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Radiofluorescence on quartz: challenges towards a dating applicationHide

Project-manager: Dr. Christoph Schmidt
Projectstart: 01.09.2013
Projectnumber: SCHM 3051/2-1 und FU 417/16-1
External partners:: Prof. Dr. Markus Fuchs - external project-manager (Universität Gießen - Institut für Geographie)

Since the early beginnings in the 1950s, luminescence dating techniques have become one of the most important dating techniques in Quaternary research. The datable event is the last sunlight exposure (optically stimulated luminescence, OSL) or heating (thermally stimulated luminescence, TL) of natural minerals like quartz or feldspar. Luminescence processes during measurement occur in the course optical (OSL) or thermal (TL) stimulation. In contrast, radiofluorescence (RF) is observed during irradiation. For feldspar, RF has been successfully tested for dating application on sediments. For natural quartz separates, however, only little is known since only few studies are available.

Using innovative measurement equipment, the aim of this project is to evaluate the potential of RF of quartz for use as a dating method. Intended as a preliminary study, the project promotes methodological research in luminescence dating and consists of five parts: (1) selection and investigation of quartz reference samples using standard methods (e.g. ICP-MS, X-ray diffractometry), (2) investigation of basic RF characteristics of the chosen quartz samples, (3) development of a software tool for RF dating analysis using the numerical programming language R, (4) development of a preliminary measurement protocol for RF dating of quartz, (5) optional: comparison of RF dating results with “conventionally” (OSL/TL) determined luminescence ages. The project is seeking for a better understanding of the RF phenomenon of quartz in particular and for deeper insights into fundamental luminescence processes in general.

Modelling quartz luminescence signal dynamics relevant for dating and dosimetryHide

Project-manager: Dr. Christoph Schmidt
 Projektstart: 1.10.2015
 Projektnumber: SCHM 3051/4-1
 Funded by: DFG
 Projectmember: Johannes Friedrich
 External partners:
    - Prof. Dr. Markus Fuchs (Universität Gießen)
    - Dr. Regina Witt (East Carolina University/USA)
    - Dr. Sebastian Kreutzer (Université Bordeaux Montaigne/FR)


Both thermally stimulated (TL) and optically stimulated luminescence (OSL) of quartz are important dating techniques in archaeology and Earth-Sciences. For obtaining reliable and precise dating results, a profound understanding of the complex processes of charge transfer in the crystal lattice is essential. Recent kinetic quartz luminescence models significantly contribute to adapting existing theories to experimental observations, by simulating quartz luminescence behaviour for different scenarios (e.g., sedimentary history, laboratory measurement conditions). Although the variety of diverse existing quartz models partially appear to succeed in simulating realistic TL and OSL signals, quartz radiofluorescence (RF, luminescence emitted during ionizing irradiation) behaviour differs substantially from model predictions. This project aims at further developing and improving ‘traditional’ kinetic as well as stochastic (‘Monte Carlo’) models towards an integrated and more comprehensive model capable of reproducing a much wider range of observed luminescence phenomena (e.g., RF signal dynamics, change in peak emission wavelength with measurement temperature) as well as reflecting the range of different luminescence behaviour observed among quartz samples from different geological or geographical origin and with various sedimentary history.

Luminescence chronologies of late Pleistocene settlements in the Romanian CarpathiansHide

Project-manager: Dr. Christoph Schmidt
Projektstart: 1.10.2013
Projektnumber: SCHM 3051/1-1
Funded by: DFG


Thermoluminescence (TL) dating of heated silex artifacts is the most direct means of determining the occupation of Paleolithic settlements in the absence of carbon-bearing material and beyond the range of the radiocarbon method. Especially with regard to late Pleistocene (Late Upper Paleolithic and Mesolithic) sites, however, the uncertainty levels of TL dates are often larger than needed for reasonable resolution of the archeological record. The project thus aims to contribute to enhancing both accuracy and precision of the TL method. Therefore, two approaches will be followed: 1) Improving methods of sample purification (magnetic separation and luminescence-based detection of radiation ‘hot spots’ within the sample) and 2) generating multiple ages per specimen by means of several TL (and OSL) emissions (‘multi-emission’ dating). The latter approach is expected to increase the reliability and precision of the artifact’s age. After verification of these methods on geological silex material, they will be applied to heated artifacts from mainly Mesolithic sites in the Romanian Carpathians for which alternative dating techniques failed so far. An additional backup of TL ages will be provided by OSL dating of adjacent sediments. The expected Mesolithic ages will reduce measurement time and allow processing of a reasonable number of samples during project run time to establish chronologies for these sites. To evaluate the developed methods, their results will be compared to ‘conventional’ dates.

RLum.Network - A scientific network to analyse luminescence data with RHide

Project-manager: Dr. Christoph Schmidt
Projektstart: 2014
Projektnumber: SCHM 3051/3-1
Funded by: DFG
Projektmember: Dipl.- Inform. (FH) Manfred Fischer
External partners:
  - Dr. Sebastian Kreutzer - (Université Bordeaux Montaigne/FR)
  - Dr. Michael Dietze - GFZ Potsdam
  - Dr. Margret Fuchs - Alfred-Wegener-Institut Potsdam
  - Christoph Burow - Uni Köln

Thematic classification
Luminescence dating is one of the most important numeric dating methods of modern quaternary science. Methodological and technical improvements of the last decades allow complex and extensive data analysis today. A deficit is, however, seen in the availability of a flexible and scalable software solution for data analysis. With the release of the software package "Luminescence" in 2012, based on the statistical programming environment R, a comprehensive set of routines for the analysis of luminescence data was successfully provided for the first time. The software is understood both as a user-friendly tool for efficient use of scientific resources (e.g. human) by established methods for data analysis and as a tool for visualization, without the need of self-made software solutions.
Secondly, the R package "Luminescence" should help increaseing the transparency of generated luminescence data (age), by open source code and comprehensible algorithms. Also it should ensure the reproducibility and comparability of results from different laboratories. The latter one is of high relevance in matters of the parallelization and correlation of geoscientific and archaeological archives.


