Magnetic studies of tephra in late Holocene peats and loessic soils from SE Iceland

Xia, Dunsheng.
(2002) Magnetic studies of tephra in late Holocene peats and loessic soils from SE Iceland. PhD thesis, University of Liverpool.

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Magnetic and geochemical properties of five late Holocene peat and loessial soil sections in SE Iceland have been studied. The aims were (i ) to establish a reliable tephrochronology for the sections, using geochemical analysis of tephra shards; (ii) to establish high resolution bulk sample records of mineral magnetic and geochemical properties; (iii) to test the ability of magnetic properties to correlate distal tephra layers; (iv) to assess the possible environmental significance of mineral magnetic time series and (v) to use records of loessial accumulation rates to assess human impact on the environment in SE Iceland. The work has been successful in establishing a reliable tephrostratigraphy for the studied sections. This was achieved using electron microprobe analyses (EMPA) of the geochemistry of tephra shards concentrated using a density separation technique. The results of detailed mineral magnetic measurements suggest that the main magnetic minerals in the tephras are probably ferrimagnetic minerals (e.g. magnetite) and canted anti ferromagnetic minerals (e.g. haematite), with abundant paramagnetic material also present. Cross plots of MrJMs vs. (Bo)c.l(Bo)c and Xfd% vs. XARM/SIRM indicate the main magnetic grain size in the tephras are pseudo-single domain (PSD) and multi domain (MD). The results indicate that the 'fingerprint' of both hysteresis and Curie temperature properties are insufficiently consistent within the tephra layers to provide an obviously sound basis for correlating tephra layers from one profile to the next. However, initial correlation of tephra layers was achieved, using all the measured magnetic parameters, by the use of the multivariate statistical measures of Similarity Coefficient (SC) and Euclidean Distance (ED). Tephra layer correlation was performed first time here using magnetic measurements. This demonstrates that magnetic techniques can potentially assist in the identification and correlation of distal tephra. Iceland offers a unique opportunity to study the role of humans in land degradation processes because of the late and well documented literature of settlements 1100 years ago. In this context, higher sedimentation rates in the upper part of two soils and one peat profile are interpreted as reflecting the effect of Landnam on deforestation and soil degradation.

Item Type: Thesis (PhD)
Depositing User: Symplectic Admin
Date Deposited: 23 Oct 2023 10:19
Last Modified: 23 Oct 2023 10:24
DOI: 10.17638/03176064
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