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Norian (Upper Triassic) sediments in western Nevada were deposited in a west-facing successor basin which was formed following the collision of the microcontinent Sonomia in the Late Paleozoic. These strata were deposited on a shelf and in a deep basin and consist of siliciclastic sandy and pelitic strata with interbedded carbonate strata.

Conodonts of the genus Epigondolella are common in the basinal strata but are rarely found in carbonates deposited on the shelf. This suggests that Epigondolella may have been facies selective. The trace fossils, Cruziana, Planolites, Skolithos, and Cylindrichnus, are present in sandstone deposited on the shelf and coupled with other sedimentologic data indicate shallow marine environments of deposition. Basinal rocks consist of distal turbidite and hemipelagite in the basal portion but in the upper part suggest shoaling. Carbonate-platform deposits cap the sequence and indicate that the basin was filled to near sea level. Epigondolella is present in both the basinal thin-bedded carbonates and in the more massive platform carbonates. Eight Epigondolella associations have been recognized elsewhere in the Norian and have been related biostratigraphically to the standard ammonoid zonation. Conodont elements representing five of these associations are recognized and have been useful for correlation of strata between the shelf and basinal lithofacies when coupled with other biostratigraphic data.

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