Orientation and composition of the network
The network consists of seven to eight graduate and post-doctoral young researchers which are active at various universities in Germany (Bayreuth, Gießen, Dresden, Freiberg and Cologne). They have come together informally during their graduation in the context of luminescence data analysis with R. The product of this cooperation is the R-package "Luminescence", whose maintenance and enhancement is done voluntarily by the authors.
On the one hand a broad expertise in geochronological respects (especially in luminescence dosimetry) is necessary, on the other hand a fundamental knowledge in dealing with the programming environment R is indispensable. The education (geology, geography, physics, computer science) and therefore the individual expertise of the network members complement each other perfectly to meet this demand. At the upcoming network meetings, technical aspects (e.g. in the sense of theory and measurement methods in luminescence dating) will be discussed, and the maintenance of the software as well as the implementation of new ideas into the existing R-Package "Luminescence" shall be enhanced.


Objectives
1) Maintenance and further development of the R-package "Luminescence”
This includes, inter alia, the analysis and discussion of new scientific developments in luminescence dating and their possible implementation into the existing software, the ongoing documentation of all new developments, ensuring the transparency, and the training of young scientists in relation to the package "Luminescence". In addition a user-oriented monograph shall be elaborated.
2) Application
This includes the use of the package in one’s own scientific environment, the global support of users through the forum which can be accessed by the existing website "www.r-luminescence.de" as well as the presentation of new functions at national and international conferences to extend the distribution of the software. In addition a certain degree of formalization in the analysis and presentation of luminescence measurement results shall be achieved.

Low-temperature thermochronometry using thermoluminescenceHide

Project-manager: Prof. Ludwig Zöller, Dr. Christoph Schmidt
Projektstart: 2014
Projektnumber: 04359
Funded by: Oberfrankenstiftung, Bayreuth

This project aims at testing the potential of red thermoluminescence (R-TL) emission of quartz for the purpose of low-temperature thermochronometry. To test the model assumptions, we investigate granitic quartz samples from a geothermal drill-hole in Weißenstadt (Fichtelgebirge) originating from depths up to 1500 m and corresponding ambient temperatures of up to 40-50 °C. It is expected that the normalized R-TL signal from near-surface samples is in dose saturation and thus does not further increase after additive irradiation.  With rising ambient rock temperature, the normalized natural TL signal should decrease due to isothermal decay and hence respond to additive laboratory irradiation. Corresponding observations of previous investigations, however, relate to quartz luminescence emissions with saturation doses 20-100 times lower than that of R-TL. In the frame of this project, basic R-TL properties will be studied and the saturation dose of R-TL might provide access to periods in the order of several hundred thousand or even a few million years. This is necessary to understand landscape development, geodynamics and georisks in geologically old and eroded mountain ranges such as the Fichtelgebirge.

After completion of the baseline investigations, it is intended to develop an R-TL thermochronometric method (i.e., a method to reconstruct the cooling history of rock) in the low-temperature range (30-50 °C) that is capable of quantifying the time necessary to erode the upper 1 km of the Earth’s crust. Provided that climate and petrology are constant, different exhumation rates of adjacent crustal blocks thus provide information on geologically recent tectonic activity and associated georisks through endogenic processes (e.g. earthquakes).

Testing the potential of auto-regenerated luminescence of zircons for high-resolution dating application to decipher Holocene landscape dynamicsHide

Project-manager: Prof. Ludwig Zöller
Projektmember:
 - Dr. Christoph Schmidt
 - Prakrit Nopradit
 - Manfred Fischer
Projektstart: 2015
Projektnumber:
Funded by: BFHZ (Bayrisch-Französisches Hochschulzentrum)
External partners:
 - Dr. Norbert Mercier (Université Bordeaux Montaigne, FR)
 - Dr, Sebastian Kreutzer (Université Bordeaux Montaigne/FR)

Luminescence-based chronologies of geo-archives are of crucial importance for Quaternary landscape development. Thermally stimulated luminescence (TL) and optically stimulated luminescence (OSL) of quartz and feldspar are mainly used for this purpose. The sedimentation age, i.e. the time of the last exposure to sunlight, is the ratio of the accumulated radiation dose in the mineral to the dose absorbed per unit of time (dose rate), which mainly results from natural radioactivity. The difficulty of reliably determining the external dose rate drastically reduces both accuracy and precision of luminescence ages. This is particularly true for Holocene samples, where higher precision is required to trace even the smallest landscape changes on historical time scales. An alternative, but so far insufficiently tested method is based on the auto-regenerated luminescence of zircons. Zircons have very high concentrations of U and Th (one to two orders of magnitude higher than typical sediment), and consequently a high internal dose rate. This makes it possible to neglect the much lower external dose rate for age calculation. The auto-regeneration method consists of simply measuring the luminescence and subsequently storing the zircon sample in the dark until a measurable luminescence signal has again been built up by the high internal radiation. The signal after this known storage period is then compared with the natural signal to determine the sedimentation age. The Pilat dune was chosen as a 'natural laboratory' to test this method because it has been intensively studied over the past few years and already has reference chronologies based on feldspar IRSL and C-14 data. These studies are intended as a pilot project to initiate bilateral cooperation between the two laboratories.


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