**2. Materials and Methods**

Our experimental design involves the measurement of selective data based on sediment samples extracted from the archaeological profile and extensive image data acquired during fieldwork. The workflow is depicted in Figure 3, and a more detailed documentation of the data processing along with scripts for the programming language R is given in Online Resources 1–3 (in Supplementary Materials).

**Figure 3.** Schematic depiction of our workflow. Image processing included principle component analysis (PCA), derivation of slope rasters, colour transformation to CIELAB (Commission Internationale de l'Eclairage), and the prediction of soil organic carbon (SOC). The standardised centred log ratio (clr) of the data acquired with the portable energy-dispersive X-ray fluorescence spectrometer (p-ED-XRF) was used. Spectroscopic measurements of the sampled material were processed using standard normal variate (SNV) transformation with detrending applied to the first derivative of the *log*(1/*R*) transformed spectrum. This allowed us to create stratigraphic delineations based on extensive and selective data and to compare the performance of colour and spectral measurements to traditional p-ED-XRF data.
