When distinguishing types of stratigraphic units, I have always respected the principle defined by Harris: stratification units are the result of deposition events, ie. deposit = pouring (deposition) of material, negative = excavation (removal) of material, structure = location of the structure dividing the stratigraphy on independent stratigraphic branches.
However, sometimes one encounters a situation where this system is not sufficient. For example, in the case of finding situations where it is necessary to record a stratigraphic feature that does not meet the definition – typically traces of overburning (fireplace, furnace), as shown in Fig. 01. Overburning does not correspond to deposition / removal of stratigraphic material, but it makes sense in record the documentation, ie assign it the identifier SU.
The cut of LaTene two-chamber pottery kiln with overburning traces on yellow loess.
René Masaryk warned me that a better way to define SU than “event of deposition” is a “process leaving traces” in the archaeological record – such as seeping water, fire that stains loess, and so on …