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 s urveyed along the narrow SW Svalbard shelf. On this shelf, formation o f cold-water carbonate sediments occurs under glaciomarine environment al conditions. Mya truncata and Hiatella arctica colonized a soft glac io marine diamicton 3000-6000 years after the final retreat of the ice dome from the SW Svalbard shelf. Since 2600 yr B.P., an increase of al ong-shelf bottom currents washed out the fine terrigenous deposits lea ving behind a shelly lag-deposit and winnowed boulders on a morainic s helf topography. The most favourable depth interval promoting the esta blishment of an amalgamated bioclastic blanket is located in 50-80 m w ater depth. In this interval, strong bottom currents prevent sedimenta tion, thus, facilitating colonisation of filter-feeding benthic commun ities dominated by Balanus balanus and Chlamys islandica. Additional s keletal components are supplied by echinoderms, bryozoans, serpulids, brachiopods and gastropods. In shallower water depths, carbonate produ ction is hampered by intense iceberg-scouring and release of ice-rafte d debris from the still glaciated hinterland of Svalbard. In deeper wa ter (>80 m), olive grey muds with dispersed pebbles rich in benthic fo raminiferans, Clinocardium ciliatum and taxodont bivalves are present on all surveyed shelf banks. The deepest unit is a blue mud in water d epths > 120 m with benthic foraminiferans, taxodont bivalves and sipun culids. 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 r esting on tillites in the geological record.