Kenneth Lepper

Equivalent dose distribution analysis of Holocene eolian and fluvial quartz sands from Central Oklahoma

Abstract Holocene quartz sands were collected from fluvial terrace deposits and eolian dune deposits adjacent to the North Canadian and Cimarron Rivers and their tributaries in Central Oklahoma. Single aliquot regenerative dose optically stimulated luminescence techniques were employed to generate equivalent dose (ED) distribution histograms for each sample. We hypothesize that the ED distributions are convolutions of the distribution arising from natural sedimentary processes, influenced primarily by the degree of solar resetting experienced by individual grains, and a distribution due to experimental error. An estimation of the experimental error distribution for each sample was made and this was then deconvolved from the experimentally measured ED distribution to reveal the ‘sedimentary process’ ED distribution. Objective methods for determining EDs, uncertainties, and confidence parameters from the deconvolved distributions are presented.

Concepts and approaches to in situ luminescence dating of martian sediments

In this paper we present the concept of a robotic instrument for in situ luminescence dating of near-surface sediments on Mars. The scientific objectives and advantages to be gained from the development of such an instrument are described, and the challenges presented by the Mars surface environment to the design and operation of the instrument are outlined.

Comparison of SAR techniques for luminescence dating of sediments derived from volcanic tuff

Abstract In this investigation we evaluate several proposed optically stimulated luminescence single-aliquot regeneration (OSL SAR) procedures to determine which technique has the greatest potential to yield accurate ages for samples collected from tuff-derived alluvial sediments within the narrow, sharply incised canyon systems of the Pajarito Plateau of northern New Mexico. The SAR data collection methods evaluated are: infrared-stimulated luminescence (IRSL), post-IR blue-OSL, IRSL with TL annealing cycles on polymineral fine-grains, and blue-OSL on quartz fine sand. A single-grain laser luminescence (SGLL) procedure for quartz sand is also evaluated. Age estimates obtained from these methods are compared with radiocarbon, soil PDI (profile development index), and IRSL multi-aliquot additive dose (MAAD) age constraints. Our results indicate that the modal D e of quartz sand SGLL dose distributions yield ages that are consistent with radiocarbon and PDI age constraints for the tuff derived sediments in this investigation and appears to be the most promising method for studies in this area. Additionally, two fine-grained polymineral methods, IRSL SAR and traditional IRSL MAAD, produced ages that were generally in agreement with the SGLL ages and with available 14 C and PDI age constraints. At the present stage of research, we advocate using quartz sand SGLL in conjunction with IRSL SAR or even IRSL MAAD for polymineral fine-grains to provide the most robust and reliable luminescence age data sets for tuff-derived sediments.

Characterization of luminescence properties of insoluble mineral grains extracted from the Greenland Summit GRIP ice core, and their potential for luminescence dating

Abstract We describe several optically stimulated luminescence (OSL) and thermoluminescence (TL) properties of insoluble mineral grains extracted from the Greenland summit GRIP ice core in order to examine the potential of these techniques for age determination of these materials. Since the dust grains examined in this work were exposed to natural and artificial light at many stages prior to luminescence analysis, the purpose of the experiments reported herein was not to make age determinations, but rather to evaluate the general suitability of dust grains extracted from ice cores for luminescence dating. The measurements indicate that the fine-grained dust has a wide dynamic dose response range, with limited saturation effects being seen until absorbed doses of ∼1000 Gy. Furthermore, the samples TL and OSL signals were stable over the time intervals evaluated in this study and readily susceptible to bleaching by exposure to sunlight. These three properties form a stable base for the development of luminescence dating procedures for insoluble mineral grains recovered from ice cores. The experiments demonstrate that such procedures can be carried out on sample masses of less than 1mg.

The effect of evaporated salt solutions on the optical dating properties of JSC Mars-1: "seasoning" for a Mars soil simulant.

Optically stimulated luminescence dating, or optical dating, is an established terrestrial geochronometric technique that is being adapted to date sedimentary deposits and landforms on the surface of Mars. Recent discoveries have highlighted the astrobiological significance and occurrence of halite on the surface of Mars. The objective of the experiments in this study was to create a simplistic analogue of the sedimentary material that would result from evaporation of ion-containing pore water out of martian regolith and evaluate the influence the evaporated salts would have on in situ optical dating of silicate sediments. The radiation dose response, as measured by infrared stimulated luminescence (IRSL), from evaporated mixtures of JSC Mars-1 and solutions of sodium chloride and calcium sulfate was documented. The results suggest that the presence of CaSO(4) and NaCl within the aggregated particles does not have adverse effects on IRSL dose response and that aggregates of this type exhibit dose response characteristics that are appropriate for optical dating.