Depositional and post-depositional controls on magnetic signals from saltmarshes on the north-west coast of Ireland

Magnetic measurements were carried out on samples from two saltmarshes depo sited during the last century on the north-west coast of Ireland. Based on profiles from cliffed saltmarsh edge, mid-marsh and supratidal locations, t he processes that affect the generation and persistence of magnetic propert ies in environments were investigated. This was done to help in understandi ng the geochemical processes affecting north-west Irish coast saltmarshes a nd to determine the frequency and provenance of sediment-laden flooding eve nts; hence, disentangling the importance of elastic and organic contributio ns to saltmarsh growth. Magnetic properties indicate depositional and postd epositional effects varying on both temporal and spatial scales. The interp retations presented here suggest that both biogenic and diagenetic processe s have a strong effect on the magnetic properties recorded: in the former c ase, the growth of magnetotactic bacteria is the main process; in the latte r case, it is reductive diagenesis, associated with organic matter decompos ition, that is important. The biogenic and diagenetic effects overprint and degrade the detrital magnetic signatures respectively. This suggests that magnetic measurements within the context of north-west Irish coast saltmars hes can provide limited information on elastic sediment input to these envi ronments. Comparisons between sites on the north-west coast of Ireland show similar magnetic properties, despite differences in deposition rates, impl ying that significant post-depositional alteration of magnetic properties o ccurs within the first 20-40 years after deposition. Magnetic properties of north-west coast Irish saltmarshes are put into a regional context by comp arison with magnetic profiles from similar sites.