INVESTIGATION OF PHYTOLITHS AS AN OSL CHRONOMETER: CAN PHYTOLITHS BE USED AS A VIABLE TOOL TO DETERMINE SEDIMENTARY DEPOSITIONAL AGE?

This study is investigating whether siliceous plant phytoliths are suitable for OSL analysis of sedimentary depositional age. Phytoliths are produced when monosilicic acid from soil is absorbed through roots of plants and is chemically altered to form silica, producing an intra or extracellular microscopic particle. Highly resistant to degradation, these silica structures are preserved in the sediment even after decomposition of organic material.

Phytoliths for this study were sub-sampled from a ~6.25 m core, intersecting two chronologically distinct alluvial terrace fills on Konza Prairie Biological Station, KS. Two 10-12 cm sections of core have been processed according to methods described below, and preliminary OSL analyses conducted.

To isolate phytoliths and determine best preparation methods for OSL analysis, different approaches from previous studies were compiled. Sediment was placed in a 10% HCl bath for 30 min, 30% H₂O₂ for 2-4 days, and wet sieved to obtain a 63-125 μm fraction. This sieve fraction underwent a 5% hexametaphosphate wash for 1 hr in an ultra-sonic bath. Mineral separation was performed using lithium-metatungstate of ~2.37 g/cm³, and XRD analyses indicated low-temperature silicate structures. Once isolated phytoliths were mounted as 1-mm aliquots and analyzed using a Risø TL/OSL DA-20 luminescence reader.

The first sample was taken from a shallow section of the core at ~2.4 m depth, chosen for its proximity to the surface, sandy texture, and lack of significant clay volume. Through OSL characterization following a low-temperature preheat quartz-SAR method we have observed exceptional dose recovery, growth exceeding 400 Gy, and equivalent doses that are comparable in magnitude to quartz samples prepared from the same portion of core. A second sample taken at ~5 m depth lacks robust characteristics observed in the first, but the reason for these differences is currently unresolved.

From analysis of further sections of core we hope to confirm results from the first sample and determine a cause for discrepancies related to sample two, while developing a more comprehensive understanding of phytolith luminescence properties. This research may provide an additional method for phytolith dating, and an alternative to quartz or feldspar OSL, applicable to many geomorphological settings.