Abstract

Salt-marsh sediments can provide important achives of past sea levels if they can besecurely dated. This thesis investigates eight methods for dating salt-marsh sediments.These include traditional and established dating methods (¹⁴C dating and theradionuclides ¹³⁷Cs and ²¹ºPb) and more novel approaches to dating the deposition ofsalt-marsh sediments (palaeomagnetic dating, the use of' atmospheric stable leaddeposition, tephra chronologies, pollen markers, SCP analysis and the use ofatmospheric ¹⁴C 'bomb spike' and high-precision AMS ¹⁴C measurements). Sites wereselected to provide contrasting sediment sequences that differed both in lithology andaccumulation rates and included salt marshes from the Taf estuary (southwest Wales),the Arne Peninsula (southern England) and Vioarholmi (western Iceland).The investigations in the Taf estuary produced the first palaeomagnetic chronology froma salt marsh. From the Arne Peninsula this thesis reports the first successful use ofbomb-spike calibrated ¹⁴C analyses in a salt marsh as well as high-precision AMS ¹⁴Cages for the 'problem' period AD 1700-1950. Stable Pb analysis at all three sitesproduced a number of chronological markers that signalled the timing of increases inindustrial Pb emissions, and the later use of Pb petrol additives during the 20th century. Inaddition, a unique isotopic signal, attributed to the working of Pb metal during the heightof the Roman Empire in Europe, was found in the Icelandic sediments.The radionuclides ²¹ºPb and ¹³⁷Cs produced precise chronologies for the last 100 yr in theTaf estuary. However, post-depositional mobility of ¹³⁷Cs on the Arne Peninsula and low²¹ºPb concentrations at Vioarholmi prevents the construction of reliable ²¹ºPb and ¹³⁷Cschronologies. In contrast, the use of tephra at Vioarholmi, and pollen and spheroidalcarbonaceous particle markers on the Arne Peninsula, showed great potential asindependent unique-event dating tools that could be used to constrain conventional ¹⁴Ccalibrations. Finally, the chronological information produced by all the individual methodswas combined to construct an integrated chronology for each site. This approachsignificantly reduced age uncertainties and produced higher resolution, and more robust,salt-marsh sedimentation histories

Document Type

Thesis

Publication Date

2007

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