Phytoliths are microscopic opaline particles commonly found in soils and sediments. They are produced in many living plant cells as the cell fills with silica, forming a solid body. Fragments of the original cellular material are trapped inside the phytolith, which is highly resistant to decomposition. Because phytoliths exist as stable entities in sediments for long periods of time, morphological analysis is used to reconstruct vegetational histories. More recently, isotopic studies of oxygen and carbon in phytoliths have been used in paleoenvironmental reconstruction. Various studies have suggested that the organic carbon trapped inside phytoliths is suitable for 14C dating since it remains protected from post-depositional contamination, but some researchers report inconsistencies in the results, advising that phytoliths may be an unreliable material. Since we also found occasions when phytoliths yielded inaccurate 14C ages, we decided that further testing was required to explain the anomalous ages.
The aim of this project was to establish the reliability of radiocarbon dating of phytoliths and to identify the critical factors in sample preparation that influence accuracy. In our view, insufficient sample preparation techniques used in previous studies were the greatest hindrance to accurate 14C AMS dates on phytoliths. We identified possible sources of contamination during pretreatment procedures that are commonly used in phytolith extraction. As a test of the reliability of our sample preparation methods, we radiocarbon dated phytoliths separated from sediments immediately above and below known-age tephras, as well as phytoliths extracted from within the tephras. We further compared our phytolith 14C age determinations with optically stimulated luminescence (OSL) ages obtained from the same sediments.
See more of Poster Session II
See more of The 10th International Conference on Accelerator Mass Spectrometry (September 5-10, 2005)