Palaeodunes as archives of environmental change - A case study from the western Murray Basin (South Australia) based on optically stimulated luminescence (OSL) dating of single and multiple grains of quartz

This study is concerned with the reconstruction of the palaeoenvironmental history of southeastern Australia for the last ~300 ka by establishing a luminescence chronology of dune sand deposition. For this purpose, a study area in the western Murray Basin in southeastern South Australia was chosen which today is characterised by semi-arid climate conditions. Vast fields of palaeodunes, stabilised by vegetation, provide evidence of past environmental change. By dating these dunes, past climatic changes can be deciphered, providing valuable information for predicting future climate change. In total, 97 samples were collected from dune sand layers and the time of their deposition was determined using multiple grain and single grain optically stimulated luminescence dating of the quartz fraction. A significant spread in equivalent doses (De) was noticed on a multiple grain scale. In order to analyse the De-distributions in more detail and to gain information on the sources of variations in equivalent doses, single grain measurements were carried out on all samples. Based on analysis of single grain De-distributions, field observations and laboratory bleaching tests, it was demonstrated that mainly microdosimetric effects and post-sedimentary mixing by bioturbation were responsible for the spread of the De-values. Although some of the dune sands exhibited intensive pre-depositional iron crusts, they were well bleached at the time of deposition. To account for the mixing of sediment layers of different age by bioturbation, De-values were calculated using the finite mixture model (Galbraith and Green 1990). The investigation of the De-distributions of samples not affected by bioturbation demonstrated that microdosimetric effects accounted for ~20% of the observed spread in De-values. This value was used to define the allowed spread of the individual components identified by the finite mixture model. Samples with De-values >200 Gy were shown to yield unreliable equivalent dose estimates due to approaching signal saturation. Phases of substantial dune sand deposition were identified for the periods 11-12 ka, 13.5-14.5 ka, 18-38 ka, 62-73 ka, 79-112 ka, 145-185 ka and 205-215 ka, thus up to Oxygen Isotope Stage 7. The oldest depositional phase demonstrates that dune sand layers of great antiquity are preserved in the western Murray Basin. Holocene events of dune sand deposition, represented by at least two luminescence ages, were recognised at 3-4 ka, 5-6 ka and 7-8 ka. Furthermore, two zero ages and an age of 1939 ± 11 AD were obtained. Comparison of the western Murray Basin dune record with a dune record of arid central Australia (Fitzsimmons et al. 2007) showed excellent agreement between the two chronologies. This implies that similar climatic conditions prevailed over major parts of Australia during the Late Quaternary The aeolian depositional phases of the western Murray Basin broadly correlate with arid conditions recorded in other southeastern Australian sedimentary archives. Phases of very limited dune sand deposition were shown to be associated with more humid conditions. However, the relatively large errors on the luminescence ages (~10%) prevent to resolve climatic fluctuations >70 ka and the identification of older non-depositional phases in detail. The oldest, but unreliable age obtained in the present study indicates that the onset of dune formation might reach back to ~450 ka. Although this estimate may not be accurate, it agrees with previous estimates of the onset of dune formation in this area. Based on a reliable minimum De-value derived from the 2*Do-value of this sample, it is demonstrated that dune formation was initiated at least 370 ka ago. This study demonstrates that dunes in semi-arid areas are excellent sedimentary archives for the reconstruction of palaeoclimatic conditions. Single grain dating is very well suitable for establishing a sound chronology of aeolian depositional phases, and ages up to ~270 ka can be obtained with this method, provided that dose rates are low. Although the dune record might be of discontinuous nature, multiple phases of dune formation and dune stability are recorded in the dunes of the western Murray Basin. Not only peaks but also gaps in this dune record can be used for the reconstruction of aridity and humidity, respectively, provided that the chronology is based on a high number of samples. However, a detailed resolution of past climatic fluctuations in the study area was only provided for the last ~70 ka and the interpretation of the dune record has to be supported by comparison with other well dated proxy data of past climatic change

Stratigraphy of Late Quaternary fluvial terraces at the confluence of the Lech and Danube valleys

