EVALUATION OF LUMINESCENCE-DATING PROCEDURES APPLIED TO LATE-HOLOCENECOLLUVIUM NEAR ST PAULS MISSION, NATAL, SOUTH-AFRICA

Colluvial deposits provide an interesting challenge for luminescence-d ating techniques because of the short and varied light-exposure histor ies of the grains prior to deposition. Results of thermoluminescence ( TL) and infrared stimulated luminescence (IRSL) measurements are prese nted for two stacked colluvial deposits from Natal. A radiocarbon date for bulk organic matter in the A horizon of the soil formed within th e surface of the lower unit provides a means of assessing the suitabil ity of various luminescence procedures for such material. The overlyin g colluvium contains grains bleached to varying extents, as shown by t he range of EDs for the coarse-grain feldspar separate obtained using the single-aliquot IRSL method. For this sample all age estimates (eit her by IRSL or TL) are too large compared with the radiocarbon age, in dicating that even the IRSL signal was not zeroed in all grains before they were buried. The underlying colluvium contains grains bleached m ore uniformly, resulting in a smaller range in the values of single-al iquot EDs; the agreement of the IRSL age with the radiocarbon age indi cates that the IRSL signals of all grains were zeroed prior to deposit ion. The TL results for this sample suggest that the signals were not totally zeroed, but had experienced considerably more light at deposit ion than the grains from the overlying unit.