Abstract
ABSTRACT: The development of optically stimulated luminescence (OSL) dating of sediments has led to considerable advance in the geochronology of the Quaternary. OSL dating is a well established technique to determine sediment burial ages from tens of years to few hundred thousand years. Recent studies have shown that Quaternary sediments of Brazil are dominated by quartz grains with high luminescence sensitivity, allowing the determination of precise and reliable OSL burial ages. In this paper, we show examples of OSL dating of quartz aliquots and single grains from different regions in Brazil, including young coastal-eolian Late Holocene (< 100 years) to Late Pleistocene (~ 150 ka) fluvial sediments. We discuss the OSL data and ages of sediments from carbonate and terrigenous (distributary and tributary systems) fluvial depositional contexts in Brazil. Most of the studied fluvial sediments show equivalent dose distributions with low to moderate dispersion, suggesting well bleached sediments. The comparison between aliquot and single grain data suggests that high overdispersion in equivalent dose distributions of some samples is more related with sediment mixture due to bioturbation than with incomplete bleaching during transport. Well bleached fluvial sediments contrast with the poor bleached pattern usually described for fluvial sediments in the literature. A large part of the fluvial sedimentary record in Brazil is older than the age limit for quartz OSL dating using blue light stimulation. Thus, isothermal thermoluminescence (ITL) dating protocols were tested for dating of fluvial sands from the Xingu River (eastern Amazonia). The studied sample can recover reliable equivalent doses up to 1600 Gy using the ITL 310oC signal. Therefore, this signal would be suitable to extend the age limit of quartz luminescence to the whole Quaternary or beyond (> 2 Ma) in the low dose rate (0.5 - 1.0 Gy/ka) environments typical for Brazilian sediments.
Highlights
Luminescence dating of minerals was proposed by Aitken et al (1964) as a method to determine the firing age of archaeological ceramic materials
We present the basic principles of optically stimulated luminescence (OSL) dating, along with examples of OSL dating of Late Holocene to Late Pleistocene sediments from coastal and continental settings in Brazil
Quartz from Quaternary sediments in Brazil is well suited for luminescence dating
Summary
Luminescence dating of minerals was proposed by Aitken et al (1964) as a method to determine the firing age of archaeological ceramic materials. OSL became a widely applied method for dating Quaternary terrigenous sediments following the methodological work of Murray and Wintle (2000), by introducing the single-aliquot regenerative dose (SAR) protocol. Luminescence dating is a well established method to determine burial ages of quartz and potassium feldspar from Holocene to Pleistocene sediments (100 ka; Murray & Wintle 2003, Rhodes 2011, Buylaert et al 2012). Quaternary sediments in Brazil are suitable for luminescence dating in the Holocene to Late Pleistocene range, especially due to the widespread occurrence of quartz grains with high OSL light intensity. OSL signals are bleached faster than TL signals when minerals grains are exposed to sunlight (Godfrey-Smith et al 1988) This is a major advantage of OSL over TL for determining the burial ages of Holocene and Late Pleistocene sediments. Further detailed about the SAR protocol for quartz can be found in Wintle and Murray (2006)
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