Direct dating of marine sediments using optically stimulated luminescence techniques: Insights from ODP cores 658B and 659A

Luminescence dating of deep ocean sediments is hampered by disequilibrium in both the 238U and 235U decay series, leading to changes in environmental dose rate over time. This disequilibrium is caused by the incorporation of unsupported “excess” insoluble isotopes (230Th and 231Pa) and “authigenic” uranium isotopes without their decay products. Excess and authigenic isotope activity can be measured or modelled and used to determine dose rate evolution and estimate appropriate dose rates for age calculation. Comparison of measured and modelled data for two Ocean Drilling Program cores, 658B and 659A, implies that excess isotope activity needs to be measured. Calculated ages are relatively insensitive to small variations in authigenic isotope activity and this quantity can be modelled sufficiently accurately for age determination. Luminescence data for both cores are consistent with independent age models, though saturation of the quartz signal causes underestimates for some deeper samples.