Chronologies of sedimentary changes in the south Bohai Sea,China: constraints from luminescence and radiocarbon dating

The alternation of terrestrial and marine deposits is an indicator of past environmental and sea‐level changes. The age of deposition is usually dated by means of radiocarbon. However, radiocarbon dates of molluscan shells from coastal areas may be complicated by various sources of carbon, and problematic for deposits of 40–50 ka or older. Herein, we apply the Optically Stimulated Luminescence (OSL) dating method to date samples from terrestrial and marine/coastal sediments extracted from three cores in the south Bohai Sea, China. Multiple‐ and single‐aliquot regenerative‐dose procedures using OSL signals from fine‐silt (4–11 μm), coarse‐silt (38–63 μm) and fine‐sand (63–90 or 90–125 μm) quartz were employed to determine the equivalent dose (D _e). The results showed that: (i) OSL ages from quartz of different grain sizes and different protocols are consistent with each other; (ii) for Holocene samples, most of the radiocarbon dates agree well with OSL ages; (iii) for pre‐Holocene samples, radiocarbon dates cluster at 40–50 ¹⁴ C ka BP, whereas OSL ages are in stratigraphic order from 11 ka to 176 ka. Because of the self‐consistency of the quartz OSL ages, the stratigraphic agreement in the three cores, and the clustering of the radiocarbon dates, we suggest that the quartz OSL ages are more reliable with respect to dating the samples from the south Bohai Sea. Finally, the four marine strata identified in the south Bohai Sea are likely to have formed during the Holocene, Marine Isotopic Stage (MIS) 3–5, MIS 6 and probably MIS 7, respectively.     

New data on the sedimentation rate in the Sea of Azov in the Late Holocene

The sedimentation rates in the Sea of Azov for the period of the last 2000 years (Late Azov stage) were studied by methods of absolute geochronology, lithology, and biostratigraphy. The average sedimentation rate of the Late Azov deposits varied from 0.4–0.8 to 1.5–2.0 mm per year. It reached as much as 4.0–6.0 mm per year in the areas close to the sharp coasts and was defined by the area geomorphology. The scheme of the lithological transects, sedimentation rates, and absolute age of the sediments is presented. The palaeoecology peculiarities of deposit accumulation during the Late Azov stage are described from the diatom and spore-pollen analyses.     

Radiocarbon dating of quaternary loess deposits,Banks Peninsula,Canterbury, New Zealand

Quaternary loess deposits containing charcoal and in situ organic matter constituents from Banks Peninsula, New Zealand, were subjected to various physical and chemical treatments before radiocarbon assay. A stepwide procedure was used in which each component was radiocarbon dated before and after the treatments were applied. The criterion adopted for judging the effectiveness of a treatment is an increase in the radiocarbon age of loess layer. On this basis the oldest and therefore the most reliable date was obtained from the intra-loess charcoal and its humic acid extract. By comparison, the radiocarbon ages of organic matter constituents of the whole or partitioned loess were much younger, and are considered to represent only average ages for the particular layers concerned. No advantage was gained by dating the carbon-enriched clay-humus fraction as opposed to whole loess samples. There is an apparent conflict between our dates and current interpretation of loess stratigraphy and chronology in the South Island of New Zealand, which requires further investigation. This uncertainty apart, the upper layers of multiple loess deposits are clearly much older than earlier reports indicate, and it follows that the correlation of these deposits with late-glacial events both within and beyond New Zealand is even more tenuous and unreliable than previously thought to be the case.     

