Thermoluminescence dating of ocean sediments

TLDR

Radiation from radionuclides in ocean sediments increases thermoluminescence, which is used for dating. Three methods separate sunlight‑reduced residual TL from radiation‑induced TL; the preferred method measures the reduction after a standard sunlamp exposure versus administered gamma dose, extrapolates to zero reduction to derive the natural dose, and relates it to age using dose‑rate equations. TL ages for six samples from each of two cores ranged from 9–140 ka, with satisfactory agreement to independent Cycladophora davisiana and 18O/16O stratigraphic dates for one core, and age uncertainty dominated by water‑content uncertainty.

Abstract

We describe data on the thermoluminescence (TL) of ocean sediments which leads us to propose that exposure to sunlight prior to deposition reduces any previously acquired TL to a small "residual" value. Subsequent radiation from radionuclides in the sediment increases the TL and this increase is used for dating. Three methods of separating these two TL components are described. In the preferred one the reduction in TL (R) caused by a standard sunlamp exposure is measured as a function of an administered gamma dose; extrapolation to R = 0 yields the natural dose.An equation relating this dose to the age and to dose rates derived from radioactivity analyses is presented. The details are given for six samples from each of two cores and their TL ages calculated; these range from 9–140 ka. For one core independent dates from Cycladophora davisiana variations and an 18 O/ 16 O stratigraphic marker were available for comparison; the agreement is satisfactory. The TL age uncertainty is primarily set by the uncertainty in the water content.