Search

Luminescence rock surface burial and exposure dating approaches hold enormous potential to contribute to the archaeological sciences. These methods enable the dating of previously undatable archaeological site types and can be used to determine how and when lithic artefacts have been sequentially buried and transported. Studies have already used these approaches to overcome limitations of classical dating methods to constrain the ages of lithic artefact discard and post-depositional movement at surface scatter sites, to chronologically constrain rock art production by dating rockfall and exposure events, as well as dating a variety of rock-based archaeological features such as pavements, petroforms, megalithic structures, and walls. Here, we present a review of these developing methods, including an introduction to the underlying principles and applications, a series of case studies, and a discussion of the obstacles and complexities to be considered when applying these methods. We conclude with a discussion of future applications and developments, including direct dating of rock engravings, buried artefacts, megalithic stone structures, and chert artefacts. With ongoing work and applications, luminescence rock-surface dating has the potential to become widely applicable, shining new light on a diverse range of previously intractable archaeological contexts. [ABSTRACT FROM AUTHOR]

Increasing evidence suggests that supergene exotic copper deposits were emplaced during periods of geomorphic quiescence and pulses of humidity in arid environments. We tested this idea in the Centinela Mining District in the Atacama Desert (northern Chile). We collected 14 sand samples at depth (up to 110 m) in two open‐pit mines (Central Tesoro and Mirador) exposing Miocene sediment, and located in the El Tesoro Basin, which hosts two exotic copper‐rich orebodies. We inverted the 10Be and 21Ne concentrations by using a two‐box model (IMIS, inversion of multi‐isotopes in a sedimentary basin) composed of an eroding source of sediment and a depositional sedimentary basin, and by selecting denudation and sedimentation rate histories that can explain our data. The ages found demonstrate that the two exotic orebodies were deposited during a narrow period between 14 Ma (10 Ma younger than previously thought) and 9.5 Ma, when an ignimbrite covered the sedimentary sequence. The dated lower exotic copper orebody was deposited during or just before a sharp decrease in the sedimentation rates (from >100 to 0.5–5 m/Ma), which is consistent with published sedimentological and carbonate isotopic data in this district. This confirms the idea that exotic deposits form during a quiescence of the geomorphic activity. Nevertheless, our model suggests that the back‐ground denudation rate providing sediment to these basins between ca. 14 Ma and ca. 9.5 Ma was surprisingly high (>250 m/Ma) for such an arid environment. These denudation rates can be explained by a relatively rapid local back‐scarp retreat providing most of the sediment to these basins and possibly a wetter climate compared to the present. Then, during the period 10–7 Ma, the denudation rates decreased to >50 m/Ma. This decrease may correspond to a local progressive decrease in the slope of the surrounding hills, or to a progressive aridification, or a combination of both phenomena. [ABSTRACT FROM AUTHOR]

Landscape evolution is modulated by the regional tectonic uplift, climate change, and river dynamics. However, how to distinguish these mechanisms through the research of surface exhumation and fluvial incision remains controversial. In this study, cosmogenic 10Be, 26Al, and 21Ne concentrations in quartz from cave deposits, modern river sediments, and bedrocks were measured to constrain the applicability of cosmogenic 21Ne and discuss Quaternary landscape evolution history in the Guizhou Plateau, southeast China. Using the 26Al-10Be and 21Ne-10Be pairs to distinguish the cosmogenic 21Ne concentration from the excess 21Ne, we found that the nucleogenic 21Ne produced by the U and Th decay in quartz is significant in the samples although there is the possibility of inherited cosmogenic 21Ne. Combining with previous studies, we suggest that the precise approach for applying the cosmogenic 21Ne could be reached by (1) estimating the contribution from nucleogenic 21Ne, (2) avoiding samples with complex burial histories to exclude inherited cosmogenic 21Ne, and (3) combining the 10Be-26Al-21Ne nuclides method for the Quaternary samples. In addition, both pre-burial basin denudation rates and burial ages derived from the 26Al-10Be pair were used to determine the different timescale surface denudation rate and fluvial incision rate in relation to previous work. The consistency of the different timescales pre-burial basin denudation rate, 36Cl surface denudation rate, and modern basin denudation rate indicates that the landscape-scale surface denudation has been likely stabilized since the Quaternary in the Guizhou Plateau area. The slightly higher river incision rates than the local surface denudation rate show that the river dynamics may not have reached a steady-state due to the regional tectonic uplift in the Guizhou Plateau. [ABSTRACT FROM AUTHOR]

