DEPOSITIONAL SIMILARITIES IN SELECTED LATE DEVONIAN KELLWASSER HORIZONS: GERMANY, MOROCCO, AND EASTERN UNITED STATES

The Kellwasser (KW) Events have been recognized globally in high Frasnian marine beds often expressed as two distinctive dark shale or carbonate units that record wide spread and persistent intervals of substrate anoxia and coincide with one of the five severest mass-extinction events in Earth history. In a stratigraphic section in the Moroccan Meseta near M’rirt the Lower and Upper Kellwasser intervals are preserved in a 1.2 m thick interval. The Lower Kellwasser Beds (LKW) consist of 22 cm of locally brecciated grayish black cephalopod limestones lying disconformably on medium gray biopackstones. Conodonts in the LKW are dominated by species of Icriodus and Polygnathus. The Upper Kellwasser (UKW) Beds consist of 15 cm of dark shale and discrete nodules of dark gray laminated limestone. Conodonts in the nodules are dominated by species of Palmatolepis and Polygnathus; icriodids are absent. The Frasnian-Famennian boundary is placed at the top of the shale where it is overlain by medium gray brecciated and irregularly bedded biopackstones/wackestones containing Palmatolepis, Icriodus, and Polygnathus. Palmatolepis increases in relative abundance in the overlying bed. The LKW interval at M’rirt is remarkably similar to the Steinbruch Schmidt and Thuringian Kahlleite sections in Germany, notable in the decline in conodont abundance and relative decrease in palmatolepids and increase in icriodids at the onset of the dark gray carbonates – suggesting conodont biofacies are not responding to sea-level fluctuation, per se. The lithology and conodont fauna changes in the UKW interval and across the Frasnian-Famennian boundary are similar to those found in Germany and in southern France. The pattern of the Kellwasser beds is also developed in the offshore clastic-dominated strata of the Appalachian Basin pointing to global effects influencing deposition in comparable facies settings. Although there has been intense research on the KW interval during the past three decades, the cause for the mass-extinction associated with the KW Event interval remains enigmatic. A combination and interaction of different factors, e.g., changes in sea-level, climate, ocean currents, ocean chemistry, position of continents – of which one or the other might be the main trigger leading to the mass-extinction event – seems most probable.