The semichatovae Transgression (basal upper Frasnian) in Morocco

The semichatovae Transgression marks an episode of major eustatic sea level rise in the Upper Devonian. It is commonly described by the wide spread of the index conodont Palmatolepis semichatovae and has been proposed to define the boundary between the middle and upper Frasnian substages within Frasnian conodont zone 11. The index species is known from the Moroccan Meseta (Mrirt region) but so far absent from the cratonic northern Gondwana shelf (Anti-Atlas). There, the eustatic event has been roughly recognized based on lithological and geochemical changes, which indicate a drastic turnover of low-oxygen water masses. We attempt to provide conclusive evidence for the event and associated environmental changes in a transect from the Meseta to the eastern Anti-Atlas by applying multiple methods, such as geochemical proxies for detrital input and hypoxia, stable carbon isotopes, microfacies developments, and changes of conodont assemblages. Outcrops were chosen to represent different facies types, from pelagic carbonate platform to more argillaceous intrashelf basins. The goal is to provide additional information on both the timing and duration of the event, as well as the environmental impact it had on the Gondwana margin. New detailed bio- and chemostratigraphic data shall assist the ongoing search for formal substage definition and stratotype selection.