The environmental significance of the trace fossil Rhizocorallium jenense in the Lower Triassic of western Spitsbergen

David Worsley, Atle Mørk
2001 Polar Research  
The 500 m thick Lower Triassic succession of western Spitsbergen comprises two shale-dominated formations, which both show upwardcoarsening motifs. These reflect repeated coastal progradations into a basin dominated by low energy fine-clastic sediments. The trace fossils Rhizocorallium jenense and Skolithos are found in the coarser parts of these units and variations in size and orientation of R. jenense give important palaeoenvironmental information. Rhizocorallium jenense occurs in
more » ... ated siltstones and sandstones, whose deposition interrupted prevailing intermediate energy levels. Size variations and trace fossil abundance suggest an optimal habitat in the shoreface zone, with poorer adaptation to both more offshore and shallower environments. Age-equivalent marine sediments on northeastern Greenland also contain local abundant occurrences of Rhizocorallium. These Arctic occurrences contrast with the same trace fossil's distribution in the Jurassic of Britain and France, where it characterizes shallower and higher energy environments; such sequences on Spitsbergen show an ichnofauna dominated by Skolithos and bivalve escape shafts. Orientations shown by the R. jenense U-tubes show a generally, but not solely, unimodal distribution, with the curved distal ends usually oriented toward onshore. Presumed aperture lineations show strongly unimodal trends, probably related to longshore currents. Burrows in beds at the top of individual storm lobe units show more complex patterns, probably reflecting both current and wave reworking following lobe abandonment. All finds suggest early colonization by the burrowing organisms. These were not followed by other burrowers, either because of the nutrient-poor nature of the sediment or because of high sedimentation rates.
doi:10.1111/j.1751-8369.2001.tb00037.x fatcat:u4xfripbrvcsfiqdyet2fpkdsm