The Disappointment Bay Formation is a geologic formation in Nunavut, extending from Ellesmere Island in the east to Bathurst Island in the west.

[1] It preserves fossils dating back to the Devonian period, primarily of invertebrates.

Vertebrate remains are rare in this formation.

Indeterminate spine fragments are found throughout the Lowther Island off-reef limestones but are rare.

[2] A 2-centimeter wide fragment found in the 2 m-level ammonoid bed of Young Island may represent a cyathaspidid.