Famennian Ammonoids Research Articles

Famennian (Late Devonian) ammonoids from the Ouarourout section (Saoura Valley, Algeria)

In North Africa, the ammonoids constitute an important part of the Devonian marine macro-invertebrates. New material has been recently collected in the ‘Argiles de Marhouma’ Formation from several sections located near Béni-Abbès in the Saoura Valley (Ougarta Mountains, Algerian Sahara). Red nodular limestones (i.e., ‘griotte’ facies) characterize this formation rich in ammonoids. The assemblages from the Ouarourout section are composed of Goniatitida and Clymeniida constituting 30 species and 19 genera belonging to 11 families, with Cyrtoclymenia, Erfoudites, Kosmoclymenia, Planitornoceras, Platyclymenia, and Prionoceras, as the most abundant genera. The taxonomic comparison and the biostratigraphic correlations are made by considering the assemblages recorded in the Anti-Atlas of Morocco, which are very close to those observed in Algeria. In the Ouarourout area, the ‘Argiles de Marhouma’ Formation contains middle and late Famennian ammonoid assemblages and three biostratigraphic intervals can be identified: Planitornoceras, Platyclymenia and Medioclymenia.

Advanced gonioclymeniid ammonoids from Central Europe

Advanced gonioclymeniids comprise two families, Gonioclymeniidae and Sphenocly-meniidae. These are the phylogenetic end-members of the order Clymeniida, and are usually rarely represented in the Late Famennian ammonoid assemblages of Central Europe. The two families include the latest Famennian genera Finiclymenia, Medioclymenia and Sphenoclymenia. Most of their species are poorly known and some are revised here. We describe the new species Finiclymenia langei, Finiclymenia czarnockii and Medioclymenia media to complement the knowledge of Famennian ammonoid diversity.

Sporadoceratid ammonoids from the Shotori Range (east-central Iran) – a case of putative gigantism caused by hydraulic sorting?

The Shotori Range of east-central Iran (east of Tabas) has yielded Famennian ammonoid assemblages dominated by the family Sporadoceratidae. Four genera Maeneceras Hyatt, 1884, Iranoceras Walliser, 1966, Sporadoceras Hyatt, 1884 and Erfoudites Korn, 1999 are represented. The conodont assemblage of one sample containing Iranoceras revealed an Upper marginifera Zone age. The ammonoid assemblages are characterised by comparatively large specimens; they reach conch diameters of 300 mm (including the body chamber) and the mean size is larger than 100 mm. The preservation of the material from the Shotori Range and size comparison with sporadoceratid assemblages from the Anti-Atlas of Morocco and the Rhenish Mountains of Germany suggest that hydraulic sorting has resulted in a bias towards large conchs, explaining the size distribution, rather than latitudinal differences. The new species Maeneceras tabasense is described; the genus Iranoceras is revised with a new description of the two species Iranoceras pachydiscus (Walliser, 1966) and Iranoceras pingue (Walliser, 1966).

An assemblage of pyritized middle Famennian ammonoids from the Velbert Anticline (Rhenish Mountains)

An assemblage of pyritized middle Famennian ammonoids from the Velbert Anticline (Rhenish Mountains)

Uppermost Famennian stratigraphy and facies development of the Reigern Quarry near Hachen (northern Rhenish Massif, Germany)

As a contribution to the ongoing international revision of the Devonian/Carboniferous boundary, we present a bed-by-bed study of the Reigern Quarry in the northern Sauerland (Rhenish Massif, Germany), which is famous as an uppermost Famennian ammonoid locality. Currently exposed are ca. 2.5 m of strongly cyclic Wocklum Limestone, conformably overlain, but with a long hiatus (topmost Famennian to upper Tournaisian), by laminated radiolarites and a thin metabentonite of the Lower Carboniferous Hardt Formation. The nodular limestones are pelagic mud-wackestones with some sporadic occurrences of cephalopod float-rudstones. The exposed part of the Wocklum Limestone falls in the successive Bispathodus ultimus ultimus and Siphonodella (Eosiphonodella) praesulcata (s.l.) zones. It yielded two new Siphonodella (Eosiphonodella) species left in open nomenclature, Neopolygnathus communis aff. dentatus and the possibly stratigraphically relevant Bispathodus ultimus corradinii ssp. nov. The upper range of Palmatolepis gracilis semisigmoidalis is significantly expanded. The conodont faunas mostly belong to variants of the pelagic Palmatolepis-Bispathodus biofacies; but in the lower part of the succession, there is a new Neopolygnathus biofacies that previously has not been recorded from deeper-water, pre-Hangenberg Crisis strata. Neopolygnathus is interpreted as a palaeoecological generalist that variably blossomed in outer or inner shelf facies and after other conodont groups declined. The mostly loose ammonoid faunas comprise almost 30 taxa and fall mostly in the lower Wocklumian Kalloclymenia subarmata and Muessenbiaergia bisulcata zones (Upper Devonian = UD VI-A1/A2), which agrees with previous ammonoid-conodont correlations.

The late Famennian ammonoid succession in the vicinity of Béni Abbès (Saoura Valley, Algeria)

The late Famennian ammonoid succession in the vicinity of Béni Abbès (Saoura Valley, Algeria)

Upper Devonian (Famennian) Ammonoids from the Canning Basin, Western Australia

The inter-reef Virgin Hills Formation in the Canning Basin of Western Australia contains a diverse and abundant ammonoid fauna. This fauna is comparable in taxonomic diversity and abundance to the rich ammonoid faunas of Europe and North Africa. Of the four Stufen of the Famennian part of the classic German section, three (doII, III, IV, and V) are represented in Western Australia by ammonoids. The similarity of the Western Australian material with that of Europe and North Africa is remarkable, and suggests strongly the existence of an interbreeding relationship between the ammonoid populations of these areas which are now separated geographically by approximately 13,500 kilometers. Of the 36 recognized genera of Devonian goniatites known from Europe, 13 genera are described from Western Australia, as are four of the 32 known genera of clymeniids. Furthermore, the occurrence and nature of the ammonoid fauna indicates a close approximation of a living assemblege, or biocoenose. Several ontogenetic sequences which have long been recognized in Europe, and subsequently redescribed in Famennian strata of the Sahara region of North Africa, are duplicated by the Famennian ammonoids of Western Australia.

The Devonian period

Summary A review of the radiometric evidence suggests that the top of the Devonian should be dated at about 345 m.y. and the base of the system at about 395 m.y. Using cumulative thickness methods the age of the base of the Upper Devonian is estimated at 358 m.y. and that of the base of the Middle Devonian at 370 m.y. Famennian ammonoid species zones must each represent about a million years. Suggestions are made as to where future radiometric work of importance to the time-scale might be undertaken.