Gegenstand dieser Studie ist die würm-spätglaziale und holozäne Talentwicklung am Zusammenfluss von Lech und Donau im Nördlichen Alpenvorland. Die morphologischen Formen im Untersuchungsgebiet wurden mit Hilfe von Geländekartierungen und digitalen Geländemodellen aufgenommen. Die Ablagerungen beider Flüsse wurden in zahlreichen Aufschlüssen untersucht und deren Alter mit Radiokarbon- sowie Lumineszenzdatierungen bestimmt. Daneben wurden auch archäologische Daten und historische Karten genutzt, um die Altersstellung der einzelnen Terrassen einzugrenzen. Im Untersuchungsgebiet bildet eine spätglaziale Niederterrasse die älteste Flussterrasse innerhalb des Talbodens, die allerdings nur im Donautal unterhalb der Lechmündung erhalten ist. In beiden Tälern sind präboreale bis boreale Terrassenflächen nur kleinräumig verbreitet, während ein Sockelschotter gleichen Alters weiträumig unter jüngeren Ablagerungen anzutreffen ist. Atlantische Flussbettablagerungen sind im Untersuchungsgebiet nicht zu finden. Dagegen dominieren subboreale und subatlantische Terrassen das Lechmündungsgebiet. Die heutigen Flussläufe von Lech und Donau werden von bis zu sechs subatlantischen Terrassen begleitet. Deren Verbreitung und morphologisches Erscheinungsbild verweist im Donautal oberhalb der Lechmündung auf einen mäandrierenden Flusslauf, die der jüngsten Lechterrasse auf ein verzweigtes Gerinnebettmuster. Unterhalb der Lechmündung treten dagegen Übergangsformen beider Flussgrundrisstypen auf.researc

Chronostratigraphy of the Hochterrassen in the lower Lech valley (Northern Alpine Foreland)

Hochterrassen (High or Higher Terraces) are a prominent geomorphological feature of the Northern Alpine Foreland and have traditionally been attributed to the Rissian glaciation. However, distinct morphological sublevels observed for this feature have often raised the question of their age. This issue is exemplarily investigated here on the Langweider and Rainer Hochterrassen in the lower Lech valley using different relative and numerical dating techniques. The lowest sublevel, the Übergangsterrasse is only preserved in small patches at the western rim of the Rainer Hochterrasse and is most probably of early Würmian age. The sublevel of the Jüngere Hochterrasse is older than the Last Interglacial, as indicated by luminescence ages of overlying loess/palaeosol sequence and the development of a luvisol on top of the terrace gravel. This terrace is composed of stacked gravel units that represent at least two accumulation phases correlating with Marine Isotope Stage (MIS) 6 for the top gravel and MIS 7 to MIS 10 (or older) for the basal gravel. It is not yet clear, if the deposition of the basal gravel unit corresponds to one or more aggradation phases during the Middle Pleistocene. The highest sublevel, the Ältere Hochterrasse also shows a compositon of two stacked gravel units but so far, no numerical ages have been achieved for these units.researc

Človekov vpliv na okolje v prazgodovini: primer z obrežja Ljubljanice pri Špici (Ljubljana)

