Fractures and Biopores in Weichselian Clayey Till Aquitards at Flakkebjerg, Denmark

Klint, Knud Erik S.; Gravesen, Peter

doi:10.2166/nh.1999.0015

Cited by 48 publications

(31 citation statements)

References 16 publications

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“…The lower part of the Flakkebjerg till has been previously interpreted as a deposit from the main glacial advance, c. 20 ka BP (Klint & Gravesen 1999). We do not share this interpretation, although there is agreement on the origin of the hard upper till.…”

Section: Geologic Observationscontrasting

confidence: 73%

“…A yet to be explored mechanism, which may in a simple way explain the till property variation with depth, is the effect of a freezing ice-stream base. Till with properties similar to those of Sprogø Till in Storebaelt has been found near the township of Flakkebjerg, which is situated about 10 km NE of the Here, several pits were excavated to depths of 5 m (Klint & Gravesen 1999;Christoffersen 1998).…”

Section: Geologic Observationsmentioning

confidence: 91%

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Signature of palaeo‐ice‐stream stagnation: till consolidation induced by basal freeze‐on

Christoffersen

Tulaczyk

2003

Boreas

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A combination of glaciological theory and geological observations was used to investigate the possibility of till consolidation being driven by basal freeze-on beneath a stagnating, mid-latitude palaeo-ice stream. We focused on the case of the Baltic Ice Stream that advanced into Denmark at c. 15 ka BP and which left behind a characteristic till sequence consisting of a strong and well-consolidated till crust underlain by weak and poorly consolidated till. Our hypothesis is that basal freezing caused the markedly higher consolidation of the uppermost till layer. The freezing may have either triggered or simply just accompanied ice-stream stoppage. To test the feasibility of this hypothesis, we have developed a numerical model that couples ice-stream dynamics to timedependent changes of till properties. Despite relatively mild palaeo-climatic conditions in this area during Late Pleistocene deglaciation ($0°C), the ice-stream model is capable of producing basal freezing when the effect of horizontal advection of cold ice is included. Our simulations of till response to basal freezing are based on thermodynamic concepts adapted from permafrost studies. Dewatering of till by basal freeze-on may lead to overconsolidation (OCR>10). Based on the history of effective pressure changes in the till, we can predict postglacial till strength profiles using the SHANSEP method. In a series of numerical experiments we have examined the response of till strength to basal freeze-on induced beneath a decaying ice sheet. We have come reasonably close to reproducing shear strength profiles for till deposited by the Baltic Ice Stream. These observations are most consistent with palaeo-ice-stream stagnation triggered by basal freezing and followed by abrupt retreat (<100 years) due to high surface ablation rates (>10 ma À1 ).

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Section: Geologic Observationscontrasting

confidence: 73%

Section: Geologic Observationsmentioning

confidence: 91%

Signature of palaeo‐ice‐stream stagnation: till consolidation induced by basal freeze‐on

Christoffersen

Tulaczyk

2003

Boreas

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“…From c. 4.5 m, the fracture frequency increased to an intermediate level corresponding to the observed change from reduced to oxidized conditions in Unit 2.3, and remained at this level until the bottom of the excavation. These observations are in line with interpretations from the studies of Hendry (1982); Ruland et al (1991); Klint and Gravesen (1999) and Harrar et al (2007), where fracture frequency in tills decreases rapidly from oxidized to reduced conditions. The exposed 24 by 17 m excavation is depicted in a 2D conceptual geological model (Fig.…”

Section: Geoelectrical Profiles and Data From Excavationsupporting

confidence: 90%

Geoelectrical mapping for improved performance of SUDS in clay tills

et al. 2015

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Many cities of the Northern Hemisphere are covered by low permeable clay tills, posing a challenge for stormwater infiltration practices. However, clay tills range amongst the most heterogeneous types of sediments and infiltration rates can vary by several orders of magnitude. This study evaluates if a 2D geoelectrical system can reveal such heterogeneity at field scale and thus be used to optimize the hydraulic performance of stormwater runoff infiltration systems. The assessment is based on a field study where data from non-invasive geoelectrical data are compared with data from invasive geological methods, including borehole soil sample descriptions, one excavation description and a near-surface spear auger-mapping project. The experiments returned a significant correlation of geoelectrical and spear auger-mapped surface sediments. Furthermore, a highly permeable oxidized fracture zone in greater depths could be revealed on the 2D geoelectrical profiles. The successful determination of highly permeable zones harbors potential for improved hydraulic performance of infiltration SUDS (sustainable urban drainage systems).

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“…The Bjerge Å catchment is a moraine landscape characterised by a relatively flat surface and river valleys (Klint and Gravesen, 1999) The upper layer consists of a clayey and sandy till with a large number of fractures and biopores. Below this layer that acts as an aquitard, various layers and lenses of alluvial and glacial clay and sand are located.…”

Section: Hydrogeologymentioning

confidence: 99%