OSL dating of sediments from the Gobi Desert,Southern Mongolia

The present study focuses on the chronological relationship between alternating dune sand and silty water-lain sediments in the central part of the Khongoryn Els dune field in the Gobi Desert, Southern Mongolia. The 23 m high section evolved from the construction of a natural dam by west–east moving sand dunes and fluvial inundation by a river system from the mountain ranges in the south. To resolve the chronology of events, optically stimulated luminescence (OSL) dating was applied and from sedimentological and geochemical analysis the depositional processes could be characterised. Quartz OSL dating of these sediments is hindered by feldspar contamination. Thus, dating of coarse-grain K-feldspars is applied to provide a more reliable chronostratigraphy. As this fraction might be influenced by signal loss over geological time scales, the extent of fading is measured and corrected for. The resulting ages fit well in a supraregional reconstruction of Central Asian palaeoclimate. The data imply that the basal aeolian sediments were deposited 27 ka ago, while the major part of the profile was accumulated in a rather short period of time around ～15 ka. The temporal differentiation implies that the stratification of aeolian and fluvial sediments is not caused by long term climatic variations. It rather represents arid conditions with episodical fluvial activity. Samples between 20 and 15 m depth could not be taken, but it is assumed that this part of the section represents an extremely arid time period with an intensive remobilisation of sand around LGM. A dune overlying the section was deposited during the Late Holocene and represents the ongoing aridity in this region.     

Investigation on age and genesis of silcretes in Queensland (Australia)–Preliminary results

Silcretes from Queensland (Australia) were dated by means of the electron spin resonance dating technique. The results range from 1.5 to 10.8 million years; therefore, these silcretes were formed between the upper Miocene and the early Pleistocene. For a conclusive interpretation of the data geochemical and thin section analyses were also carried out. ESR dating of silcretes for the first time offers a direct approach to a chronostratigraphic framework of the genesis of these duricrusts, and of the palaeoclimatic events attributed to them.     

Applying SAR-IRSL methodology for dating fine-grained sediments from Lake El’gygytgyn, north-eastern Siberia

Lake El’gygytgyn is situated in a 3.6 Ma old impact crater in north-eastern Siberia and probably represents one of the most complete archives of Arctic climate change. Investigated here is the potential of infra-red stimulated luminescence (IRSL) using the single-aliquot regenerative-dose (SAR) approach for dating sediments from this lake. Independent age control is available from a published age model of a parallel core that is based on tuning sediment proxies with regional insolation and the results of previous multiple aliquot IRSL dating. Although the site is located within volcanic bedrock, anomalous fading seems to have little effect on the calculated ages. The modelled water content for the entire time of burial is seen as the most prominent uncertainty at this particular site. Despite these potential error sources, SAR-IRSL ages are in acceptable agreement with the given timeframe and clearly point to the possibility to establish independent chronologies at this site up to at least 400,000 years.     

Comparative Risk Assessments for the City of Cologne – Storms, Floods, Earthquakes

In this paper a methodology for a multi-risk assessment of an urban area is introduced and performed for the city of Cologne, Germany, considering the natural hazards windstorm, flooding and earthquake. Moreover, sources of the uncertainty in the analysis and future needs for research are identified. For each peril the following analyses were undertaken: hazard assessment, vulnerability assessment and estimation of losses. To compare the three hazard types on a consistent basis, a common economic assessment of exposed assets was developed. This was used to calculate direct economic losses to buildings and their contents. The perils were compared by risk curves showing the exceedence probability of the estimated losses. In Cologne, most of the losses that occur frequently are due to floods and windstorms. For lower return periods (10–200 years) the risk is dominated by floods. For return periods of more than 200 years the highest damage is caused by earthquakes.