Chemical distinction between lithogenic and pedogenic iron oxides in environmental magnetism : a search for the perfect solution

Abstract

One of the goals in environmental magnetism is to understand the link between climate change and the characteristics of magnetic particles in rocks, soils and sediments. Rock-magnetic analyses sometimes are non-unique, which hinders an unambiguous identification of the magnetic particles that carry the climatic information. In this thesis, several complementary methods from chemistry and soil science are examined to explore whether they can assist in improving the determination of mineral-magnetic climate proxies. The first two parts of this thesis describe the results of tests with chemical extraction techniques (CBD and AAO-Fe2+ methods) on natural samples from a Czech loess-paleosol sequence as well as synthetic samples. The results indicate that both methods remove part of the pedogenic (climatically influenced) iron oxides, although in a varying degree. Neither method was able to remove the newly formed pedogenic particles with sufficient efficiency without affecting the lithogenic fraction as well. In combination with new mineral-magnetic techniques (FORC diagrams and automated IRM component analysis) the extraction methods did provide valid information about the composition of the samples which could not be retrieved from standard rock-magnetic data alone. A new technique in electrochemistry (voltammetry of microparticles) is discussed in the final part of this thesis. This technique was tested here for the first time on natural loess and paleosol samples to determine whether it is suitable for identifying and quantifying the magnetic mineral composition in natural samples. The results indicate that the technique is well suited for identifying as well as quantifying the weak magnetic minerals such as hematite, even when these are present in small amounts. With this thesis we have introduced and improved techniques for determining the magnetic mineral composition of natural samples, and the results have brought us a step closer to understanding the climate signal of magnetic particles in soils and sediments.