Didier Néraudeau

Late Permian–Middle Jurassic lithospheric thinning in Peru and Bolivia, and its bearing on Andean-age tectonics

Abstract Integrated studies and revisions of sedimentary basins and associated magmatism in Peru and Bolivia (8–22°S) show that this part of western Gondwana underwent rifting during the Late Permian–Middle Jurassic interval. Rifting started in central Peru in the Late Permian and propagated southwards into Bolivia until the Liassic/Dogger, along an axis that coincides with the present Eastern Cordillera. Southwest of this region, lithospheric thinning developed in the Early Jurassic and culminated in the Middle Jurassic, producing considerable subsidence in the Arequipa basin of southern Peru. This ∼110-Ma-long interval of lithospheric thinning ended ∼160 Ma with the onset of Malm–earliest Cretaceous partial rift inversion in the Eastern Cordillera area. The lithospheric heterogeneities inherited from these processes are likely to have largely influenced the distribution and features of younger compressional and/or transpressional deformations. In particular, the Altiplano plateau corresponds to a paleotectonic domain of “normal” lithospheric thickness that was bounded by two elongated areas underlain by thinned lithosphere. The high Eastern Cordillera of Peru and Bolivia results from Late Oligocene–Neogene intense inversion of the easternmost thinned area.

Phase contrast X-ray synchrotron imaging: opening access to fossil inclusions in opaque amber.

A significant portion of Mesozoic amber is fully opaque. Biological inclusions in such amber are invisible even after polishing, leading to potential bias in paleoecological and phylogenetic studies. Until now, studies using conventional X-ray microtomography focused on translucent or semi-opaque amber. In these cases, organisms of interest were visualized prior to X-ray analyses. It was recently demonstrated that propagation phase contrast X-ray synchrotron imaging techniques are powerful tools to access invisible inclusions in fully opaque amber. Here we describe an optimized synchrotron microradiographic protocol that allowed us to investigate efficiently and rapidly large amounts of opaque amber pieces from Charentes (southwestern France). Amber pieces were imaged with microradiography after immersion in water, which optimizes the visibility of inclusions. Determination is not accurate enough to allow precise phylogenetic studies, but provides preliminary data on biodiversity and ecotypes distribution; phase contrast microtomography remains necessary for precise determination. Because the organisms are generally much smaller than the amber pieces, we optimized local microtomography by using a continuous acquisition mode (sample moving during projection integration). As tomographic investigation of all inclusions is not practical, we suggest the use of a synchrotron for a microradiographic survey of opaque amber, coupled with microtomographic investigations of the most valuable organisms.

Découverte d’un dépôt paralique à bois fossiles, ambre insectifère et restes d’Iguanodontidae (Dinosauria, Ornithopoda) dans le Cénomanien inférieur de Fouras (Charente-Maritime, Sud-Ouest de la France)

Resume Un gisement paralique inedit, d’âge Cenomanien inferieur, avec du bois fossile, de l’ambre insectifere et des restes de vertebres, a ete decouvert sur l’estran de la presqu’ile de Fouras (Charente-Maritime, France), a la suite d’une tempete qui a temporairement ote du littoral les nappages de cordons sableux et de vasieres. L’assemblage de bois fossiles contient trois taxons de coniferes ( Agathoxylon , Podocarpoxylon , Brachyoxylon ) et un Ginkgoxylon . Les insectes de l’ambre correspondent a des Dipteres, des Hymenopteres et des Homopteres. Les restes de vertebres sont principalement representes par des carapaces de tortues terrestres (Solemydidae), des vertebres de serpents ( Simoliophis ) et des ossements de dinosaures, appartenant probablement au genre Iguanodon . Pour citer cet article : D. Neraudeau et al., C. R. Palevol 2 (2003).

New Psychodids from the Cretaceous Ambers of Lebanon and France, with a Discussion of Eophlebotomus connectens Cockerell, 1920 (Diptera, Psychodidae)

Abstract Two new psychodid flies, Eophlebotomus gezei sp. nov. and E. carentonensis sp. nov., are described from Lebanese and French Lower Cretaceous ambers. They are considered here to form part of the same genus as the Upper Cretaceous Burmese amber, Eophlebotomus connectens Cockerell, 1920. These discoveries allow the description of the antenna and male genitalia of this enigmatic genus. Although the new species of Eophlebotomus share numerous characters with the Phlebotominae, especially the male genital structures, we retain this genus in the stem-group of the Sycoracinae and Trichomyiinae.

Un faciès de type falun dans le Cénomanien basal de Charente-Maritime (France)

Resume Des depots calcareo-sableux et coquilliers non consolides du Cenomanien basal charentais (SO France), riches en mollusques, en echinodermes et en microrestes de vertebres, sont definis comme un exemple remarquable de faluns cretaces. Une description lithologique de ces faluns cenomaniens est proposee pour deux gisements de reference (Archingeay et Cadeuil, Charente-Maritime) et l’inventaire de leur faune caracteristique est detaille, notamment pour les mollusques, les echinodermes et les vertebres. Les caracteristiques lithologiques et faunistiques de ces faluns cenomaniens sont ensuite interpretees en termes paleogeographiques et paleoclimatiques.

