Ferromanganese rock varnish in north Norway: a subglacial origin
A thin, dark brown rock varnish is described from ice-smoothed bedrock on the forefield of a glacier in North Norway. It occurs only in narrow strips (ca 100 mm or less wide) which run roughly parallel to the ice front and along the top edges of small treads of a series of bedrock steps. The varnish...
| Published in: | Earth Surface Processes and Landforms |
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| Main Authors: | , , , |
| Format: | Article in Journal/Newspaper |
| Language: | unknown |
| Published: |
Wiley
1990
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| Subjects: | |
| Online Access: | http://eprints.gla.ac.uk/99675/ https://doi.org/10.1002/esp.3290150308 |
| Summary: | A thin, dark brown rock varnish is described from ice-smoothed bedrock on the forefield of a glacier in North Norway. It occurs only in narrow strips (ca 100 mm or less wide) which run roughly parallel to the ice front and along the top edges of small treads of a series of bedrock steps. The varnish is hard, thin (< 10 μm) and consists of an iron/manganese deposit, greatly enriched in these elements compared with the composition of the underlying gabbroic bedrock. It is suggested that the varnish formation is due to localized changes in Eh/pH conditions in subglacial regelation ice and meltwater at the top of the bedrock steps. These changes may be due to CO2 and/or O2 degassing from water held at higher pressures under the ice than in cavities downstream where the ice is decoupled from the bedrock. Glacier retreat rates indicate that the varnish has remained exposed subaerially at the surface for about twenty years, and its restricted occurrence suggests that it is not of biological origin but rather is essentially authigenic. Possible subglacial origins for associated iron and silica precipitates are also suggested. |
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