Summary: In this study, a differential phase‐shift‐keying (DPSK) demodulator, which is implemented by digital circuit, is proposed. A differential voltage clipper is used to generate narrow pulses at the extremum of the received modulated signal. Regarding the DPSK signal, the outputs of the clipper have double frequency. In order to halve the frequency, a frequency divider is applied to get synchronous clock. Two binary counters are used to detect phase variation; the data are recovered after two times sampling. This technique removes the need for voltage controlled oscillator (VCO). The proposed demodulator is postlayout simulated in a 0.18‐μm CMOS process, with a power of 64 μW and active area of 68 × 70 μm2. The demodulator recovers 10 Mb/s data rate at 10‐MHz carrier frequency using a 1.8‐V power supply. [ABSTRACT FROM AUTHOR]

In situ cosmogenic nuclides are an important tool for quantifying landscape evolution and dating fossil‐bearing deposits in the Cradle of Humankind (CoH), South Africa. This technique mainly employs cosmogenic 10‐Beryllium (10Be) in river sediments to estimate denudation rates and the ratio of 26‐Aluminium (26Al) to 10Be (26Al/10Be), to constrain ages of sediment burial. Here, we use 10Be and 26Al concentrations in bedrock and soil above the Rising Star Cave (the discovery site of Homo naledi) to constrain the denudation rate and the exposure history of soil on the surface. Apparent 10Be‐derived denudation rates obtained from pebble‐ to cobble‐sized clasts and coarse‐sand in soil (on average 3.59 ± 0.27 m/Ma and 3.05 ± 0.25 m/Ma, respectively) are 2‐3 times lower than the bedrock denudation rates (on average 9.46 ± 0.68 m/Ma). In addition, soil samples yield an average 26Al/10Be ratio (5.12 ± 0.27) that is significantly lower than the surface production ratio of 6.75, which suggests complex exposure histories. These results are consistent with prolonged surface residence of up to 1.5 Ma in vertically mixed soils that are up to 3 m thick. We conclude that the 10Be concentrations accumulated in soils during the long near‐surface residence times can potentially cause underestimation of single‐nuclide (10Be) catchment‐wide denudation rates in the CoH. Further, burial ages of cave sediment samples that consist of an amalgamation of sand‐size quartz grains could be overestimated if a pre‐burial 26Al/10Be ratio calculated from the surface production is assumed. © 2019 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

• Pre-Acheulean industry dating at Dungo IV site (Baia Farta, Benguela, Angola). • Burial of the hominin occupation surface since at least 614 ka. • Apparent maximum uplift rate at the site of 170 m.Ma −1. Along the Angolan coast, the Early Paleolithic sites of Dungo IV and V (Baia Farta, Benguela) have delivered a rich pre-Acheulean lithic industry testifying the antiquity of the hominin settlement in western Africa despite the current absence of any hominin fossil in the area. In Dungo IV, the Paleolithic level is located on a conglomeratic paleo-beach (104 m a.s.l.) buried under an at least 3 m thick sandy layer. In Dungo V, two unearthed large whale fossils are associated with numerous lithic tools intimately mixed with the whale bones. This is the oldest evidence of stranded marine mammal scavenging by hominins in this part of Africa. The lack of volcanism and fossils makes chronological constrain difficult. Considering its configuration, the Dungo IV site may be relevant for a dating based on both the 10Be and 26Al cosmogenic nuclides. For this purpose, a depth profile all along the sandy layer overlying the archeological layer has been sampled. Statistical treatments performed on the 26Al/10Be ratios obtained for the depth profile demonstrate that they all belong to the same population. If we consider that the samples have always been at or close to their sampling depth, the regression modeling allows computing that the surface sedimentary layer has been emplaced at least 614 ka ago and less than 662 ka ago. On the other hand, if we consider that the surface deposit has been truncated, burial durations ranging from 585 ka to 786 ka and truncations lower than 4 m result from the modeling of the evolution of the 10Be and 26Al concentrations as a function of depth. The analyses of four pre-Acheulean artefacts lead to a minimum burial duration of 730 ka and a maximum burial duration of 2.11 Ma. The low pre-burial denudation rates modeled from the data acquired for the stone tools as well as for the overlying layer (1–16 m.Ma −1) imply large inherited 26Al and 10Be concentrations. The post-depositional maximum denudation rate of 71 m.Ma −1 associated with both the lithic artefacts and the surface sedimentary layer (considering that the samples have always been at or close to their sampling depth) as well as the deduced maximum uplift rate of ∼170 m.Ma −1 are in agreement with the known tectonic evolution and the climatic variability of this area. This study confirms the antiquity of the hominin presence in western Africa more than 2000 km away from the closest old hominin fossil sites. [ABSTRACT FROM AUTHOR]

