No abstract

In Belgium, the Lower Kellwasser Event (LKW) corresponds to the relative sea-level maximum of the first ('Aisemont sequence' (AS)) of the two late Frasnian third-order sequences that are recognized here, but the Upper Kellwasser Event (UKW) may have been triggered by a series of tsunamites. The end of the middle Frasnian carbonate platform and reefs is caused by the sea-level drop and emersion of the last middle Frasnian third-order sequence ('Lion sequence') in the Lower rhenana Zone. The end of the 'Petit-Mont' mudmound growth during the transgressive (TST) and highstand (HST) systems tracts of the AS was caused by sea-level fall and emersion at the top of this sequence. The coral and brachiopod extinction in the Upper rhenana Zone, during the second late Frasnian third-order sequence ('Lambermont sequence' (LS)), is progressive and due to the widespread development of the dysoxic and anoxic facies, before the UKW. Only the LS TST has been identified. No sea-level fall has been recognized in relation to the UKW or near the Frasnian-Famennian boundary. The late Frasnian extinctions are more likely to be related to the decrease in the atmospheric oxygen rate and its impact on marine environments and, to complete, the UKW.

The biostratigraphic significance of selected uppermost Famennian (Upper Devonian) and lower Tournaisian (Mississippian) brachiopod genera, belonging to the orders Rhynchonellida (e.g. Araratella), Spiriferida (e.g. Sphenospira, Prospira), Spiriferinida (Syringothyris) and Productida (except Chonetidina), is discussed. Owing to the difficulties of identifying productidine and strophalosiidine genera, in contrast to rhynchonellides and spiriferides, the biostratigraphic potential of the former has generally been overlooked. Brachiopods flourished in neritic environments that were unfavourable for conodonts and ammonoids. In the absence of the latter traditional marker fossils, they are potentially important for locating the Devonian–Carboniferous boundary in shallow water depositional settings in conjunction with rugose corals and foraminifers. On a worldwide scale, further work is required to reach a better assessment of the aftermath of the Hangenberg biological Crisis on brachiopods, notably in revising the faunas from the classical areas of the Famennian and Tournaisian stages in Western Europe.

Brachiopods of the orders Strophomenida, Orthotetida, and Athyridida from the late middle Frasnian–early Famennian interval (hassi to triangularis conodont zones) in the Namur-Dinant Basin (southeastern margin of Laurussia; southern Belgium) are described. Nine genera and subgenera represented by 12 species are recognized here. One new genus, Retrorstrophia, and one new species, Douvillina area, are erected. Crinisarina stainbrooki is proposed to solve the homonymy between C. reticulata (Gosselet, 1877) and Cleiothyridina reticulata Stainbrook, 1947, the type species of Crinisarina Cooper and Dutro, 1982. A lectotype is selected and illustrated for C. reticulata. A new name is also proposed for Athyris reticulata Chen and Xu, 2000, which is assigned here to Crinisarina: C. shashishanensis nom. nov. In southern Belgium, the last representatives of the families Douvillinidae and Leptostrophiidae (Strophomenida) are from the Upper rhenana Zone (late Frasnian). Athyridid brachiopods, especially the representatives of the subfamily Cleiothyridininae constituted a significant part of the early Famennian recovery faunas with spiriferids and rhynchonellids, just after the late Frasnian mass extinction.

In the Saoura Valley (Ougarta Basin, Saharan Algeria), the lower–upper Famennian part of the essentially shally Marhouma Formation is characterized by deep-water facies and includes horizons rich in ammonoids (goniatites and clymeniids) and blind to eye-reduced phacopide trilobites. They are also rich in small-sized and smooth rhynchonellide brachiopods, investigated here for the first time in order to detail their post-Kellwasser recovery. Rhynchonellides clearly predominate in the brachiopod assemblages (representing 90% of the whole assemblage, with 10 species) composed otherwise of athyridides, orthides and spiriferides. Rhynchonellides are mostly represented by relatively flat leiorhynchids and rozmanariids consistent with poor oxygenation on the sea floor. One new species is described (Evanidisinurostrum saouraense sp. nov.); four genera, previously known only from the south-eastern margin of Laurussia, are reported for the first time from the northern margin of Gondwana: the leiorhynchid Sphaeridiorhynchus and the rozmanariids Leptoterorhynchus, Pugnaria and Novaplatirostrum.

The palaeoenvironment of the ‘black marble’ of Denée [Dinant sedimentation area (DSA), southern Belgium], included in the Molignée Formation of Lower Carboniferous (Viséan) age, is discussed. This fossil conservation deposit (‘fossil Lagerstätte’) yielded a rare but remarkably preserved macrofauna (including fishes, echinoderms and brachiopods). It developed in a confined intra‐platform basin progressively filled by distal calcareous turbidites originating from the southward prograding shelf to the north. This basin was bordered to the south by a discontinuous barrier of Waulsortian mud mounds built against a major synsedimentary fault separating the DSA from the southern Avesnois sedimentation area (ASA). The alternations of laminated (‘black marble’ facies) and bioturbated (‘thick‐bedded’ facies) lithofacies occurring within the Molignée Formation imply that the palaeoenvironment recorded several anoxic to dysoxic periods alternating with more oxygenated ones due to sea‐level fluctuations of low magnitude and was strongly influenced by the basin architecture inherited from the late Tournaisian. Copyright © 2007 John Wiley & Sons, Ltd.

No abstract

No abstract