Forty-eight Devonian conodont zones are now recognized worldwide: 11 zones in the Lower Devonian, 10 zones in the Middle Devonian, and 27 zones in the Upper Devonian. Only five of these zones have not yet been recognized in the western United States. Conodonts, which range from Cambrian to Triassic, attained their maximum faunal diversity and abundance during the Late Devonian, when each conodont zone lasted about 0.5 m.y. Because each zone represents such a short interval of geologic time, conodonts provide an indispensable tool for petroleum exploration in the Rocky Mountain, Overthrust belt, and Great Basin regions.

Conodont color-alteration index (CAI) values have been used successfully to predict cool areas of potential production in otherwise thermally overcooked regions. Their use has also been demonstrated as follows.

1. Conodonts, by providing virtual time planes, suggest the complex relations between source beds in the Pilot basin and reservoir rocks in the enclosing carbonate platform.

2. Conodonts have been used to determine rates of sedimentation of source rocks and other synorogenic sediments of the Antler orogeny. These rates range from 1 to 400 m/m.y. They also demonstrate that deposition was episodic and that there were times and areas of nondeposition within marine basins.

3. Conodonts precisely date Antler orogenic events, which governed eustacy and caused marine transgressions and regressions on the craton. For example, the emplacement of the Roberts Mountains thrust took approximately 8 m.y.

4. Conodonts are used for biofacies analysis and for paleotectonic reconstructions. For example, within the Late Devonian Polygnathus styriacus Zone, eight different conodont biofacies, with almost mutually exclusive faunas, have been used to reconstruct five paleotectonic settings ranging from peritidal to offshore pelagic.

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