We assess if variations in the in situ cosmogenic 26Al/10Be production ratio expected from nuclear physics are consistent with empirical data, knowledge critical for two-isotope studies. We do this using 313 samples from glacially transported boulders or scoured bedrock with presumed simple exposure histories in the Informal Cosmogenic-nuclide Exposure-age Database (ICE-D) from latitudes between 53°S to 70°N and altitudes up to 5000 m above sea level. Although there were small systematic differences in Al/Be ratios measured in different laboratories, these were not significant and are in part explained by differences in elevation distribution of samples analyzed by each laboratory. We observe a negative correlation between the 26Al/10Be production ratio and elevation (p = 0.0005), consistent with predictions based on the measured energy dependence of nuclear reaction cross-sections and the spatial variability in cosmic-ray energy spectra. We detect an increase in the production ratio with increasing latitude, but this correlation is significant only in a single variate model, and we attribute at least some of the correlation to sample elevation bias because lower latitude samples are typically from higher elevations (and vice versa). Using 6.75 as the 26Al/10Be production ratio globally will bias two-isotope results at higher elevations and perhaps higher latitudes. Data reported here support using production rate scaling that incorporates such ratio changes, such as the LSDn scheme, to minimize such biases.

Abstract In this study, we investigate the potential of rock surfaces to provide luminescence burial ages for boulders from moraine deposits. We sampled four boulders from a terminal moraine at the Malta Valley, Austria, all deposited ∼2 m below the present ground surface, and measured the IRSL signal as a function of depth into the boulder surfaces. It is clear from these profiles that all four boulders were exposed to at least some daylight prior to final deposition, and in one boulder, there is evidence for multiple exposure/burial events. The profiles show that the luminescence signal at the surface of two boulders must have been completely zeroed before burial. The burial doses derived from these two well-reset surfaces can thus be safely used to calculate burial ages, which may be the same as the depositional age of the terminal moraine. The IRSL signals from both boulders seem to suffer from anomalous fading with g-values of up to 15% decade−1. The younger fading-corrected age of ∼14 ka is in agreement with the deposition of the terminal moraine and coincides with the assumed Gschnitz stadial, while the older age of ∼39 ka most likely represents an earlier event during which this boulder was exposed to light. Our results suggest that there is a high probability of sampling light-exposed and even well-bleached boulders from moraine deposits. We thus conclude that rock surface luminescence dating offers the possibility of obtaining reliable ages for moraine deposition. Even boulders which are partially bleached and thus not suitable for dating can provide insight into transportation pathways as well as depositional processes in glacial environments leading to a better understanding of the dynamics of glaciers. Highlights • First luminescence depth profiles from alpine glacial boulders. • Records of several burial and exposure events are identified in moraine boulders. • Identifying glacial transport mechanisms through rock surface luminescence depth profiles. [ABSTRACT FROM AUTHOR]

