bluuebunny/crossref_metadata_2025_split huggingface dataset:
Palaeoenvironmental reconstruction and OSL dating of terrestrial Eemian deposits in the southeastern Netherlands
Authors: Schokker Jeroen , Cleveringa Piet , Murray Andrew S. 
Published: March 2004

AbstractThe Roer Valley Graben in the southeastern Netherlands is a subsiding area situated just south of the maximum extent of the Pleistocene glaciations. In this area, Eemian (marine isotope stage 5e) clastic and organic deposits have been preserved in a terrestrial sedimentary environment. Deposition took place in the early Eemian (regional pollen zones E2–E3) and late Eemian (E5–E6A–E6B). The sedimentary sequence contains a hiatus during the E4A–E4B–E5 regional pollen zones. Sedimentary and palynological data reveal that both the presence and extent of the Eemian deposits are intimately linked to the local groundwater‐level history and clastic sediment flux. Changes in these environmental factors are likely to be related to changes in the global climate. Optically stimulated luminescence (OSL) dating has been applied to provide an absolute time frame for the Late Quaternary deposits in the area. This study is thereby the first to present a reliable quartz OSL dating (114±12 ka) for terrestrial Eemian deposits in The Netherlands. Copyright © 2004 John Wiley & Sons, Ltd.
Luminescence dating of quaternary sediments: recent advances
Authors: Duller G. A. T. 
Published: March 2004

AbstractLuminescence dating is unique amongst geochronological methods in dating the deposition of sediments based upon the properties of the constituent minerals. For Quaternary sediments the event being dated is the last exposure of the grains to daylight, and an implicit assumption is that this exposure was sufficient to remove any pre‐existing signal. Until recently it has been difficult to test this assumption, other than by dating samples from a given depositional context with an age that is known from independent methods. There have been a series of technological and methodological developments in the past 5–10 yr that make it possible to undertake many replicate measurements of the luminescence from a single sample and hence to explicitly test whether for a specific sample all the grains had their luminescence signal reset at deposition. This allows the reliability of the luminescence age to be assessed. Where all the grains in a sample were not exposed to sufficient daylight to reset their luminescence signal, the apparent age will be an average value of the luminescence from all the grains measured at one time. Where many grains are measured simultaneously, this will overestimate the depositional age. The distribution of apparent age can be made clear by reducing the number of grains being measured in a given experiment, ultimately to the point of measuring individual sand‐sized mineral grains. Copyright © 2004 John Wiley & Sons, Ltd.
Towards a Holocene tephrochronology for Sweden: geochemistry and correlation with the North Atlantic tephra stratigraphy
Authors: Boygle Jane 
Published: March 2004

AbstractNorthern Europe has been affected by fallout of tephra from volcanic eruptions in Iceland throughout at least the Late‐glacial and Holocene. Microscopic volcanic ash horizons found in the British Isles, northern Germany and Scandinavia (e.g. Hekla 4) now provide important regional isochrons. Over recent years analytical techniques such as electron probe microanalysis (EPMA) have helped identify these distal tephra layers by glass geochemistry. Early tephra work in Sweden used refractive indices and bracketing radiocarbon dates for identification, resulting in tentative correlation. This paper presents geochemical data for Icelandic Holocene tephra in Sweden. Several sites in central Sweden have four distinct mid‐Holocene tephra layers. Correlation with the Icelandic record indicates that the following tephra layers are present: Hekla 4 (ca. 3830 yr BP), Kebister tephra (ca. 3600 yr BP), Hekla 3 (ca. 2880 yr BP) and Askja ad 1875. Preliminary analyses suggest that more, previously unidentified, tephra layers are present in low concentrations in the region, indicating potential for expanding the Swedish tephrochronology for palaeoecological and palaeoenvironmental work in northern Europe. Copyright © 2004 John Wiley & Sons, Ltd.
A coherent high‐precision radiocarbon chronology for the Late‐glacial sequence at Sluggan Bog, Co. Antrim, Northern Ireland
Authors: Lowe J. J. , Walker M. J. C. , Scott E. M. , Harkness D. D. , Bryant C. L. , Davies S. M. 
Published: March 2004

