Early Devonian (Lochkovian – early Emsian) bioevents and conodont response in the Prague Synform (Czech Republic)

Abstract

The Devonian succession of the Prague Synform is characterized by two major lithofacies: shallow-water biodetrital, mostly crinoidal limestones that also include a reefal skeletal accumulation of Pragian age, and a more pelagic facies that is represented mostly by calcisiltites. Among the several Devonian prominent sea-level fluctuations, some can be traced globally, e.g., the Basal Pragian and Kačák events. In recent years, conodont biostratigraphy of the Early Devonian (Lochkovian, Pragian and early Emsian) of the Prague Synform has been refined. The regional subdivision of the Lower Devonian in its type area has been greatly improved by the integration of new biostratigraphic, chemostratigraphic, sedimentological, and petrophysical data that has, in turn, strengthened global correlations for this interval in Earth's history. The complete conodont biozonation of the Early Devonian interval (basal Lochkovian – earliest Emsian) in the Prague Synform includes 17 biozones, which can be applied to sections representing various depositional environments and have more global applicability than previously proposed ‘global’ conodont biozonations. The zonal scale enables a precise biostratigraphic delimitation of the major Early Devonian biotic events (Silurian-Devonian Boundary Event, Lochkovian-Pragian Event and Basal Zlichovian Event). There were major changes in the conodont fauna in response to the Silurian-Devonian Boundary and Lochkovian-Pragian events, however the Basal Zlichovian Event was only characterized by a very gradual transition in the conodont fauna. In parallel to the traditional events defined for the Prague Synform, seven other significant conodont events have been documented. These events represent major turnovers in the conodont fauna that have a direct impact on conodont biostratigraphy, specifically at a global scale. The Icriodus and Irregularis events are congruent with the lower boundaries of the Lochkovian and Pragian stages, respectively. The conodont events established in the Prague Synform largely reflect variations in the seawater depth but are generally independent of lithological changes within sections of the Prague Synform.