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  • 1
    Publication Date: 2018-06-20
    Description: Publication date: Available online 18 June 2018 Source: Quaternary Geochronology Author(s): Meenakshi, Pankaj Kumar, J.P. Shrivastava, Rakesh Chandra, Sundeep Chopra, G.S. Roonwal, Rajveer Sharma High resolution 14 C AMS ages from sequential layers in the late Quaternary Dilpur Formation in Indian Kashmir, reveal glacial and inter-glacial climatic changes archived in this more or less complete aeolian-palaeosol record. The 14 C AMS ages are consistent and fit well within the time window of ∼45–50 ka. Considering the thicknesses (at corresponding stratigraphic heights), the ages obtained for the S1 palaeosol layer provided high resolution ages for the early Holocene period. When compared to the sedimentation rate based time estimates for the successive layers showed direct relationship between absolute ages and the time involved in the deposition. Based on the extrapolation of 14 C AMS ages of the Shankerpora section, the incidences of glaciations occurred at 67–71 ka and 124–127 ka. The glacial and interglacial cycles spanning ∼130 ka encompass a variable number of palaeosols. Temporally, these observations correlate well with the two glaciations earlier reported from the loess palaeosol succession of Xiagaoyuan, Gansu Province, western Chinese Loess Plateau, suggesting perhaps that similar climatic conditions prevailed in this region. Graphical abstract
    Print ISSN: 1871-1014
    Electronic ISSN: 1878-0350
    Topics: Geosciences
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  • 2
    Publication Date: 2018-06-13
    Description: Publication date: Available online 12 June 2018 Source: Quaternary Geochronology Author(s): Teresa Jordan, Nicolás Blanco, Andrés Quezada, Arturo Jensen, Paulina Vásquez, Fernando Sepúlveda Ritter et al. (2018) analyzed the Quaternary history of a purported paleo-lake in the Atacama Desert of northern Chile. They provide a much more thorough analysis than previous publications of the field relationships where there are landform benches surrounding a bedrock knob, Cerro Soledad. They conclude that the benches formed due to shoreline erosion by a paleo-lake while Cerro Soledad rose in elevation due to tectonic activity. Ritter et al. (2018) also used terrestrial cosmogenic nuclide (Neon, Beryllium, and Aluminum) data to determine a history of the landforms, and thus what they conclude is a history of former lake levels and uplift rate. This Comment examines the distribution of mapped geological units, especially Pliocene lake deposits, relative to the locations sampled and described by Ritter et al. (2018). We find that some of the benches sampled for cosmogenic nuclide dating occur on Miocene and Pliocene lacustrine strata, which opens the possibility that clasts were recycled from Miocene-Pliocene lake deposits into the Pleistocene bench clast population. We reach the alternative interpretation that differential resistance to erosion by hillslope processes created most benched forms on the flanks of Cerro Soledad, rather than generation of the benches by shoreline processes. An alternative exhumation scenario which utilizes the cosmogenic exposure ages better explains many of the landforms. In this scenario, the cosmogenic nuclide exposure dates reveal valley-scale denudation in response to tectonic uplift of Cerro Soledad, reduction of valley floor elevation by dissolution of evaporite units, and capture of the valley by the Loa River, rather than shoreline erosion. Irrespective of the alternative interpretation, the exposure history chronological information provided by Ritter et al. (2018) provides new opportunities to examine environmental fluctuations in the central Atacama Desert.
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    Topics: Geosciences
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  • 3
    Publication Date: 2018-06-06
    Description: Publication date: Available online 4 June 2018 Source: Quaternary Geochronology Author(s): Xiao Fu, Tim J. Cohen, Kirstie Fryirs Fluvial terraces in the upper Hunter catchment, southeastern Australia provide a long-term record of river activity in response to climate change in the late Quaternary. Single-grain optically stimulated luminescence (OSL) dating of quartz was applied in this study to investigate the timing of the formation of three fluvial terraces in the upper Hunter catchment. A detailed examination of luminescence properties of individual quartz grains revealed some correlation between their OSL decay rates, intrinsic brightness and dose saturation characteristics. Some quartz grains containing a higher proportion of non-fast components exhibited low brightness in OSL signals and high dose saturation levels. Some grains with slow OSL decays passed the standard rejection criteria, but are likely to yield underestimated equivalent doses (D e s) because of a higher contribution of non-fast components, which were shown to have low thermal stability. Different rejection criteria, including the fast ratio, the dose saturation level and the OSL sensitivity criteria, were tested on the single-grain D e results. The application of a fast ratio rejection criterion was able to successfully identify thermally unstable grains. A new rejection criterion based on dose saturation property was also applied to improve the age of one sample with a large D e . Our dating results identify multiple phases of river valley aggradation in the upper Hunter catchment since late Marine Isotope Stage (MIS) 6; at ∼ 138 ka, ∼90–94 ka, ∼65 ka, ∼26 ka and ∼18 ka. The aggradational episodes of the terraces are correlated with glacial or stadial periods since MIS 6 and these phases of valley-floor aggradation are inferred to be a function of increased sediment supply during the cold periods resulting from strong periglacial activities in the adjacent Australian highlands.
