Pre-Quaternary landscape evolution in the Scottish Highlands

Abstract

The development of the relief of the Scottish Highlands is traced over the last 400 Ma. Evidence from Late Palaeozoic and Mesozoic sediments and near-surface volcanic and igneous rocks shows that post-Devonian erosion of basement has been < 1–2 km and that the main morphotectonic units of the Highlands were already established by the end of the Palaeozoic. During the Mesozoic, the Highlands experienced several major erosional cycles, beginning with uplift, reactivation of relief and stripping of cover rocks, followed by progressive reduction of relief through etchplanation and culminating in extensive marine transgressions in the Late Triassic, Late Jurassic and Late Cretaceous. In the Early Tertiary major uplift affected the Highlands, with downwarping and block movements along basin margins, but levels of uplift and denudation around the Tertiary igneous centres cannot be extrapolated to other areas. Buchan and Caithness remained relatively stable and Mesozoic relief elements were maintained during gradual surface lowering. Earth movements of lesser magnitude continued episodically until at least the end of the Tertiary. After 50 Ma the Highland terrain evolved by dynamic etching, with deep weathering of varied geology under warm to temperate humid environments leading to a progressive differentiation of relief, with formation of basins, valleys, scarps and inselbergs often closely adjusted to lithostructural controls.

Quaternary evolution of glaciated gneiss terrains: pre-glacial weathering vs. glacial erosion

“…It is possible the study area was inundated and partially covered by marine sediments during the late Mesozoic, but any such sedimentary rocks have disappeared since. Hall (1991) suggests that the present-day large-scale topography of NW Scotland, including the summit height approaching 1000 m and the cliff retreat now characterising the steeper west-facing topography of NW Scotland, was largely established during the Tertiary. …”

Calculating Quaternary glacial erosion rates in northeast Scotland

“…(3) Remnants of the preglacial landscape survive in this area (Fitzpatrick, 1963;Sugden, 1968Sugden, , 1989Hall and Sugden, 1987;Hall and Mellor, 1988;Hall et al, 1989;Hall, 1991;Hall and Connell, 1991;Ballantyne, 1994). These palaeo-features allow the reconstruction of the preglacial relief, an essential pre-requisite for determining the location and depth of erosion by former ice sheets.…”

“…These reflect the slow etching of the raised basement block by differential chemical weathering under first tropical and then temperate environments during the Tertiary. At the end of the Tertiary, the relief was dominated by etch surfaces, mantled by thick sandy weathering covers and closely adjusted to litho-structural controls (Hall, 1991).…”

“…(2) The presence of major relief elements, such as erosion surfaces, hills, basins and valleys, which form a 'paleic relief' (Gjessing, 1968) that is dissected by the fomrs of glacial erosion (Sugden, 1968) and which appear to have developed under temperate conditions, in the late Tertiary by a combination of differential deep chemical weathering and fluvial erosion (Hall, 1991).…”

“…(3) The presence of minor landforms, such as tors (Ballantyne, 1994), small basins floored by weathered rock (Hall, 1986), scarps (Hall, 1986) and valley benches markin8 the former valley floor (Hall, 1991) which appear to be broadly of preglacial age.…”