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Frasnian plants from the Dra Valley, southern Anti-Atlas, Morocco

BRIGITTE MEYER-BERTHAUD^*,, MARTIN RÜCKLIN, AUDE SORIA^*, ZDZISLAW BELKA and HUBERT LARDEUX^¶

^* Botanique et Bioinformatique de l’Architecture des Plantes, UMR 5120 CNRS-CIRAD, PS2/TA40, Boulevard de la Lironde, 34398 Montpellier Cedex 5, France
Staatliches Museum für Naturkunde Karlsruhe, Erbprinzenstraße 13, 76133 Karlsruhe, Germany
Institute of Geology, Adam Mickiewicz University, ul. Maków Polnych 16, 61-606 Pozna, Poland
^¶ Le Verger-Beaucé, 35 520 Melesse, France

Author for correspondence: meyerberthaud{at}cirad.fr

Anatomically preserved plant fragments are reported from Devonian marine deposits exposed in the Dra Valley of southern Anti-Atlas, Morocco. Associated conodont and tentaculite faunas indicate that the sediments yielding plants, which consist of black shales with intercalated calcareous concretions, are early Frasnian in age and most probably represent Zone 2 of the conodont zonation. This is the first record of Frasnian plants in North Africa. The specimens found all correspond to decorticated portions of axes. Six are referable to Callixylon, the organ genus corresponding to anatomically preserved axes of the progymnosperm tree Archaeopteris. Based on wood characters, especially ray structure, they are assigned to the species C. henkei, formerly described from the Famennian of Europe. One single specimen is compared to Xenocladia, a cladoxylopsid genus previously known from the Middle Devonian of Europe, USA and Kazakhstan. Interestingly, Archaeopteridales and Cladoxylopsida are two groups that dominate the younger plant assemblages of Famennian age recently described from the eastern Anti-Atlas. Callixylon henkei-type axes occur both in the Frasnian and in the Famennian deposits of the Anti-Atlas and they are all devoid of growth rings. These results are in accordance with a close position of Gondwana and Euramerica during Late Devonian times.

Key Words: Devonian • Anti-Atlas • Morocco • palaeobotany • fossil wood