A broad area of shallow-shelf carbonates of Nahanni age (Eifelian-Givetian) borders the Canadian Shield in the District of Mackenzie, N.W.T. To the west, in the region of Deadman’s Valley in the South Nahanni area, these carbonates pass to a basinal facies within about three miles.

Examination of the sediments and fauna across this transition permitted correlation between shelf and basin and the recognition of a number of faunal communities. On the basis of environmental deductions interpreted for these faunal communities, and of lithosome geometry and the character of the sediments, it is concluded that the Nahanni Formation sediments were deposited on a broad, slightly restricted shallow shelf, that their basinal equivalents were laid down in a marginal cratonic trough, and that a moderately steep shelf edge or epeiric slope separated the two. A shoal was developed near the edge of the shelf.

The boundary between the shelf and the deeper basin in Arnica (Eifelian and older) times was much more abrupt and was defined by the Manetoe barrier reef.

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