*3.2. Clustering Results—Sedimentological Data*

Clustering results (groups) of the p-ED-XRF data are documented in Figure 6. The groups produced by depth-constrained hierarchical cluster analysis of the transformed element concentrations capture the main stratigraphic layers of the profile and, together with the on-site delineation and the sedimentological record (Figure 5), serve as a reference for the quality of all clustering results: Groups 1 and 2 cover areas of dark material, which are characterised by high water contents and are situated in layer A and at the top of layer B (sublayer 5, see Figures 5 and 6). Layer C is grouped together with the surrounding materials of layers B and D in the results of both clustering approaches.

Clustering of the pre-processed spectra of the samples showed a noteworthy influence of grinding. While layer C is grouped with the topmost layer in the ground data, it is grouped with the darker part of layer B when samples are not ground (Figure 6). Both ground and not ground samples clearly

delineate data of layer A from the rest of the data in the clustering results. Layer C is assigned to a separate group in the ground data only. Compared to the results of the p-ED-XRF data, the groups produced on the basis of the spectral data are spatially more consistent. Depth-constrained clustering increases this consistency (Figure 6).

Groups produced by the clustering of both RGB and multispectral pixel data capture layer A homogeneously. Additionally, the hierarchical clustering assigns darker parts of layers B and D to groups 1 and 2. The clustering of the RGB data groups layers A and C, while the clustering of the multispectral data groups layer C with the darker parts of layer B. Both data sets assign the topmost part of layer B (sublayer 5, see Figure 6) to groups 1 and 2. Including depth-constrained clustering showed a positive effect on group homogeneity for both RGB and multispectral-based clustering results; layer A and sublayer 5 are captured as one single group. Both depth-constrained cluster approaches of the pixel data, however, do not capture layer C, but group it together with the surrounding materials of layers B and D.
