Reply to 'Challenges with dating weathering products to unravel ancient landscapes'

Abstract

<i>Introduction</i>: As the title of the correspondence by Fossen et al.1 suggests, determining the age of landscape elements of the Earth surface is difficult. We thus welcome the opportunity to clarify our arguments on the contentious themes touched upon by Fredin et al.2 The age of landscapes has been a recurring research topic for the last century. Often, landscape ages can be deduced indirectly through morphostratigraphic correlations leading to relative chronologies. However, when working in geological contexts where a sedimentary cover is not present1, and the traditional geochronological tools are not suitable, not only are absolute dates of etch surface formation essentially impossible to obtain, but even relative chronologies are challenging. In an attempt to circumvent this problem, we have applied an untested methodology to date pockets of weathering products at three different sites in Scandinavia (Ivö southern Sweden, Utsira High offshore Norway, Bømlo west Norway) by K-Ar dating of illite formed authigenically during the weathering of the crystalline host rock2. Our results support weathering in the Late Triassic at all studied localities.