New data on sedimentation and biostratigraphy of ancient and New Azov Deposits (Sea of Azov)

Applying the methods of absolute geochronology and lithology, it has been established that the average sedimentation rate in the Sea of Azov over the last 6000 years (Ancient and New Azov times) varied from 0.2 to 2.0 mm/year. Its minimum values are confined to transit and sediment-starved zones coinciding with the directions of the main marine currents. It has been indicated that changes in the water level of the Sea of Azov occur with lag relative to landscape–climate phases. The obtained data confirm the relation between marine and terrestrial processes occurring in the Sea of Azov region: transgressive phases are preceded by general humidification in adjacent regions, while regressive phases correlate with climate aridization. The biostratigraphic analysis of the Holocene sections examined reveals the unstable behavior of the sea level during their formation. The results of diatom analysis confirm development of the Phanagoria and Korsun Regressions and Nymphea Transgression. Frequent fluctuations of the Sea of Azov the level determined the rhythmical structure of the sedimentary sequence saturated with autochthonous and allochthonous organic matter.     

Late holocene climate changes in the Sea of Azov region

The results of paleoclimatic reconstructions made with the help of the information-statistical method developed by V.A. Klimanov based on palynological data from the Sea of Azov bottom sediments. For the period of the last 3000 years, four phases of warm and dry climates and three phases of relatively cool and humid climates were identified. The latter phases were characterized by wider expansion of tree vegetation in the region around the Sea of Azov. The range of mean annual temperatures between warmer and cooler intervals was about 4°C.     

Establishing the Late Pleistocene-Holocene sedimentation boundary in the southern North Sea using OSL dating of shallow continental shelf sediments

This paper provides insight into the fate of Late Weichselian and Early Holocene sediments accumulated in the German sector of the southern North Sea. A combination of optically stimulated luminescence (OSL) dating and radiocarbon dating was applied to set up the chronology. Seven cores were studied to obtain ten quartz OSL samples and ten radiocarbon samples. The core locations were chosen along a southeast to northwest transect along the western side of the Elbe palaeovalley, giving a good coverage of the entire German North Sea area. All samples for OSL dating showed a significant scatter in the equivalent dose (D_e) distribution of quartz due to heterogeneous bleaching. The Minimum Age Model (MAM-3) was found to be the most suitable to extract true burial ages. It was inferred from the study that sedimentation did still occur during the late deglaciation period in many areas. These are mainly Late Weichselian glaciofluvial or glaciolacustrine sediments directly overlain by early Holocene fluvial and/or transgressive deposits and followed by modern marine sands. However, considerable late Weichselian erosion or a possible period of non-deposition was observed in the highland area to the northeast of the Dogger Bank and a small discontinuity in the near-shore region was noticed, probably due to early Holocene fluvial erosion. Relicts of a palaeo-river bank or terrace were identified in core 14VC to the east of the Dogger Bank. A possible interpretation of the Pleistocene-Holocene interface along the core transect is provided based on lithology and measured OSL and radiocarbon ages.     

Dynamics of Background Radiation in Russian Seas (New Data on the Sea of Azov)

Doklady Earth Sciences - New data on the concentration of 137Cs in the water and bottom sediments of the Sea of Azov are analyzed. The factors determining the entry and redistribution of...     

环渤海海岸带14C数据集（Ⅱ）

作为晚更新世与全新世地层年代测定的一种重要手段,¹⁴C测年被广泛应用于地质样品的年代测定。但对于¹⁴C数据的系统校正,迄今未得到应有的重视。文章在环渤海海岸带¹⁴C数据集(Ⅰ)的基础上,对所收集的421个由其他研究者获得的环渤海海岸带¹⁴C数据进行了系统校正。并讨论了百年、千年与万年尺度的¹⁴C数据校正效果。结果表明,直接测定值与系统校正值之间的差值常有数百年至两千年的差别。经统一校正的¹⁴C年龄,最大限度地接近样品太阳历纪年的“真实”年龄,从而有助于更加准确地重建该地区的晚更新世晚期以来的地质年代史,并可与考古纪年及其他测年方法获得的绝对年龄直接对比。     

南海古海啸重建与海啸沉积研究进展

中国东海、南海等近海临近琉球海沟、马尼拉海沟等俯冲带,地震频发.过去的海啸研究主要关注历史文献分析、海啸数值模拟等,据此评估中国近岸海啸灾害的历史和风险.历史时期是否引发了海啸,特别是具有特大致灾风险的大海啸记录,目前还不明确.近年来,本课题组通过对海岛、海洋沉积和海岸带及其岛屿的沉积过程、海啸遗迹和历史记录研究,阐述...     