The thick Cenozoic sedimentary sequence of the Linxia Basin contains abundant well-preserved mammalian fossils, which provide significant information on the paleoenvironmental processes and mammalian evolution associated with the uplift and expansion of the Tibetan Plateau. Ambiguous age estimations have been made for some coarse-grained sedimentary units in the basin, which have led to the misinterpretation of biostratigraphic and magnetostratigraphic age models. To resolve these issues, we present radiometric dating of three late Cenozoic sedimentary units ("Liushu", Hewangjia, and Jishi formations) in the eastern Linxia Basin using cosmogenic 26Al/10Be and 10Be/21Ne burial methods. isotope measurements for the upper "Liushu" Formation indicate a 10Be/21Ne burial age of 11.70 ± 0.17 Ma. This age is older than, but not contrary to, recently revised bio-magnetostratigraphic work. The 26Al/10Be burial age of the Hewangjia Formation is 3.06 (+0.36/−0.31) Ma and had been underestimated by post-burial muon production possibility, while the 26Al/10Be burial age of the Jishi Formation is 2.50 (+0.20/−0.18) Ma and had been overestimated due to inherited cosmogenic nuclides from recycled deposits. The new age from the Jishi Formation delays the initial deposition of conglomerates in the Linxia Basin to no earlier than 2.5 Ma and constrains an important episode of tectonic uplift of the northeastern Tibetan Plateau to 2.5–3.1 Ma. The age of the Equus fauna of Longdan is revised to the Early Quaternary (ca. 2.1–1.9 Ma). Our new age determinations significantly refine the terrestrial sequence chronology of the Linxia Basin and associated mammalian faunas of the late Miocene to the early Pleistocene. • Cosmogenic nuclide burial dating is applied in the Linxia Basin. • A 26Al/10Be age for the Jishi Formation is 2.50 (+0.20/−0.18) Ma. • A 26Al/10Be age Hewangjia Formation estimate is 3.06 (+0.36/−0.31) Ma. • A 21Ne/10Be age for the "Liushu" Formation is 11.70 ± 0.17 Ma. • Tectonic uplift of the northeastern Tibetan Plateau occurred ∼2.5–3.1 Ma. [ABSTRACT FROM AUTHOR]

Assessment of vertical movements of tectonically bounded blocks is crucial for determination of geohazards in densely inhabited zones, such as the border zone of western Slovakia and eastern Austria. The morphostructure of the Malé Karpaty Mts. divides the Vienna and Danube basins in the Western Carpathian – Eastern Alpine junction, and its neotectonic activity is of high importance. This study was focused on 26Al/10Be burial dating of fluvial sediment in the Stará Garda Cave, located in the central part of the mountains. The structural research revealed predisposition of forming of horizontal passages in low angle to subhorizontal bedrock stratification together with low-grade metamorphic foliation. Fluvial origin of the passages was inferred from mezoscale erosional features on the bedrock as well as from facies character of the well preserved sedimentary profile. Cave sediment was according to petrographic analysis derived from a watershed comparable to recent one of the Stupavský Potok Stream. Three analysed dating samples provided low values of isotopic concentrations, allowing us only to calculate the minimum burial age of the deposit of 1.72 Ma. Assuming the low position of the cave above recent surface streams, resulting maximum incision rate of 26 m/Ma indicates very low uplift of the mountains horst during the Quaternary. The slow incision of the river network is in good agreement with a widespread preservation of the planation surface called "Mid-mountain level". In contrast are relatively high values of palaeodenudation rates inferred from isotopic concentrations. Generally, our results indicate that the Malé Karpaty Mts. horst underwent relatively intense but short uplift in the Early Pleistocene, followed by very moderate uplift up to the recent. Key words: Western Carpathians, Malé Karpaty Mts., fluvial cave sediment, burial dating, Early Pleistocene, neotectonics. Zgodnja pleistocenska starost fluvialnih sedimentov v jami Stará Garda, ki jo je dala 26Al/10Be datacija: uporabnost za geomorfni razvoj Nizkih Karpatov (Zahodni Karpati) Ocena vertikalnih premikov tektonsko omejenih blokov je ključna za določitev geohazardov v gosto naseljenih območjih. Morfostruktura Malih Karpatov deli Dunajski in Donavski bazen na stičišču Zahodnih Karpatov – Vzhodnih Alp in njegova neotektonska aktivnost je zelo pomembna. Študija se je posvetila 26Al/10Be dataciji fluvialnih sedimentov v jami Stará Garda v osrednjem delu gorovja. Strukturna raziskava je razkrila predispozicijo oblikovanja vodoravnih jamskih rovov pod nizkim kotom v odvisnosti od subhorozontalne stratifikacije kamnine ter tudi z nizko stopnjo metamorfne foliacije. Na fluvialno poreklo rovov smo sklepali iz srednje velikih erozijskih oblik na njihovih stenah kot tudi iz lastnosti faciesov dobro ohranjenega sedimentnega profila. Glede na petrografske analize jamski sediment izhaja iz povodja, ki je primerljiv z recentnim povodjem potoka Stupavský. Trije analizirani vzorci so nam dali nizke vrednosti koncentracij izotopov, ki so nam omogočile le izračun najnižje pokopne starosti sedimenta, ki je znašala 1,72 Ma. Če upoštevamo, da leži jama nizko nad recentnimi vodnimi tokovi, dobimo maksimalno hitrost vrezovanja dolin samo 26 m/Ma, kar kaže na zelo majhen tektonski dvig v času kvartarja. Počasno vrezovanje rečne mreže se dobro ujema s široko ohranjenim uravnanim površjem, imenovanim »Srednjegorska uravnava«. V nasprotju pa so sorazmerno visoke vrednosti hitrosti paleodenudacije, ki izhajajo iz koncentracij izotopov. Na splošno naši rezultati kažejo, da je bil horst Nizkih Karpatov podvržen relativno močnemu, toda kratkemu dvigovanju v spodnjem pleistocenu, ki mu je sledil zmeren dvig do sedanjosti. Ključne besede: Zahodni Karpati, Nizki Karpati, fluvialni jamski sedimenti, pokopna datacija, starejši pleistocen, neotektonika.

