The natural history of the Hardangerfjord 5. Studies of the deep-water sediments with the continuous seismic profiler

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Abstract
This paper reports the results of a low frequency, continuous seismic profiling study of the deep-water sediments in the Hardangerfjord near Norheimsund. Layers of sediment are revealed by echo sequences of slowly varying travel time which were observed in the deep central trench of the fjord. Echo sequences from the rock floor beneath the sediments vary more rapidly and can be traced continuously to the rock walls of the fjord. The sediments have a maximum estimated thickness of 80 to 145 meters and consist of four to six acoustically reflecting layers. The layers show evidence of compaction but are otherwise quite level, often having slopes less than 1:1000 from the horizontal which extend for several kilometers. A seismic profile along the entire length of the Maurangerfjord reveals a continuous record of the rock floor beneath the sediments and protruding through them. The sediment layers appear to be related between isolated ponds of sediment and their distribution suggests that they were supplied locally but were spread out extensively along the length of the fjord.