1Department of Physical Geography and Quaternary Geology, and Bolin Centre for Climate Research, Stockholm University, 10691 Stockholm, Sweden
2Department of Geology, Lund University, 22362 Lund, Sweden
3Department of Geographical and Earth Sciences, East Quadrangle, University Avenue, University of Glasgow, Glasgow G12 8QQ, UK
4Department of Geography, Norwegian University of Science and Technology (NTNU), 7491, Trondheim, Norway
5Geological Survey of Norway, Leiv Eirikssons vei 39, 7491 Trondheim, Norway
6Institute of Geomatics and Risk Analysis, University of Lausanne, 1015 Lausanne, Switzerland
7Royal Netherlands Meteorological Institute, Wilhelminalaan 10, 3732 GK De Bilt, the Netherlands
8Department of Physics, Purdue University, West Lafayette, Indiana, USA
Received: 22 Jan 2014 – Discussion started: 10 Feb 2014
Abstract. Autochthonous blockfield mantles may indicate alpine surfaces that have not been glacially eroded. These surfaces may therefore serve as markers against which to determine Quaternary erosion volumes in adjacent glacially eroded sectors. To explore these potential utilities, chemical weathering features, erosion rates, and regolith residence durations of mountain blockfields are investigated in the northern Swedish Scandes. This is done, firstly, by assessing the intensity of regolith chemical weathering along altitudinal transects descending from three blockfield-mantled summits. Clay / silt ratios, secondary mineral assemblages, and imaging of chemical etching of primary mineral grains in fine matrix are each used for this purpose. Secondly, erosion rates and regolith residence durations of two of the summits are inferred from concentrations of in situ-produced cosmogenic 10Be and 26Al in quartz at the blockfield surfaces. An interpretative model is adopted that includes temporal variations in nuclide production rates through surface burial by glacial ice and glacial isostasy-induced elevation changes of the blockfield surfaces. Together, our data indicate that these blockfields are not derived from remnants of intensely weathered Neogene weathering profiles, as is commonly considered. Evidence for this interpretation includes minor chemical weathering in each of the three examined blockfields, despite consistent variability according to slope position. In addition, average erosion rates of ~16.2 and ~6.7 mm ka−1, calculated for the two blockfield-mantled summits, are low but of sufficient magnitude to remove present blockfield mantles, of up to a few metres in thickness, within a late Quaternary time frame. Hence, blockfield mantles appear to be replenished by regolith formation through, primarily physical, weathering processes that have operated during the Quaternary. The persistence of autochthonous blockfields over multiple glacial–interglacial cycles confirms their importance as key markers of surfaces that were not glacially eroded through, at least, the late Quaternary. However, presently blockfield-mantled surfaces may potentially be subjected to large spatial variations in erosion rates, and their Neogene regolith mantles may have been comprehensively eroded during the late Pliocene and early Pleistocene. Their role as markers by which to estimate glacial erosion volumes in surrounding landscape elements therefore remains uncertain.
Revised: 09 Jun 2014 – Accepted: 24 Jun 2014 – Published: 21 Jul 2014
Goodfellow, B. W., Stroeven, A. P., Fabel, D., Fredin, O., Derron, M.-H., Bintanja, R., and Caffee, M. W.: Arctic–alpine blockfields in the northern Swedish Scandes: late Quaternary – not Neogene, Earth Surf. Dynam., 2, 383-401, doi:10.5194/esurf-2-383-2014, 2014.