Assessment of vertical movements of tectonically bounded blocks is crucial for determination of geohazards in densely inhabited zones, such as the border zone of western Slovakia and eastern Austria. The morphostructure of the Malé Karpaty Mts. divides the Vienna and Danube basins in the Western Carpathian - Eastern Alpine junction, and its neotectonic activity is of high importance. This study was focused on 26Al/10Be burial dating of fluvial sediment in the Stará Garda Cave, located in the central part of the mountains. The structural research revealed predisposition of forming of horizontal passages in low angle to subhorizontal bedrock stratification together with low-grade metamorphic foliation. Fluvial origin of the passages was inferred from mezoscale erosional features on the bedrock as well as from facies character of the well preserved sedimentary profile. Cave sediment was according to petrographic analysis derived from a watershed comparable to recent one of the Stupavský Potok Stream. Three analysed dating samples provided low values of isotopic concentrations, allowing us only to calculate the minimum burial age of the deposit of 1.72 Ma. Assuming the low position of the cave above recent surface streams, resulting maximum incision rate of 26 m/Ma indicates very low uplift of the mountains horst during the quaternary. The slow incision of the river network is in good agreement with a widespread preservation of the planation surface called "Mid-mountain level". In contrast are relatively high values of palaeodenudation rates inferred from isotopic concentrations. Generally, our results indicate that the Malé Karpaty Mts. horst underwent relatively intense but short uplift in the Early Pleistocene, followed by very moderate uplift up to the recent. [ABSTRACT FROM AUTHOR]

Riverbluff Cave, in Greene County, Missouri, is a short single passage between the James River and its direct tributary, Ward Branch. Before stream incision the cave functioned as a spillway/piracy between the two streams during high-discharge events and accumulated a sequence of stratified fluvial sediments within the cave. Five cosmogenic-nuclide burial ages for these sediments range from 0.984 to 0.570 Ma. These ages are consistent with both the stratigraphic order of the samples and the inferred position of the Matuyama/Brunhes paleomagnetic boundary. These ages indicate that sandy channel-facies deposits derived from Ward Branch entrances began to accumulate within the cave as early as 0.984±0.065 Ma. This facies is capped by highly fossiliferous gravel beds dated at 0.658±0.065 Ma, which contain abundant mammoth bones (possibly Mammuthus trogontherii) and other vertebrates. The high concentration implies that this deposit may record some type of mass-mortality event. By 0.570±0.072 Ma, all Ward Branch entrances had been abandoned because of incision, and a laminated red clay derived from backflow from flooding along the James River capped the older channel sediments. [ABSTRACT FROM AUTHOR]

