Modelling and Comparing the Caledonian and Permo‐Triassic Erosion Surfaces with Present‐Day Topography Across Highland Scotland: Implications for Landscape Inheritance

Abstract

The Caledonian Orogeny marks a starting point for the evolution of the Scottish Highlands. There is debate as to the level of erosion that the Highlands have experienced since the Devonian and the extent to which the Highland landscape reflects Permo-Triassic rather than Caledonian events. Data on the position and elevation of the Caledonian and Permo-Triassic unconformities have been used to create topographic models of both surfaces. A variety of computer mapping packages have been used that allow the interpreter to control many of the mapping parameters, creating models of surfaces that honour the data and maintain realistic surface trends. The effects of these parameters have been tested in a series of sensitivity experiments. The modelled Caledonian erosion surface has proved to be a good indicator of the present-day surface, suggesting that the Highlands are an exhumed landscape. This indicates that there has been limited denudation of basement rocks since the end of the Devonian. The model of the Permo-Triassic erosion surface has lower altitude and less relief than the model of the Caledonian surface, suggesting onlap onto a positive Highland block. Palaeomagnetic results showing Permo-Triassic reddening and fissuring of Highland basement rocks are interpreted as reflecting re-occupation of an older surface.

The evolution of western Scandinavian topography: A review of Neogene uplift versus the ICE (isostasy–climate–erosion) hypothesis

“…The present-day high topography is better explained as the remnants of topography, which survived the extensional collapse, onshore and (mainly) offshore rifting processes following the Caledonian Orogeny, as well as erosion. A similar point of view has recently been expressed for the Scottish Caledonides (Macdonald et al, 2007). On this rifting background, the main contributions to the driving mechanism of our hypothesis are isostasy, climate, and erosion.…”

“…We instead consider the topography to be exhumed from topography produced during the Caledonian Orogeny, as for Scotland (Macdonald et al, 2007).…”

Reply to comment regarding the ICE-hypothesis

“…Regarding the longevity of the Scottish Caledonides, which is doubted by Lidmar-Bergström and Bonow on the grounds of the paper by Macdonald et al (2007), which they believe we say the opposite of, which we do not, we have obtained the following personal comment (David Macdonald, 20 February 2009): "I believe that the Caledonian surface controls the present-day surface of the east Highlands and the eastern part of the Northern Highlands. I think that this block has been mostly above sea-level since the Devonian.…”

Hypotheses and observations on the origin of the landscape of southern Norway—A comment regarding the isostasy-climate-erosion hypothesis by Nielsen et al. 2008

“…They concluded that most of the erosion over the Scottish Highlands since formation of the Caledonian surface has been in cover rocks. Nielsen et al (2009) claim that the Macdonald et al (2007) paper provides support for their ICE hypothesis but, it shows that the basement was eroded to an Upper Devonian unconformity across the whole area, which has been repeatedly buried and re-exposed, which is against everything that Nielsen et al (2009) are claiming.…”

“…In a paper on Scotland, Macdonald et al (2007) tried to reconstruct a sub-Silurian/Devonian surface (the Caledonian surface) and a Permo-Triassic surface. They concluded that most of the erosion over the Scottish Highlands since formation of the Caledonian surface has been in cover rocks.…”