GRAIN SIZE ANALYSIS OF NATURALLY OCCURING COARSE GRAINED SEDIMENT THROUGH LASER DIFFRACTOMETRY WITH DIRECT COMPARISON TO ADDITIONAL TECHNIQUES

An understanding and determination of grain size is one of the most essential measures in a sedimentologic study. Grain size distributions are an important source of information when interpreting the sedimentary environment and as a proxy for paleohydrology.

In order to critically assess the value of grain size data sets, various methods must be directly compared for analysis. We have conducted a series of methodological experiments involving settling tube/ pipette analysis, SediGraph techniques and laser diffraction techniques using the Malvern Mastersizer 2000 on coarse-grained sediments with a medium grain size of 150 µm to 300 µm.

These various methods for measuring grain size vary greatly in their methodology and analytic error which makes the results difficult to compare when reading scientific literature. Often, the analytical error is not even reported. Detailed methodological measurements of very fine-grained sediments by laser diffraction have been reported to yield an uncertainty of ~5% at 2 sigma. These methodological procedures are followed in this study for the laser diffraction measurements on the Mastersizer 2000. The methodology for the fine-grained material was replicated with coarse-grained material as a standard for comparison to the other measurement techniques.

These comparative method studies enhance the resolution of grain size as a sedimentologic proxy and allow past studies to be directly compared to newer analytical techniques.