Annick Boullier

Evolutionary patterns in the terebratulid genus Caryona Cooper (Brachiopoda, Jurassic of France)

The study of ontogenetic and morphological changes in different species of the brachiopod genus Caryona COOPER (Terebratulidae) from the Lower Callovian‐Lower Oxfordian of northern France shows a succession (and an interference) of processes which vary according to the characters studied. This is an example of “mosaic evolution”;. The ontogenetic changes result from heterochrony, especially acceleration and hypermorphism. The main phylogenetic tendency is peramorphosis in most characters. This evolutionary pattern agrees with phyletic gradualism. Moreover, analysis of the internal characters demonstrates the limited value of these in discrimination of the various genera.

Conditions d'installation d'un seuil corallien dans l'intervalle transgressif Oxfordien moyen et supérieur p.p. entre le bassin tellien et son avant-pays (Ouest algérien) ; implications paléogéographiques

Abstract The Tiaret-Guertoufa coral-reef, dated of Middle and Upper Oxfordian p.p., is studied in the palaeotectonic and palaeogeographic context of Western Algeria. The present note puts the emphasis on: 1) the harrier-role played by this bioherm (apex reef of block) on a pelagic shoal which has separated the Tellian Basin and its Foreland; 2) the determinant action of the distensive tectonics in the control of sedimentation during this period; 3) the transgressive character, at the Oranian scale, of the carbonated episode marked by a succession of backstepping high-frequency sequences. This transgressive condensed interval (Transversarium and Bifurcation zones) may he integrated into a positive sequence (of 3rd order? in Vails sense) which seems to reveal a general movement of eustatic rise during Oxfordian in the Tethyan domain.