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    Topics: Geosciences
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  • 4
    Publication Date: 2018-06-04
    Description: Publication date: Available online 2 June 2018 Source: Quaternary Geochronology Author(s): Maurycy Żarczyński, Wojciech Tylmann, Tomasz Goslar This study compares different methods to count biogenic varves in Lake Żabińskie in northeastern Poland. To perform this comparison, we used 2000 years-long varved sediment record from this lake because of the well-preserved laminations as well as the independent age controls, i.e. 29 AMS 14 C dates, 137 Cs activity peaks and volcanic glass shards (1875 AD Askja cryptotephra). Microscopic investigations of thin sections allowed us to identify six major varve microfacies along the sediment profile. Using these microfacies, we tested three counting methods and different approaches of counting uncertainty estimation. These methods provided comparable numbers of varves (1943 ± 30, 2034 ± 34, 2028 +34 / -53 ) and similar shapes in the age-depth relations. However, in two methods, we found possible disadvantages in arbitrary assumptions and subjective decisions in the process of chronology building, procedures leading to age underestimation as well as problems with reliable and objective estimations of counting uncertainty. Based on these results, we propose the counting method which include analyses of major varve microfacies and three independent counting without the need for varve-by-varve microscopic investigations. This method provided acceptable results (〈5% uncertainty) and was more objective and less time-consuming. Semi-automatic counting using μXRF Ca record in the sediments was also tested and provided results that can serve as a first approximation of the number of varves. Our study also indicates that different counting strategies may lead to different uncertainty estimations, which may be important in the reliable interpretation of proxy data.
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    Topics: Geosciences
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  • 5
    Publication Date: 2018-05-30
    Description: Publication date: Available online 28 May 2018 Source: Quaternary Geochronology Author(s): Junjie Zhang, Sheng-Hua Li Standardised growth curves (SGCs) were established for extracts of potassium feldspar (K-feldspar), plagioclase and polymineral grains from various geological settings (deserts, loess, lake or fluvial deposits) from Northern China. Single-aliquot regenerative-dose (SAR) protocol was used with the measurements of multiple elevated temperature post-IR IRSL (MET-pIRIR) signals from 50 °C to 250 °C with an interval of 50 °C. Regenerative-dose normalisation was applied for the SGC construction. The shapes of the SGCs of K-feldspar vary between IRSL signals measured at different temperatures. For coarse grains (63–180 μm), the SGCs of the K-feldspar, plagioclase and polymineral fractions are close to each other. However, the polymineral fine grains (4–11 μm) have a distinct SGC from the coarse-grain fractions. It may be caused by the difference in alpha irradiation. Two test doses (145 Gy and 72.5 Gy) were applied to construct the SGCs of K-feldspar. The SGC built with the larger test dose has a larger characteristic saturation dose ( D 0 ). Test dose used for equivalent dose ( D e ) measurements need to be the same as the test dose used for SGC construction, otherwise the SGC D e may not be accurately estimated. With the same test dose used, the SGC D e values estimated from the SGCs are identical with the D e values generated from individual dose response curves.
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    Topics: Geosciences
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  • 6
    Publication Date: 2018-05-27
    Description: Publication date: Available online 25 May 2018 Source: Quaternary Geochronology Author(s): M. Fuchs, J. Lomax Stone pavements are typical landforms in arid environments, composed of a monolayer of clasts at the surface, associated with an underlying unit of eolian fines. They represent important paleoenvironmental sediment archives, for which reliable chronostratigraphic age constraints are needed. In a first study on stone pavements from the Mojave Desert/USA and Badia Desert/Jordan it could be demonstrated that optically stimulated luminescence dating (OSL) on quartz represents a promising dating method for the eolian fines, but quartz OSL results remained challenging, because the D e distributions were unexpectedly broad and OSL fine- and coarse-grain ages were significantly different (Fuchs et al., 2015). The reason for this age difference was unclear and methodological as well as geomorphological arguments were proposed. Here we present new quartz OSL results from additional study sites and various environmental settings, to better understand possible methodological or geomorphological reasons for the previously detected age characteristics. Stone pavements from the Negev Desert/Israel, from Fuerteventura/Spain and from the Black Rock Desert/USA are investigated in this new study, and their OSL results derived from different grain sizes are compared and discussed.
