Les ammonites de l'Hettangien, du Sinémurien et du Pliensbachien inférieur de la Dorsale de Grande Kabylie (Algérie).

Jean-Louis DOMMERGUES, Gérard CATTANEO, Ramdane AÏTE & Jean-Pierre GÉLARD

fr Geodiversitas 30 (3) - Pages 539-576

Published on 30 September 2008

The Hettangian, Sinemurian and Early Pliensbachian ammonites of the Great Kabylia (Algeria).

The studied ammonite faunas include about thirty species indicating the Hettangian, the Sinemurian and/or the early Pliensbachian (Carixian). These faunas have been collected in four fossiliferous localities of the Kabylia Chain, “Dorsale kabyle” or “Chaîne calcaire” in the French literature (Djurdura and Chellat massifs, Algeria). This small part of the Alpin belt extending from the Strait of Gibraltar to Calabria is understood as a portion of the south passive margin of the ALKAPEKA micro-continent or “Mesomediterranean terrane” which was located within the western (Mediterranean) part of the Tethyan realm. During the Early Jurassic, the extensional tectonic activity of this margin bears witness to an active rifting phase. The most fossiliferous outcrops (late Sinemurian and/or early Pliensbachian) are rather thin, more or less nodular and ferruginous deposits close to the “ammonitico rosso” facies. Faunas are usually both condensed and reworked. From a paleobigeographical point of view, they indicate obvious Mediterranean (west Tethyan) affinities: most of the species are only, or principally, known in the western Tethys. Phylloceratoidea and Lytoceras are plentiful and suggest the closeness of a deep basin (Maghrebian trough) and the possibility of connections between this trough and the oceanic Tethyan basins. Nevertheless, the Algerian faunas also include, in a significant proportion, notable forms which can not be easily attributed to any previously known taxa. Unfortunately they are usually single and more or less incompletely preserved specimens. Opposite to the Phylloceratoidea and Lytoceras which indicate oceanic affinities these peculiar forms suggest the possibility of some temporary phases of basin partitioning.

Keywords :

Mollusca, Cephalopoda, Ammonites, Early Jurassic, western Tethys, Kabylia, Algeria, biostratigraphy, palaeobiogeography, palaeobiodiversity

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