion cubic metres (500 tcf) of gas in place in all the coal in Alberta.
The timeline below follows work by David A. Eberth and Sandra L. Kamo published in 2019.[7]
| Ankylosaurs reported from the Horseshoe Canyon Formation | |||||
|---|---|---|---|---|---|
| Genus | Species | Stratigraphic position | Material | Notes | Images |
| [Five] skulls, mandibles, cervical vertebra, caudal vertebrae, dorsal vertebrae, sacrocaudal vertebrae, sacrum, illium, ischium, partial pelvis, coossified ribs, femur, ?manual phalanx, tail clubs, numerous cervical half-rings and osteoderms.[8][9] | Anankylosaurineankylosaurid also known from the middleDinosaur Park Formation and closely related toAnkylosaurus.[10] | 
| |||
E. longiceps[11] | Upper Horsethief[11] | A skull with mandible, dorsal vertebrae, dorsal vertebrae, sacral vertebrae, caudal vertebrae, cervical ribs, dorsal ribs, humerus, radius, ulna, radius, ilia, ischia, both pubes (?), femur, tibia, fibula and osteoderms.[11] | Apanoplosaurinnodosaurid also known from the lower Dinosaur Park Formation and closely relatedDenversaurus.[12] | 
| |
E. tutus | Walter Coombs (1971) synonymisedAnodontosaurus lambei withE. tutus. However, recent studies suggest thatAnodontosaurus is distinct enough fromEuoplocephalus to be placed in its own genus and species.[8][13] Furthermore, all Horseshoe Canyon Formationankylosaurine specimens were suggested to be reassigned toAnodontosaurus.[9] | 
| |||
| Hadrosaurs reported from the Horseshoe Canyon Formation | ||||||
|---|---|---|---|---|---|---|
| Genus | Species | Location | Stratigraphic position | Material | Notes | Images |
Horsethief; likely present in Drumheller. |  | |||||
H. altispinus | Morrin and Tolman. | "[Five to ten] articulated skulls, some associated with postcrania, isolated skull elements, isolated postcranial elements, many individuals, embryo to adult."[14] |  | |||
S. osborni | Upper Morrin and Tolman. | "Complete skull and skeleton, [two] complete skulls."[14] |  | |||
Color key
| Notes Uncertain or tentative taxa are insmall text; |
| Ceratopsians reported from the Horseshoe Canyon Formation | ||||||
|---|---|---|---|---|---|---|
| Genus | Species | Stratigraphic position | Material | Notes | Images | |
Horsethief, Morrin, and Tolman; may have been present in Drumheller[16] | [Two] nearly complete skulls and [seven] partial skulls.[16] | A chasmosaurine ceratopsid contemporaneous and closely related toArrhinoceratops.[16] |  | |||
A. brachyops[17] | Horsethief[17] | A nearly complete skull.[17] | Achasmosaurineceratopsid restricted to the holotype specimen as Farke (2007) assigned the referred specimen ROM 1439 toTorosaurus.[18] |  | ||
E. xerinsularis[19] | Carbon[19] | Premaxillae, maxillae, rostral, supraorbital horncore with lacrimal, prefrontal, frontal, postorbital, jugal, epijugal, quadratojugal, quadrate, partial parietal, squamosal frill, braincase, syncervical, cervical vertebrae, dorsal vertebrae, ribs and fragments of ossified ligaments.[19] | A largechasmosaurineceratopsid that may represent asenior synonym ofOjoceratops from theOjo Alamo Formation.[20] |  | ||
Upper Tolman[22] | An isolated braincase.[22] | Aleptoceratopsidceratopsian also known from theSt. Mary River Formation.[21] |  | |||
P. canadensis[23] | Drumheller and Horsethief[23] | [Two] partial skulls.[23] | Acentrosaurineceratopsid also known from theSt. Mary River Formation.[23] |  | ||
| Pachycephalosaurids reported from the Horseshoe Canyon Formation | ||||||
|---|---|---|---|---|---|---|
| Genus | Species | Location | Stratigraphic position | Material | Notes | Images |
S. edmontonense[25] | Tolman[24] | A pachycephalosaurinepachycephalosaurid also known from theHell Creek andKirtland Formation.[25] |  | |||
| Thescelosaurids reported from the Horseshoe Canyon Formation | ||||||
|---|---|---|---|---|---|---|
| Genus | Species | Location | Stratigraphic position | Material | Notes | Images |
P. warreni | Tolman | A partially articulated skeleton and partial skull. | Athescelosauridneornithischian. |  | ||
