Mid-Neogene Mediterranean marine-continental correlations: an alternative interpretation

Recent revised magnetostratigraphic and astrochronologic calibrations of several calcareous planktonic microfossil datum events (in particular Coccolithus miopelagicus and Neogloboquadrina acostaensis) combined with our magnetobiostratigraphic investigation of a 10 m-thick section at Ecotet, near Lyon (France), in which terrestrial micromammals (Vallesian Zone MN9) are intercalated with calcareous nannoplankton and planktonic foraminifera belonging to Zones NN6-NN8 and N14-15 (=M11 and M12), respectively, lead us to question the recent recalibration by Krijgsman et al. [(1996) Eart Planet. Sci. Lett. 142, 367-380) of the Aragonian/Vallesian (MN7-8/MN9) boundary with Chron C5r.1r (~11.1 Ma) and the lower/upper Vallesian (MN9/10) boundary with Chron C4Ar.2n (~9.6-9.7 Ma). Ecotet, with a uniform reverse polarity, is shown to be assignable uniquely to Chron C5r. Interregional correlation of Ecotet with Mediterranean terrestrial stratigraphies indicates that Progonomys (whose First Occurrence (FO) has been traditionally placed in Mediterranean Mammal Zone MN10) was already present in Mediterranean Zone MN9 at ~11.4 Ma and did not experience a 2 million-year delay in its putative prochoresis from Asia

Direct ESR dating of the Pleistocene vertebrate assemblage from Khok Sung locality, Nakhon Ratchasima Province, Northeast Thailand

We report here the first direct dating study of the faunal assemblage from Khok Sung locality, Thailand. This palaeontological site is of great biochronological, palaeoenvironmental and biogeographical significance. Firstly, it has yielded a rich and diversified Pleistocene vertebrate fauna with up to 15 mammalian species from 13 genera, 10 reptile species, as well as fish and bird remains. Interestingly, while most of the mainland Southeast Asian Pleistocene mammal fossils originate from cave deposits, the Khok Sung fossil layer is located within an 8 m thick fluvial terrace. Secondly, it is geographically located in an area of major importance for reconstructing the migration pathway of large mammals between South China and Java. Combined US-ESR dating of five teeth provides two possible ages of 130 - 29 ka and 217 - 36 ka for the fossils. The reason for the occurrence of these two age groups lies in the fact that it was not possible to obtain sediments that were directly associated with the measured samples, nor was it possible to carry out in situ gamma dose rate measurements due to the high water level. Sediment samples recovered from museum specimens show significantly variable concentrations of radioelements. Both options are equally plausible, as independent methods did not provide firm evidence favouring one or the other age range. The results illustrate the intrinsic limitations of the ESR dating method when fossil teeth are not collected in situ during the excavation. Regardless whether the age of the Khok Sung fauna corresponds to MIS 7 or early MIS5, it is nevertheless one of the oldest assemblages directly dated in the region. Further efforts are required for more accurate fossil identification and attribution and for additional numerical dating in this region to improve the biochronological framework of the Pleistocene mammalian faunas in Southeast Asia, which presently remains quite imprecise.Aspects of this study have been funded by the Australian Research Council Future Fellowship grant FT150100215 granted to M.D., an ANU-CSC Scholarship to F.F., and by the C.N.R.S. “Eclipse” Program and the Department of Mineral Resources (Bangkok)

Presence of a Gomphotheriidae indet. (Proboscidea, Mammalia) in the Vallesian fauna of Afoud AF6 (Ait Kandoula Basin, Morocco), inferred from the enamel microstructure of a molar chip

International audienceThe Ait Kandoula basin is one of the richest Miocene micromammals bearing areas known in the South of the High-Atlas, whereas the large mammal remains are scarce. The Afoud section in the center of the basin is well calibrated with the Geomagnetic Polarities Time Scale (KC95), and shows a succession of six fossiliferous layers. Beside rodents, the Aloud AF6 layer yields among some large mammal remains, a proboscidean identified as a Gomphotheriidae indet. from the enamel microstructure of a molar chip. This determination is grounded on the thickness of the enamel, on the prisms type, on the thinness and characteristics of the 3D zone and outside on the preferential course of the prisms. (c) 2006 Elsevier SAS. Tous droits reserves

