Relief and saprolites through time on the Baltic Shield

Abstract

The relief of basement rocks in high latitudes has most often been interpreted as the result of glacial erosion, although over large areas its character of exhumed paleoplains has been known for a long time. The relief in the Precambrian basement of Sweden has therefore been analysed in relation to remnants of late Proterozoic and Phanerozoic cover rocks. Most of the shield was exposed in the late Proterozoic. The end result was an extremely flat surface, the primary peneplain. It was covered by Palaeozoic rocks, which preserved this surface until re-exposure. As a sub-Cambrian surface it makes up the present scenery in large parts of eastern and central Sweden. The South Swedish Dome is a key area for the geomorphic analysis of the shield, as it has Palaeozoic cover rocks on its northern and eastern slopes and Mesozoic rocks on its southern and western ones. Based on the experience from this area, classification of the relief in the whole country, and experiences from the tropics on relief evolution, two theoretical schemes were constructed for a discussion of the relief differentiation. The analysis of the relationship between relief, saprolite, and cover rocks through time led to the conclusion that the most important factor for the present relief differentiation is the time of exposure of the basement surface during the Phanerozoic. This has important applications for the evaluation of Phanerozoic crustal movements as well as implications for the assessment of glacial erosion. The approach is thought to be most valuable for comparative studies of shield geomorphology in general and with the Laurentian Shield in particular.