Ice marginal deposits
Ice marginal deposits appear as ridges on the seabed, where currents and waves have winnowed away fine material so that only coarse-grained sediments are left behind. Near the end of the last glaciation, there were pauses and minor advances during retreat that left ice marginal deposits, both big and small, in the fjords and along the coast. Ice marginal deposits include terminal moraines and glaciofluvial sediments. Moraines usually contain poorly sorted sediments with a mixture of grain sizes, while glaciofluvial deposits are made up of well sorted sand and gravel.
Due to continental uplift after the last glaciation, many ice marginal deposits are today found on dry land, while others may be found in shallower water than where they were formed. Wave and current action has winnowed the sediments, resulting in the formation of pebbly beaches and beach ridges and the deposition of finer material in deeper water. In the deep fjords, ice marginal deposits are commonly covered with finer-grained sediments.
Mapping reveals that the ice marginal deposits are found in many fjords. The largest of such deposits was formed during the Younger Dryas, 10 000 years ago, and these deposits follow the entire coast line in a more-or-less continuous manner. In this period, the Raet moraine in Vestfold and the Tautra Ridge in the Trondheimsfjord was deposited. The Tautra Ridge has been designated by Norwegian authorities as a protected area due to its species-rich coral reef, which emerged due to the underlying geological substrate and ocean currents. The submarine continuation of Raet is found in Jomfruland (Telemark) and Tromlingen (Aust-Agder). Large ice marginal deposits are also found at Lista (Vest-Agder), Jæren (Rogaland), outer Hardangerfjord (Hordaland), the islands north of Ålesund, as well as several other places in Norway.
The biological diversity of ice marginal deposits has yet to be fully mapped. These substrates stand out from their surroundings, and a variety of flora and fauna is found on these deposits compared to adjacent areas.