Revised stratigraphy of the Eifelian (Middle Devonian) of southern Belgium: sequence stratigraphy, global events, reef development and basin structuration

1. Introduction and historical background As properly summarized by Bultynck (2006), the ‘systeme calcaire de Couvin’ was introduced by Gosselet (1860) and included in a broad sense, the lower Middle Devonian limestone and related shale in southern Belgium. The term ‘Couvinien’ was introduced by Dupont (1885) to designate the fossiliferous strata below the Givetian limestone. The Couvinian limestone and shale unit was mapped under the sign ‘Cobm’ and ‘Cobn’ respectively on the geological map of Belgium at 1/40 000 (Maillieux, 1912). Maillieux & Demanet (1929) also introduced a litho-biostratigraphic scale for the Couvinian in which the ‘Calcaire de Couvin’ was designated by the sign ‘Co2a-b’ and the overlying shale units by the sign’Co2c’ and ‘Co2d’. The term Couvin Formation (Fm) was introduced by Bultynck et al. (1991) to replace the formerly used ‘Calcaire de Couvin’. The limited extension of the ‘Calcaire de Couvin’ and its thinning and disappearance eastwards are known since Dewalque (1861) and Gosselet (1860, 1888). However, most subsequent works have eluded this question and focused either on the Couvin area where the stratotype is exposed (Tsien, 1969; Bultynck, 1970), or on the Jemelle area where the limestone unit is entirely replaced by the fine-grained siliciclastics of the Jemelle Fm (Godefroid, 1968). Between these areas, the Eifelian succession is affected by strong and rapid lateral variations making the correlation scheme difficult to establish. The recent re