Infrared Radiofluorescence Dating: New Insights into the (Upper) Dating Limit, Grain Size and Feldspar Chemistry

Abstract

Accurate luminescence dating of feldspar has long been hampered by the effect of athermal signal loss (anomalous fading) when using luminescence dating techniques that make use of recombination centres. Infrared radiofluorescence (IR-RF) dating is a luminescence dating technique that makes use of the principal trap and is therefore theorised to not suffer from fading to a significant extent. Extensive laboratory investigations have been done to better constrain and exploit the IR-RF signal and mechanisms but remarkably few have applied the technique to large sequences of natural sediments with known age control. In this dissertation the utility and effectiveness of IR-RF dating was investigated and tested on coarse-, mid- and polymineral fine-grains of feldspar with a view to evaluating the upper dating limit of IR-RF as well as compared IR-RF with the recently developed novel infrared photoluminescence (IRPL) dating technique. Initially 10 coarse-grained K-feldspar samples (~25 to ~900 ka) from the Luochuan loess-paleosol sequence were measured and compared with age control and it was found that a bleaching time of 1500 s (between the natural and regenerated measurements) underestimated across all but the youngest sample while a longer bleach of 20 000 s resulted in good agreement with the age control up to 300 ka (5 samples) and underestimated for the older samples. Construction of the natural and laboratory dose response curves across the sequence revealed significantly different curve shapes for the shorter bleaching time and consistent curve shapes for the longer bleaching time, highlighting the importance of the longer bleach time. The potential of the IR-RF signal for dating was then tested on 6 polymineral fine-grained samples, and it was observed that the IR-RF signal did not describe the characteristic decreasing stretched exponential curve shape, these results were compared with Na- and K-feldspar mid-grain fractions of the same samples. The essentially flat curves were attributed to the dominance of Na- feldspar and quartz in the polymineral fine grains. Despite the flat IR-RF signals and poor dose recoveries, the age results for the polymineral fine-grains were consistent with age control up to 300 ka, the Na-feldspar mid-grains up to 350 ka and the K-feldspar mid-grains up to 200 ka. A comparison of two IR-RF signals (at room temperature, RFRT; and at 70 °C, RF70) and two IRPL signals (stimulated at 880 nm, IRPL880; and at 955 nm, IRPL955) on 4 coarse-grained coastal sediments (~ 133 to 223 ka) from Sardinia showed good agreement with age control for all signals within 2σ. The IR-RF signal is an effective dating tool up to 300 ka for coarse- and polymineral fine-grains and it’s performance is comparable with IRPL dating.

Die Dissertation ist gesperrt bis zum 31. August 2025 !