Detailed investigations of sequences containing the Kellwasser Bio-event near the Frasnian-Famennian boundary demonstrate a stepwise character of influences on different groups of organisms over a time span of more than 1 my. Therefore the term Kellwasser Crisis (KW Crisis) is introduced. Extraordinary episodes of the KW Crisis, like e.g. the Upper KW Horizon, develop stepwise, too. The KW Bio-event demands a multicausal explanation. A model of successive and/or interacting processes is presented.