A comparison of TT-OSL and post-IR IRSL dating of coastal deposits on Cap Bon peninsula, north-eastern Tunisia

In this study thermally transferred (TT) OSL and post-IR elevated temperature IRSL (290 °C) (pIRIR290) dating are applied to deposits covering coastal terraces on the Cap Bon peninsula, Tunisia. Both methods perform well under standard performance tests; dose recovery tests using a modern analogue show that doses relevant to our study can be recovered accurately. Residual signals in the modern analogue for both signals are very small (∼2 Gy). For the younger (<250 ka) deposits reasonable good agreement of the ages is observed between both methods, and in addition with standard quartz OSL dating. Systematic discrepancy in ages is found for the older sediments. The TT-OSL underestimate (compared to the pIRIR290 ages) is most likely due to the short lifetime of the TT-OSL trap; we estimate a lifetime of ∼0.7 Ma at 19 °C (mean ambient air temperature of the study area). This is the first time this lifetime has been derived from geological data and it is within the range of previously published laboratory estimates. This result suggests that TT-OSL is not likely to provide a significant extension of the age range beyond that available from other methods. Our preferred pIRIR290 ages suggest that the geological setting on Cap Bon is not as simple as previously suggested.