Over the last three decades, theoretical and technical developments have considerably fostered and intensified the use of terrestrial (or in situ) cosmogenic nuclides as a geochronometer in a variety of environments at the Earth's surface for the Late Cenozoic. These dating methods, including both surface exposure and burial dating, also significantly benefited to fluvial geomorphology. They opened new dating horizons for different kinds of fluvial archives at distinct time scales and thereby provided new insights into previously unanswered questions. This contribution aims at providing a concise (but not exhaustive) overview of these dating applications in a variety of fluvial environments (e.g. river terraces, alluvial fans, in cave-deposited alluvium). Therefore, it briefly presents the fundamental principles of both surface exposure and burial dating, together with a clear statement of the main methodological issues arising from the use of these methods in fluvial contexts. For each dating applications, key information about sampling procedures in the field and representative case studies are also provided. [ABSTRACT FROM AUTHOR]

Following the publication (Granger DE et al., Nature 2015;522:85-88) of an 26Al/10Be burial isochron age of 3.67±0.16 Ma for the sediments encasing hominin fossil StW573 ('Little Foot'), we consider data on chert samples presented in that publication to explore alternative age interpretations. 10Be and 26Al concentrations determined on individual chert fragments within the sediments were calculated back in time, and data from one of these fragments point to a maximum age of 2.8 Ma for the sediment package and therefore also for the fossil. An alternative hypothesis is explored, which involves re-deposition and mixing of sediment that had previously collected over time in an upper chamber, which has since been eroded. We show that it is possible for such a scenario to yield ultimately an isochron indicating an apparent age much older than the depositional age of the sediments around the fossil. A possible scenario for deposition of StW573 in Member 2 would involve the formation of an opening between the Silberberg Grotto and an upper chamber. Not only could such an opening have acted as a death trap, but it could also have disturbed the sedimentological balance in the cave, allowing unconsolidated sediment to be washed into the Silberberg Grotto. This two-staged burial model would thus allow a younger age for the fossil, consistent with the sedimentology of the deposit. This alternative age is also not in contradiction to available faunal and palaeomagnetic data. [ABSTRACT FROM AUTHOR]

Existing methods of cosmogenic nuclide burial dating perform well provided that sediment sources undergo steady rates of erosion and the samples experience continuous exposure to cosmic rays. These premises exert important limitations on the applicability of the methods. And yet, high mountain sediment sources are rife with transient processes, such as non-steady erosion by glacial quarrying and/or landsliding, or temporary cosmic-ray shielding beneath glaciers and/or sediment. As well as breaching the premises of existing burial dating methods, such processes yield samples with low nuclide abundances and variable 26Al/10Be ratios that may foil both isochron and simple burial-age solutions. P–PINI (Particle-Pathway Inversion of Nuclide Inventories) is a new dating tool designed for dating the burial of sediments sourced from landscapes characterized by abrupt, non-steady erosion, discontinuous exposure, and catchments with elevation-dependent 26Al/10Be production ratios. P–PINI merges a Monte Carlo simulator with established cosmogenic nuclide production equations to simulate millions of samples (10Be–26Al inventories). The simulated samples are compared statistically with 10Be–26Al measured in field samples to define the most probable burial age. Here, we target three published 10Be–26Al datasets to demonstrate the versatility of the P–PINI model for dating fluvial and glacial sediments. (1) The first case serves as a robust validation of P–PINI. For the Pulu fluvial gravels (China), we obtain a burial age of 1.27 ± 0.10 Ma (1σ), which accords with the isochron burial age and two independent chronometers reported in Zhao et al. (2016) Quaternary Geochronology 34, 75–80. The second and third cases, however, reveal marked divergence between P–PINI and isochron-derived ages. (2) For the fluvial Nenana Gravel (USA), we obtain a minimum-limiting burial age of 4.5 ± 0.7 Ma (1σ), which is compatible with unroofing of the Alaska Range starting ∼ 6 Ma, while calling into question the Early Pleistocene isochron burial age presented in Sortor et al. (2021) Geology 49, 1473–1477. (3) For the Bünten Till (Switzerland), we obtain a limiting burial age of <204 ka (95th percentile range), which conforms with the classical notion of the most extensive glaciation in the northern Alpine Foreland assigned to the Riss glaciation (sensu marine isotope stage 6) contrary to the isochron burial age presented in Dieleman et al. (2022) Geosciences , 12, 39. Discrepancies between P–PINI and the isochron ages are rooted in the challenges posed by the diverse pre-burial 26Al/10Be ratios produced under conditions characteristic of high mountain landscapes; i.e., non-steady erosion, discontinuous cosmic-ray exposure, and elevation-dependent 26Al/10Be production ratios in the source region, which are incompatible with the isochron method, but easily accommodated by the stochastic design of P–PINI. [ABSTRACT FROM AUTHOR]

