Hervé Bocherens

Ecological distribution of Cenomanian terrestrial plants based on 13C/12C ratios

The Cenomanian lagoonal member of the `Argiles du Baugeois (Anjou, France) yielded a rich and exceptionally well-preserved fossil leaf flora. Stable carbon isotope ratios of fossil plants were measured in order to investigate the presence of a palaeoenvironmental signal. The small intraspecies variations of δ13C values observed for most of the fossil leaves suggested that the isotopic signal had not been significantly altered. Hence, an isotopic approach was used as an attempt to assist in reconstructing the ecological distribution of the flora. The 13C-enrichment of the fossil leaves suggested that the plants underwent water or salt stress. The occurrence of the conifer Frenelopsis suggested, at least locally, a saline environment such as a lagoon. According to their decreasing δ13C values, all the plants collected could have been distributed along a decreasing salinity transect from the lagoon to a flood plain. The predominant species, Eretmophyllum andegavense, a fossil ginkgo, exhibited a wide range of δ13C values. This could indicate that this taxon grew in a wide range of habitats with varying salinities. The origin of the organic matter appeared to be terrestrial with a major contribution from water-stressed plants such as Frenelopsis, as suggested by the similarity between δ13C values of the conifer and the sedimentary organic matter. δ13C values of the sediment indicated stable palaeoenvironmental conditions during the deposition of the `Argiles du Baugeois member. Hence, while detailed palaeovegetation reconstructions are generally limited to the few deposits which present in-situ palaeoflora, the contribution of isotope geochemistry could allow reconstructions for a wider range of fossil plant deposits.

Isotope reconstruction of plant palaeoecology. Case study of Cenomanian floras from Bohemia

Palaeoenvironments inferred from stable carbon isotope ratios of fossil plants collected from various environments of the Cenomanian of Bohemia were compared with palaeobotanical and sedimentological data to test the use of isotope ratios as a record of local palaeoenvironments and fossil-plant ecology. A number of isotope and biogeochemical patterns suggested that stable carbon isotope ratios in the Cenomanian plants from Bohemia have not been significantly affected by diagenesis. Stable carbon isotope ratios of the palaeoflora from one of the sections studied were used as a reference for a non-stressed habitat since both sedimentological and palaeobotanical evidence suggested that the fossil flora underwent no environmental stresses that could have influenced its δ13C values. Comparisons of δ13C values of the other palaeofloras with that of the reference section, allowed inference of the palaeoenvironmental stresses undergone by fossil plants. These palaeoenvironmental patterns deduced from 13C/12C ratios are in agreement with the palaeoenvironments previously reconstructed by sedimentological and palaeobotanical studies. Combining evidence from those studies with isotope data provided detailed insights into the palaeoecology of the plants studied. Finally, stable carbon isotope ratios allowed precise characterisation of the ecology of the best-represented species of the deposits studied, the ginkgoalean plant Eretmophyllum obtusum and the conifer Frenelopsis alata, which were quite common in the salt-marsh environments in Europe during the Cenomanian. Hence, stable carbon isotope ratios can help in evaluating the environmental stresses undergone by fossil plants and the combination of these results with palaeobotanical and sedimentological data can provide detailed insights into fossil-plant ecology.

Effects of fungal infection on lipid extract composition of higher plant remains: comparison of shoots of a Cenomanian conifer, uninfected and infected by extinct fungi

The lipid fraction extracted from uninfected shoots of a fossil conifer, Frenelopsis alata, was analysed by gas-chromatography‐mass-spectrometry, and compared with shoots of the same conifer infected by extinct epiphyllous fungi, so as to study the eAects of fungal infection on the chemical composition of extracts from higher plant remains. The extracts from the uninfected shoots appeared to be composed of (i) common constituents of higher plant lipids such as n-alkanes and fatty acids, (ii) elemental sulphur, and (iii) substantial amounts of terpenoids characteristic of conifers, such as cadalene, beyerane, dehydroabietane and related compounds. Comparison of this extract with that of fungalinfected shoots revealed, in addition to the aforementioned compounds, the presence of substantial amounts of hydroxysuccinic acid and functionalised benzoic compounds that were interpreted as degradation products of lignin by fungi. This study aAorded preliminary indications of the composition of extracts from higher plant remains infected by fungi. # 2000 Elsevier Science Ltd. All rights reserved.

Evolution of the chemical composition of Ginkgo biloba external and internal leaf lipids through senescence and litter formation

External and internal lipids were analysed in fresh, senescent and litter leaves of Ginkgo biloba to derive qualitative and quantitative information on the changes that occur during the very early stages of diagenesis, and to identify potential biomarkers of the only living Ginkgoale. Analysis of fresh leaves led to the identification of additional compounds, including several series of phenolic constituents, and showed differences between the external and internal lipids (absence/presence of some components, relative abundances and distributions of some series). Pronounced differences concerned with the evolution of content (as wt.% of whole leaves) were observed between the internal lipids (regular decrease from fresh to senescent and to litter leaves) and the external lipids (no significant changes in content). Molecular studies showed variations in the relative abundances and distributions of most constituents of G. biloba leaf lipids which reflect different degrees of stability during the first stages of diagenesis. It also appeared that (i) the phenolic components and the co-occurrence of α-tocopherol and nonacosan-10-ol could be useful biomarkers of G. biloba, and (ii) most of the internal lipids continue to be exported to the leaf surface where they are further degraded during senescence and litter formation.

Émergence de la production laitière au Néolithique ? Contribution de l'analyse isotopique d'ossements de bovins archéologiques

Resume Letude de la variabilite intra-individuelle de la composition isotopique en azote du collagene osseux sur une serie de mandibules de bœuf du site neolithique de Bercy (Paris, debut du IV e millenaire av. J.-C.) a montre que les jeunes bovins y etaient sevres a un âge compris entre 6 mois et 1 an. Ce resultat ne contredit pas linterpretation du pic de mortalite des individus âges de 6 a 12 mois, mis en evidence sur le profil dabattage des bovins de ce site, comme un pic dabattage ≪ post-lactation≫, qui pourrait etre lindice de lorientation de leconomie vers lexploitation du lait.

Comportements alimentaires au Moyen Âge à Grenoble : application de la biogéochimie isotopique à la nécropole Saint-Laurent (XIIIe–XVe siècles, Isère, France)

Abstract Isotopic analysis of 13 C and 15 N of 47 bones from Saint-Laurent de Grenoble cemetery (Grenoble, Isere), from the end of medieval period (XIIIth–XVth centuries AD) allowed to define the food status of animals with regard to the humans and to discuss the variability amongst adults. Adults who died young and those with small stature may have had diets poor in animal protein. The consumption of animal proteins was more important in the XVth than in the XIVth century and could illustrate a typical urban food economy providing its population with a more diversified diet than in rural areas.

Comparison of leaf lipids from a fossil ginkgoalean plant and its extant counterpart at two degradation stages: diagenetic and chemotaxonomic implications

Comparative characterisation of total lipids from fresh leaves and leaves from litter of Ginkgo biloba demonstrated that all lipid constituents were degraded during the early stages of diagenesis. However, as shown by calculation of degradation levels, some of these compounds were preferentially degraded and a stability scale was established for G. biloba leaf lipids. Leaf lipids preserved in Eretmophyllum andegavense, a ginkgoalean plant of Cenomanian age, appeared less complex than those of G. biloba, its extant counterpart. The presence of dimethoxyalkylcoumarins, characteristic constituents of G. biloba, confirmed on chemical grounds the phylogenetic link between both ginkgoalean plants; it also revealed a relatively high degree of preservation of some lipids of E. andegavense.