SOILS AS A MARKER OF TIME: TAKING GEOMORPHIC CONTEXT INTO ACCOUNT (Invited Presentation)

Soils that have not yet fully adapted to their climatic, geomorphic and lithological condition, can be used as markers of time. I will first briefly review various properties of such non-equilibrium soils that can be used for this purpose, and indicate the typical timescales over which they can be used. I will then use two case studies, one from the Colorado Rocky Mountains, and one from Spitsbergen, to illustrate how topographic position can and must be accounted for in such studies. In the Rocky Mountains, properties from 9 soil profiles were used to attempt to shed light on the relative age of glacial and periglacial landforms from the Bull Lake glaciation or younger. This age had formerly been controversially discussed. On Spitsbergen, properties of 30 soils on ridge and trough positions within a series of Holocene marine terraces were used to constrain a soil-landscape evolution model. Both studies clearly show that soil properties not only vary between soils of different age, but also within groups of soils of similar age – and that topographic position is a main determinant for the latter variation. The reason for this is clear: soils in different parts of the landscape develop at different speeds and in different directions. Implications for the use of soils as markers of time are discussed.