Abandoned shorelines and the late quaternary history of lake George,New South Wales

A study of the geomorphology, surficial sediments, and soils of the Lake George Basin, in particular those at its northwestern end, led to the recognition of a set of abandoned shoreline features lying at a range of altitudes up to 37 m above lake bottom. The altitudes and soils were used to establish a relative age sequence of abandoned shorelines which was related to an absolute time‐scale by radiocarbon dating.     

Zircon geochemistry and U–Pb age at rare metal deposits of syenite in the Ukrainian Shield

The distribution of rare and rare earth elements in zircon at the Yastrebets, Azov (Zr–REE–Y), and Perzhan (Be) rare metal deposits of the Ukrainian Shield was studied. Additional evidence for magmatic genesis of these deposits is obtained: unaltered zircon is characterized by a magmatic REE distribution spectrum with a somewhat higher δ¹⁸O value than that of the mantle (6.6‰ on average). The final formation stage of the deposit was marked by predominance of fluids enriched in Y, REE, Nb, and heavy oxygen, resulting in anomalous geochemical characteristics of zircon rims and alteration zones (up to 81500 Y ppm, over 10300 ppm Nb, and 13.9‰ δ¹⁸O). The age of zircon formed in ore-bearing Yastrebets and Azov nonnepheline syenite deposits was estimated at ~1770 Ma (U–Pb, SHRIMP-II).     

系列^14C样品贝叶斯法日历年龄校正研究进展

系列^14C样品贝叶斯法日历年龄校正研究已成为当前^14C年代学中一个热点,系统综述了时序已知、时序间隔已知和时序间隔近似已知系列^14C样品日历年龄校正研究的历史、原理、计算方法及其在树轮、泥炭、地层等领域上应用进展,对影响系列样品贝叶斯分析获得^14C日历年龄区间的主要因素以及未来发展方向作了归纳。大量事例研究结果表明系列样品贝叶斯分析的实质在于贝叶斯方法从统计的角度灵活地把地层信息以概率方式加入到^14C日历年龄校正过程中,获得比单个^14C年代校正精度更高的日历年龄。     

The Littorina transgression in the southwestern Baltic Sea: new insights based on proxy methods and radiocarbon dating of sediment cores

Rößler, D., Moros, M. & Lemke, W. 2010: The Littorina transgression in the southwestern Baltic Sea: new insights based on proxy methods and radiocarbon dating of sediment cores. Boreas, 10.1111/j.1502‐3885.2010.00180.x. ISSN 0300‐9483. The Littorina transgression is one of the most pronounced environmental events in the Holocene history of the Baltic Sea. It changed the hydrographic system from the freshwater Ancylus Lake into the brackish‐marine Littorina Sea. Here, 18 cores from two western Baltic basins, Mecklenburg Bay and the Arkona Basin, were analysed. We show that, besides biological indicators, sedimentary organic carbon, C/N ratio, bulk δ¹³C isotope values and carbonate content display clearly the transition from Ancylus Lake to the Littorina Sea. The first appearances of benthic foraminifers, marine molluscs and ostracods represent the onset of brackish‐marine conditions in the bottom waters. Central Arkona Basin sediments display more abrupt shifts in geochemical parameters and microfossil records at the transition from Ancylus Lake to the Littorina Sea than those from Mecklenburg Bay. Mixing of reworked Ancylus material with Littorina Sea stage material was stronger in Mecklenburg Bay, resulting in less pronounced proxy parameter changes and older bulk material dates. Radiocarbon dating of both calcareous material (benthic foraminifers, mollusc shells) and bulk fractions at the transgression horizon shows large age discrepancies. Based on calcareous fossil dates it appears that marine waters began to enter Mecklenburg Bay c. 8000 cal. a BP. In the Arkona Basin the first marine signals are recorded approximately 800 years later, c. 7200 cal. a BP. This indicates a transgression pathway via the Great Belt into Mecklenburg Bay and then into the Arkona Basin.     

