On– and Offshore Deep Weathered Basement Rocks, Norway

There has been an increasing awareness that surface processes next to tectonic processes have a large impact on the topography in Norway. Especially in the northern part in the Nordland county with its steep and high mountain chains, tectonic processes and erosion of the sedimentary succession seem not sufficient to explain the relief. Remnants of deeply weathered basement rocks indicate a deep alteration and later erosion of the bedrock and must be considered as another factor in the development of the relief. Weathered bedrock is also preserved offshore Norway, underlying large parts of the Mesozoic sedimentary rocks. A better understanding of the weathering processes and the distribution of deeply weathered zones onshore Norway is an important factor for society and economy in Norway. Offshore, weathered rocks can act as both reservoirs and migration routes for hydrocarbons. During a joint project of NGU and NPD comprehensive mapping of deep-weathering in Norway and resistivity measurements were carried out, investigating the processes and to estimate the magnitude of the weathering. We present results of the study from the Lofoten-Vesterålen and the Hamarøya area where rather thick layers of deep-weathered bedrock of up to 150 m thickness were observed.