| 1. |
- Alexanderson, Helena, et al.
(författare)
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Holocene Chronology of the Brattforsheden Delta and Inland Dune Field, SW Sweden
- 2015
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Ingår i: Geochronometria. - : Walter de Gruyter GmbH. - 1897-1695. ; 42:1, s. 1-16
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Tidskriftsartikel (refereegranskat)abstract
- Brattforsheden is a large glacifluvial deposit in southwestern Sweden and associated with it is one of Sweden's largest inland dune fields. Although the relative ages of the Brattforsheden deposits are well known, absolute ages from the area are few. In this study we have used optically stimulated luminescence (OSL), surface exposure (Be-10) and radiocarbon (C-14) dating to provide an absolute chronology for the deglaciation and for the Holocene development of the aeolian dunes. Our data show that the deglaciation took place just before 11 ka (11.5 +/- 0.6 ka OSL, 11.3 +/- 0.8 ka Be-10), in line with the C-14-based regional deglaciation age. Aeolian dunes started forming immediately after deglaciation and were active for at least 2000 years, well after vegetation had established. Renewed aeolian activity occurred 270-180 years ago, resulting in the deposition of sand sheets. Comparison between dating methods and studies of OSL dose distributions show that glacial, glacifluvial and littoral sediments suffer from incomplete bleaching and thus that mean OSL ages from such deposits overestimate the true depositional age. By using small aliquots and statistical age models, this effect can partly be countered. Also, some of the Be-10 ages appear too old, which may be due to previous exposure.
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| 2. |
- Alexanderson, Helena, et al.
(författare)
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Optical dating of a Late Quaternary sediment sequence from Sokli, northern Finland
- 2008
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Ingår i: Geochronometria. - : Walter de Gruyter GmbH. ; 32, s. 51-59
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Tidskriftsartikel (refereegranskat)abstract
- Interstadial and non-glacial stadial sediments collected in boreholes from Sokli in northeastern Finland have been dated by optically stimulated luminescence on quartz and feldspar grains. The quartz OSL ages follow stratigraphic order, with one exception, and support the litho- and biostratigraphical correlation with the NW European mainland climate-stratigraphy and the marine oxygen-isotope stages. Feldspar IRSL dates generally overestimate the age, probably due to incomplete bleaching. The data show that during the last glacial cycle northeastern Finland was not glaciated until MIS 5b, around 90 ka. Interstadial conditions occurred around ~94 ka (MIS 5c), ~74-80 ka (MIS 5a) and 42-54 ka (MIS 3). The OSL ages have large standard errors mainly due to small sample sizes, relatively poor luminescence characteristics and uncertainties in dose-rate determinations.
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| 3. |
- Alexanderson, Helena
(författare)
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Residual OSL signals from modern Greenlandic river sediments
- 2007
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Ingår i: Geochronometria. - : Walter de Gruyter GmbH. - 1897-1695. ; 26, s. 1-9
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Tidskriftsartikel (refereegranskat)abstract
- Ripple-laminated sandy deposits at shallow water depths in four rivers on Jameson Land, East Greenland were sampled for optically stimulated luminescence (OSL) dating. Silt-sized grains have significantly higher equivalent doses (~1.1 Gy) than sand grains (~0.1 Gy). This suggests that coarse grain-size fractions are better bleached and more suitable than fine grains for OSL dating of glaciofluvial/fluvial sediments. A sample from a sidebar deposited during the spring flood yielded 1.0 Gy (~500 years) while a subaerial deposit was completely zeroed. The spring flood deposit is considered to be most similar to deglacial conditions and incomplete bleaching of this amount (1 Gy) is generally not a significant source of error for sediments of Pleistocene age. Most samples have rather poor luminescence characteristics and are affected by thermal transfer if preheat temperatures at or above 260°C are used.
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| 4. |
- Esper, Jan, et al.
(författare)
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LONG-TERM SUMMER TEMPERATURE VARIATIONS IN THE PYRENEES FROM DETRENDED STABLE CARBON ISOTOPES
- 2015
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Ingår i: Geochronometria. - : Walter de Gruyter GmbH. - 1733-8387 .- 1897-1695. ; 42:1, s. 53-59
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Tidskriftsartikel (refereegranskat)abstract
- Substantial effort has recently been put into the development of climate reconstructions from tree-ring stable carbon isotopes, though the interpretation of long-term trends retained in such timeseries remains challenging. Here we use detrended delta C-13 measurements in Pinus uncinata tree-rings, from the Spanish Pyrenees, to reconstruct decadal variations in summer temperature back to the 13th century. The June-August temperature signal of this reconstruction is attributed using decadally as well as annually resolved, 20th century delta C-13 data. Results indicate that late 20th century warming has not been unique within the context of the past 750 years. Our reconstruction contains greater amplitude than previous reconstructions derived from traditional tree-ring density data, and describes particularly cool conditions during the late 19th century. Some of these differences, including early warm periods in the 14th and 17th centuries, have been retained via d13C timeseries detrending - a novel approach in tree-ring stable isotope chronology development. The overall reduced variance in earlier studies points to an underestimation of pre-instrumental summer temperature variability derived from traditional tree-ring parameters.
