Issues with integrating carbonate sand texture data generated by different analytical approaches: A comparison of standard sieve and laser-diffraction methods

Abstract

Palaeoenvironmental reconstructive work relies on sediment-texture information as a proxy for particle-transport dynamics. As the integration of data from multiple sources is often sought for studies at the regional scale, a body of work exists that addresses compatibility levels of different analytical approaches. Past insights are derived predominantly from siliciclastic deposits. This study instead addresses standard sieve and laser-diffraction methods of texture analysis on a suite of carbonate beach sands from San Salvador Island, Bahamas. While the near-equant grain shapes of siliciclastic sands generate comparable results between methods, our findings show that laser diffraction tends to overestimate the coarser fractions in carbonate sands, given indiscriminate measurement of elongate particle axes. Peloidal grains that have width-to-length ratios on the order of 0.5 can pass through much smaller mesh sizes when sieved than diffraction would suggest. The resulting deviation in analytical outputs significantly influences measures of skewness, sorting, and other derivative metrics, which vary by up to several Wentworth classes between procedures. Meaningful integration of texture data obtained by different methods is ill-advised when dealing with carbonate beach sands. Similar problems are documented for muddy deposits, wherein platy clay minerals favor size-overestimation by laser diffraction and a size underestimation by settling tube technique. An improved understanding of methodological biases resulting from application of different particle-size methods is needed to help facilitate data-reconciliation efforts. This study provides a glimpse of issues facing the integration of carbonate sand-texture information, troublesome given prevalence of irregular grain shapes.