Deep-weathered rock in western Sweden

Abstract

Several sites with deep‑weathered rock covered by till have been found in western Sweden. All sites lie in glacial stoss‑ or lee‑side positions. The ma­terial is unconsolidated, in some cases glacially tectonized.

The weathered rock reveals neoformed minerals like smectite, kaolinite, and goethite. These minerals are typical for lateritic weathering which took place in southern Sweden during Triassic‑Tertiary times. Smectite may have formed under recent conditions, too.

By analysing the clay and silt fractions of the till, superimposing the deep weathered rock, it was found that products from the deep weathered rock, like smectite, kaolinite, and goethite, had been mixed into the till by glacial processes.

The 'survival' of these weathered rock masses from glacial erosion is mainly explained by referring to their stoss‑ and lee‑side positions in relation to the movements of the Quaternary ice‑sheets. This is also the case with other finds of deep‑weathered rocks beneath till, reported from southern Sweden in the literature. Glacial erosion decapitated the existing remains of the saprolite, since sheet‑wash, solifluction etc. had carried away its 'original' top‑layers during the transition between the Tertiary and the Quaternary.