AbstractSeventy‐five radiocarbon dates are presented from Sluggan Bog in Co. Antrim, Northern Ireland. The Holocene peats are underlain by Late‐glacial sediments, which also appear to have accumulated largely in a mire environment. The radiocarbon dates, from the Late‐glacial and early Holocene part of the profile, were obtained from the humic and humin fractions of the sedimentary matrix, and from plant macrofossils. The last‐named were dated by AMS and the sediment samples by radiometric (beta counting) methods. Age–depth models for the three dating series show a very high level of agreement between the two fractions and the macrofossils. No statistically significant difference is found between the beta counting and AMS results. Three tephras were located in the profile, the uppermost of which is in a stratigraphical position suggestive of the Vedde Ash, but the geochemical and radiocarbon evidence do not support this interpretation. The lower ashes are in the correct stratigraphical position for the Laacher See and Borrobol tephras, attributions substantiated by the radiocarbon evidence, but not by the geochemical data. The Sluggan sequence has generated one of the most internally consistent radiocarbon chronologies for any Late‐glacial site in the British Isles, and it is suggested that in future more effort should be devoted to the search for, and analysis of, Late‐glacial mire sequences, rather than the limnic records that have formed the principal focus of Late‐glacial investigations hitherto. Copyright © 2004 John Wiley & Sons, Ltd.
River terrace sequences: templates for Quaternary geochronology and marine–terrestrial correlation
Authors: Bridgland David , Maddy Darrel , Bates Martin 
Published: March 2004

AbstractFluvial sequences, particularly terrace staircases, represent archives of Quaternary palaeoclimatic fluctuation and can serve as stratigraphical frameworks for geochronology and for correlation with other depositional environments, in particular, the global marine oxygen isotope record. Fluvial lithostratigraphical frameworks also provide contexts for records, from fossils and artefacts, of faunal evolution and human occupation; conversely, both records can be means of relative dating of riverine sequences.Three fluvial sequences are examined as case studies. First is the Severn–Avon system in the English Midlands, which has biostratgraphical evidence and an amino acid geochronology, together with marker inputs from three different glaciations. The Somme sequence of northern France, famous for its Palaeolithic artefact assemblages, again has biostratigraphy and an amino acid geochronology and has also been dated with reference to overlying loess/palaeosols sequences. The fluvial terraces of the River Arun, the final case study, lack dating evidence but are interspersed within the Sussex raised beach staircase. Although various lines of evidence suggest that the rivers discussed have formed terraces in response to climatic fluctuation, an intriguing difference is that interglacial sediments occur at the bases of terrace formations in the Severn–Avon, whereas in the Somme they occur at the tops of sequences, beneath loessic overburden. Copyright © 2004 John Wiley & Sons, Ltd.
Bayesian analysis of radiocarbon chronologies: examples from the European Late‐glacial
Authors: Blockley S. P. E. , Lowe J. J. , Walker M. J. C. , Asioli A. , Trincardi F. , Coope G. R. , Donahue R. E. 
Published: March 2004

AbstractAlthough there are many Late‐glacial (ca. 15 000–11 000 cal. yr BP) proxy climate records from northwest Europe, some analysed at a very high temporal resolution (decadal to century scale), attempts to establish time‐stratigraphical correlations between sequences are constrained by problems of radiocarbon dating. In an attempt to overcome some of these difficulties, we have used a Bayesian approach to the analysis of radiocarbon chronologies for two Late‐glacial sites in the British Isles and one in the Adriatic Sea. The palaeoclimatic records from the three sites were then compared with that from the GRIP Greenland ice‐core. Although there are some apparent differences in the timing of climatic events during the early part of the Late‐glacial (pre‐14 000 cal. yr BP), the results suggest that regional climatic changes appear to have been broadly comparable between Greenland, the British Isles and the Adriatic during the major part of the Late‐glacial (i.e. between 14 000 and 11 000 cal. yr BP). The advantage of using the Bayesian approach is that it provides a means of testing the reliability of Late‐glacial radiocarbon chronologies that is independent of regional chronostratigraphical (climatostratigraphical) frameworks. It also uses the full radiocarbon inventory available for each sequence and makes explicit any data selection applied. Potentially, therefore, it offers a more ‘objective’ basis for comparing regional radiocarbon chronologies than the conventional approaches that have been used hitherto. Copyright © 2004 John Wiley & Sons, Ltd.
The age and chronostratigraphical significance of North Atlantic Ash zone II
Authors: Austin William E. N. , Wilson Lindsay J. , Hunt John B. 
Published: March 2004

