Mineral magnetic characterization of the Upper Pleniglacial Nussloch loess sequence (Germany): an insight into local environmental processes

Samuel N. Taylor, (1) , France Lagroix (1) , Denis-Didier Rousseau (2, 3) , Pierre Antoine (4)

1 IPGP - Institut de Physique du Globe de Paris
2 LDEO - Lamont-Doherty Earth Observatory
3 LMD - Laboratoire de Météorologie Dynamique (UMR 8539)
4 LGP - Laboratoire de géographie physique : Environnements Quaternaires et Actuels

(1) First comprehensive environmental magnetism study of the Nussloch (Rhine River Valley, Germany) loess/palaeosol deposit. (2) Bulk ferrimagnetic concentration parameters are dominantly controlled by variations in coarse-grained MD ferrimagnetic particles of detrital aeolian origin. (3) The imprint of waterlogging-induced redoxomorphic processes on the magnetic record is observed by dissolution of fine-grained magnetic minerals. (4) The interpretation of magnetic susceptibility variations alone within loess and palaeosol deposits following the wind-vigour or pedogenic enhancement models will be hindered by waterlogging-induced redoxomorphic processes, if present. S U M M A R Y Presently, most loess/palaeosol magnetic susceptibility records are interpreted as following either the wind-vigour model or the pedogenic enhancement model. However redoxomorphic processes induced by waterlogging, often referred to gleying in the loess literature, are also known to alter loess deposits but their impact on loess/palaeosol magnetic susceptibility records has received little attention. The reported rock magnetic study aims to characterize the mineral magnetic response of loess to waterlogging-induced redoxomorphic processes, thus improving our understanding of mineral magnetic changes within loess deposits with respect to environmental and climate conditions. The Nussloch loess-palaeosol deposit (Rhine Valley, Germany) was targeted because it is one of the best-studied Pleniglacial deposits for Western Europe in which numerous tundra gley intervals have been identified. Moreover, a comprehensive high-resolution environmental magnetism study has never been undertaken for this site. Various rock magnetism experiments were conducted at both room and low temperatures to characterise the composition, concentration and relative magnetic grain size of the mineral magnetic assemblage. The relative changes in magnetic parameters within the investigated loess interval are primarily controlled by (1) varying concentrations of coarse-grained ferri-magnetic particles of detrital (aeolian) origin and (2) dissolution of fine-grained ferrimagnetic particles related to in situ post-depositional alteration promoted by waterlogging-induced re-doxomorphic processes. Goethite is found to be ubiquitous throughout the studied interval and is argued to have both a primary (aeolian) and secondary (in situ) origin. We conclude, that redoxomorphic processes induced by waterlogging, if present, will hinder the interpretation of magnetic susceptibility variations within loess and palaeosol deposits following the expected relationships dictated by the wind-vigour and the pedogenic enhancement magnetism models.

Domaines: Planète et Univers [physics]

Samuel N. Taylor,, France Lagroix, Denis-Didier Rousseau, Pierre Antoine. Mineral magnetic characterization of the Upper Pleniglacial Nussloch loess sequence (Germany): an insight into local environmental processes. Geophysical Journal International, 2013, ⟨10.1093/gji/ggu331⟩. ⟨insu-01351766⟩