Conodont biofacies patterns in the Kellwasser Facies (upper Frasnian/lower Famennian) of the eastern Anti-Atlas, Morocco

Abstract

The abundant conodont fauna of a black limestone and shale lithology (Kellwasser facies) of late Frasnian/early Famennian age provides a significant example of environmental control on conodont distribution and abundance. Conodont collections from the Upper gigas and Upper crepida zones of the eastern Anti-Atlas were examined. Biofacies maps for the conodont genera Palmatolepis, Polygnathus, Icriodus, Ancyrodella, and Ancyrognathus were constructed and their facies distribution patterns analysed. No significant restriction in conodont distribution was observed to be caused by the rise and extension of oxygen-depleted water over the platform during the late Frasnian/early Famennian. The abundance of conodonts, however, appears to have been related to optimal food supply in the oxygenated portion of the water column. Conodont biofacies patterns observed in the Upper Devonian of the eastern Anti-Atlas do not fit a simple ecological model involving distance from shore and depth of water. The faunas of two intervals investigated exhibit a similar level of species diversity, the pattern of which evidently follows the platform-basin configuration, but the majority of species shows a more or less random distribution. The onset of black sediment deposition was characterized by the dominance of Polygnathus and Icriodus, whereas towards its termination during the Upper crepida Zone time interval the genus Palmatolepis clearly predominated. This difference is a consequence of both a rise of sea-level and of evolutionary changes in the composition of the conodont fauna during the early Famennian.