The Kačák event (late Eifelian, Middle Devonian) on the Belgian shelf and its effects on rugose coral palaeobiodiversity

were located in the southern hemisphere (e.g. Stampfli et al. 2002, 2013; Scotese 2014), with a major mountain range running on the northeastern margin of Laurussia to Gondwana: the Appalachian range (Fig. 1) (DeSantis 2010, Scotese 2014). This period of time is marked by one of the most significant modifications in palaeobiogeography with the precipitated end of the strong faunal endemism of the Emsian–Eifelian and the initiation of the Givetian– Frasnian cosmopolitanism (Oliver & Pedder 1979b). During the early Emsian to late Eifelian interval, three distinct faunal assemblages allow the definition of three different marine realms (Oliver & Pedder 1979a, 1979b, 1994; May 1995, 1997b), separated by various barriers. The Malvinokaffric Realm (MKR), located along the margins of Gondwana (Fig. 1), is relatively poor in corals and it is characterized by cold-water species (Oliver 1990; Oliver & Pedder 1979a, 1979b, 1994; May 1995, 1997b). The East Americas Realm (EAR), located on the eastern part of North America and the northern part of South America (Fig. 1), is characterized by subtropical marine faunas and high degree of endemism (Oliver 1990; Oliver & Pedder 1979a, 1979b, 1994; May 1995, 1997b). The Old World Realm (OWR) covers the Palaeothetys Ocean and the margins of Laurussia, Kazakhstania and Siberia as well as the Chinese blocks and E Australian terranes (Fig. 1). It is also characterized by widespread subtropical marine faunas (Oliver 1990; Oliver & Pedder 1979a, 1979b, 1994; May, 1995, 1997b). The EAR is isolated from the OWR by a continental arch (Fig. 1) and the Appalachian mountain range (Oliver & Pedder 1979a; May 1995, 1997b). Whereas the lowest sea level of the Devonian was recorded during the Emsian (May 1995, 1997b), the Middle Devonian recorded one transgressive pulse. This eustatic increase led to the collapse of the continental arch that separated the EAR from the OWR, and to the opening of a passageway allowing the migration of marine faunas between the two realms (Oliver & Pedder 1979a, DeSantis & Brett 2011). The faunal turnovers observed in the EAR are a probable consequence of this major