301-2 Assessment of Purity of Biogenic Silica Samples for Luminescence Analysis

Session: Geochronology (Posters)

Presenting Author:

Authors:

Abstract:

In recent work (Spencer et al., 2024, Quat. Geochron. 82, 101544) we have demonstrated that optically stimulated luminescence (OSL), infrared stimulated luminescence (IRSL), and thermoluminrescence (TL) signals can be measured from opal phytolith mineraloids. The phytoliths were separated from sediments and soils using density separation (<2.37 gcm^-3) and Stokes’ law settling methods, and we used SEM techniques to make qualitative assessment of the morphology and purity of the samples. A suite of biogenic silica samples, including phytoliths extracted from commercial straw using dry ashing (up to ~550°C) techniques, and a series of phytolith and diatom standard and reference materials, show similar OSL, IRSL, and TL signals. Our SEM analyses suggested a range in sample purity, with samples extracted from sediment being the least pure, emphasizing the difficulty of extracting pure samples from sediment deposits with floatation techniques.

In the work presented here we have been investigating methods to identify and quantify “contaminant” minerals in our phytolith and biogenic silica materials, ultimately with the aim to determine the extent to which the luminescence derives only from biogenic silica. We have conducted XRD and Raman spectroscopy to assess the relative proportion of amorphous to crystalline components to determine a crystallinity or purity index, and the extent to which the OSL signals are thermally quenched to indicate the presence of quartz. Results of these assessments of purity for the biogenic silica samples will be discussed.

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-11269

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