Fjord infill in a high-relief area: Rapid deposition influenced by deglaciation dynamics, glacio-isostatic rebound and gravitational activity

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Abstract

Lyså, A., Hjelstuen, B. O. & Larsen, E. 2009: Fjord infill in a high-relief area: Rapid deposition influenced by deglaciation dynamics, glacio-isostatic rebound and gravitational activity. Boreas, 10.1111/j.1502-3885.2009.00117.x. ISSN 0300-9483.

Seismic profiles and gravity cores have been collected from the previously glaciated Nordfjord system on the west coast of Norway. The results give new information about the deglaciation history of the area and contribute to our understanding of fjord fill in high relief areas. During the last deglaciation, up to 360 m of sediments was deposited in the 135 km long fjord system. Shortly after the coastal area became ice-free, ∼12 300 14C years BP, the first ice-marginal deposits were formed, probably due to a minor glacier re-advance. The greatest volume of sediments in the fjord was deposited during the Allerød ice recession period, the Younger Dryas re-advance and the succeeding ice retreat period until the ice disappeared from the fjord in early Preboreal. During the Allerød, the fjord was ice-free and glaciomarine stratified sediments were deposited. The ice margin is suggested to have been located just west of Lake Strynevatnet before the advance during the Younger Dryas. In the late phase of the Younger Dryas, and within the succeeding ∼1000 years, the glacio-isostatic rebound was rapid, and extensive re-sedimentation took place. Slide activities continued into mid-Holocene, albeit with less intensity and were followed by normal and calm marine conditions that prevailed until the present. One huge rock avalanche into the fjord took place between 2200 and 1800 14C yr BP, probably triggering a tsunami and several slides in the fjord. Even though glacigenic sediments totally dominate in terms of sediment volume, the present study underlines the importance of re-sedimentation and other gravitational processes in such fjord settings.

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