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

Abstract

a b s t r a c tTectonics and erosion are the driving forces in the evolution of mountain belts, but the identification of their relative contributions remains a fundamental scientific problem in relation to the understanding of both geodynamic processes and surface processes. The issue is further complicated through the roles of climate and climatic change. For more than a century it has been thought that the present high topography of western Scandinavia was created by some form of active tectonic uplift during the Cenozoic. This has been based mainly on the occurrence of surface remnants and accordant summits at high elevation believed to have been graded to sea level, the inference of increasing erosion rates toward the present-day based on the age of offshore erosion products and the erosion histories inferred from apatite fission track data, and on over-burial and seaward tilting of coast-proximal sediments.In contrast to this received wisdom, we demonstrate here that the evidence can be substantially explained by a model of protracted exhumation of topography since the Caledonide Orogeny. Exhumation occurred by gravitational collapse, continental rifting and erosion. Initially, tectonic exhumation dominated, although erosion rates were high. The subsequent demise of onshore tectonic activity allowed slow erosion to become the dominating exhumation agent. The elevation limiting and landscape shaping activities of wet-based alpine glaciers, cirques and periglacial processes gained importance with the greenhouse-icehouse climatic deterioration at the Eocene-Oligocene boundary and erosion rates increased. The flattish surfaces that these processes can produce suggest an alternative to the traditional tectonic interpretation of these landscape elements in western Scandinavia. The longevity of western Scandinavian topography is due to the failure of rifting processes in destroying the topography entirely, and to the buoyant upward feeding of replacement crustal material commensurate with exhumation unloading.We emphasize the importance of differentiating the morphological, sedimentological and structural signatures of recent active tectonics from the effects of long-term exhumation and isostatic rebound in understanding the evolution of similar elevated regions.

The early Quaternary North Sea Basin

“…The role of continued regional and local tectonic activity into the late Cenozoic is still debated. Most evidence favours a model of passive thermal subsidence enhanced by sediment loading in the central North Sea and marginal uplift owing to denudation and unloading of the Norwegian landmass (Huuse 2002;Nielsen et al 2009;Anell et al 2010;Goledowski et al 2012).…”

The periglacial engine of mountain erosion – Part 2: Modelling large-scale landscape evolution

“…Low-relief areas at high elevations have been traditionally interpreted as evidence for accelerated rock uplift following peneplanation at base level (Lidmar-Bergström et al, 2000;Japsen et al, 2009). Our experiments provide a viable alternative: low-relief areas may develop more or less in situ via mechanisms unrelated to either base level or tectonism (Anderson, 2002;Nielsen et al, 2009;Steer et al, 2012). Whether high summit flats in the mountains of Norway and Greenland are uplifted remnants of peneplains (LidmarBergström et al, 2000;Japsen et al, 2009, e.g.…”

“…Small and Anderson, 1998;Anderson, 2002;Anderson et al, 2006;Munroe, 2006) and the Caledonian mountains in Scotland, Scandinavia, and Greenland (e.g. Rea et al, 1996;Fabel et al, 2002;Phillips et al, 2006;Nielsen et al, 2009;Goodfellow, 2012). Summit flats are typically mantled thinly with regolith that is widely held to be the product of frost-driven physical weathering (Anderson, 2002;Ballantyne, 2010;Goodfellow, 2012), although there is disagreement concerning the timing of their formation, the contribution of chemical weathering, and relationships to climate (Rea et al, 1996;Whalley et al, 2004;Strømsøe and Paasche, 2011;Goodfellow, 2012).…”

“…Recent studies of the Norwegian mountains suggest that, although characterised by low erosional activity during recent glacial cycles, high-elevation, low-relief areas may have contributed notable sediment volumes to offshore basins over the last 2.8 Myr (Steer et al, 2012). It seems that accounting for the long-term development of the summit flats requires the processes at play to be integrated throughout the Quaternary period, and possibly even further back because periglacial erosion may have been active several million years before glaciers were introduced into the landscape (Nielsen et al, 2009).…”

Passive margins: overview

“…Nielsen et al 2008). In west Greenland, Japsen et al (2006) describe three separate phases of uplift: broadly Oligocene (36-30 Ma), Miocene (11 Ma) and Pliocene (7-2 Ma), all clearly post-dating the classical rift shoulder-related uplift in the Eocene.…”