AbstractRhyolitic tephra with the geochemical characteristics of North Atlantic Ash Zone (NAAZ) II are described from the giant piston core MD95‐2006 from the northeast Atlantic Ocean. Shard size distribution indicates that the tephra represent a wind‐sorted, primary air‐fall deposit, but with a mode close to 200 μm they are too coarse to be air‐fall deposits at the core site, which lies ca. 1000 km from the possible tephra source. Randomly sampled shards reveal a single geochemical population belonging to the Icelandic transitional alkali magma series, suggesting that they are unlikely to represent ice rafted debris derived from Icelandic icebergs. The tephra probably represent air‐fall deposits, transported to the core site by sea ice within the northeast Atlantic gyre. The NAAZ II peak coincides with the rapid climate transition (cooling) at the end of interstadial 15, which can be assigned an age of 53 260±2660 yr BP from direct correlation with the Greenland ice‐core (GISP2) record. A comparison of the MD95‐2006 Neogloboquadrina pachyderma (sinistral) relative abundance and GISP2 δ18O records, relative to the NAAZ II isochron, suggests that this climatic event was synchronous across the North Atlantic. By direct correlation of interstadial maxima between the two records, the GISP2 time‐scale is transferred to MD95‐2006. Comparison of corrected and calibrated radiocarbon ages derived from monospecific foraminifers with the GISP2 ages at the same stratigraphical horizon suggest major age differences. These probably result from large variations in atmospheric 14C concentration and highlight the significant uncertainties associated with radiocarbon calibration during marine isotope stage 3. Copyright © 2004 John Wiley & Sons, Ltd.
Tephrochronology of last termination sequences in Europe: a protocol for improved analytical precision and robust correlation procedures (a joint SCOTAV–INTIMATE proposal)
Authors: Turney Chris S. M. , Lowe J. John , Davies Siwan M. , Hall Valerie , Lowe David J. , Wastegård Stefan , Hoek Wim Z. , Alloway Brent 
Published: March 2004

AbstractThe precise sequence of events during the Last Termination (18 000–9000 ka 14C yr BP), and the extent to which major environmental changes were synchronous, are difficult to establish using the radiocarbon method alone because of serious distortions of the radiocarbon time‐scale, as well as the influences of site‐specific errors that can affect the materials dated. Attention has therefore turned to other methods that can provide independent tests of the chronology and correlation of events during the Last Termination. With emphasis on European sequences, we summarise here the potential of tephrostratigraphy and tephrochronology to fulfil this role. Recent advances in the detection and analysis of ‘hidden’ tephra layers (cryptotephra) indicate that some tephras of Last Termination age are much more widespread in Europe than appreciated hitherto, and a number of new tephra deposits have also been identified. There is much potential for developing an integrated tephrochronological framework for Europe, which can help to underpin the overall chronology of events during the Last Termination. For that potential to be realised, however, there needs to be a more systematic and robust analysis of tephra layers than has been the practice in the past. We propose a protocol for improving analytical and reporting procedures, as well as the establishment of a centralised data base of the results, which will provide an important geochronological tool to support a diverse range of stratigraphical studies, including opportunities to reassess volcanic hazards. Although aimed primarily at Europe, the protocol proposed here is of equal relevance to other regions and periods of interest. Copyright © 2004 John Wiley & Sons, Ltd.
Hydrocarbon type analysis by thin‐layer chromatography with flame‐ionization detection: vacuum gas oils, heavy feeds, and hydroprocessed products
Authors: Barman Bhajendra N. 
Published: March 2004

