Bernard Andreu

Nouvelles datations (Hauterivien supérieur–Barrémien inférieur) dans les « Couches rouges » continentales du Haut Atlas central marocain ; conséquences sur l’âge du magmatisme et des structurations mésozoïques de la chaîne Atlasique

Abstract In the Moroccan Central High Atlas, between the Bathonian and the Aptian, marine deposits are present in three continental formations. Known to be unfossiliferous for the main part, they are attributed to the Middle Jurassic or to the Lower Cretaceous, depending on the authors. Charophytes from the top of the second formation (Iouaridene Fm), and from the base of the third one (Jbel Sidal Formation), give an Upper Hauterivian–Lower Barremian age. Thanks to these biostratigraphical data, it has been possible to distinguish the different phases of the magmatic activity and the synsedimentary tectonic events, either linked to the closure of Tethyan Atlasic troughs during the Bathonian or associated with the development of the new basins, diachronous in the Atlasic Belt, during the Lower Cretaceous.

Associations d'ostracodes et paléoécologie du Crétacé (Barrémien à Turonien) le long d'une transversale Agadir-Nador (Maroc)

Different depositional environments have been recognized by studying ostracod associations in the Barremian-Turonian interval along a section from Agadir to Nador (Morocco). The lacustrine environment is characterized by a moderate faunal density, a very low generic and specific diversity, and good-sized carapaces (smooth, punctuated or spinely) of Cyprideinae. In the supralittoral environment, the specific diversity is low and the quantity of ostracods is middle to high. Typical markers are the following genera: Virgatocypris, Mantelliana(?), Loxoconcha, Fabanella(?). The carapaces are large, smooth, punctuated or striated lengthwise. Antepaijenborchella and Loxoconcha are rather euryhaline. Marker genera are numerous and diversified in the infralittoral environment. Specific diversity and the quantity of ostracods can be low or high, but always higher than in the other environments. Some euryhaline ostracods are living on the flatform; some disappear because they are not adapted to salinity variations. The bottom is important for the spatial distribution of the species. Some species are living on a carbonate bottom, others on muddy bottoms. Monospecific Cytherella or Dolocytheridea appear in quiet littoral slikkes. In these environments instars of Paracypris pullutate. The decrease of dissolved oxygen kills a great number of species; some survive a small decrease, some a very great decrease (Cytherelloidea, Paracypris, Veenia). In carbonate environments, the carapaces are strong, large, costulated, spinely and tuberculate. The ornamentation is clear and the fossae are wide, polygonal; the solum is flat or weakly concave. A secondary ornamentation occurs in the Trachyleberididae (Cythereis, Spinoleberis, Veenia, Oertliella ?). Many opportunist genera appear: Antepaijenborchella, Cytherella, Paracypris, Dolocytheridea, Loxoconcha, Eocytheropteron, Cythereis, Veenia, Oertliella (?). Currents frequently introduce globular (Conchoecia,Buntonia) and small-sized (Pseudomonoceratina, Nigeroloxoconcha, Procytherura) ostracods from the basin or the outer shelf. Marker genera are less numerous in the circalittoral environment. Specific diversity is low to middle and the faunal density is low to high. The carapaces are smaller than in the infralittoral environment. The ornamentation is disordered and confused (?), punctuated, pitted, reticulated, sometimes absent or covered with a secondary ornamentation. The feeding is less abundant than in the infralittoral environment, and the ostracods live on sciaphilic plants. The decrease of dissolved oxygen leads to the monospecifism of Oertliella ? tarfayaensis. Different ways of life and moving can be found. Some ostracods are epibiontic (Eocytheropteron, Cythereis, Protocythere, Bythoceratina), some can swim (Nigeroloxoconcha, Procytherura, Pseudomonoceratina, Schuleridea, Dordoniella, Pontocyprella, Macrocypris), some are pelagic (Conchoecia). Introduction from the infralittoral environment is caused by saltation among thick ostracods and by suspension among globular and brittle forms.

Fluctuations of environmental factors as seen by means of statistical analyses in micropaleontological assemblages from a Liassic series

A comparative statistical study of foraminiferal and ostracode assemblages in Domerian marls from the Aquitaine basin (France) shows that the taxonomic structure of the populations fluctuates through time. Multiple Correspondences Analyses (M.C.A.) processing presence-absence data (table of taxa in the successive sample levels) were conducted. The first axis (F1) of this M.C.A. is related to faunal diversity and expresses a biotic capacity gradient. The F2 axis coincides with accomodation space and can be used to identify systems tracts and sequence boundaries. The F3 axis is interpreted as representing an oxygenation gradient. Short-term fluctuations at the systems tract or half systems tract level appear in the residuals of regressions and the distance between samples.

Apport des ostracodes à l’interprétation séquentielle du Crétacé inférieur (Berriasien–Valanginien) du bassin d’Essaouira–Agadir (Maroc)

Resume L’analyse de la faune d’ostracodes du Berriasien–Valanginien du bassin d’Essaouira–Agadir (Maroc) a permis de mettre en evidence une relation etroite entre l’evolution sequentielle de la serie (etablie sur la base de donnees sedimentologiques, biostratigraphiques et geochimiques) et l’evolution de parametres statistiques appliques aux ostracodes. Ainsi, le nombre d’individus et le nombre d’especes presentent des fluctuations comparables et suivent parfaitement l’evolution sequentielle de la serie. Les classes de frequence dominante et fortuite sont les plus significatives, le taux de renouvellement specifique montrant des valeurs extremes, des « pics » en limites de sequences et a la base des prismes transgressifs. Pour citer cet article : A. Rossi et al., C. R. Palevol 2 (2003) 133–141.

Ostracodes non marins du Crétacé supérieur des Hauts Plateaux méridionaux, Maroc oriental

Upper Cretaceous non-marine ostracods from the southern High Plateaus, eastern Morocco.The marls of the upper part of the Tigri Formation in the Upper Cretaceous of the southern High Plateaus, eastern Morocco, reveal non-marine ostracod faunas from freshwater to oligohaline environments. Despite the poor specimen preservation, 23 species belonging to 14 genera have been recognized. The generic assemblages show a global paleobiogeographic distribution both on Laurasia