QUANTIFYING THE INFLUENCE OF INTER-OBSERVER VARIATION AND MEDIUM TYPE (THIN-SECTION VERSUS POLISHED SLAB) ON ALPHA DIVERSITY ESTIMATES

Both polished slabs and thin-sections are frequently used for equal area quadrat counts when quantifying the alpha diversity (taxa-richness) of a given fossil ecosystem. While these two mediums are similar, their inherent differences in resolution may lead to discrepancies in alpha diversity estimates calculated from each. This study quantifies the differences in alpha diversity estimates produced using either polished slabs or thin-sections for equal area quadrat counts. A set of six Upper Triassic (Norian) reef carbonate samples were collected from Gosaukamm Mountain in Austria and processed to make polished slabs and thin-sections. Equal area quadrat counts were used to record all macroscopic reef building fossil organisms in each sample, and the results obtained from each polished slab were compared to those from its corresponding thin-section. An initial test for significance found no significant difference between alpha diversity estimates produced using these two mediums. Additionally, the same set of twelve samples was analyzed using the same criteria by an additional researcher, and the results were investigated to understand how inter-observer variation may influence this type of data. Bray-Curtis dissimilarity was used to compare the estimated composition of each polished slab with the corresponding thin-section, as well as the results obtained by different observers when analyzing the same sample. The results of this study show the extent of the differences that exist in the accuracy, consistency, and reliability between these mediums and between observers. By quantifying how these factors may influence paleoecological data, this study aims to establish a standard by which results can be compared across studies.