Paléontologie systématique des lagomorphes du Miocène supérieur du bassin d’Aït Kandoula (Maroc)

La présence du genre Prolagus Pomel, 1853 en Afrique du Nord est l’un des arguments les plus puissants démontrant l’existence d’échanges fauniques entre l’Europe et l’Afrique. Les plus vieux restes de Prolagus africains ont été trouvés dans la localité Messinienne d’Afoud, au sein du bassin d’Aït Kandoula (6,2 Ma), et ils ont été identifiés au cours de précédentes études comme appartenant à l’espèce Prolagus michauxi López-Martínez, 1975. Le matériel dentaire déjà analysé venant des niveaux AF12-1 et AF12-2, ainsi que le nouveau matériel collecté par la suite dans ces mêmes niveaux, constituent la base de la présente étude systématique. Cette abondance de matériel nous permet de confirmer la présence d’une unique espèce de Prolagus dans le site d’Afoud, P. michauxi. Cependant, l’attribution à P. michauxi doit être considérée avec prudence, étant donné la ressemblance morphologique évidente avec l’espèce Prolagus sorbinii Masini, 1989. Ces résultats sont en accord avec les scénarios impliquant la migration de l’espèce P. michauxi depuis le Sud de l’Europe vers l’Afrique du Nord. En plus des restes de Prolagus, des dents jugales de Leporidae ont été trouvées et cela constitue la plus vieille occurrence de ce groupe au Maroc.The occurrence of the genus Prolagus Pomel, 1853, in North Africa provides some of the strongest evidence for the existence of faunal exchanges between Europe and Africa. The oldest African Prolagus remains have been reported from the Messinian locality of Afoud in the Aït Kandoula Basin (6.2 Ma), identified during previous studies as the species Prolagus michauxi López-Martínez, 1975. Dental material already analyzed from the AF12-1 and AF12-2 levels and new material collected subsequently from the same levels form the basis of the current systematic study. This abundant material allows us to confirm the presence of a single Prolagus species in the Afoud locality, P. michauxi. However, this species’ attribution to P. michauxi must be considered cautiously, given its evident morphological resemblance to Prolagus sorbinii Masini, 1989. These results are consistent with scenarios implying the migration of P. michauxi from Southern Europe to North Africa. In addition to the Prolagus remains, cheek teeth of Leporidae have been found and this is the oldest occurrence of this group in Morocco.</p

Incisor enamel microstructure of hystricognathous and anomaluroid rodents from the earliest Oligocene of Dakhla, Atlantic Sahara (Morocco)

International audienceSeven hystricognaths and five anomaluroids have been recently described from the earliest Oligocene of the Dakhla(DAK C2) region of Morocco, based primarily on isolated cheek teeth. Here, we analyzed the enamel microstructureof thirty associated isolated fragments of incisors. Among these specimens, only three display an early stage ofuniserial Hunter-Schreger bands (HSBs), with mostly a single prism per band, but also occasionally two prisms perband (in two specimens), and a thin interprismatic matrix (IPM) that runs parallel to the prism direction, therebydocumenting incisors of anomaluroids. All other sampled incisors display an enamel with multiserial HSBs, therebydocumenting hystricognaths. For these latter, we recorded primarily an IPM crystallite arrangement describing thesubtype 2 of multiserial HSBs, but with variation including a wide amplitude in the angle (acute) formed betweenthe crystallites of IPM and those of the prisms, some variations in the frequency of the IPM sheet anastomoses, inthe number of prisms per HSBs, and variations in the inclination of the HSBs. The absence of the subtypes 2–3 and3 of multiserial HSBs in DAK C2 suggests that African hystricognathous rodents had still not achieved these mostresistant multiserial HSBs at that time. The drier, cooler climatic regime of the early Oligocene, having increased thefragmentation and opening of habitats, might have played a role in the subsequent selection of taxa having acquireda more resistant incisor enamel

Earliest Oligocene hystricognathous rodents from the Atlantic margin of northwestern Saharan Africa (Dakhla, Morocco): systematic, paleobiogeographical, and paleoenvironmental implications

