The Hastarian Substage is the lower subdivision of the Tournaisian. Its base coincides with that of the Carboniferous as defined by the first appearance of the conodont Siphonodella sulcata. Unfortunately, the oldest siphonodellids are absent across the Devonian-Carboniferous boundary in the lower part of the Hastière Formation. The top of the Hastarian is defined by the base of the succeeding Ivorian substage (as emended by Hance et al., this volume) that is recognized by the first appearance of the conodont Polygnathus communis carina. The Hastarian correlates with foraminiferal Zones MFZ1 to MFZ4, rugose coral Zones RC1 and RC2 and the Siphonodella conodont Zone. Hastarian sedimentation occurred within a south-facing ramp setting. Thin-bedded crinoidal wacke- to packstones alternating with argillaceous limestones and thick-bedded crinoidal packtones form the dominant facies.
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