CONTOURITES IN THE FRAM STRAIT

Multichannel seismic reflection profiles from the Fram Strait show many features that can be attributed to bottom-current influence on the sediments, by comparison with well-known contourite sequences elsewhere. A greater than 2 km thick contourite drift with a smooth internal reflection pattern is observed northwest of Svalbard. The currents here have probably been controlled by local topography. We interpret sequences with abundant diffractions in the broader basins to be current-related, probably deposited during periods of intensified circulation. The continental slopes on the Svalbard side have fairly continuous sequences, whereas the younger sequences on the Greenland lower slope onlaps the lowermost one. This can be attributed to differences in current regime, sediment supply, or margin subsidence. The contourites of the lower slope in the northeastern part of the strait (about 1000 m water depth) can be explained by long-term influence of the West Spitsbergen Current, but current-influenced patterns down to 3000 m water depth are not compatible with the weak deep-water circulation observed at present. The oldest contourites west of Svalbard are estimated to be of Late Miocene to Pliocene age (between 10 and 3 Ma), based on correlation to the DSDP Site 344 and inferred basement ages near the present plate boundary. Hiatuses may be present beneath the contourites. Tle onset of currents may be related to opening of the gateway between Greenland and Svalbard, to climatic cooling, and to palaeogeographic changes outside the Fram Strait. Contourite deposition has continued through the late Neogene and Quaternary, but vertical changes in the pattern suggest that current intensities have decreased through time.