Micro-XRF Applications in Fluvial Sedimentary Environments of Britain and Ireland: Progress and Prospects

Abstract

This chapter considers applications of micro-XRF in fluvial depositional environments and presents case-studies from Britain and Ireland in three key river management areas: flood reconstruction; pollution and provenance mapping; and floodplain sediment dynamics. Although fluvial sediment archives are typically shorter and more fragmented than marine and lake sediment records, they do offer significant palaeoenvironmental potential, not least because of the sensitivity of river systems to environmental change. A major consideration in micro-XRF analysis, however, is the continuity and heterogeneity of alluvial sediments and the integrity of accretionary records once they have been subjected to post-depositional processes, such as human disturbance and pedogenesis. Thus far, micro-XRF applications in fluvial environments have been limited. One research area currently being developed is the field of flood reconstruciton, where elements and, in particular, element ratios (e.g. Zr/Rb, Zr/Ti) can be used as particle size proxies. Micro-XRF core scanning technologies allow for analysis at the event-scale, which hitherto has been unachievable in silt and clay sediments. The potential to build and signifcantly enhance our understanding of longer term flooding patterns and non-stationarity, offers considerable scope for augmenting instrumental records and providing new perspectives for contemporary river management. Rapid geochemical assessment of fluvial sedimentary deposits can also be used to support floodplain reconstruction studies and pollution investigations, but greater scope will emerge from the calibration of raw XRF cout data to elemental concentrations. In this paper we demonstrate the potential for using micro-XRF data in sediment provenance investigation, but improvements in error quantification and propagation need to be explored. Given that river alluvium plays an integral role in the cycling and storage of contaminants, further applications in this field would be hugely beneficial for river managers. Although sediment heterogeneity places significant challenges to the quantification of micro-ZRF core scanner results, there has been little attempt to establish what these limitation mean in practical terms

Reconstructing human–landscape interactions in the context of ancient iron smelting on Elba Island, Italy, using sedimentological evidence

“…Also cores F‐II, F‐III, and S‐II show a distinct pattern of changing morphodynamics, such as the deposition of high magnitude flood layers and an interbedded succession of coarse and fine sediments. The geochemical pattern of Zr/Ti and Zr/Rb log‐ratios supports the interpretation as high magnitude flood deposits, because Rb, Ti, and Zr are associated to different grain‐size fractions (Turner et al, ). In core F‐III these layers date between 2.1 and 2.0 ka cal BP.…”

“…Sediments in unit V (core F‐I) and in the basal unit of core S‐I are interpreted as low‐energy, lacustrine still water deposits, as indicated by the clayish texture and occasional plant remains; relatively increased values of Fe, Al, Rb, and Ti in the elemental composition of unit V support this interpretation (cf. Cuven, Francus, & Lamoureux, , Loring, , Turner, Jones, Brewer, Macklin, & Rassner, ). The gray color and a distinct Fe‐pattern (Figure ) indicate reducing conditions as present in an oxygen‐poor environment (cf.…”

Geomorphological controls on fluvial carbon storage in headwater peatlands

“…Suspected flood couplets (Turner et al, 2015) were observed in the fine-grained facies of all cores with some being linked to clearly observable grain-size changes and organic capping. At least four of these couplets were present in most cores indicating laterally extensive deposition.…”

“…Floodplain sediments dominated by overbank deposition processes typically comprise of distinctive couplets, consisting of minerogenic sediment and an organic cap (Turner et al, 2015). The organic cap of a flood couplet within floodplain sediments downstream may represent both in-situ autochthonous accumulation and fluvially transported organics eroded from the peatlands, ultimately forming what may appear to be multiple buried soils.…”

“…As conveyors of organic and mineral sediment, water and contaminants, rivers play an instrumental role in landscape evolution, and their catchments feature a variety of depositional settings that can store sedimentological information about past and present sediment dynamics (Turner et al, 2015). River systems and their associated landforms were traditionally considered as passive pipes of terrestrial organic carbon (OC), that would eventually be delivered to the ocean, but are now viewed as active sites of OC processing, redistribution and storage (Aufdenkampe et al, 2011).…”