page_title: Bearpaw Formation
section_title: Lithology and depositional environment
hierarchical_section_title: Bearpaw Formation / Lithology and depositional environment
context_page_description: The Bearpaw Formation, also called the Bearpaw Shale, is a geologic formation of Late Cretaceous 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 Paw Mountains in Montana. It includes a wide range of marine fossils, as well as the remains of a few dinosaurs. It is known for its fossil ammonites, some of which are mined in Alberta to produce the organic gemstone ammolite.
context_section_description: The formation was deposited in the Bearpaw Sea, which was part of the Western Interior Seaway that advanced and then retreated across the region during Campanian time. It is composed primarily of dark grey shales, claystones, silty claystones and siltstones, with subordinate silty sandstones. It also includes bedded and nodular concretions (both calcareous and ironstone concretions) and thin beds of bentonite. As the seaway retreated toward the southwest, the marine sediments of the Bearpaw became covered by the deltaic and coastal plain sediments of the overlying formations.
caption: Bearpaw shale being excavated to recover ammonites for ammolite production.
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