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The Callovian Unconformity resulted from the combined effects of a prolonged lowstand of sea level and a westward shift in continental rifting, resulting in the breakup of the northwest Australian margin. The Middle Jurassic Callovian Unconformity is the main continental breakup unconformity on the northwest shelf of Australia.

In the Vulcan Sub-Basin, the Callovian Unconformity occurs at the base of a thick sequence of Upper Jurassic marine shales and merges with the Valanginian Unconformity on high fault blocks where the Jurassic is absent.

In the Carnarvon Basin, some wells display two events, an upper and lower unconformity. The Carnarvon MegaSurvey and in turn the NWSDA interpretation is tied to the Upper Callovian unconformity well pick. The importance of the horizon is its stratigraphic proximity to the Emma and Judy sands, and the Eliassen, Biggada and Legendre formations, which are important reservoirs within the basin.