AbstractThin‐layer chromatography with flame‐ionization detection (TLC‐FID) provides quantitative hydrocarbon type data as well as distribution of aromatics by ring number. This method has been applied to obtain amounts of saturates, aromatics, and polars in heavy oil distillates such as light vacuum gas oils and heavy vacuum gas oils derived from different crude sources. TLC‐FID chromatograms and resultant quantitative hydrocarbon type data show that these distillates vary markedly in aromatic contents and aromatic ring types. Similar observations are made with several fluid catalytic cracking feeds. Effects of process parameters such as operating pressure and temperature on hydroconversion of aromatics and polars from a heavy oil are assessed by TLC‐FID. It has been demonstrated that there is a preferential reduction of higher polycyclic aromatic hydrocarbons and polars with an increase of both hydrogen partial pressure and reactor temperature.
Use of binary and ternary mobile phases in reversed‐phase high performance liquid chromatographic separation of chiral compounds
Authors: Gołkiewicz Władysław , Błażewicz Anna , Matosiuk Dariusz 
Published: March 2004

AbstractThe influence of the nature of typical organic modifiers, used in reversed‐phase systems diluted with water, on retention and selectivity of chiral acetylated diamines and acetonitriles possessing pharmacological activity was investigated. Linear, semilogarithmic relationships between the logarithm of the retention factor, k, of the enantiomer and the volume fraction, Φ, of the organic modifier in the binary aqueous‐organic eluent were established for chiral stationary phases. The slope of a plot of log k vs. the modifier volume fraction depends not only on the chemical structure of the chromatographed enantiomers, but also on the nature of the modifier. Moreover, the enantioselectivity of the studied racemates also depends on the nature and concentration of the modifier and is higher for a methanol mobile phase than for acetonitrile.
Separation techniques for the analysis of artists' acrylic emulsion paints
Authors: Scalarone Dominique , Chiantore Oscar 
Published: March 2004

AbstractEmulsion paints are complex chemical systems. The main problems in their characterization are related to the similarities in polymer composition and to the presence of many different types of additives. Thus high resolution separations, sensitivity, and response specificity are required to identify simultaneously the polymer matrix and the minor components. Especially surfactants and pigments are thought to affect significantly the properties of the paint layers during ageing and their identification is the first step in evaluating the behaviour of these products in working conditions. Representative samples of acrylic emulsion paints for artists have been investigated by pyrolysis‐gas chromatography‐mass spectrometry (Py‐GC‐MS) and size exclusion chromatography‐Fourier transform infrared spectroscopy (SEC‐FTIR), and the results have been compared. All the analysed samples were bound in ethyl acrylate‐methyl methacrylate, poly(EA‐co‐MMA), or n‐butyl acrylate‐methyl methacrylate, poly(nBA‐co‐MMA), copolymers. Two types of nonionic surfactants, ethoxylated fatty alcohols and alkylaryl polyethoxylates, commonly used as emulsifiers and dispersive agents have been identified, together with a number of organic pigments.
Rapid and high‐resolution analysis of geometric polyprenol homologues by connected octadecylsilylated monolithic silica columns in high‐performance liquid chromatography
Authors: Bamba Takeshi , Fukusaki Ei‐ichiro , Nakazawa Yoshihisa , Kobayashi Akio 
Published: March 2004

AbstractA Chromolith Performance octadecylsilyl (ODS) monolithic silica column (Merck) was compared with a conventional microparticulate ODS‐bonded silica column in the high‐performance liquid chromatography separation of natural polyprenols. A system comprising two connected monolithic columns afforded an equivalent separation at half the analysis time of the conventional method. Furthermore, ten connected columns achieved a tremendously high‐resolution separation, in which the complicated series of homologous polyprenols with geometric isomerism were fully separated.
Analysis of basic compounds at high pH values by reversed‐phase liquid chromatography
Authors: Stella Cinzia , Rudaz Serge , Mottaz Manuel , Carrupt Pierre‐Alain , Veuthey Jean‐Luc 
Published: March 2004

AbstractReversed phase high performance liquid chromatography (RPLC) is currently the method of choice for the analysis of basic compounds. However, with traditional silica materials, secondary interactions between the analyte and residual silanols produce peak tailing which can negatively affect resolution, sensitivity, and reproducibility. In order to reduce these secondary interactions, which comprise ion exchange, hydrogen bonding, and London forces interactions, chromatographic analyses can be carried out at low or high pH values where silanol groups and basic compounds are mostly uncharged. The chromatographic behaviour of a particular bidentate stationary phase, Zorbax Extend C18, was studied with a set of basic and neutral compounds. Thanks to a higher chemical stability than traditional silica based supports, analyses were carried out with a high pH mobile phase, which represents a good alternative to the acidic mobile phases generally used to reduce ion exchange interactions. The performance of this bidentate stationary phase was also compared with that of other supports and it was proved that it is advantageous to work with high pH mobile phases when analyzing basic compounds.
Approaches for the coating of capillary columns with highly phenylated stationary phases for high‐temperature GC
Authors: Mayer‐Helm Bernhard X. , Rauter Walfried , Rauchbauer Georg , Tomastik Christian , Bangert Herwig 
Published: March 2004

