Assessing quartz luminescence sensitivity protocols for fine-grained sediments in marine sediment cores

Applications of quartz luminescence beyond sediment dating are expanding rapidly. A growing number of studies have successfully applied quartz optically stimulated luminescence (OSL) and thermoluminescence (TL) sensitivities in sediment provenance investigations and palaeoclimate reconstructions based on marine sediment cores, which are usually composed of fine-grained sediments (silt and clay), demanding measurements on polymineral samples. However, the procedures during sample preparation and the luminescence measurement conditions for determining the quartz OSL and TL sensitivities of fine-grained polymineral samples have not yet been extensively assessed. Here, we present the results of five different tests designed to determine whether the current procedures employed when preparing the samples and measuring their quartz luminescence sensitivities could be improved and/or simplified. The tests include assessing the dependency of quartz OSL and TL sensitivities on: (1) luminescence measurement conditions (i.e., with and without preheat, with light stimulation at room temperature and at 125 °C, based on natural and laboratory dose); (2) aliquot mass; (3) number of aliquots per sample; (4) grain size selection; and (5) feldspar content. Tests were performed on polymineral fine sediments from two marine cores, GeoB16206–1 and M78/1-235-1, recovered from the western equatorial Atlantic, close to the mouth of the Parnaíba and Orinoco rivers, respectively. In general, our results show that the procedures when preparing polymineral aliquots for quartz OSL or TL sensitivity measurements can be easily optimized on a case-by-case basis, saving time and resources. Our key result is that quartz OSL sensitivity obtained using natural signals and measured without thermal treatments (Test 1) are very similar to the results obtained using regenerative doses and preheating. This opens the possibility of reducing the OSL measurement time by 70 % and of scanning marine sediment cores with portable luminescence readers without the use of radiation sources for signal regeneration. Tests 2 and 3 show that both OSL and TL sensitivity results given by more than six aliquots or by aliquots made of 0.4 mg to 5 mg are indistinguishable. Waiting longer settling times to subsample finer fractions before mounting the aliquots (Test 4) is helpful to reduce feldspar, but it may also reduce the quartz significantly, limiting the %BOSL_1s analysis. Finally, including an etching step to reduce feldspar (Test 5) is a helpful procedure to improve the TL and OSL sensitivity analysis, but not necessarily feasible for routine application with hundreds of samples.