The archaeomagnetism of fine-grained alluvial sediment.

Floodplain environments and sediments are frequently associated with human activity. The interpretation of these associations is highly dependant upon alluvial chronology. The absolute dating of recent alluvial sediment therefore has considerable archaeological value and advances our understanding of the relationships between human activities and the landscape. The main aim of this thesis is to explore the potential of archaeomagnetism to date such fine-grained alluvial sediments in a number of different contexts including both 'natural,' (e.g. overbank, levee, channel and fluvial/estuarine) and artificial depositional environments (e.g. fishponds, a millpond and a cistern or well). One of the advantages of archaeomagnetism is that it is the date of deposition, or shortly afterwards that can be determined. The study has confirmed that waterlain sediments can often exhibit a natural remanence magnetisation. Three Italian sediments yielded good remanence data, however, because of the incomplete nature of the Italian archaeomagnetic curve the assignment of dates was tentative but encouraging for the future. Only two of the British sites, Hemington Fields and Dane valley were successfully dated using archaeomagnetism and the reasons for this are discussed. Many sediments do not appear to carry a natural remanence magnetisation because of depositional and post-depositional processes and so a second aim of this thesis is to explore and broaden our understanding of such processes through the analysis of sedimentary fabric. The remaining non-datable British sites were devoid of a remanence due to the affects of a variety of post-depositional processes. The sediment from the Marta and Fiora also revealed that sediment with an initial high magnetic content and that had experienced small scale physical post-depositional disturbance (rather than physico-chemical) can retain a natural remanence magnetisation. The complex nature of fine-grained sediment deposition and post-depositional processes is examined. A third aim of the thesis was to recommend relatively simple procedures for the in-field assessment of sediments with a high probability of being datable using archaeomagnetism. The procedures have been developed from the study of sedimentary characteristics associated with the environments used in this study.