Influence of sedimentological composition on OSL dating of glaciofluvial deposits : examples from Estonia

We assess the suitability of luminescence (TL and OSL) dating techniques for establishing a precise Late Pleistocene chronology for the northern Baltic area, and show on the basis of the fine sand/coarse silt fraction of subaqueous deposits, how sedimentological composition influences the dates obtained. Turbidity, loading by fine suspended material, water depth, velocity of outwash streams and transport length, and also perhaps rapid night-time sedimentation and incorporation of older, unbleached particles are factors that variably influence the extent of bleaching of the luminescence signal, and thus, cause variability of dates obtained. Alongside reliable dates for "late-glacial" deposits between 11 000-15 000 OSL years BP, many entirely unreliable dates from 8 000 ±300 to 114 000 ±8 000 OSL years BP have been obtained. This means that the age determination of glaciofluvial deposits is extremely difficult in practice. This applies particularly to intermorainic sediments, the exact genesis of which is unknown. The paper is addressed to the investigators wishing to use luminescence dating techniques to establishing the Pleistocene chronostratigraphy of glaciofluvial deposits.