This paper presents the results of multi-proxy palaeo-ecological research (luminescence and radiocarbon dating, grain size measurement, loss-on-ignition, pollen, microcharcoal and plant macrofossil analysis), with the aim of reconstructing palaeo-environmental conditions and the impact of prehistoric people on the vegetation in Ljubljana (central Slovenia). The results of luminescence dating and pollen analysis suggest that the Late Copper Age (ca. 2500 cal. BC) archaeological settlement at Špica, which is located on the embankment of the Ljubljanica River, was built directly on silty sediment, which was deposited during the Last Glacial Maximum (LGM, ca. 20 ka). Late glacial and early/middle Holocene sediment, which is missing, was presumably removed by fluvial processes. Therefore, only environmental conditions in the late prehistory after ca. 2500 cal. BC were reconstructed. The results of palynological research suggest that mixed forests with beech, fir, oak, and hornbeam were growing near the Špica settlement. Human impact on the environment was moderate, with weak traces of agricultural activities. After the abandonment of the settlement, the traces of human impact on the environment became more apparent, especially in the Iron Age, when the pollen of plants growing on (abandoned) fields and ruderal ground (cereals, goosefoot, mugwort) and grazing indicators (ribwort plantain) increases. Fir, which is sensitive to grazing and fire, declines. A major clearance of beech forest is dated in the Early Roman Age, most probably in mid-1st century BC (ca. 162 cal. BC–AD 52). These changes of vegetation can be associated with prehistoric and Roman archaeological sites of Tribuna and Prule, which is in the vicinity of Špica.V članku so predstavljeni rezultati paleoekoloških multidisciplinarnih raziskav, s pomočjo katerih smo rekonstruirali nekdanje okoljske razmere in vpliv prazgodovinskih prebivalcev Ljubljane na takratno vegetacijo. Rezultati luminiscenčnega datiranja in pelodne analize kažejo, da je bila poznoeneolitska (pribl. 2500 cal. BC) naselbina na obrežju Ljubljanice na Špici postavljena neposredno na meljast sediment, ki se je odlagal med viškom zadnje poledenitve pred približno 20.000 leti. Poznoglacialni in zgodnje-/srednjeholocenski sediment, ki manjka, je verjetno odnesla voda, zato lahko rekonstruiramo le prazgodovinske okoljske razmere od sredine 3. tisočletja pr. n. št. naprej. Na podlagi rezultatov palinološke raziskave lahko sklepamo, da so v bližini arheološke naselbine na Špici uspevali mešani gozdovi, v katerih so prevladovali bukev, jelka, hrast in navadni gaber. Človekov vpliv je bil zmeren, zaznamo lahko šibke sledove poljedelskih aktivnosti. Po opustitvi naselbine na Špici sledovi človekovega vpliva na okolje postanejo intenzivnejši, še zlasti v železni dobi, ko naraste delež peloda rastlin, značilnih za (opuščena) polja in ruderalna tla (žita, metlikovke, pelin) ter pašnike (ozkolistni trpotec). Delež jelke, ki je občutljiva za pašo in požiganje gozda, upade. Večje izsekavanje bukovega gozda je datirano v zgodnjerimsko obdobje, najverjetneje v sredino 1. st. pr. n. št. (162 pr. n. št.–52 n. št.). Opisane spremembe vegetacije lahko povežemo s prazgodovinskimi in rimskodobnimi arheološkimi najdišči na Tribuni in Prulah, v neposredni bližini Špice

Performance tests using the lexsyg luminescence reader

International audienc

OSL, TL and IRSL emission spectra of sedimentary quartz and feldspar samples

International audienc

Dose recovery tests using Ti-related ESR signals in quartz : First results

Experimental results from ESR dose recovery tests using Ti-related absorption lines in sedimentary quartz will be presented and discussed. The tests were performed on two Late Pleistocene Australian dune sands with a known burial dose based on OSL measurements. The regenerative dose technique (after thermal annealing) was used to detect any differences between ESR estimates of the natural dose, and ESR estimates of an equal laboratory gamma-dose. The studied absorption lines show consistent results with regard to the laboratory dose, but inconsistencies regarding the recovery of the natural dose. Line-shape changes between the natural and artificially induced ESR signals are a matter of concern. These changes are probably the result of the different relative abundance of Ti–H and Ti–Li centres in the naturally irradiated and artificially irradiated sample

Daily adaptive proton therapy - the key to innovative planning approaches for paranasal cancer treatments

Background: For proton therapy of paranasal tumors, field directions avoiding volumes that might change during therapy are typically used. If the plan is optimized on the daily anatomy using daily adapted proton therapy (DAPT) however, field directions crossing the nasal cavities might be feasible. In this study, we investigated the effectiveness of DAPT for enabling narrow-field treatment approaches. Material and methods: For five paranasal tumor patients, representing a wide patient spectrum, anatomically robust 4-field-star and narrow-field plans were calculated and their robustness to anatomical and setup uncertainties was compared with and without DAPT. Based on the nominal planning CTs, per patient up to 125 simulated CTs (simCTs) with different nasal cavity fillings were created and random translations and rotations due to patient setup uncertainties were further simulated. Plans were recalculated or re-optimized on all error scenarios, representing non-adapted and DAPT fractions, respectively. From these, 100 possible treatments (60 GyRBE, 30 fx) were simulated and changes in integral dose, target and organs at risk (OARs) doses evaluated. Results: In comparison to the 4-field-star approach, the use of narrow-fields reduced integral dose between 29% and 56%. If OARs did not overlap with the target, OAR doses were also reduced. Finally, the significantly reduced target coverage in non-adapted treatments (mean V95 reductions of up to 34%) could be almost fully restored with DAPT in all cases (differences <1%). Conclusions: DAPT was found to be not only an effective way to increase plan robustness to anatomical and positional uncertainties, but also opened the possibility to use improved and more conformal field arrangements.ISSN:0284-186XISSN:1651-226