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| 5. |
- Gaar, Dorian, et al.
(författare)
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PERFORMANCE OF DIFFERENT LUMINESCENCE APPROACHES FOR THE DATING OF KNOWN-AGE GLACIOFLUVIAL DEPOSITS FROM NORTHERN SWITZERLAND
- 2014
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Ingår i: Geochronometria. - : Walter de Gruyter GmbH. - 1733-8387 .- 1897-1695. ; 41:1, s. 65-80
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Tidskriftsartikel (refereegranskat)abstract
- Luminescence properties of two samples taken from sand lenses in proglacial outwash deposits of a piedmont glacier that reached the Swiss midlands during the Last Glacial Maximum are investigated in detail. Deconvolution of CW-OSL decay curves shows that the fast component dominates the OSL signal of quartz. The chemistry of single feldspar grains, in particular the K content in different grains, is determined using wavelength dispersive spectrometry (electron microprobe), revealing an average 12.9 wt.% K of the grains contributing to the IRSL signal. D-e distributions are investigated in order to gain insights into partial bleaching, and agreement is found for quartz OSL and feldspar IR50 and pIRIR(225) ages for small aliquots and single grains when applying the Minimum Age Model. These ages are also consistent with independent age control. For one sample, ages determined using the Central Age Model result in highly overestimated ages for both feldspar and quartz.
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| 6. |
- Holzkämper, Steffen, 1974-
(författare)
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Stable isotopes in tree rings as proxies for winter precipitation changes in the Russian Arctic over the past 150 years
- 2008
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Ingår i: Geochronometria. - : Walter de Gruyter GmbH. - 1897-1695. ; 32, s. 37-46
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Tidskriftsartikel (refereegranskat)abstract
- We present results from an analysis of tree ring width and stable carbon and oxygen isotopes in tree ring cellulose of Siberian Spruce collected from remote forest islands in the northwestern Russian tundra. Ring width is often considered a proxy for summer temperatures. The aim of this pilot study was to test whether stable isotopes can provide additional information about climate during the growth of trees in this extreme environment. Comparison of ä13C and ä18O with observed meteorological data shows that there is a link between stable isotopes and winter precipitation. This may be explained by the strong influence that snow exerts on the isotopic composition of soil moisture during spring and early summer, when the new cellulose is formed. Our results show that winter precipitation in the study area was increasing from 1865-1900, and thereafter decreasing until ~1930. The 1960-1980 period was again rather humid, followed by a drying trend until 1990. The study highlights the potential of stable carbon and oxygen isotopes in tree rings as proxies for winter precipitation.
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| 7. |
- Preusser, Frank, et al.
(författare)
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Comparing different post-IR IRSL approaches for the dating of Holocene coastal foredunes from Ruhnu Island, Estonia
- 2014
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Ingår i: Geochronometria. - : Walter de Gruyter GmbH. - 1733-8387 .- 1897-1695. ; 41:4, s. 342-351
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Tidskriftsartikel (refereegranskat)abstract
- Different post-IR Infrared Stimulated Luminescence (IRSL) approaches are applied to sediments from a Holocene coastal foredune sequence on Ruhnu Island in the eastern Baltic Sea. The comparison of D (e)-values and ages determined by the different approaches is complimented by fading and bleaching experiments. The fading experiments imply strong fading of IRSL (50A degrees C) signals and no fading of any of the post-IR IRSL signals, but this is not confirmed by the determined D (e)-values. In fact, post-IR IRSL (150A degrees C) D (e)-values agree within errors with those calculated for IRSL (50A degrees C). From the bleaching experiments it is inferred that the higher values observed for post-IR IRSL at more elevated stimulation temperatures (225A degrees C/290A degrees C) are likely related to either thermal transfer and/or slow-to-bleach components within the signal. For the dating of the Holocene foredune sequence of Ruhnu Island, the post-IR IRSL (150A degrees C) approach is preferred and these agree with the limited independent age control available from radiocarbon dating. Accordingly, the sequence formed between ca. 7.0 ka and 2.5 ka ago.
