At the front of the Mackenzie Mountains west of Norman Wells, the Upper Devonian Imperial Formation was deposited by a fan-slope complex that prograded southwest from an eastern basin margin. Laterally extensive submarine fan deposits are composed of intercalated sandstone lobe and lobe fringe deposits. Sandstone lobes are composed of thick-bedded turbidites reflecting high sediment fallout rates. Lobe fringe deposits are thin-bedded turbidites deposited under upper flow regime conditions. Slope facies are shale-dominant, but include turbidites deposited by both fine-grained dilute flows and thin-bedded facies deposited under upper flow regime conditions but low sediment fallout rates. Near the eastern edge of the study area, at Imperial River, shallow marine deposits are preserved above and below slope deposits, a relationship interpreted to record local shelf construction at the basin margin during initial stages of subsidence. Near the western edge of the study area, at Flyaway Creek, Imperial Formation is composed entirely of shale, marking the western extent of well developed base-of-slope submarine fan deposits. In the western area Imperial Formation is overlain by Tuttle Formation sandstone, which marks an increase in the grain size of sediment supplied to the southwestward prograding slope system.