Age assignment of a diatomaceous ooze deposited in the western Amundsen Sea Embayment after the Last Glacial Maximum

Reliable dating of glaciomarine sediments deposited on the Antarctic shelf since the Last Glacial Maximum (LGM) is challenging because of the rarity of calcareous (micro‐) fossils and the recycling of fossil organic matter. Consequently, radiocarbon (¹⁴C) ages of the acid‐insoluble organic fraction (AIO) of the sediments bear uncertainties that are difficult to quantify. Here we present the results of three different methods to date a sedimentary unit consisting of diatomaceous ooze and diatomaceous mud that was deposited following the last deglaciation at five core sites on the inner shelf in the western Amundsen Sea (West Antarctica). In three cores conventional ¹⁴C dating of the AIO in bulk samples yielded age reversals down‐core, but at all sites the AIO ¹⁴C ages obtained from diatomaceous ooze within the diatom‐rich unit yielded similar uncorrected ¹⁴C ages between 13 517 ± 56 and 11 543 ± 47 years before present (a BP). Correction of these ages by subtracting the core‐top ages, which probably reflect present‐day deposition (as indicated by ²¹⁰Pb dating of the sediment surface at one core site), yielded ages between ca. 10 500 and 8400 cal. a BP. Correction of the AIO ages of the diatomaceous ooze by only subtracting the marine reservoir effect (MRE) of 1300 a indicated deposition of the diatom‐rich sediments between 14 100 and 11 900 cal. a BP. Most of these ages are consistent with age constraints between 13.0 and 8.0 ka for the diatom‐rich unit, which we obtained by correlating the relative palaeomagnetic intensity (RPI) records of three of the sediment cores with global and regional reference curves. As a third dating technique we applied conventional radiocarbon dating of the AIO included in acid‐cleaned diatom hard parts extracted from the diatomaceous ooze. This method yielded uncorrected ¹⁴C ages of only 5111 ± 38 and 5106 ± 38 a BP, respectively. We reject these young ages, because they are likely to be overprinted by the adsorption of modern atmospheric carbon dioxide onto the surfaces of the diatom hard parts prior to sample graphitisation and combustion for ¹⁴C dating. The deposition of the diatom‐rich unit in the western Amundsen Sea suggests deglaciation of the inner shelf before ca. 13 ka BP. The deposition of diatomaceous oozes elsewhere on the Antarctic shelf around the same time, however, seems to be coincidental rather than directly related. Copyright © 2009 John Wiley & Sons, Ltd.     

系列14C样品贝叶斯法日历年龄校正研究进展

系列14C样品贝叶斯法日历年龄校正研究已成为当前14C年代学中一个热点,系统综述了时序已知、时序间隔已知和时序间隔近似已知系列14C样品日历年龄校正研究的历史、原理、计算方法及其在树轮、泥炭、地层等领域上应用进展,对影响系列样品贝叶斯分析获得14C日历年龄区间的主要因素以及未来发展方向作了归纳.大量事例研究结果表明系列样品贝叶斯分析的实质在于贝叶斯方法从统计的角度灵活地把地层信息以概率方式加入到14C日历年龄校正过程中,获得比单个14C年代校正精度更高的日历年龄.     

