Alicja Chruścińska

Age and sedimentological features of fluvial series in the Toruń Basin and the Drwęca Valley (Poland)

The deposits of the Toruń Basin are dominated by a few-metre thick sand series which fill up buried valley-like depressions. In many cases they underlie the Weichselian till which builds up the ice marginal streamway (pradolina) terraces or they are exposed at the basin slopes. As the results of the geological and sedimentological studies, as well as of the dating of the deposits at the sites in the Toruń Basin indicate, the deposits include two fluvial series accumulated before the advancement of the Leszno Phase ice sheet, i.e. in Middle Weichselian and at the beginning of Late Weichselian. The oldest fluvial series connected with the Saalian Glaciation was found at the mouth section of the Drwęca Valley. The fluvial system of the Toruń Basin during Middle Weichselian and at the beginning of Late Weichselian developed in two phases of the sand-bed braided river. During the first one the river channel were dominated by large mid-riverbed sandbars, while during the second phase the water flow was smaller and, as a result, low transverse sandbars and two-dimensional dunes developed. Other active river channel also showed low-energy flows, more intensive meandering than in the case of the braided rivers, as well as sandy side-bars. Analysis of the rounding and frosting of the quartz grains indicate that the studied series of the Weichselian sandy deposits represent alluvia of a river which were fed from two diverse sources. The first one might have represented the alluvia of a warm river which transformed its load, while the other one might have mainly carried the underlying Quaternary deposits.

Chronostratigraphy of the Vistulian Glaciation on the Kujawy Moraine Plateau (Central Poland) Based on Lithostratigraphic Research and OSL Dating

Chronostratigraphy of the Vistulian Glaciation on the Kujawy Moraine Plateau (Central Poland) Based on Lithostratigraphic Research and OSL Dating The subject of the investigations presented here is fixing dilemmatic character (transgressive or recessive) of the Poznań phase of the Vistulian (Weichselian) Glaciation and answering the question about the possibility of lithostratigraphic separation of this phase from the Leszno phase in the region of so called Vistula lob. Here we present the outcomes of the research project carried out on a few tills exposures, which constitute the sedimentological record of the last ice sheet advance on the Kujawy Moraine Plateau. The absolute ages of 17 samples (collected from fluvial deposits uncovered in the geological logs) have been determined by means of the OSL method applying the single aliquots regenerative (SAR) dose protocol. The OSL data are analysed with regard to supposed bleaching conditions at the moment of the last transport and deposition of the material. In conclusion, some remarks on suitability of fluvial sands for OSL dating are made. In most of the investigated sites, there appears to exist only a single till level associated with the main stage of the Vistulian Glaciation. This fact and the results of OSL dating support the hypothesis, that the Poznań phase in Kujawy Moraine Plateau is not a distinct lithostratigraphic unit, but it is a recessive phase of the last glaciation.

USING THE TL SINGLE-ALIQUOT REGENERATIVE-DOSE PROTOCOL FOR THE VERIFICATION OF THE CHRONOLOGY OF THE TEUTONIC ORDER CASTLE IN MALBORK

Using the TL Single-Aliquot Regenerative-Dose Protocol for the Verification of the Chronology of the Teutonic Order Castle in Malbork The Teutonic Order Castle in Malbork is one of the precious medieval monuments in Europe. Because of the lack of natural rock resources in Pomerania, its walls are built almost exclusively of bricks. The huge volume and rich historical knowledge about the Malbork Castle makes it a marvellous object for TL dating. The parts of well known age can serve for the verification and improvement of dating method. Subsequently, gained in such way knowledge and experience can be applied for discovering the history of the rest of the castle. Here, the preliminary results of investigations which are still in progress, are presented for 5 brick samples. The applied TL dating procedure is described in detail. The very good accuracy of equivalent dose is achieved by the TL single-aliquot regenerative-dose protocol. The effect of wall inhomogeneity connected with the difference between the activity of the brick and mortar is discussed.

Estimation of OSL trap parameters by optical “cleaning” — a critical study

The so-called thermal “cleaning” applied in thermoluminescence analysis allows distinguishing TL signal originating from different traps of comparable thermal depths. Here, the detailed study on the suitability of a similar approach — which can be called optical “cleaning” — for the analysis of OSL process has been carried out by means of computer modelling. The optical “cleaning” is realized by short optical stimulation applied directly after irradiation. It turns out that this approach does not help to separate signals related to various traps having similar optical cross-section (OCS) values. For some sets of trap parameters, sufficiently good reconstruction of the trap optical cross-sections can be achieved by the analysis of the conventional OSL curve obtained directly after sample irradiation, while the OSL curve analysis after “cleaning” does not provide any additional data. For other cases the analysis of both curves with and without “cleaning” leads to optical cross-section values different from those assumed in the model, but just in such situations the optical “cleaning” can be helpful. The differences between the OSL components of the conventional curve and the one obtained after “cleaning” can be used as indicators of an incompatibility of the trap parameters obtained from the OSL analysis with their actual values.

Luminescence dating of bricks from the gothic Saint James Church in Toruń

Saint James Church in Toruń is one of the most important gothic monuments in Poland. The date of the beginning of its construction is known from historical reports but the earlier history of the site remains undiscovered. During the archaeological excavations in years 2010 and 2011 five brick samples were collected for luminescence dating as well as four additional samples from the brick surroundings for the dose rate estimation. The equivalent dose was determined by TL and OSL methods. The TL results differ significantly from the OSL results but the last ones are verified by historical knowledge and radiocarbon dating. Establishing the dose rate from gamma rays needs a special attention because of the complex course of the foundations of the church. The details of the applied approach are presented in the current work. The results obtained indicate that a solid brick construction existed at the site of the presbytery of the Saint James Church before it was build.

Ancient thermoluminescence investigated by the fractional glow technique

Abstract The purpose of our research was to determine the energy density spectrum of traps responsible for ancient thermoluminescence (TL). The ancient TL (natural TL) occurs in some geological materials as result of excitation by natural ionising radiation. In such a case, the dose rate is very low in comparison with sources used in laboratories. The improved version of fractional glow technique (FGT) is for the first time applied to ancient TL. Geological material of high purity (mainly quartz grains) is chosen to avoid any pretreatment. It allows to observe natural TL unaffected by any artificial processes. Since FGT requires relatively high level of accumulated TL only old samples can be investigated. At least two groups of traps at 1.5 and 1.7 eV can be seen in the obtained energy spectra. However, our results show that TL in the range used for dating is determined by the traps at 1.7 eV. This group of traps, with the frequency factor ranging from 1012 to 1013 s−1, is characteristic of quartz. Hence, the corresponding live time of the trapped carriers ranges from 106 to 107 yr. This way the fundamental assumption of TL dating method is directly confirmed.