Evidence for marine microfossils from amber

Amber usually contains inclusions of terrestrial and rarely limnetic organisms that were embedded in the places were they lived in the amber forests. Therefore, it has been supposed that amber could not have preserved marine organisms. Here, we report the discovery amber-preserved marine microfossils. Diverse marine diatoms as well as radiolarians, sponge spicules, a foraminifer, and a spine of a larval echinoderm were found in Late Albian and Early Cenomanian amber samples of southwestern France. The highly fossiliferous resin samples solidified ≈100 million years ago on the floor of coastal mixed forests dominated by conifers. The amber forests of southwestern France grew directly along the coast of the Atlantic Ocean and were influenced by the nearby sea: shells and remnants of marine organisms were probably introduced by wind, spray, or high tide from the beach or the sea onto the resin flows.

The oldest ant in the Lower Cretaceous amber of Charente-Maritime (SW France) (Insecta: Hymenoptera: Formicidae)

Gerontoformica cretacica n. gen., n. sp., until now the oldest known ant, is described after a putative worker specimen, from the Uppermost Albian amber of France. Although its characters are those of modern ants, it does not fit in any recent ant subfamilies.

Taphonomy and palaeoecology of mid-Cretaceous amber-preserved microorganisms from southwestern France

ABSTRACT The investigation of microorganisms preserved in amber from Charente-Maritime (southwestern France) provides new insights into the mid-Cretaceous amber forest ecology. Amber from the localities of Archingeay-Les Nouillers and Cadeuil is unique due to the plethora of microinclusions and macroinclusions as well as the preservation of litter organisms. Soil microorganisms such as actinomycetes, sheathed prokaryotes, carnivorous fungi (Ascomycota), algae, testate amoebae and nematodes indicate that the resin solidified in terrestrial or limnetic-terrestrial microhabitats on the forest floor. Furthermore, arboreal and even marine microorganisms are preserved in the amber. This micro-assemblage suggests that the amber forest was located close to the sea shore or was at least temporarily under marine influence.

Changing biodiversity of Mediterranean irregular echinoids from the Messinian to the Present-Day

Morphological and palaeoecological changes in irregular echinoid diversity during the Late Miocene Messinian stage have been analysed at the scale of the Sorbas Basin of southeast Spain. Biometrical and statistical analyses established the validity of species differentiation. An example is given for Messinian, Pliocene and Recent Schizaster species: S. saheliensis and S. canaliferus. Palaeoecological analyses show that irregular echinoid faunas record environmental changes, especially sea-level variations, with contrasting ecomorphological gradients for deepening and shallowing trends. Deepening is indicated by the stratigraphic succession of Clypeaster altus, associated Clypeaster marginatus^Spatangus^Schizaster and then Brissopsis species whereas shallowing is indicated by the opposite succession. The survival of Brissopsis, typically a stenohaline and relatively deep marine organism, in the marls interbedded within the uppermost Messinian gypsum of the Sorbas Basin testifies to the existence of marine connexions between this basin and other Mediterranean marine areas during the end of the evaporitic episode. Tabulation of irregular echinoid species diversity at eight time intervals between the Tortonian/Messinian boundary and the present-day (inclusive) for the Mediterranean Basin as a whole indicates a progressive increase in diversity from the latest Tortonian to the upper part of the pre-evaporitic Messinian before a fall in diversity during the salinity crisis. However, survivals after the crisis are very numerous, representing 78% of the maximum pre-evaporitic value.

The oldest modern therian mammal from Europe and its bearing on stem marsupial paleobiogeography

We report the discovery of mammalian tribosphenic teeth from the basal Cenomanian of southwestern France that we refer to a new primitive marsupial-like form identified as a basal taxon of Marsupialiformes, a new clade recognized here to include the crown group Marsupialia and primitive stem lineages more closely related to Marsupialia than to Deltatheroida. Arcantiodelphys marchandi gen et sp nov. shares several significant marsupial-like features (s.l.) with marsupialiform taxa known from the North American Mid-Cretaceous. Among marsupialiforms, it shows a closer resemblance to Dakotadens. This resemblance, which is plesiomorphic within “tribotherians,” makes Arcantiodelphys one of the most archaic known Marsupialiformes. Moreover, Arcantiodelphys is characterized by an original and precocious crushing specialization. Both the plesiomorphic and autapomorphic characteristics of Arcantiodelphys among Marsupialiformes might be explained by an Eastern origin from Asian stem metatherians, with some in situ European evolution. In addition, the presence of a mammal with North American affinities in western Europe during the early Late Cretaceous provides further evidence of a large Euramerican biogeographical province at this age or slightly before. Concerning the paleobiogeographical history of the first stem marsupialiforms during the Albian–Cenomanian interval, 2 possible dispersal routes from an Asian metatherian ancestry can be proposed: Asia to Europe via North America and Asia to North America via Europe. The main significance of the Archingeay-Les Nouillers mammal discovery is that it indicates that the beginning of the stem marsupialiforms history involved not only North America but also Europe, and that this early history in Europe remains virtually unknown.