After further study, this was interpreted as a preparation layer for the later floor surface SU427, of which only a part is preserved.
3 possibilities: 1) layer that has been hardened by use of the floor surface (SU427) above it - most likely. 2) layer intentionally compacted in preparation for the floor above (preparation surface). 3) an actual floor surface - but layer above did not easily peel off, so this possibility is less likely. It seems most likely that this layer is a natural layer that was compacted by the construction and use of the battufo floor surface above (SU427), but the other two possibilities listed above remain.
ceramics illustration