| Maniraptors reported from the Horseshoe Canyon Formation | ||||||
|---|---|---|---|---|---|---|
| Genus | Species | Stratigraphic position | Material | Notes | Images | |
A. curriei[26] | Horsethief[26] | [Two] frontals.[26] | Atroodontidtheropod that adds to the diversity of North American troodontids.[26] | |||
A. borealis[27] | Upper Tolman[27] | Ulna, tibiae, metatarsals, manual ungual, pedal phalanxes and unidentified pedal phalanges.[27] | An mononykinalvarezsaurid specialized for digging insect nests.[27] |  | ||
A. pennatus[28] | Horsethief[28] | A palatine, mandibles, ceratobranchials, axis, cervical vertebrae, dorsal vertebrae, pectoral girdles, sternal plate, forelimb, ilium, femur, tibia and fibula.[28] | Acaenagnathidoviraptorosaur recovered as sister taxon toElmisaurus .[28] |  | ||
A. marshalli[29] | Lower Horsethief[29] | Premaxillae, maxilla, dentaries, teeth and numerous bone fragments.[29] | Adromaeosaurid; teeth indicate it may have been present across all members.[29] |  | ||
E. curriei[30] | Horsethief, Morrin, and Tolman[30] | A maxilla, probable palatine, partial braincase, cervical vertebrae, dorsal vertebrae, caudal vertebrae, synsacrum, an anterior and a posterior cervical rib, a mid-dorsal rib, fragments of ilia, ischium, both pubes, partial tibia, and unidentifiable bones.[30] | A caenagnathid oviraptorosaur known from material previously assigned toChirostenotes.[30] |  | ||
Color key
| Notes Uncertain or tentative taxa are insmall text; |
| Ornithomimids reported from the Horseshoe Canyon Formation | ||||||
|---|---|---|---|---|---|---|
| Genus | Species | Location | Stratigraphic position | Material | Notes | Images |
D. brevitertius | Several specimens.type specimen |  | ||||
O. currelli | Junior synonym ofO. edmontonicus | |||||
O. edmontonicus | Drumheller, Horsethief, Morrin, and Tolman | Several specimens,type specimen | An ornithomimid |  | ||
S. altus | Drumheller, Horsethief, and Morrin |  | ||||
Color key
| Notes Uncertain or tentative taxa are insmall text; |
| Tyrannosaurids reported from the Horseshoe Canyon Formation | ||||||
|---|---|---|---|---|---|---|
| Genus | Species | Location | Stratigraphic position | Material | Notes | Images |
A. arctunguis | Junior synonym ofA. sarcophagus |  | ||||
A. sarcophagus | Horsethief, Morrin, and Tolman; likely present in Drumheller and Carbon. | Several skeletons and partial skeletons,type specimen | Atyrannosaurid which was the most common large carnivore in the area.[31][32] | |||
D. sp. | Suggested from the skeleton of an immature tyrannosaurid (CMN 11315), thorough analysis of this specimen supports a referral toA. sarcophagus.[33] An isolatedmaxilla and teeth from anEdmontosaurus bonebed were also mistakenly referred toDaspletosaurus, however all the tyrannosaurid material in the bonebed was confirmed to belong toA. sarcophagus.[34] | |||||
Color key
| Notes Uncertain or tentative taxa are insmall text; |
| Mammals reported from the Horseshoe Canyon Formation | ||||||
|---|---|---|---|---|---|---|
| Genus | Species | Location | Stratigraphic position | Material | Notes | Images |
D. coyi |  | |||||
Color key
| Notes Uncertain or tentative taxa are insmall text; |
| Reptiles reported from the Horseshoe Canyon Formation | ||||||
|---|---|---|---|---|---|---|
| Genus | Species | Location | Stratigraphic position | Material | Notes | Images |
S. mccabei | "a skull, partial lower jaws, and partial postcranial skeleton" | |||||
C. albertensis | "partial skeleton with partial skull" |  | ||||
L. ultimus | "a partial skeleton" | aplesiosaur of uncertain classification | ||||
B. morrinensis | "nearly complete shell" | |||||
Color key
| Notes Uncertain or tentative taxa are insmall text; |
| Fish reported from the Horseshoe Canyon Formation | ||||||
|---|---|---|---|---|---|---|
| Genus | Species | Location | Stratigraphic position | Material | Notes | Images |
| Boreiosturion[40] | B. labyrinthicus | Edmonton. | Partial skull. | Asturgeon. | ||
H. armaserratus | ||||||
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