A succession of Frasnian mounds on the southern border of the Dinant Synclinorium (Belgium) was investigated for their facies architecture, sedimentary dynamics and palaeogeographic evolution. Seven mound facies were defined from the Arche (A) and Lion (L) members, each characterized by a specific range of textures and association of organisms (A2/L2: red or pink limestone with stromatactis, corals and crinoids; A3/L3: grey, pink or green limestone with stromatactis, corals and stromatoporoids; A4/L4: grey limestone with corals, peloids and dasycladaceens; A5/L5: grey microbial limestone; A6/L6: grey limestone with dendroid stromatoporoids; A7/L7: grey laminated limestone with fenestrae; and A8/L8: grey bioturbated limestone). Laterally equivalent sediments include substantial reworked material from the buildups and background sedimentation. Textures and fossils suggest that A2/L2 and A3/L3 facies developed close to storm wave base, in a subphotic environment. Facies A4/L4, occurring near fair weather wave base in the euphotic zone, includes lenses of A5/L5 with stromatolitic coatings and thrombolithes. A6/L6 corresponds to a slightly restricted environment and shows a progressive transition to fenestral limestone of A7/L7. This facies was deposited in a moderately restricted intertidal area. A8/L8 developed in a quiet lagoonal subtidal environment. The mounds started with A2/L2 or A3/L3 in which microbial lenses and algal facies A4/L4 became progressively more abundant upwards. Following 20 m of laterally undifferentiated facies, more restricted facies occur in the central part of the buildups. This geometry suggests the initiation of restricted sedimentation, sheltered by bindstone or floatstone facies. The facies interpretation shows that after construction of the lower part of the mounds during a transgression and a sea-level highstand, a lowstand forced reef growth to the margin of the buildups, initiating the development of atoll-like crowns during the subsequent transgressive stage. The persistence of restricted facies results from the balance between sealevel rise and reef growth.

ABSTRACT. The continental and mainly conglomeratic Booischot Formation is formally introduced for the strata intersected close to the base of the Booischot borehole from the Campine Basin. It is nearly 400 m thick and its upper part is Upper Givetian to Upper Frasnian in age whereas its lower part has not been dated so far. The Booischot borehole is overlain by the Upper Devonian marine Aisemont and Falisolle Formations which are capped by Famennian sandstones assigned to the Evieux Formation. These latter three lithostratigraphic units are also present in the Heibaart borehole, above a few metres of the Middle Frasnian Huccorgne Formation which rest directly on the Caledonian basement of the Brabant Massif, without any trace of the Booischot Formation. It appears that in the Campine Basin, the Devonian transgression arrived very late during the Frasnian. The Devonian succession at the northern margin of the Brabant Massif is very different from that of the north side of the Namur Basin and the Visé area characterized more particularly by the occurrence of Givetian marine deposits. Some rugose corals of this stage are figured for the first time from the Visé area. The conglomerates of the Booischot Formation are also compared to similar thick strata from the Givetian of NW Germany.

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Cystiphylloides marennense n. sp., C. minimum (Wedekind, 1922), Atelophyllum emsti (Wedekind, 1922), Thamnophyllum godefroidi n. sp., Spinophyllum longiseptatum (Lütte, 1984) and Iowaphyllum sp. have been mainly collected on the south side of the Dinant Synclinorium, close to the boundary between the Lower and the Middle Givetian. Indeed, this material comes mostly from the lower part of the Mont d’Haurs Formation which is characterized by a high biodiversity. The genus Atelophyllum Wedekind, 1925 has been preferred to Mesophyllum Schlüter, 1889 and Lekanophyllum Wedekind, 1924 as the holotype of its type species Atelophyllum emsti has been figured in both transverse and longitudinal sections. A colony of Iowaphyllum is observed for the first time in the Givetian of Belgium. As a whole, the fauna of the Mont d’Haurs Formation is widely distributed in various areas of the Old World Realm (Europe, Asia and Australia). However, it shows strong affinities with the neighbouring countries of Belgium and especially with the Givetian rugose corals of the Eifel Hills, the Bergisches Land and the Sauerland in Germany.

ABSTRACT.The new genus Potyphyllum is erected with Cyathophyllum ananas Goldfuss, 1826 as type species, for which a neotype is selected here from the north side of the Namur Basin. It is a massive pseudocerioid rugose coral like Frechastraea Scrutton, 1968 with rather large corallites, spindle-shaped dilated septa as well as some horseshoe and inner dissepiments. In the Belgian Upper Frasnian, Potyphyllum ananas and P. veserense (Coen-Aubert, 1974) occur mainly in the Upper Palmatolepis rhenana conodont Zone. The latter two coral taxa, together with diverse species of Frechastraea and Phillipsastrea D'Orbigny, 1849, permit dating of the red marble lenses from the Petit-Mont Member which are developed at different levels of the Champ Broquet Formation, in the Dinant Synclinorium. In this lithostratigraphic unit are also incorporated the Neuville and Les Valisettes Members, formerly considered as two separate formations. At the present time, Potyphyllum is only known from Western and Eastern Europe.