Messinian events in the Black Sea

Past hydrological interactions between the Mediterranean Sea and Black Sea are poorly resolved due to complications in establishing a high‐resolution time frame for the Black Sea. We present a new greigite‐based magnetostratigraphic age model for the Mio‐Pliocene deposits of DSDP Hole 380/380A, drilled in the southwestern Black Sea. This age model is complemented by ⁴⁰Ar/³⁹Ar dating of a volcanic ash layer, allowing a direct correlation of Black Sea deposits to the Messinian salinity crisis (MSC) interval of the Mediterranean Sea. Proxy records divide these DSDP deposits into four intervals: (i) Pre‐MSC marine conditions (6.1–6.0 Ma); (ii) highstand, fresh to brackish water conditions (~6.0–5.6 Ma); (iii) lowstand, fresh‐water environment (5.6–5.4 Ma) and (iv) highstand, fresh‐water conditions (5.4–post 5.0 Ma). Our results indicate the Black Sea was a major fresh‐water source during gypsum precipitation in the Mediterranean Sea. The introduction of Lago Mare fauna during the final stage of the MSC coincides with a sea‐level rise in the Black Sea. Across the Mio‐Pliocene boundary, sea‐level and salinity in the Black Sea did not change significantly.     

Late Pleistocene raised beaches of coastal Estremadura,central Portugal

We present new stratigraphic, sedimentological, and chronological data for a suite of tectonically raised beaches dating to Marine Isotope Stages 5, 4, and 3 along the Estremadura coast of west-central Portugal. The beach deposits are found in association with ancient tidal channels and coastal dunes, pollen bearing mud and peat, and Middle Paleolithic archaeological sites that confirm occupation of the coastal zone by Neanderthal populations. The significance of these deposits is discussed in terms of the archaeological record, the tectonic and geomorphic evolution of the coast, and correlation with reconstructions of global climate and eustatic sea-level change. Direct correlation between the Estremadura beach sections is complicated by the tectonic complexity of the area and the age of the beach deposits (which are near or beyond the limit of radiocarbon dating). Evidence from multiple sites dated by AMS radiocarbon and optical luminescence methods suggests broad synchroneity in relative sea-level changes along this coast during Marine Isotope Stage 3. Two beach complexes with luminescence and radiocarbon age control date to about 35 ka and 42 ka, recording a rise in relative sea level around the time of Heinrich Event 4 at 39 ka. Depending on assumptions about eustatic sea level at the time they were deposited, we estimate that these beaches have been uplifted at rates of 0.4–4.3 mm yr^?1 by the combined effects of tectonic, halokinetic, and isostatic processes. Uplift rates of 1–2 mm yr^?1 are likely if the beaches represent sea level stands at roughly 40 m below modern, as suggested by recent eustatic sea level reconstructions. Evidence from coastal bluffs and the interior of the study area indicates extensive colluvial, fluvial, and aeolian sedimentation beginning around 31 ka and continuing into the Holocene. These geomorphic adjustments are related to concomitant changes in climate and sea level, providing context that improves our understanding of Late Pleistocene landscape change and human occupation on the western Iberian margin.     

40Ar/39Ar Dating of Xuebaoding Granite in the Songpan-Garzê Orogenic Belt, Southwest China, and its Geological Significance

