St. Mary River Formation facts for kids
Quick facts for kids St. Mary River FormationStratigraphic range: Early Maastrichtian |
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Strata of the St. Mary River Formation at the St. Mary Reservoir spillway.
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| Type | Geological formation |
| Underlies | Willow Creek Formation |
| Overlies | Bearpaw Formation |
| Thickness | up to 762 metres (2,500 ft) |
| Lithology | |
| Primary | Sandstone, shale |
| Other | Mudstone, coal |
| Location | |
| Coordinates | 49°36′N 114°06′W / 49.6°N 114.1°W |
| Approximate paleocoordinates | 49°36′N 86°30′W / 49.6°N 86.5°W |
| Region |  Alberta, Montana |
| Country |  Canada, USA |
| Type section | |
| Named for | St. Mary River |
| Named by | George Mercer Dawson |
| Year defined | 1883 |
The St. Mary River Formation is a special layer of rock found in southwestern Alberta, Canada, and northwestern Montana in the USA. It's like a giant history book made of stone! This formation was created during the Late Cretaceous period, which was a very long time ago, between 65 and 67 million years ago.
It was first studied in 1883 by a scientist named George Mercer Dawson. He found these rocks along the St. Mary River, which is how the formation got its name. Scientists study these rocks to learn about ancient Earth, including the plants and animals that lived there.
Fossils found here include parts of dinosaurs, ancient shells, plant remains, and even trace fossils, which are signs of animal activity like footprints.
Contents
What Are St. Mary River Rocks Made Of?
The St. Mary River Formation is mostly made of two main types of rock: sandstone and shale. Think of it as two different layers, each telling a different story about where the rocks formed.
Lower Rock Layers
The bottom part of the formation, about 30 to 60 meters (100 to 200 feet) thick, formed in brackish water. This means the water was a mix of fresh and salty water, like in an estuary where a river meets the sea. Here, you'll find fine-grained sandstones, grey shales, and carbon-rich mudstones. There are also beds of coal, which formed from ancient plants.
Upper Rock Layers
The rest of the formation formed in freshwater environments, like rivers and floodplains. These layers have a mix of sandstone and siltstone. You might also find small amounts of carbon-rich shale and coal here too.
How Big is the St. Mary River Formation?
The St. Mary River Formation is like a giant wedge of sediments. It gets thinner as you go east. In some places, like along the Crowsnest and Castle Rivers, it can be as thick as 762 meters (2,500 feet)! Along the Oldman River, it's about 457 meters (1,500 feet) thick.
Where Does the St. Mary River Formation Fit?
This rock formation sits on top of other rock layers. It lies above the Blood Reserve Sandstone or the Bearpaw Formation. On top of the St. Mary River Formation, you'll find the Willow Creek Formation.
The St. Mary River Formation stretches from Glacier County, Montana all the way north to the Little Bow River in Alberta. In some areas, it blends into another rock layer called the Horseshoe Canyon Formation.
What Fossils Are Found Here?
The St. Mary River Formation is a treasure trove of fossils! Scientists have found many different types of ancient life preserved in these rocks.
Ancient Shells: Molluscs
In the lower, brackish water parts of the formation, you can find many shells of ancient Ostrea (like oysters) and Corbicula (a type of clam). In the freshwater layers above, there are shells from freshwater and land-dwelling molluscs. You can often find shells of freshwater mussels in the river sandstones.
Plant Life: Flora
Scientists have found many types of plant fossils in the St. Mary River Formation. In 1949, 18 different species of plant leaves were described. Later studies found even more, bringing the total to at least 32 species!
These plant fossils include ferns, Ginkgo trees, conifers (like pine trees), and a plant similar to a water caltrop. There are also at least six types of large monocot leaves, which are from plants like grasses or lilies, and even a type of palm tree.
Ancient Mammals
Some fossils of ancient mammals have also been found in the St. Mary River Formation. These were studied and described by scientists in 1974.
Dinosaurs of the St. Mary River Formation
While not many full dinosaur skeletons have been found here, the St. Mary River Formation is famous for something else: dinosaur footprints!
Dinosaur Footprints and Tracks
Many dinosaur footprints and trackways have been discovered along the St. Mary and Oldman Rivers. In one area, scientists found over 100 layers of rock with dinosaur tracks! This is one of the highest numbers of track-bearing layers ever reported from a single rock section.
One amazing footprint even showed the first record of skin impressions from the bottom of a hadrosaur (duck-billed dinosaur) foot. Imagine seeing the texture of a dinosaur's skin preserved in stone!
Ornithischian Dinosaurs
Ornithischian dinosaurs are a group of plant-eating dinosaurs. Here are some that have been found in the St. Mary River Formation:
- Anchiceratops: Remains of this horned dinosaur have been found in Alberta.
- Edmontonia: This was an armored dinosaur, like a walking tank. Its fossils have been found in Alberta.
- Montanoceratops: Another horned dinosaur, found in Montana.
- Pachyrhinosaurus: This large horned dinosaur had a big, rough boss instead of a horn on its nose. Fossils have been found in Alberta.
- Regaliceratops: A horned dinosaur with a unique frill, found in Alberta.
Theropod Dinosaurs
Theropods are a group of mostly meat-eating dinosaurs, like T. rex. Some theropod fossils have also been found here:
- Albertosaurus: A large, meat-eating dinosaur related to T. rex, found in Alberta.
- Saurornitholestes: A smaller, agile predator, possibly related to raptors. Fossils have been found in Alberta.
- Troodon: A smart, bird-like dinosaur with large eyes. Fossils have been found in Alberta.
Color key
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Notes Uncertain or tentative taxa are in small text; |
Images for kids
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A drawing of Montanoceratops
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An artist's idea of what Pachyrhinosaurus looked like
