Ditch and pit fills from four archaeological sites in the Baixo Alentejo region of Portugal were studied to explore the relationship between Luminescence Profiling (IRSL, OSL, TSL, sensitivity and sensitization) and X-ray diffraction (XRD) analyses. Series of small (ca. 10 g) samples were collected, through the different fill materials. XRD results show that the predominant mineral is calcite (40-90%), and this exhibited the strongest relationships with luminescence behaviour. In the present sites it was often related to high absorbed doses, and so to residual signals rather than low dose rates. Commonly, the calcite content and the absorbed dose value tended to increase from the top to the bottom of a section. Layers with lower calcite content and residual luminescence signals were used to stratigraphically define different phases of accumulation. The best reset luminescence signals for dating at these sites come from the layers with the lowest calcite content. In other cases similar absorbed doses through archaeological stratigraphies, independent of composition, were interpreted to indicate that signals in the different mineral fractions were well reset prior to accumulation in the structure.