Environmental magnetism as a dating proxy for recent overbank sediments of (peri-)industrial regions in the Czech Republic and UK

- We tested the hypothesis that magnetic parameters can be used as a dating proxy.
- The hypothesis was tested in floodplain profiles from (peri-)industrial regions.
- Magnetic enhancement in the profiles was identified as anthropogenically induced.
- The profiles were divided to three groups based on their characteristics.
- Comparison with other dating methods proved qualities of magnetic dating approach.

Twenty five floodplain sediment profiles from seven rivers in eastern Czech Republic and three in north west England were collected to examine the hypothesis that magnetic enhancement in recent sediments is predominantly of anthropogenic origin and that magnetic parameters can be used as a dating proxy reflecting changes in intensity of industry sources over time. Natural sources of magnetic enhancement were excluded and anthropogenic enhancement was identified as exhibiting elevated values of χlf, ARM, SIRM, SIRM/χ and S-ratios with low values of χfd%. Magnetic spherules, typically formed through fossil fuel combustion processes, were observed by scanning electron microscopy (SEM) in these sediments. To assess the potential of magnetic parameters as a chronometer, the approach was compared with frequently used dating techniques: concentrations of heavy metals and 137Cs.The floodplain profiles were divided to three groups according to the characteristics of their trends with depth in magnetic parameters; χlf in particular, and the suitability of magnetic properties as a dating proxy. Group 1, which included the majority of the profiles, exhibited magnetic enhancement in the upper part of its profiles and a single maximum in χlf. This group exhibited a clear suitability for our proposed 'magnetic dating' as the magnetic record reflected the industrial history of the region and was aligned with the chronologies of the other dating techniques. Profiles magnetically enhanced throughout their depth and lacking any clear trend comprised group 2; here a mineral magnetic approach to dating was limited as the magnetic signal was diluted by a high sedimentation rate or impacted by local anthropogenic factors. All profiles from England were included in group 3 because their magnetic depth profiles were influenced by natural sources of magnetic particles or specific sedimentary conditions, and a longer industrial history and thus needed an individual interpretation. However, they still reflected the regional deposition history of industrial sources of ferrimagnetic particles. Overall, magnetic parameters proved to be an efficient dating proxy with potential for recently aggrading rivers.