Defining rock-forming components of Holocene freshwater carbonates via univariate statistical and mixture analysis of computer tomography data

Abstract

Carbonate rocks are among the sedimentary systems which preserve information on the formation and diagenetic history expressed in its composition (distribution of its major rock-forming components (RFC). For estimating RFC proportions at the micro-scale, a simple counting of visible RFCs in thin sections using overlaid grids is a long-used, well-established technique. However, computer tomography (CT) analysis provides us with quantitative data in 3D at both the scale of the entire sample and a resolution defined by dimensions of the voxels at the micro-scale. The quantitative data expressed in Hounsfield units (HU) correlates with the density of RFCs. In this work statistical properties of CT-based data for selected freshwater carbonate samples from the Danube-Tisza Interfluve have been assessed using histograms and boxplots. Univariate statistical parameters characterize each sample. The maximum-likelihood method of mixture analysis has been adapted to recover and estimate the parameters of these subpopulations. Subpopulations have been defined in the form of overlapping intervals using statistical parameters gained (mean±2STD). Five major components have been defined: empty and partially or entirely filled pores by calcite, limestone micrite, dolomite micrite matrix and limonite saturated matrix.