Ecological distribution of Cenomanian terrestrial plants based on C-13/C-12 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 investigat e the presence of a palaeoenvironmental signal. The small intraspecies vari ations of delta(13)C values observed for most of the fossil leaves suggeste d that the isotopic signal had not been significantly altered. Hence, an is otopic approach was used as an attempt to assist in reconstructing the ecol ogical distribution of the flora. The C-13-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 delta(13)C values, all the plants collected could have been distributed along a decreasing salinity tr ansect from the lagoon to a flood plain. The predominant species, Eretmophy llum andegavense, a fossil ginkgo, exhibited a wide range of delta(13)C val ues. This could indicate that this taxon grew in a wide range of habitats w ith varying salinities. The origin of the organic matter appeared to be ter restrial with a major contribution from water-stressed plants such as Frene lopsis, as suggested by the similarity between delta(13)C values of the con ifer and the sedimentary organic matter. delta(13)C values of the sediment indicated stable palaeoenvironmental conditions during the deposition of th e 'Argiles du Baugeois' member. Hence, while detailed palaeovegetation reco nstructions are generally limited to the few deposits which present in-situ palaeoflora, the contribution of isotope geochemistry could allow reconstr uctions for a wider range of fossil plant deposits. (C) 1999 Elsevier Scien ce B.V. All rights reserved.