The strandflat is the up to 60 km-wide flat lowland and shallow-sea erosion surface extending for 1800 km along the coast of the Norwegian glaciated passive margin. However, after more than one hundred years of study its age of formation and regional variation in height remain obscure. Here, I link offshore dated surfaces to the strandflat to give insight on its age and processes of formation.
I conclude that the strandflat was formed during the last 2.6 million years because linearly extended, pre-Quaternary, offshore surfaces are intersected by, and hence predate, the strandflat. Massive glacial erosion and transport shaped onshore and offshore landscapes, but waves and other levelling erosional processes gradually transformed this glaciated landscape to a strandflat. A wide strandflat could form because the coastline was highly segmented, basement rock weakened by brittle faults and fractures and the coastal zone remained fixed. When the land was glaci-isostatically depressed, but with the icefront still in the fjords, waves could cut the cliffs on the islands and inner strandflat into a wider platform. The strandflat is widest and flattest along the mid-Norwegian margin. The more irregular strandflat along the west coast of southern Norway is a paleo-strandflat that was modified by erosion after the Norwegian Channel was formed (~0.8 Ma). Flexural isostatic subsidence from the weight of the North Sea Fan and Bjørnøya Fan extends to the coast of Stad and Troms, respectively, where the strandflat is below sea level. The strandflat in Lofoten and Vesterålen, rising northwards from submerged to exposed, is limited to subcropping basement.
No strandflat exists around the coasts of southern Norway and Finnmark.