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Berit Oline Hjelstuen, University of Bergen (Norway)
Haflidi Haflidason, University of Bergen (Norway)
Hans Petter Sejrup, University of Bergen (Norway)
Astrid Lyså, Geological Survey of Norway (Norway)
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Fjords represent important repositories between land masses (source system) and the open ocean (sink systems). Newly collected high-resolution TOPAS profiles from the previously glaciated Nordfjord system, on the west coast of Norway, reveal sedimentary processes and depositional environments during a paraglacial time period in more detail than previously possible. The seismic data show that the fjord basins are characterized by a well-laminated lower unit that is overlain by acoustic transparent lensoidal bodies. We infer the lower unit, which is up to 350 m thick, to be composed of glacimarine/plumite-like sediments. The transparent bodies represent slide debrites that have volumes of up to 0.25 km3. The well-laminated sediments were deposited from the fjord mouth to the fjord head as the Fennoscandian Ice Sheet progressively retreated from the coast at c. 12.7 14C ka BP. The fjord system was then ice free for a short time period prior to the Younger Dryas readvance. The Younger Dryas ice sheet covered the inner fjord system, without evacuating the thick well-laminated sediment unit. We associate the overlying slide debrites, that are found in all fjord basins, to failure episodes related to the rapid isostatic adjustments that accompanied the withdrawal of Younger Dryas ice sheet. This implies that the well-laminated unit in Nordfjord has been deposited in only 1500-2000 years, and that sediment rates as high as 25 cm/yr may have existed during deposition. This high-rate environment might have promoted condition for the creep-like deformation features which we observed in the inner fjord system.
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