Optical dating of K-feldspar grains from Middle Pleistocene lacustrine sediment at Marathousa 1 (Greece)

Zenobia Jacobs,Bo Li,Panagiotis Karkanas,Vangelis Tourloukis,Nick Thompson,Eleni Panagopoulou,Katerina Harvati

doi:10.1016/j.quaint.2018.06.029

Abstract

Post-infrared infrared stimulated luminescence (pIRIR) measurements are reported for multiple aliquots of potassium-rich feldspar grains from sedimentary deposits at Marathousa 1 and Choremi Mine in the Megalopolis Basin in southern Greece. Ages were obtained for 9 samples from the deposits that over- and underlie as well as include the archaeological and palaeontological deposits at Marathousa 1. These sediments are sandwiched between lignite seams II and III and thought to represent sediment deposition during a single glacial period. A single age was obtained for a sample from Choremi mine. The equivalent dose estimates are based on a newly developed method presented elsewhere, and environmental dose rate determinations followed standard procedures. A specific focus of this paper is the determination of a representative estimate of time-averaged palaeo-water content of the organic and sand-rich deposits and the impact of porosity and compaction on these estimates. Ages are presented using two water content scenarios. These final ages have relatively large uncertainties, making it difficult to accurately assign deposition to a single oxygen isotope stage (OIS). Taking uncertainty into account, sediment deposition at Marathousa 1 occur sometime during OIS 12 and 11 and at Choremi mine during MIS 8. When combined with other proxy information, these results support the interpretation that the peat deposits (represented by lignite seams II and III) were deposited during warm interglacial periods, and that the intervening clastic materials were deposited during glacial periods. In this case, the ages are best interpreted as supporting deposition of sediments during MIS12. This is consistent with one of the proposed age models, but younger than the other.

Highlights

Marathousa 1 is a recently discovered Middle Pleistocene site located in the lacustrine sediments of the lignite mines of the Megalopolis basin in southern Greece (Panagopoulou et al, 2015; Harvati, 2016; Tourloukis and Harvati, 2018; Panagopoulou et al, this issue)
An initial attempt to obtain an age for a single sediment sample, using both quartz optically stimulated luminescence (OSL) and potassium-rich (K) feldspar infrared stimulated luminescence (IRSL) methods was unsuccessful; both the OSL and post-infrared IRSL signals were in dose saturation and only minimum ages could be calculated
The time elapsed since the light-sensitive electron traps were emptied can be determined from measurements of the luminescence signals from K-feldspar—from which the equivalent dose (De) is estimated—together with determinations of the radioactivity of the sample and the material surrounding it to a distance of ∼30 cm

Summary

Introduction

Marathousa 1 is a recently discovered Middle Pleistocene site located in the lacustrine sediments of the lignite mines of the Megalopolis basin in southern Greece (Panagopoulou et al, 2015; Harvati, 2016; Tourloukis and Harvati, 2018; Panagopoulou et al, this issue). An initial attempt to obtain an age for a single sediment sample, using both quartz optically stimulated luminescence (OSL) and potassium-rich (K) feldspar infrared stimulated luminescence (IRSL) methods was unsuccessful; both the OSL and post-infrared IRSL (pIRIR) signals were in dose saturation and only minimum ages could be calculated. Obtaining a reliable estimate of the equivalent dose (De) from K-feldspar grains required the development of a new procedure based on a multiple aliquot regenerative dose (MAR) procedure and the pIRIR signal from K-feldspar grains. This method is presented in Li et al (2017) and forms the basis for De determination in this study. An accurate estimate of the water content is essential as water attenuates

Methods

Results

Conclusion