Palaeoenvironments of vertebrates on the southern shore of Tethys: The nonmarine Early Cretaceous of Tunisia

Through the Late Jurassic and Early Cretaceous, the southern shore of the Tethys Ocean migrated north and south over short distances. These vicissitudes are documented in the 'continental intercalaire', a long series of mainly non-marine sediments deposited across North Africa. A combined taxonomic, physical and chemical taphonomic study provides independent lines of evidence for reconstruction of palaeoenvironments within this marginal marine setting. The Douiret, Chenini and Oum ed Diab formations from the Tataouine basin of southern Tunisia span the later part of the Early Cretaceous. Microvertebrates from four sites in these formations show different modes of physical abrasion, time averaging, and mixing, based on a taphonomic analysis using a combination of physical and chemical methods. The taxonomic composition of each assemblage, and trends in rare earth element (REE) compositions of bones, from each locality were used as independent lines of evidence to indicate differences in early depositional environments. The Jebel Boulouha assemblage (Douiret Formation) is interpreted as a terrestrial carbonate-rich environment with relatively little mixing. The Touil el Mra assemblage (Oum ed Diab Formation) suggests a marginal marine environment with some mixing of previously interred bones. The Oued el Khil assemblage (Chenini Formation) and the Oum ed Diab assemblage (Oum Ed Diab Formation) are more equivocal, suggesting mixed freshwater and marine influences. Interpreting salinity in marginal marine settings is difficult, and best attempted from multiple, independent lines of evidence. We suggest that REE geochemistry can contribute to palaeoenvironmental reconstruction when used in combination with other, independent physical, palaeontological and/or geochemical methods. (c) 2006 Elsevier B.V. All rights reserved.