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Upper Givetian and Frasnian ichthyoliths from Bas-Boulonnais (Pas-de-Calais, France): preliminary record

Claire DERYCKE, Alain BLIECK, Denise BRICE & Nicolas MOURAVIEFF

en Bulletin du Muséum national d'Histoire naturelle, 4ème série – section C – Sciences de la Terre, Paléontologie, Géologie, Minéralogie 17 (1-4) - Page

Published on 01 September 1995

New finds of Upper Givetian and Frasnian fishes from Boulonnais contribute to project IGCP 328 which aims to create a data base of microremains for biostratigraphical, palaeoecological and palaeobiogeographical correlations. Morphological and histological data are presented to integrate the ichthyoliths in a systematic frame. The composition of the fauna is typical of Upper Devonian times comprising Symmorium? sp., Ctenacanthus sp. and other chondrichthyan elements; acanthodians are present with Ptomacanthus? sp. and Acanthodes sp. An inferognathal of Rhynchodus? sp. is identified. Actinopterygians are represented by Moythomasia sp., and sarcopterygian remains include an undetermined Onychodontida, undet. Porolepiformes and Spodichthys? sp. All the previously published and the newly described taxa are situated in the Givetian to Famennian stratigraphical scale of the Ferques inlier. The richest assemblages come from 1) the middle Givetian, lower Blacourt Formation, 2) the uppermost Givetian-lowermost Frasnian (lowermost and lower Polygnathus asymmetricus conodont zones), lower Beaulieu Formation, and 3) the upper Frasnian (upper P. asymmetricus and Ancyrognathus triangularis zones), Ferques Formation. The Blacourt Formation assemblage is dominated by placoderms. The newly described lower Beaulieu Formation assemblage is much poorer in placoderms but richer in chondrichthyans, acanthodians, actinopterygians and sarcopterygians. The Ferques Formation assemblage on the contrary seems to be devoid of sarcopterygians, but placoderms, chondrichthyans, actinopterygians and acanthodians do occur.
Keywords :
Ichthyoliths, Upper Devonian, Boulonnais (France), biostratigraphy, palaeogeography, histology, systematics, placoderms, chondrichthyans, acanthodians, actinopterygians, sarcopterygians