PORTABLE X-RAY FLUORESCENCE SPECTROSCOPY OF COASTAL SALT MARSH CORES: POTENTIAL FOR USE IN LATE PLEISTOCENE STRATIGRAPHY AND PALEOTEMPESTOLOGY

Characterizing variations in the major components of marsh sediments is the basis of many salt marsh studies, including studies of Quaternary sea level, paleoseismology, geoarchaeology, and paleotempestology. The purpose of this study is to show how major sediment variations in a coastal salt marsh can be represented geochemically, and analyzed easily using hand-held field-portable X-ray fluorescence spectrometry. Such XRF units are increasingly common as they are in wide use for environmental and geochemical investigations.

Several cores of Holocene salt marsh sediment from Wassau Island, Georgia, were analyzed as part of an investigation into Holocene to Recent hurricane activity along the Georgia coast (Kiage et al., 2011). The salt marsh behind the barrier island contains sandy horizons that are interpreted as overwash deposits formed at times of dune breach by large hurricanes. Such horizons were identified on the basis of loss on ignition coupled with coarse grain size analyses.

Concurrent analyses of the core by hand-held XRF showed that the sandy horizons had some characteristic geochemical features. In particular, the quartz-rich sandy horizons were low in Fe content (total Fe < 5 g/kg), as opposed to clay-rich horizons that had Fe as high as 40 g/kg. The statistical relationship between loss on ignition and Fe content is not significant, however, because it is complicated by organic content. Organic-rich peats have both high loss on ignition as well as low Fe content (5-15 g/kg). Another complicating factor is that the thickness of sand horizons is in some cases much less than the spot size of the XRF analyzer, which is ~0.5 cm. Depending on the sedimentary context, other potential geochemical indicators include Ca (shell horizons), K (clay), and heavy metals (accessory minerals).

Despite the complications, if the equipment is available it offers an inexpensive and rapid source of geochemical data that can help to contextualize other stratigraphic observations.