AbstractTwo highly phenylated tetramethyl‐p‐silphenylene–diphenylsiloxane copolymers were coated on fused silica capillary columns and used as stationary phases in GC. The copolymers offered new insights into the coating process and column preparation due to their physicochemical properties. The fused silica capillary surface had to be pretreated in various ways to achieve a homogeneous film and a well deactivated surface: etching with ammonium bifluoride; leaching with sodium hydroxide and hydrochloric acid; silylation with tetraphenyldimethyldisilazane and triphenylsilylamine. Droplet formation was observed on tetraphenyldimethyldisilazane silylated surfaces leading to capillary columns with low separation efficiency. The topology of inhomogeneous films was investigated by light microscopy, scanning electron microscopy, and Auger electron spectroscopy. It became apparent that the stationary phase did not form droplets but islands, which are connected by a wetting layer according to the Stranski‐Krastanov growth mode. Both copolymers are potential stationary phases for high‐temperature GC with promising properties. They offer a higher overall polarity than 75% phenyl, 25% methyl‐polysiloxanes in combination with increased thermal stability and reduced bleed levels.
Determination of volatile fatty acids in landfill leachates by ion‐exclusion chromatography
Authors: Yamamoto Atsushi , Yasuhara Akio , Kodama Shuji , Matsunaga Akinobu , Suzuki Shigeru , Mohri Shino , Yamada Masato 
Published: March 2004

AbstractAn ion‐exclusion chromatographic method with on‐line desalinization for the determination of volatile fatty acids in landfill leachates is described. Highly sensitive conductivity detection of the organic acids was achieved by using dilute p‐hydroxybenzoic acid solution as an eluent. Interference with mineral acids was reduced by treatment with barium chloride solution prior to desalinization. A silver‐loaded cation‐exchange guard column for the desalinization was installed in series with the analytical column to avoid the contamination of organic acids. This method features detection limits of 0.01 mg L–1 formic acid, 0.02 mg L–1 acetic acid, 0.05 mg L–1 propionic acid, and 0.1 mg L–1 butyric acid, respectively, with an injection of 20 μL sample. Application of the on‐line desalinization LC method is illustrated for leachate samples from a Japanese sanitary landfill.
A modified HPLC method for the determination of aspartic acid racemization in collagen from human dentin and its comparison with GC
Authors: Benešová Terezie , Honzátko Aleš , Pilin Alexandr , Votruba Jaroslav , Flieger Miroslav 
Published: March 2004

AbstractThe D/L ratio of aspartic acid enantiomers in proteins of low turnover is generally accepted as a reliable procedure for age determination. In our study, twelve samples of eyetooth dentin were analyzed for age determination. The pure insoluble collagen isolated from eyetooth dentin was obtained by an EDTA demineralization process. Free amino acids obtained after collagen hydrolysis were converted intoo‐phthaldialdehyde‐N‐acetyl‐L‐cysteine (OPA‐NAC) derivatives for HPLC analysis under modified conditions and into trifluoroacetic acid isopropyl esters for GC analysis, respectively. The modified HPLC procedure used phosphate buffer and acidified sample matrix prior to injection which resulted in suppression of peak tailing of both diastereomers, thus allowing achievement of both good selectivity and good resolution. To ensure the high accuracy of the developed method the other parameters, i. e. specificity, precision, linearity, LOD, and LOQ, were also determined. Nine collagen samples covering the age range of 18 to 84 years were used for the determination of coefficient of racemization (KR) and calculation of parameters for age estimation. The regression equations for the data set analyzed were as follows:KR= 0.0005 × age + 0.0262 (R 2= 0.9639) for HPLC, andKR= 0.0006 × age + 0.0319 (R 2= 0.9374) for GC, respectively.