Sedimentological and geochemical environment of the Fugløy Reef off northern Norway

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Abstract

A number of reefs are found along the coast of northern Norway, and a cluster of particularly high reefs off Troms County at 70°N are known collectively as the Fugløy Reef. The reefs, up to 40 m high and more than 200 m wide, consist mainly of the reef-building Lophelia pertusa. Most of the reefs identified in the study area are located on moraine ridges in water depths of 140–190 m, and in water masses dominated by the relatively warm and saline Norwegian Current. Several of the reefs are located on the flanks of channels incising the moraine highs, where currents are tidally dominated and periodically reach velocities of 30 cm/s. Gravity cores were acquired from the reefs and their surroundings, and thorough analyses of the sampled sediments provide valuable information about three (paleo-) sedimentary environments surrounding the reefs. The immediate vicinity of the reefs consists of coarse and unsorted deposits that are interpreted to be moraine material deposited by the retreating inland ice. Elevated current velocities have prevented fine sediments from settling since the ice retreated. The second province is a pockmarked basin at water depths down to ∼300 m. Gravity cores from the basin reveal silty sand deposits of more than 4 m thickness representing postglacial sedimentation in the area. Gas analyses reveal that the hydrocarbons found in the sediments clearly are of biogenic origin, although it is somewhat enigmatic whether biogenic gas is the sole driving force behind the pockmarks in the area. No direct link between the reefs and the pockmarks is found. The third sedimentary province is characterised by resedimentation of coral debris, clearly illustrated by sorted deposits and U/Th-datings from the allochthonous deposits. Remobilisation of coral debris is modest in areal extent, but an important mechanism linked to the occurrence of the coral reefs.