Paleobiology of the Neoproterozoic Svanbergfjellet Formation, Spitsbergen

A fossil Lagerstätte from the 700-750 Ma old Svanbergfjellet Formation of northeastern Spitsbergen offers a substantially enhanced view of late Proterozoic paleobiology. Fossils occur primarily as organic-walled compressions in shales and permineralizations in chert; secondary modes of preservation include bedding-plane imprints and mineral replacements in apatite and goethite(?). The depositional setting of all fossiliferous horizons is broadly peritidal with highest taxonomie diversity occurring in shallow subtidal settings; the details ofincluded fossil assemblages contribute to improved paleoecological resolution. The often distinct constituents of shale- and chert-hosted fossil assemblages appear to be a product of both paleoenvironment and fundamentally dissimilar taphonomic pathways, such that only forms with inferred wide ecological tolerance appear in both. Consideration of taphonomic processes also provides a variety of useful taxonomic insights, on the one hand permitting some resolution of so-called wastebasket taxa, such as Chuaria, and on the other acknowledging the taxonomic disparity that can occur in simple forms like Siphonophycus and Oscillatoriopsis. True multicellular (including coenocytic) eukaryotes are a conspicuous component of the Svanbergfjellet assemblage: of eight distinct taxa, one can be identified as a coenobial/colonial chlorocoecalean and three as filamentous siphonocladaleans (Chlorophyta). Other forms are problematic, but severaI show significant cell, or possibly tissue, differentiation. A review of Proterozoic multicellular organisms reveals that a coenocytic grade of organization was common among early metaphytes and supports the view that eellularity is a derived condition in many 'multicellular' lineages. Nineteen acritarch taxa are preserved in the Svanbergfjellet sediments. Ten of these show a readily identifiable ornamentation and contribute significantly to Neoproterozoic biostratigraphy; a world-wide and exclusively Late Riphean distribution of the acanthomorph Trachyhystrichosphaera aimika identifies it as a particularly valuable index fossil. The Svanbergfjellet fossil assemblage preserves a total of 63 distinct forms, of which 56 are treated taxonomically. As much as possible, principles of 'natura!' taxonomy are applied, such that taphonomic and ontogenetic variants are declined separate taxonomic status. Major taxonomic revisions are offered for the acritarchs Trachyhystrichosphaera and Chuaria as well as for the prokaryotic-grade filaments: Cephalonyx, Cyanonema, Oscillatoriopsis, Palaeolyngbya, Rugosoopsis, Siphonophycus, Tortunema, and Veteronostocale. Newly erected taxa include 7 new genera: Palaeastrum, Proterocladus, Pseudotawuia, Valkyria, Cerebrosphaera, Osculosphaera and Pseudodendron; 14 new species in 12 genera: Palaeastrum dyptocranum, Proterocladus major, Proterocladus minor, Proterocladus hermannae, Pseudotawuia birenifera, Valkyria borealis, Cerebrosphaera buickii, Osculosphaera hyalina, Pseudodendron anteridium, Dictyotidium fullerene, Germinosphaera jankauskasii, Trachyhystrichosphaera polaris, Siphonophycus thulenema and Digitus adumbratus; and 7 new combinations: Leiosphaeridia wimanii, Eoentophysalis croxfordii, Cephalonyx geminatus, Oscillatoriopsis amadeus, Siphonophycus typicum, Siphonophycus solidum and Tortunema Wernadskii.