Pleistocene climate and environment reconstruction by the paleomagnetic study of a loess-paleosol sequence (Cérna Valley, Vértesacsa, Hungary)

Abstract

Four paleosol layers indicating wet and moderate periods and five loess layers indicating dry and cold climate were separated by different methods. The following climate cycle model, based on the development of the sediment sequence created by the influence of climatic, geologic and geomorphologic phenomena, was established by detailed paleomagnetic studies (e.g. anisotropy of magnetic susceptibility (AMS), isothermal remanent magnetization (IRM), frequency dependence of magnetic susceptibility (κ FD ), etc.):-A well-foliated magnetic fabric predominantly built up by multi-domain ferromagnetic minerals (magnetite, maghemite) was developed during the semi-arid (350-400 mm/y) and cold loessification period of the Pleistocene. The magnetic fabric can reflect the direction of dust deposition and/or the paleoslope.-The accumulation period of dust was followed by the more humid (650 mm/y) pedogenic period indicated by the enrichment of superparamagnetic minerals and by the disturbed or inverse magnetic fabric developed during pedogenesis by different processes (e.g. leaching and/or bioturbation).-The third period following the pedogenic period is the humid erosional phase indicated by the finely layered reworked loess. The magnetic fabric built up by multi-domain ferro-and superparamagnetic minerals is characterized by better-aligned directions of principal susceptibilities than in the wind blown material. Sheet wash and other waterlogged surface processes appeared in the fabric of these layers. This process is possibly connected to sudden, rare yet significant events with high precipitation and absence of vegetation.-The cycle was closed by the beginning of the next dust accumulation period.

Geology of Hungary

“…Magnetic susceptibility borehole logs contributed to clarifying the climatic conditions of individual Quaternary layers Bradák et al 2009). The distal provenance of thin tuff horizons (Paks Tephra, Bag Tephra) was determined by means of their detailed petrographic evaluation (Gábris et al 1991;Sági et al 2008).…”

Hungarian national report on IAGA 2007–2010

“…Finally, the magnetic identification and the widespread occurrence of greigite in the sediments of Lake Pannon were discussed in the papers of Babinszki et al (2007), Babinszki and Márton E (2009), and the magnetic method was applied to climatic and environmental reconstructions during the Pleistocene by Bradák et al (2009Bradák et al ( , 2010. In an earlier paper (Illés-Almár and Almár 2006) it was demonstrated that there is a North-South asymmetry in the thermospheric density with higher densities over the Northern hemisphere in average.…”