<正>Thus far,our understanding of the emplacement of Xuebaoding granite and the occurrence and evolution of the Songpan-Garze Orogenic Belt has been complicated by differing age spectra results.Therefore,in this study,the ~(40)Ar/~(39)Ar and sensitive high resolution ion micro-probe(SHRIMP) U-Pb dating methods were both used and the results compared,particularly with respect to dating data for Pankou and Pukouling granites from Xuebaoding,to establish ages that are close to the real emplacements.The results of SHRIMP U-Pb dating for zircon showed a high amount of U,but a very low value for Th/U.The high U amount,coupled with characteristics of inclusions in zircons,indicates that Xuebaoding granites are not suitable for U-Pb dating.Therefore,muscovite in the same granite samples was selected for ~(40)Ar/~(39)Ar dating.The ~(40)Ar/~(39)Ar age spectrum obtained on bulk muscovite from Pukouling granite in the Xuebaoding,gave a plateau age of 200.1±1.2 Ma and an inverse isochron age of 200.6±1.2 Ma.The ~(40)Ar/~(39)Ar age spectrum obtained on bulk muscovite from Pankou granite in the Xuebaoding gave another plateau age of 193.4±1.1 Ma and an inverse isochron age of 193.7±1.1 Ma. The ~(40)Ar/~(36)Ar intercept of 277.0±23.4(2σ) was very close to the air ratio,indicating that no apparent excess argon contamination was present.These age dating spectra indicate that both granites were emplaced at 200.6±1.3 Ma and 193.7±1.1 Ma,respectively.Through comparison of both dating methods and their results,we can conclude that it is feasible that the muscovite in the granite bearing high U could be used for ~(40)Ar/~(39)Ar dating without extra Ar.Based on this evidence,as well as the geological characteristics of the Xuebaoding W-Sn-Be deposit and petrology of granites,it can be concluded that the material origin of the Xuebaoding W-Sn-Be deposit might partially originate from the Xuebaoding granite group emplacement at about 200 Ma.Moreover,compared with other granites and deposits distributed in various positions in the Songpan-Garze Orogenic Belt,the Xuebaoding emplacement ages further show that the main rare metal deposits and granites in peripheral regions occurred earlier than those in the inner Songpan-Garze.Therefore,~(40)Ar/~(39)Ar dating of Xuebaoding granite will lay a solid foundation for studying the occurrence and evolution of granite and rare earth element deposits in the Songpan-Garze Orogenic Belt.     

Luminescence dating of neotectonic activity on the southwestern coastal plain,Taiwan

The southwestern coastal plain of Taiwan is heavily urbanised, with a population of more than 6 million. The area is known to be subsiding, and the resulting basin is filled with thick fluvial deposits, of at least 200 m thickness. In the past century, three large earthquakes have occurred in the area; two caused surface ruptures, and resulted in large property loss and more than 2000 casualties. There is an urgent need for an understanding of the dynamics and recurrence intervals of this neotectonic activity, but little is known of the chronology of the late Pleistocene deposits. Recently more than 20 cores longer than 250 m were taken from the coastal plain as part of a large hydrogeological investigation, and basic data on lithology, hydrogeology and palaeobiology were collected. The base of these cores is beyond the ¹⁴C age limit, and so the application of luminescence dating to these sediments has been investigated.Optically stimulated luminescence methods have been applied to quartz sand-sized grains extracted from 29 samples. Dosimetry based on gamma spectrometry is also compared with ICP-MS and XRF analyses. In the age range up to ∼40 ka, radiocarbon ages are compared with the luminescence results, to give confidence that the initial bleaching of these sediments was sufficient. The luminescence ages are then discussed and differential rates of basin subsidence are deduced. It is clear from these data that the study area is tectonically active, and it may be that regions of similar subsidence rate correlate with identifiable geological structures.     

The first case study of 230Th/U and 14C dating of mid-valdai organic deposits

From the viewpoint of precision and reliability of radioisotopic dating, deposits whose quantitative age can be determined through several methods of geochronometry are of special interest. The mutually conforming finite ¹⁴C and ²³⁰Th/U dates of buried Neopleistocene organic deposits, taken from the Tolokonka section by the North Dvina River (100 km downstream from the city of Kotlas), have been obtained for the first time in Russia. The stratigraphical reference of these results to those obtained via the optically induced luminescence for upper and lower bedding layers has been established. The presented geochronometric data have allowed us to consider the age of oxbow lake organic deposits completely reliable and refer the time of their formation to the Tyrbei warming within the MIS-3. The applicability of the new version of the ²³⁰Th/U method for dating of interglacial and interstadial deposits, for the purpose of solving the Middle and Late Neopleistocene chronostratigraphy issues, is confirmed.