Stratigraphic architecture and infill history of a deglaciated bedrock valley based on georadar, seismic profiling and drilling

Abstract

The sediment fill of a silled bedrock valley in Western Norway has been investigated with respect to stratigraphy and infill history using a combination of mapping, georadar, seismic profiling and drilling. A small outlet glacier occupies the head of the valley that displays a stepwise down-valley profile and terminates in a lake at 29 m above sea-level. The valley is surrounded by high, steep bedrock slopes and is characterized by a series of filled basins each limited by sills of bedrock or moraine accumulations. Till, glacial outwash and/or rockslide deposits fill in the lower half of the two larger basins. (Fan) delta deposits fringed by the deposits of alluvial fans and colluvial cones dominate the upper fill of most basins. (Fan) delta deposits interfinger downstream with lake sediments in the larger basins and fluvial deposits comprise the top fill. The overall infill pattern was controlled by deglaciation as well as basin size and shape. An overall decreasing sediment supply following deglaciation is shown in the fill of a larger basin down-valley, whereas a recently increasing sediment supply during glacier growth is reflected primarily in an upstream basin. Only the lowermost basin was exposed to a sea-level drop from 75 m above sea-level to the present lake level associated with incision and river migration. This observation is in contrast to the basins above marine influence where incision has been limited due to fixed downstream sills resulting in insignificant erosion except for some fan-head entrenchment. It follows that the fills of these small valley basins display progradational and aggradational trends of deposition and paraglacial reworking has been limited. Additionally, the study demonstrates that georadar profiling, combined with other methods, is very useful for comprehensive investigation of valley basins.

Spatial variations of surface water chemistry and chemical denudation in the Erdalen drainage basin, Nordfjord, western Norway

“…The Erdalen drainage basin (surface area 79.5 km 2 ; elevation range 29 m-1888 m a.s.l. ), situated at 61°50′N, 07°10′E, is connected to the Jostedalsbreen ice cap and is glaciated in its upper areas (Beylich et al, 2009Hansen et al, 2009;Beylich, 2010, 2012-this issue). Geologically, the inner Nordfjord belongs to the Jostedals Complex and the lithology is primary composed of Precambrian granitic orthogneisses with some patches of quartz monzonites (Lutro and Tveten, 1996).…”

Influences of the Little Ice Age glacier advance on hillslope morphometry and development in paraglacial valley systems around the Jostedalsbreen ice cap in Western Norway

“…Both valleys are typical for the region regarding the high shares of exposed bedrock surfaces along the valley walls alternating with clearly lower shares of surfaces comprised by talus cones, alluvial and colluvial fans (Hansen et al, 2009). The mean longitudinal length of slope debris/slope regolith cover in both valleys varies from approximately 700 m in the lower parts of the headwater areas to only 200 m in the uppermost parts of the headwater systems, with a mean value of 400 m for both study sites.…”

Cryostratigraphy, sedimentology, and the late Quaternary evolution of the Zackenberg River delta, northeast Greenland

“…Recent studies have presented models for infilling of formerly glaciated fjord valleys from Greenland (Hansen, 2001(Hansen, , 2004, Norway (Nemec et al, 1999;Eilertsen et al, 2006;Hansen et al, 2009;Eilertsen et al, 2011), Canada (Marchand et al, 2013), Sweden (Plink-Björklund andRonnert, 1999), and Germany (Winsemann et al, 2007). These investigations demonstrate that fjord valleys are primarily infilled during deglaciation and RSL fall, resulting in a complex stratigraphy, which can vary substantially between locations.…”