Grès à Voltzia: Preservation
in Early Mesozoic Deltaic
and Marginal Marine Environments
THE GRÈS À VOLTZIA (VOLTZIA SANDSTONE) OF NORTH eastern France, named after the abundant remains of the conifer Voltzia heterophylla, has become famous as a Lagerstätte in which a large number of invertebrates–including jellyfish, annelid worms, spiders, insects, and crustaceans–exhibit a high degree of soft-bodied preservation. The Grès à Voltzia is the uppermost formation of the Buntsandstein (Triassic) of continental Europe, and its depositional environment records the gradual change of a deltaic setting to a marginal marine environment (Gall 1971, 1985; Gall, Grauvogel-Stamm, and Papier 1995). The lower part of the Grès à Voltzia, the Grès à meules, represents mainly deltaic environments, whereas the upper Grès à Voltzia, the Grès argileux, marks the beginning of the marine Muschelkalk transgression (Gall 1985; Gall, Grauvogel-Stamm, and Papier 1995). Soft-part preservation of fossils is restricted to certain layers within the Grès à meules, and this chapter, therefore, concentrates on the lower Grès à Voltzia.
The complex depositional environment of the Grès à Voltzia is expressed in several distinct sedimentary facies, each with its characteristic floral and faunal associations (Gall and Grauvogel-Stamm 1984; Gall 1985) These include (1) large sandstone lenses containing poorly preserved plant remains and bones of stegocephalid amphibians and representing rapid accumulation of deposits in fluvial channels; (2) thin intercalated lenses of green silty claystone deposited in stagnant waters of