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    Topics: Geosciences
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  • 7
    Publication Date: 2018-05-27
    Description: Publication date: Available online 25 May 2018 Source: Quaternary Geochronology Author(s): A. Galli, M. Caccia, M. Martini, L. Panzeri, F. Maspero, S. Fiorentino, M. Vandini, E. Sibilia This paper deals with a Thermoluminescence (TL) study of ancient mosaic tesserae from the qasr (winter residence) of Khirbat al-Mafjar, amazing palace of the Islamic caliphs located in the plain of Jericho. In literature, works dealing with the dating of mosaic tesserae usually rely on the dosimetric properties of the microcrystalline inclusions in the silica matrix rather than on the matrix itself. On the other hand, in the last decades, commercial glasses have been demonstrated to be suitable for retrospective accidental dosimetry. In this work, we applied a protocol widely used for the mobile phones’ glasses, the so-called “pre-bleached with blue LEDs” protocol, to evaluate the archeological dose absorbed by some Khirbat al-Mafjar tesserae in order to confirm their dating based on archaeological evidence. As for commercial glasses, the TL signal from ancient tesserae presents anomalous fading and it is light sensitive. The experimental protocol circumvents these problems isolating the thermally more stable TL signal with an optical pretreatment and allowing the determination of a fading curve for each analyzed sample. Using an integrative approach, we estimated the fading correction for these tesserae and we retrieved their ages. The results are partially in agreement with those hypothesized on historical ground and show good potentialities for the dating of amorphous archaeological glassy materials.
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    Topics: Geosciences
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  • 8
    Publication Date: 2018-05-21
    Description: Publication date: August 2018 Source: Quaternary Geochronology, Volume 47 Author(s): E.L. Matchan, D. Phillips, E. Traine, D. Zhu Intraplate continental basaltic volcanic provinces (ICBVPs) occur on all continents and represent some of the most enigmatic volcanic systems. Constraints on the origin(s) and evolution of ICBVPs are predicated on detailed knowledge of eruption histories, which are often poorly quantified. Although the 40 Ar/ 39 Ar geochronology method has been applied successfully to lava flows, age determinations on scoria cones and maars are more challenging. In this study, we test the potential of entrained anorthoclase megacrysts to yield accurate 40 Ar/ 39 Ar ages for scoria cones and maars from the Pliocene-Holocene Newer Volcanic Province (NVP) of south-eastern Australia. The NVP is an ICBVP containing >400 eruption centres with ages spanning 4.6 Ma – 5 ka. K-Ar and 40 Ar/ 39 Ar age data exist for a large number of lava flows, but age constraints for scoria cones and maars that lack associated lavas are rare. High-precision 40 Ar/ 39 Ar step-heating data were measured on anorthoclase megacrysts from five eruption centres in the NVP. From youngest to oldest, anorthoclase xenocrysts from Mount Noorat (n = 3), Mount Leura (n = 2), Mount Shadwell (n = 3), and The Anakies East Cone (n = 2) yielded reproducible mean inverse isochron ages of 101.75 ± 0.96 ka (2σ), 165.4 ± 1.6 ka (2σ), 353.8 ± 1.9 ka (95% CI), and 2.178 ± 0.005 Ma (95% CI), respectively. In contrast, Lake Keilambete anorthoclase (n = 2) produced discordant age spectra and incongruous isochron/mini-isochron ages of 433.5 ± 7.2 ka (2σ) and 413.4 ± 4.5 ka (2σ). A single anorthoclase megacryst from Mount Franklin gave an age of 126.3 ± 7.2 ka (95% CI). By directly comparing megacryst age results with recently published, high-precision (〈1%) ages for basalt groundmass samples from two of the eruption centres, we show that megacryst ages are indistinguishable from, or very similar to (within a few thousand years) corresponding alkali basalt ages (Mount Shadwell and Mount Leura). In another case, distinctly different ages for two megacrysts from the Lake Keilambete eruption centre suggest that some megacryst formation events may pre-date basalt magmatism by ca. 20 ka or more. Overall, high-temperature alkali feldspar megacrysts (and potentially other K-bearing megacrysts), found in ICBVPs worldwide, appear to be valuable tools for approximating host basalt eruption ages, or at the very least, providing maximum eruption age constraints. The new data also reveal a previously unidentified increase in volcanic activity in the NVP at ca. 200–110 ka. Graphical abstract
