Bioturbating animals control the mobility of redox-sensitive trace elements in organic-rich mudstone

Bioturbating animals modify the original mineralogy, porosity, organic content, and fabric of mud, thus affecting the burial diagenetic pathways of potential hydrocarbon source, seal, and reservoir rocks. High-sensitivity, synchrotron rapid scanning X-ray fluorescence elemental mapping reveals that producers of phycosiphoniform burrows systematically partition redox-sensitive trace elements (i.e., Fe, V, Cr, Mn, Co, Ni, Cu, and As) in fine-grained siliciclastic rocks. Systematic differences in organic carbon content (total organic carbon >1.5 wt%) and quality (D13Corg~0.6‰) are measured between the burrow core and host sediment. The relative enrichment of redox-sensitive elements in the burrow core does not correlate with significant neo-formation of early diagenetic pyrite (via trace metal pyritization), but is best explained by physical concentration of clay- and silt-sized components. A measured loss (~-15%) of the large-ionic-radius elements Sr and Ba from both burrow halo and core is most likely associated with the release of Sr and Ba to pore waters during biological (in vivo) weathering of silt- to clay-sized lithic components and feldspar. This newly documented effect has significant potential to inform the interpretation of geochemical proxy and rock property data, particularly from shales, where elemental analyses are commonly employed to predict reservoir quality and support paleoenvironmental analysis

Discovery and paleoenvironmental implications of a Zoophycos-group trace fossil (?Echinospira) from the Middle Pennsylvanian Sydney Mines Formation of Nova Scotia

The discovery of a Zoophycos-group trace fossil questionably attributed to Echinospira is reported from the Middle Pennsylvanian Sydney Mines Formation of Nova Scotia. Zoophycos-group trace fossils are composed of a central axis from which helicoidally arranged sheets of spreite emanate, giving the appearance of stacked cones. Such traces are commonly reported from marine paleoenvironments throughout the Phanerozoic. This occurrence, the first of its kind in the Maritimes Basin, provides further evidence for marine influence during the deposition of these dominantly terrestrial coal-bearing successions. RÉSUMÉ On signale la découverte d’un ichnofossile du groupe Zoophycos rattaché de façon douteuse à Échinospira dans la formation du Pennsylvanien moyen de Sydney Mines, en Nouvelle-Écosse. Les ichnofossiles du groupe Zoophycos sont constitués d’un axe central duquel émanent des feuilles de spréite disposées de façon héliocoïdale leur conférant l’aspect de cônes étagés. Ces ichnofossiles sont communément signalés dans les paléoenvironnements marins du Phanérozoïque. La présence de cet ichnofossile particulier, premier du genre dans le bassin des Maritimes, fournit une autre preuve de l’influence marine pendant la sédimentation de ces successions carbonifères en prédominance terrestres. [Traduit par la rédaction

First evidence for locomotion in the Ediacara biota from the 565 Ma Mistaken Point Formation, Newfoundland

Evidence for locomotion in the Precambrian fossil record is scant. Reliable Ediacaran trace fossils are all younger than 560 Ma, and consist of relatively simple horizontal burrows and trails from shallow-water deposits. Here we describe an assemblage of macroscopic locomotory traces from deep-water environments at Mistaken Point, southeastern Newfoundland, Canada, dated to ca. 565 Ma. These trails extend the record of complex trace fossils back into the earliest Avalonian biota. Our new evidence for large motile organisms on the seafloor at this time suggests that at least some of these early Ediacaran organisms, whose biological affinities are widely debated, could have been muscular and of metazoan grade