The Dzerzhinka Section (eastern slope of the South Urals): an overview of the fauna and facies around the Devonian-Carboniferous boundary

The Devonian-Carboniferous boundary section near the village of Dzerzhinka (vicinity of Verkhneuralsk) on the Ural River on the eastern slope of the South Urals, Russia, contains a wide variety of fossil invertebrates, including foraminifers, ostracodes, ammonoids, conodonts, and brachiopods. Diverse Upper Famennian assemblages are associated with wackestone-grainstone microfacies and bioclastic-volcaniclastic arenite, suggesting normal marine sedimentation in a volcanic-arc setting. The presence of well-established shallow-water benthic communities associated with the basinal Palmatolepis conodont biofacies and breccias is difficult to interpret. The latest Devonian and earliest Mississippian Siphonodella praesulcata and S. sulcata conodont zones are missing from the succession, indicating a discontinuity of sedimentation that is, associated with a hardground with phosphorite nodules. By the time of the S. quadruplicata Zone, normal marine sedimentation resumed, while the shelf continued to subside and was eventually overlain by siliciclastic and cherty sediments.