International audienceHystricognathous rodents are among the most common members of African mammal faunas of the mid-Paleogene, but their record has so far remained limited to North and northeast Africa. Here we report the first Paleogenerecord of hystricognaths from the Atlantic margin of North Africa. The fossils come from the westernmost part of the Sahara,east of the Dakhla peninsula, Morocco, from estuarine deposits dating to the earliest Oligocene (Dakhla level C2 [DAK C2]).Several tens of isolated teeth plus three jaw fragments document seven species of hystricognaths (Gaudeamus cf. aslius, G. cf.hylaeus, Phenacophiomys occidentalis, gen. et sp. nov., Birkamys aff. korai, Mubhammys atlanticus, sp. nov., Neophiomysminutus, sp. nov., and ?Phiocricetomys sp.). Despite the extensive east-west geographic distance, the majority ofhystricognath taxa recorded in DAK C2 document primarily close relatives of taxa that are known from a latest EoceneEgyptian locality (L-41) and from early Oligocene localities of both Egypt and Libya. This highlights the widespread eastwestdistribution of hystricognaths across North Africa, a distribution that reflects the existence of roughly similar tropicalenvironmental conditions in northern latitudes of Africa at that time. The presence of seven hystricognath species plus fiveanomaluroid species in sympatry during the earliest Oligocene demonstrates that rodents were particularly diverse near theglobal cooling recorded at the Eocene-Oligocene transition. We describe and compare the species and new species ofhystricognaths with their sub-coeval counterparts from northern and northeastern Africa and then discuss thepaleobiogeographic and paleoenvironmental implications of that discovery

La dislocation de la plateforme carbonatée dévonienne de la Meseta marocaine dans le Maroc central occidental

Dislocation of the Devonian carbonate platform of the moroccan Meseta in western central Morocco. Lithostratigraphic and sedimentological studies of Devonian strata in the western central Morocco show that a carbonate platform was progressively built-up in this area during the Lower Devonian (individualisation stage). By Middle Devonian time, this platform was completly established to be subsequently dismantled by Upper Devonian tectonic movements following the opening of basins in central Morocco.L'étude lithostratigraphique et sédimentologique des terrains dévoniens du Maroc central occidental permet de mettre en évidence l'installation progressive dès le Dévonien inférieur d'une plate-forme carbonatée (stade d'individualisation) dont la maturation s'affirme au Dévonien moyen. A partir du Dévonien supérieur, cette plate-forme est le siège d'une importante dislocation interprétée comme induite par des mouvements tectoniques liés à l'ouverture de bassins dans le Maroc central pendant cette époque.Chakiri S., Benammi Mouloud, Tayebi Mohamed, Tahiri Abdelfattah. La dislocation de la plateforme carbonatée dévonienne de la Meseta marocaine dans le Maroc central occidental. In: Géologie Méditerranéenne. Tome 28, numéro 3-4, 2001. pp. 181-191

Preliminary magnetostratigraphic study of the Late Cretaceous dinosaur site from Villeveyrac-Meze Basin, southern France

International audienceA magnetostrati graphic study was performed on continental Upper Cretaceous beds in the L'Olivet quarry, Villeveyrac-Meze Basin (Herault, France). Nearly all specimens subjected to progressive thermal demagnetization procedures exhibit opposite polarities for the low- and high-temperature magnetization components. The high-temperature component shows reverse polarity, characteristic of the Late Cretaceous magnetization, which is well isolated between 200 degrees and 450 degrees C. The overall mean paleomagnetic direction (incl. = -39.1 degrees, decl. = 160.7 degrees, k = 15, a(95) = 10) suggests a counterclockwise vertical axis rotation of about 15.1 degrees +/- 8.3 with respect to the expected Late Cretaceous direction calculated from the Eurasian polar wander curve (incl. = -49.0 degrees, decl. = 174 degrees). Combined with local biostratigraphic data, the L'Olivet sequence can be correlated with polarity chron C33.lr, corresponding to the Early Campanian with an age of 83.5 to 79.5 Ma

Earliest Oligocene estuarine deposits from Dakhla (Morocco) yield the first Paleogene rodent assemblage of the Atlantic margin of Northwestern Saharan Africa: paleobiogeographical and paleoenvironmental implications

International audienc