The Devonian-Carboniferous boundary in the Moravian Karst (Czech Republic)

Abstract

The continuous and well-accessible Devonian-Carboniferous boundary successions of the Czech Republic are part of the Brunovistulian Unit, which belongs to the Variscan Rhenohercynian Zone of the Bohemian Massif. The well-studied sections, with almost continuous carbonate sedimentation, crop out in the Moravian Karst area and are characterised by carbonate turbidites (Lesni lom) and hemipelagic successions (Křtiny). In the Lesni lom quarry, a complete succession of conodont zones of the Devonian-Carboniferous boundary interval (Upper expansa, praesulcata, costatus-kockeli, kockeli, sulcata/kuehni, bransoni, duplicata zones) was documented in calciturbidites and can be correlated with coeval foraminiferal zones (Quasiendothyra kobeitusana, Quasiendothyra konensis and Tournayellina pseudobeata zones). The Hangenberg Crisis and its three phases can be well recognised both with lithological, biostratigraphical and geochemical approaches in the Lesni lom section. At Křtiny, the nodular limestones yielded conodonts of the Devonian-Carboniferous boundary interval, but missing protognathodid fauna hampered identification of the kockeli Zone. A stratigraphic gap covering the basal part of the sulcata/kuehni Zone or strong condensation can be inferred from the occurrence of the transitional morphotype Si. sulcata-bransoni at the base of this zone. The tested “Montpellier criterion” for the Devonian-Carboniferous boundary redefinition can be used only in the Lesni lom section, where the first Protognathodus kockeli occurs above the regressive Hangenberg Sandstone Event deposits.