Palaeoecology of boreal invertebrate faunas from the Upper Jurassic of Central East Greenland

Abstract

The Upper Jurassic of Milne Land, Greenland, is a transgressive-regressive sequence ranging from offshore shallow sandbar complexes in the Late Oxfordian to outer shelf muds in the Kimmeridgian and Early to Middle Volgian. Within the Middle Volgian rapid shoreline progradation led to deposition of inner-shelf silts and nearshore sands. Within this envirobmental framework 22 benthic macroinvertebrate associations and several assemblages occur. They are dominated by suspension-feeding bivalves, less commonly by brachiopods or detritus-feeding serpulid polychaetes. Despite frequently low rates of sedimentation and plenty of suitable substrates, surprisingly few shells are bored or encrusted, which may reflect biogeographic factors. Although some inter- and intraspecific interactions are recorded, the associations are thought to have been largely controlled by environmental parameters. Low-diversity associations are related to low oxygen conditions at the sea floor or unstable, shifting substrates, but in some cases may have been due to biotic interactions. Levels with reduced rates of sedimentation and glauconite formation are characterized by epifaunal associations, those with higher rates of sedimentation by infaunal or semi-infaunal associations.The temporal and spatial distribution pattern of the benthic invertebrate fauna is fairly complex due to the interplay of several biotic and abiotic factors, the absence of strong environmental gradients in outer-shelf areas, and diagenetic overprint selectivity removing low-density faunas.Among bivalves, species replacement through time was, in most cases, ecological.