Grain-size distribution of volcaniclastic rocks 1: A new technique based on functional stereology

Abstract

The power of explosive volcanic eruptions is reflected in the grain size distribution and dispersal of their pyroclastic deposits. Grain size also forms part of lithofacies characteristics that are necessary to determine transport and depositional mechanisms responsible for producing pyroclastic deposits. However, the common process of welding and rock lithification prevents quantification of grain size by traditional sieving methods for deposits in the rock record. Here we show that functional stereology can be used to obtain actual 3D volume fractions of clast populations from 2D cross-sectional images. Tests made on artificially consolidated rocks demonstrate successful correlations with traditional sieving method. We show that the true grain size distribution is finer grained than its representation on a random 2D section. Our method allows the original size of vesicular pumice clasts to be estimated from their compacted shapes. We anticipate that the original grain-size distribution of welded ignimbrites can also be characterized by this method. Our method using functional stereology can be universally applied to any type of consolidated, weakly to non-deformed clastic material, regardless of grain size or age and therefore has a wide application in geology.

Grain-size distribution of volcaniclastic rocks 2: Characterizing grain size and hydraulic sorting

“…In this paper, the grain size distribution of coarse (>2 mm) fraction of volcaniclastic rocks deposited under water is statistically reconstructed by image analysis and functional stereology, using photographs of outcrops and scans of rock slabs (Jutzeler, 2012;Jutzeler et al, 2012). We explore grain size characteristics in terms of modal grain size distribution, matrix ratio, and statistical parameters such as median (D 50 ),…”

“…Data extracted from image analysis give a large choice of parameters on which to characterize and classify clastic aggregates. One of the most straightforward parameters is determining the volume of components, as volume is directly proportional to its area on a representative cross section (Reid, 1955), in contrast to object size distribution (Proussevitch et al, 2007b;Jutzeler et al, 2012).…”

“…The quantification of grain size distributions of volcaniclastic facies is greatly extended by using combined techniques of image analysis and functional stereology, developed in Jutzeler et al (2012). Clast types and their relative volume can be determined by image analysis for any clastic deposit, unconsolidated or not, on the condition that the image shows a sufficiently even surface.…”

Stereological estimation of aggregate gradation using digital image of asphalt mixture

“…The stereological method was mainly used to evaluate the three dimensional structure with two dimensional measurements [18]. So the real gradation of asphalt concrete could be estimated by stereological method.…”

“…So it is meaningful to improve the assumption of aggregate in stereological conversion. In addition, the stereological coefficients of spherical particle were determined by theoretical method [18]. Many typical methods such as Saltykov method [19] had been used to estimate the gradation in previous studies [16].…”