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  • 9
    Publication Date: 2018-05-21
    Description: Publication date: Available online 15 May 2018 Source: Quaternary Geochronology Author(s): J.-H. May, S.K. Marx, W. Reynolds, L. Clark-Balzan, G.E. Jacobsen, F. Preusser Swamps in the seasonal tropics have good potential for the reconstruction of late Quaternary monsoonal dynamics. Their successful use, however, has often been compromised by chronological limitations introduced by a variety of depositional and post-depositional processes actively modifying the swamp deposits. We here present and discuss the results of a multiple dating approach at Table Top Swamp (TTS) in northern Australia (the ‘Top End’). Single-grain luminescence dating of quartz was successfully used to provide chronology in the lowermost core where insufficient organic material prevents the application of radiocarbon dating. In the uppermost, fine-grained and peaty section of the core, two different organic fractions (pollen concentrate and humins) were dated with AMS radiocarbon yielding significantly different chronologies. While this could point to the incorporation of younger pollen into the profile along seasonal dry cracks, older humins may also move up in the profile due to vertical mixing. Additional, spatially highly resolved measurements of the bulk OSL signal (Ln and Ln/Tn) combined with data on down-core variation in K, Th, and U concentration, grain size and moisture content were used to (i) guide the development of an age-depth relationship (i.e. age model) for the entire core based on three different data input scenarios, and (ii) test the applicability of novel luminescence screening techniques in seasonal swamp settings. Results suggest only minor differences among the applied models and scenarios, providing an overall reliable representation of the depositional history in the swamp. Even though all resulting age-depth models have relatively large uncertainties in the lower part of the core, there are significant changes in sedimentation rate over time, providing a chronological basis for a more detailed palaeoenvironmental analysis at TTS. The approach used may also be useful in developing age models in other complex environments, and has shown the importance of understanding carbon pathways as well as controls on luminescence signals when developing age models.
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  • 10
    Publication Date: 2018-05-21
    Description: Publication date: Available online 14 May 2018 Source: Quaternary Geochronology Author(s): Robin Blomdin, Arjen P. Stroeven, Jonathan M. Harbor, Natacha Gribenski, Marc W. Caffee, Jakob Heyman, Irina Rogozhina, Mikhail N. Ivanov, Dmitry A. Petrakov, Michael Walther, Alexei N. Rudoy, Wei Zhang, Alexander Orkhonselenge, Clas Hättestrand, Nathaniel A. Lifton, Krister N. Jansson Spanning the northern sector of High Asia, the Altai region contains a rich landform record of glaciation. We report the extent, chronologies, and dynamics of two paleoglaciers on opposite flanks of the Ikh Turgen mountains (In Russian: Chikhacheva Range), straddling the border between Russia and Mongolia, using a combination of remote sensing-based glacial geomorphological mapping, 10 Be surface exposure dating, and geomorphometric analysis. On the eastern side (Mongolia), the Turgen-Asgat paleoglacier, with its potential for developing a large accumulation area (∼257 km 2 ), expanded 40 km down valley, and mean ages from a latero-frontal moraine indicate deglaciation during marine oxygen isotope stage (MIS) 3 (45.1 ± 1.8 ka, n = 4) and MIS 2 (22.8 ± 3.3 ka, n = 5). These minimum age constraints are consistent with other 10 Be glacial chronologies and paleoclimate records from the region, which indicates glacier culmination during cold and wet conditions coinciding with MIS 3 (piedmont-style glaciation; inferred for a few sites across the region) and glacier culmination during cold and dry conditions coinciding with MIS 2 (mainly valley-style glaciation; inferred from several sites across the region). On the western side (Russia), the Boguty paleoglacier had a smaller accumulation area (∼222 km 2 ), and advanced 30 km down valley across a low gradient forefield. Surface exposure ages from two moraine complexes on this side of the mountains exhibit wide scatter (∼14–53 ka, n = 8), making paleoclimate inferences and comparison to other proxies difficult. Ice surface profile reconstructions imply that the two paleoglaciers likely shared an ice divide.
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