Bioclastic carbonate sediments on the southwestern Svalbard shelf

The poleward continuation of one of the largest known Arctic carbonate factories, the western Spitsbergenbank of the Barents Sea, has been surveyed along the narrow SW Svalbard shelf. On this shelf, formation of cold-water carbonate sediments occurs under glaciomarine environmental conditions. Mya truncata and Hiatella arctica colonized a soft glacio marine diamicton 3000-6000 years after the final retreat of the icedome from the SW Svalbard shelf. Since 2600 yr B.P., an increase of along-shelf bottom currents washed out the fine terrigenous deposits leaving behind a shelly lag-deposit and winnowed boulders on a morainic shelf topography. The most favourable depth interval promoting the establishment of an amalgamated bioclastic blanket is located in 50-80 m water depth. In this interval, strong bottom currents prevent sedimentation, thus, facilitating colonisation of filter-feeding benthic communities dominated by Balanus balanus and Chlamys islandica. Additional skeletal components are supplied by echinoderms, bryozoans, serpulids, brachiopods and gastropods. In shallower water depths, carbonate production is hampered by intense iceberg-scouring and release of ice-rafted debris from the still glaciated hinterland of Svalbard. In deeper water (>80 m), olive grey muds with dispersed pebbles rich in benthic foraminiferans, Clinocardium ciliatum and taxodont bivalves are present on all surveyed shelf banks. The deepest unit is a blue mud in water depths > 120 m with benthic foraminiferans, taxodont bivalves and sipunculids. Compared to Spitsbergenbank, carbonate production is much more restricted and impoverished on the SW Svalbard shelf, but is still an instructive modern example for the formation of skeletal carbonates resting on tillites in the geological record.