Horseshoe-Canyon-Formation
The Horseshoe Canyon Formation is a sequence of sedimentary rocks of the Late Cretaceous Period, which is digested in the Canadian province of Alberta. This formation is known for its rich fauna of fossil vertebrates; famous are their particular dinosaur fossils. Stratigraphically, it belongs to the Edmonton group, together with the Whitemud Formation, the Battle Formation and the Scollard Formation. The Horseshoe Canyon Formation is up to 230 meters thick and consists of mudstones, sandstones and coal- leading slate. It was deposited during the late Campanian ( 83.5 to 70.6 mya ) and the early Maastrichtian ( 70.6 to 65.5 mya ) from; Outcrops are found especially in the area around Drumheller and further north along the Red Deer River in Trochu, but also in the city of Edmonton. The formation is named after the Horseshoe Canyon (type locality), an approximately 3 -kilometer-long gorge, which is located 17 kilometers southwest of Drumheller on Highway 9. The name ( "Horseshoe Canyon " ) describes the horseshoe- shaped course of the canyon.
Geological History
The Horseshoe Canyon Formation forms the lowermost lithostratigraphic unit of the Edmonton group over it, from bottom to the hanging wall, are the White mouth, Battle, and the Scollard Formation. Under the Horseshoe Canyon Formation are marine deposits of the Bearpaw Formation, which show that this area millions of years ago was covered by a sea, the Western Interior Seaway. During the deposition time of the Horseshoe Canyon Formation, the sea withdrew more and more. While the upper third of the formation shows strong marine influences, there are the lower two-thirds of sediments that were deposited in rivers great flood levels. From the deposits of these flood levels, the bulk of the vertebrate fossils. However, the retreat of the sea was by no means complete - by the ever-changing sea level resulted in a variety of different environments at different times and places: In addition to the flood levels there were marine habitats in coastal areas, deltas, lagoons, estuaries and tidal flats. The coal layers indicate peat swamps.
Fossil Fauna
The vertebrate fauna of the formation is well documented. Finds of fishing include, among other things, sharks, rays, sturgeons, gar and bowfin -like -like with a. In the sea of plesiosaurs Leurospondylus lived while in freshwater turtles and crocodiles as Champsosaurus Leidyosuchus and Stangerochampsa lived. The terrestrial fauna was formed, among other mammals from the group of Multituberculaten and the marsupial Didelphodon; However, the dominant land vertebrates were the dinosaurs. Among the herbivores in particular dominated the Hadrosauriden of which dates back half of all dinosaur fossils found: Well known are the types of Edmontosaurus regalis, Saurolophus osborni and Hypacrosaurus altispinus. Also common were brachyops and Eotriceratops xerinsularis Ceratopsia with the types Pachyrhinosaurus canadensis, Anchiceratops ornatus, Arrhinoceratops. Rare were Ankylar as Euoplocephalus tutus and Edmontonia longiceps or Pachycephalosaurier as Stegoceras edmontonense. Another ornithischians is the Ornithopod Parksosaurus warrenae. Among the theropods Ornithomimiden as Dromiceiomimus brevitertius, Ornithomimus edmontonicus and Struthiomimus altus were particularly common. The Spitzenprädator was the Albertosaurus sarcophagus Tyrannosauride, which could only be detected in this formation. Smaller predators include Ricardoestesia isosceles one, the Caenagnathiden Chirostenotes pergracilis, the Troodon formosus and the troodontids Dromaeosauriden Atrociraptor marshalli, Dromaeosaurus sp. and Saurornitholestes sp. In the Horseshoe Canyon Formation is also found the remains of about chickens large Alvarezsauriden Albertonykus borealis, the smallest known dinosaur from North America. The fossil evidence supports the hypothesis of the origin of this unusual Dinosaurierklade in South America and its spread across North America to Asia.
In addition, the arthropod fauna of the Upper Cretaceous habitat well documented by amber finds in the coal beds of the Horseshoe Canyon Formation in Edmonton and Drumheller. The previously identified form of amber rich fauna (botanical fossils are extremely rare ) confirms the previously derived from the vertebrate finds habitats.