HR: 09:15h
AN: C51C-06    [Abstracts]
TI: Blockfields of Neogene origin: Challenging the paradigm
AU: Stroeven, A P
EM: arjen.stroeven@natgeo.su.se
AF: Department of Physical Geography and Quaternary Geology, Stockholm University, Stockholm, 10691, Sweden
AU: * Goodfellow, B W
EM: brad.goodfellow@natgeo.su.se
AF: Department of Physical Geography and Quaternary Geology, Stockholm University, Stockholm, 10691, Sweden
AU: Fabel, D
EM: Derek.Fabel@ges.gla.ac.uk
AF: Department of Geographical and Earth Sciences, University of Glasgow, Glasgow, G12 8QQ, United Kingdom
AU: Fredin, O
EM: Ola.Fredin@NGU.NO
AF: Geological Survey of Norway, Leiv Eirikssons vei 39, Trondheim, 7040, Norway
AU: Derron, M
EM: Marc-Henri.Derron@NGU.NO
AF: Geological Survey of Norway, Leiv Eirikssons vei 39, Trondheim, 7040, Norway
AU: Caffee, M W
EM: mcaffee@purdue.edu
AF: Department of Physics, Purdue University, West Lafayette, IN 47907, United States
AU: Bintanja, R
EM: bintanja@gmail.com
AF: None, Griend 14-42, Lelystad, 8225 VC, Netherlands
AB: The prevailing paradigm for cold-climate in situ blockfields is that they are remnants of Neogene deep weathering profiles. This opinion is frequently based on the presence of large quantities of interstitial silt and clay and/or the presence of clay minerals, such as gibbsite and kaolinite. Using in situ-produced cosmogenic isotopes ¹⁰Be and ²⁶Al, XRD, and XRF to study blockfield regolith in the northern Swedish mountains, we challenge this paradigm. Incorporating surface burial by ice sheets, the isostatic response to ice sheet loading and unloading, and subaerial surface erosion, the cosmogenic data indicate that the regolith has been accumulating nuclides for up to 464.5 ka. The ubiquitous presence of chlorite makes it impossible to distinguish kaolinite according to standard XRD techniques. However, gibbsite is present in glacial till in addition to wet- location blockfield regolith. Coupled with the ubiquitous presence of poorly crystallized hydroxides, vermiculization in wet-locations, and an absence of smectite, incipient chemical weathering is indicated. Furthermore, XRF data indicate dominance of the interstitial fine matrix by a foreign component, likely of aeolian origin. All of our observations can be explained by processes operating within the Quaternary timeframe. Because we do not need to appeal to Neogene deep weathering to account for the characteristics of blockfields in the northern Swedish mountains we conclude that these blockfields may have Quaternary origins.
DE: 0710 Periglacial processes
DE: 0712 Cryosol
DE: 0790 Weathering (1625, 1886)
SC: Cryosphere [C]
MN: 2007 Fall Meeting