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| 8. |
- Rufer, Daniel, et al.
(författare)
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Proposing new approaches for dating young volcanic eruptions by luminescence methods
- 2012
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Ingår i: Geochronometria. - : Walter de Gruyter GmbH. - 1733-8387 .- 1897-1695. ; 39:1, s. 48-56
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Tidskriftsartikel (refereegranskat)abstract
- The application of luminescence dating to young volcanic sediments has been first investigated over three decades ago, but it was only with the technical innovations of the last decade that such analyses became viable. While current analytical procedures show promise for dating late Quaternary volcanic events, most efforts have been aimed at unconsolidated volcanic tephra. Investigations into direct dating of lava flows or of non-heated volcanoclastics like phreatic explosion layers, however, remain scarce. These volcanic deposits are of common occurrence and represent important chrono- and volcanostratigraphic markers. Their age determination is therefore of great importance in volcanologic, tectonic, geomorphological and climate studies. In this article, we propose the use of phreatic explosion deposits and xenolithic inclusions in lava flows as target materials for luminescence dating applications. The main focus is on the crucial criterion whether it is probable that such materials experience complete luminescence signal resetting during the volcanic event to be dated. This is argued based on the findings from existing literature, model calculations and laboratory tests.
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| 9. |
- Sanders, Luciana M., et al.
(författare)
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Pu240+239 DEPOSITIONAL SIGNATURES AS A VIABLE GEOCHRONOLOGICAL TOOL IN THE AMAZON BASIN
- 2017
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Ingår i: Geochronometria. - : DE GRUYTER OPEN LTD. - 1733-8387 .- 1897-1695. ; 44:1, s. 142-149
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Tidskriftsartikel (refereegranskat)abstract
- Anthropogenic radionuclide signatures associated with nuclear testing are increasingly utilized in environmental science to explore recent sedimentation. In this study, we assess the suitability of Pu radioisotope analysis in floodplain lake environments in the Amazon Basin to form geochronologies during the 20th century. The Pu-240 + Pu-239 (Pu240+239) signatures in six sediment cores indicate sediment accumulation rates in the floodplain lakes of the major rivers; Amazon (2.3 mm year(-1)), Tapajos (10.2 and 2.4 mm year(-1)) and Madeira (3.4, 4.2 and 6.2 mm year(-1)). The results from this study show that Pu240+239 fallout activities, and the well documented (Pu-240/Pu-239) atomic ratios of the above ground nuclear tests which began in the 1950s, are sufficient and well preserved in Amazon flood-plain lake sediments to infer chronologies. Lead-210 dating analyses in the same sediment cores produced comparable sediment accumulation rates at three of the six sites. The differences between dating methods may be attributed to the different time scale these dating methods represent and/or in the solubility between Pb and Pu along the sediment column. The geochronologies derived from the Pu240+239 and Pb-210 methods outlined in this work are of interest to identify the effects of changing sediment accumulation rates during the previous century as a result of development, including deforestation, along the Amazon Basin which increased towards the middle of the 20th century. This study shows that Pu dating provides a viable alternative geochronology tool for recent sediment accumulation (previous similar to 60 years) along the Amazon Basin.
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| 10. |
- Zaytseva, Ganna I., et al.
(författare)
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Radiocarbon pottery dating : the chemical compounds of organic fractions, the reliability of C-14 dates (preliminary results)
- 2012
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Ingår i: Geochronometria. - : Walter de Gruyter GmbH. - 1733-8387 .- 1897-1695. ; 39:4, s. 233-240
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Tidskriftsartikel (refereegranskat)abstract
- In recent times, a large number of radiocarbon dates appeared for the Southern Neolithic on the basis of pottery dating because other organic matter has practically not been preserved. There are two organic fractions of pottery useful for dating: food residues and carbon from the pottery matrix itself. Food residues are often dated, but this material is not always preserved and is prone to being removed during the cleaning of the pottery. The clay mass of the pottery contains carbon, often directly visible upon breaking of the pottery. The article focusses on determining the chemical composition of the organic fractions in the pottery and the origin of the carbon. For this aim we used the nuclear magnetic resonance (NMR) method to identify the chemical compounds in the food residue and in the pottery matrix. As an example we used pottery from the Neolithic sites: Zamost'e (Central Russia) and the Varfolomeevskay sites (Southern European Russia, Low Volga region) from archaeological collections. The results obtained demonstrate that the food residue and the pottery matrix contain practically the same organic compounds, even if the relative abundances of various compounds are different in these materials. The origin of the carbon from pottery is discussed.
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