*4.2. Sedimentological Data*

By quantitatively analysing sediment properties, we were able to explain several characteristics of the profile in detail. Clustering results suggest that the topmost parts of layer B (sublayer 5) are related to layer A or the intermediate stone layer. The observed high values of water content and SOC suggest sublayer 5 to be either related to construction work (compression by overlying stones) or resembling (together with the overlying stones) a prehistoric surface, which would have been of similar character to the topmost stone layer described by May [35]. Similarly to sublayer 5, the colour of layer C seems to be influenced mainly by a high water content. However, slightly increased SOC may also indicate a prehistoric surface here. The observed similarities also explain why layer C is often clustered with layer A or sublayer 5.

The performed hierarchical cluster analysis of the examined sediment properties produced similar results for the p-ED-XRF data and the recorded VIS-NIR data (Figures 5 and 6). We see this as an indicator that selective or extensive spectroscopy should be considered a fast and efficient alternative to laboratory analyses when one is aiming for the delineation of layers or an objective confirmation of the observed variance in a profile. Spectroscopy in comparison to laboratory analyses is easy and fast to apply, non-destructive, cost-efficient in the long term, and also more environmentally friendly. While our study supports the idea of using spectroscopy during archaeological excavations due to the aforementioned benefits, the methodological approach should still be considered experimental—currently, clear limitations regarding the ease of use and the on-site applicability exist.

Throughout our study, depth-constrained clustering generally improved the results, which supports preferability of this method when clustering layers, as, e.g., Schmidt et al. [43] proposed. Depth-constrained clustering also improved clustering results of the sampled pixel values significantly (Figure 6) and—with the exception of layer C—captured overall variability of the profile. Layer C is generally treated similarly in the image data and the selective data, as it is either clustered with layer A or darker parts of layers B and D. It is also noteworthy that layer C was captured most accurately by the spectral data of ground sediment samples, which underlines the potential of VIS-NIR spectroscopy for stratigraphic analyses. In addition, both the selective pixel-based approach and the extensive image-based approach distinguish between layer A and the rest of the profile.
