Magnetic investigation of peat sediments from the mountain in Arid Regions

Abstract

Detailed and systematic magnetic analysis was conducted on continuous peat depositional sequences from the Altay Mountains in arid regions, Northwest China. Based on magnetic properties, such as composition, concentration and grain-size, the magnetic-variation mechanism of these minerals can be discussed in peat sediments that are rich in organic matter under redox conditions. The results are showed as follows: The concentration of ferrimagnetic minerals has a low enrichment degree. Magnetite, hematite, a great deal of diamagnetic organic matter and some paramagnetic components have been identified in peat sediments, and there is no magnetotactic bacteria (MTB). The grain sizes are mainly fine particles, but meanwhile there are also coarse particles-multidomain (MD). The results further reveal that the major variations of ferrimagnetic minerals in the peat sediments occur during the short period of post-depositional processes. As for the possible mechanism, we argue that the pseudo single domain (PSD) and MD magnetite on the peatland surface are dissolved and refined in the acid waterlogged sub-oxic conditions, which results in low concentration and smaller grain sizes. Furthermore, we also speculate that no long-term burial-diagenetic dissolution processes take place in the peat sediments and little magnetite dissolution happens under the condition of alkaline and reductive environments in which the peat is buried deeply.