# Geochronology/Optically stimulated luminescence

Dating techniques of interest to archaeologists include thermoluminescence, optically stimulated luminescence, electron spin resonance, and fission track dating, as well as techniques that depend on annual bands or layers, such as dendrochronology, tephrochronology, and varve chronology.

## Quartz

In quartz a short daylight exposure in the range of 1–100 seconds before burial is sufficient to effectively “reset” the OSL dating clock.
Single Quartz OSL ages can be determined typically from 100 to 350,000 years BP, and can be reliable when suitable methods are used and proper checks are done.

## Sediments

Optical dating using Optically stimulated luminescence (OSL) has been used on sediments.

## Multiple-aliquot-dose method

In multiple-aliquot testing, a number of grains of sand are stimulated at the same time and the resulting luminescence signature is averaged. The problem with this technique is that the operator does not know the individual figures that are being averaged, and so if there are partially prebleached grains in the sample it can give an exaggerated age.

## Single-aliquot-regenerative-dose method

In contrast to the multiple-aliquot method, the Single-aliquot-regenerative-dose (SAR) method tests the burial ages of individual grains of sand which are then plotted. Mixed deposits can be identified and taken into consideration when determining the age

## Infrared stimulated luminescence

Infrared stimulated luminescence (IRSL) dating of potassium feldspars has been used.

## Feldspars

Feldspar IRSL techniques have the potential to extend the datable range out to a million years as feldspars typically have significantly higher dose saturation levels than quartz, though issues regarding anomalous fading will need to be dealt with first. Ages can be obtained outside this these ranges, but they should be regarded with caution. The uncertainty of an OSL date is typically 5-10% of the age of the sample.

## Surfaces

Surfaces made of granite, basalt and sandstone, such as carved rock from ancient monuments and artifacts in ancient buildings has dated using luminescence in several cases of various monuments.

## Thermoluminescence

Thermoluminescence (TL) research was focused on heated pottery and ceramics, burnt flints, baked hearth sediments, oven stones from burnt mounds and other heated objects.
TL can be used to date unheated sediments.
TL dating of light-sensitive traps in geological sediments of both terrestrial and marine origin became more widespread.

## Calcite

TL traps in calcite could be bleached by sunlight as well as heat.

## Radiocarbon dating and OSL

In a study of the chronology of arid-zone lacustrine sediments from Lake Ulaan in southern Mongolia, OSL and radiocarbon dates agreed in some samples, but the radiocarbon dates were up to 5800 years older in others.
The sediments with disagreeing ages were determined to be deposited by aeolian processes: westerly winds delivered an influx of $^{14}$ C-deficient carbon from adjacent soils and Paleozoic carbonate rocks, a process that is also active today; reworked carbon changed the measured isotopic ratios, giving a false older age, but the wind-blown origin of these sediments were ideal for OSL dating, as most of the grains would have been completely bleached by sunlight exposure during transport and burial, the OSL dating method is superior to the radiocarbon dating method, as it eliminates a common ‘old-carbon’ error problem.

## Allerød Oscillation

The "Allerød Chronozone, 11,800 to 11,000 years ago".
"Lommel (1) is in northern Belgium, near the border with the Netherlands. At 12.94 ka (2), this site was a large late Glacial sand ridge covered by open forest at the northern edge of a marsh. More than 50 archaeological sites in this area indicate frequent visits by the late Magdalenians, hunter-gatherers who were contemporaries of the Clovis culture in North America. Throughout the Bölling-Allerod, eolian sediments known as the Coversands blanketed the Lommel area. Then, just before the Younger Dryas began, a thin layer of bleached sand was deposited and, in turn, was covered by the dark layer marked "YDB" above. That stratum is called the Usselo Horizon and is composed of fine to medium quartz sands rich in charcoal. The dark Usselo Horizon is stratigraphically equivalent to the YDB layer and contains a similar assemblage of impact markers (magnetic grains, magnetic microspherules, iridium, charcoal, and glass-like carbon). The magnetic grains have a high concentration of Ir (117 ppb), which is the highest value measured for all sites yet analyzed. On the other hand, YDB bulk sediment analyses reveal Ir values below the detection limit of 0.5 ppb, suggesting that the Ir carrier is in the magnetic grain fraction. The abundant charcoal in this black layer suggests widespread biomass burning. A similar layer of charcoal, found at many other sites in Europe, including the Netherlands (3), Great Britain, France, Germany, Denmark, and Poland (4), also dates to the onset of the Younger Dryas (12.9 ka) and, hence, correlates with the YDB layer in North America."
Usselo is the type site for the 'Usselo Soil', the 'Usselo horizon' or 'Usselo layer', a distinctive and widespread Weichselian (Lateglacial) buried soil, paleosol, found within Lateglacial eolian sediments known as 'cover sands' in the Netherlands, western Germany, and western Denmark; classified as either a weakly podzolized Arenosol or as a weakly podzolized Regosol, where numerous radiocarbon dates, optically stimulated luminescence dates, pollen analyses, and archaeological evidence from a number of locations have been interpreted to show that the Usselo Soil formed as the result of pedogenesis during a period of landscape stability during the Allerød oscillation that locally continued into the Younger Dryas stadial as a marker bed.
The abundant charcoal, which is found in the Usselo Soil, and contemporaneous Lateglacial paleosols and organic sediments across Europe, may have been created by wildfires caused by a large bolide impact, based upon the reported occurrence of alleged extraterrestrial impact indicators and hypothetical correlations with Clovis-age organic beds in North America. However, the contemporaneous nature of the Usselo Soil with Clovis-age organic beds in North America, the presence of impact indicators within it, and the impact origin of the charcoal may only be apparent.

## Marine Isotope Stage 3

    Stone hand axes found at Lynford Quarry
* Discoid hand axe
* Cordiform hand axe
* Amygdaloid hand axe
In archaeology, a bout-coupé is a type of handaxe that constituted part of the Neanderthal Mousterian industry of the Middle Palaeolithic. The handaxes are bifacially-worked and in the shape of a rounded triangle. They are only found in Britain in the Marine Isotope Stage 3 (MIS 3) interglacial between 59,000 and 41,000 years BP, and are therefore considered a unique diagnostic variant.
Lynford Quarry is the location of a well-preserved in-situ Middle Palaeolithic open-air site near Mundford, Norfolk.
The site, which dates to approximately 60,000 years ago, is believed to show evidence of hunting by Neanderthals (Homo neanderthalensis). The finds include the in-situ remains of at least nine woolly mammoths (Mammuthus primigenius), associated with Mousterian stone tools and debitage. The artefactual, faunal and environmental evidence were sealed within a Middle Devensian palaeochannel with a dark organic fill. Well preserved in-situ sites of the time are exceedingly rare in Europe and very unusual within a British context.
The site also produced rhinoceros teeth, antlers, as well as other faunal evidence. The stone tools on the site numbered 600, made up of individual artefacts or waste flakes. Particularly interesting were the 44 hand axes of sub-triangular or ovate form.
The site was dated to Marine Isotope Stage 3 using Optically Stimulated Luminescence dating of the sand from the two layers of deposits within the channel.

## Neanderthals

In "Greece [optically stimulated luminescence (OSL) dating] has produced dates of over 400,000 years old. The sampling itself took place by moonlight… as exposure to the sun would ruin the process, having initially studied in detail the stratigraphy".