Oldman Formation, Geological formation in southern Alberta, Canada.

The Oldman Formation is a Late Cretaceous stratigraphic unit of the Belly River Group in southern Alberta, named for exposures along the Oldman River between its confluence with the St. Mary River and Lethbridge. It consists mainly of light-colored, fine-grained sandstones that are yellowish, steep-faced and blocky in outcrop, with lesser siltstone and mudstone. The formation is about 40 metres thick at Dinosaur Provincial Park and thickens toward the southwest.

The Oldman Formation was named for exposures along the Oldman River between its confluence with the St. Mary River and the city of Lethbridge. It is a member of the Belly River Group, overlies the Foremost Formation and is separated from the Dinosaur Park Formation above by a regional disconformity. Its sediments were deposited in the middle Campanian, between about 77.5 and 76.5 million years ago.

The formation's name comes from exposures along the Oldman River between its confluence with the St. Mary River and Lethbridge. Its dinosaur fauna includes Albertaceratops nesmoi, named in part for the nearby town of Nemo, and the hadrosaur Corythosaurus casuarius. The same beds also yield fish such as Myledaphus bipartitus and the gar Lepisosteus occidentalis.

The exposed sections are accessible across the southern prairie landscape, best explored during field trips or guided walks from spring through fall. Sturdy footwear and weather protection are advisable since the open slopes can shift between wet and dry conditions.

The formation's sediments came mainly from northwestern Montana, and the unit thickens toward the southwest from about 40 metres at Dinosaur Provincial Park. Its sandstones, siltstones and mudstones were laid down in river channels and floodplains between roughly 77.5 and 76.5 million years ago, during magnetic polarity Chron 33n.