Type Formation Region British Columbia Named for Mount Hulcross Underlies Boulder Creek Formation Primary Slate, Mudstone | Other Siltstone Country Canada Overlies Fort St. John Group Unit of Fort St. John Group | |
Thickness Up to 135 metres (440 ft) | ||
The Hulcross Formation is a geologic formation in the Western Canada Sedimentary Basin in northeastern British Columbia that was deposited in marine environments during the late Albian stage of the Early Cretaceous period. At one time considered to be a member of the Commotion Formation, it was elevated to formation status by D.F. Stott in 1982. It preserves ammonites and other fossils.
Contents
Lithology
The Hulcross Formation consists of dark grey to black shales and mudstones that were deposited in marine environments. The sediments coarsen upward and thin beds of siltstone and platy sandstone are present in the uppermost part. Sideritic ironstone concretions are common.
Thickness and Distribution
The Hulcross Formation is present in northeastern British Columbia throughout the foothills of the Canadian Rockies between the Peace and Kakwa Rivers, where it reaches thicknesses of up to 135 metres (440 ft). It is exposed along the Peace River eastward from the foothills almost as far as its confluence with the Halfway River.
Relationship to Other Units
The Hulcross Formation is part of the Fort St. John Group. Originally described as a member of the Commotion Formation, the Hulcross was elevated to formational status along with the other members of the Commotion by D.F. Stott in 1982, who proposed that the term 'Commotion Formation' be abandoned.
The shales of the Hulcross abruptly overlie the sandstones of the Gates Formation and grade into the overlying sandstones of the Boulder Creek Formation. It is equivalent to the Harmon Member of the Peace River Formation in the Peace River plains to the east, and to the Wildhorn Member of the Scatter Formation in the Liard River region.