Nearly identical sequences of pre-Illinoian glacial till are present throughout the north–central United States in Iowa, Nebraska and Missouri. In each of these states three tills with normal magnetic remanence have been found above two - three tills with reversed remanence, and the lithologic differences among successive tills are nearly the same. Each till is capped by a mature paleosol, except for the two youngest reversed-polarity tills, which are nearly identical in lithology and separated by immature weathering profiles. These results seem to indicate that deposits from five major pre-Illinoian glaciations are present throughout this entire region. Cosmogenic-nuclide burial ages provide relatively precise ages for the three earliest glaciations that reached northeast Missouri: ca. 2.4, 1.3 and 0.76 Ma. Ages of the youngest two glaciations in this area are less precise, but both are between ∼0.2 and 0.4 Ma. The tills in Nebraska and western Iowa have not been dated directly, but are constrained by the ages of interbedded tephra, and these limits are consistent with the burial ages in Missouri for tills in the same relative stratigraphic positions, with one exception. Two of the three normal-polarity tills in Nebraska/western Iowa are present below the 0.64 Ma Lava Creek B tephra, and thus should be between 0.64 and 0.78 Ma in age. However, only one of the normal-polarity tills in northeast Missouri is within this range. This discrepancy indicates either a problem with the age constraints or that the till sequence is more complex than yet recognized. [ABSTRACT FROM AUTHOR]

Accuracy and precision in the measurement of natural aluminium abundances in quartz can affect the reliability of 26 Al exposure dating and 26 Al/ 10 Be burial dating. At ANSTO, aliquots extracted from the HF solutions of dissolved quartz are treated in our laboratory, whereas ICP-OES analysis is performed at a commercial laboratory. The long-term inter-run reproducibility of our in-house standards show a limiting precision in Al measurements of 3–4% (1 σ ), which is lower than the claimed precision of Al analysis by ICP-OES. This indicates that unaccounted random errors are incorporated during our aliquot preparation. In this study, we performed several controlled tests to investigate effects of possible inconsistencies and variances during our aliquot preparation procedure. The results indicate that our procedure is robust against any subtle change in the preparation procedure, e.g., fuming temperatures, fuming reagents, and drying conditions. We found that the density of the solutions dispatched for ICP analysis is occasionally variable due to the presence of residual fuming reagents in the solution. A comparison of the results between the calibration curve and standard addition methods show that the former results are consistently lower than the latter by up to ∼14%. Similar offsets have been reported by previous studies. The reason for these discrepancies is mostly likely matrix effect, which is not accounted for by the calibration curve method. Further tests by varying matrix with impurities such as HF, HClO 4 , H 2 SO 4 and Si identified that Si could cause lower offset in Al measurements; however, our ICP solutions are confirmed to be free from Si and the cause of matrix effect remains to be investigated. Hence, care must be taken for the measurement of Al concentrations in quartz by ICP-OES, either by ensuring that matrix effect is fully accounted for or by routinely employing standard additions when required. [ABSTRACT FROM AUTHOR]

Following the publication (Granger DE et al., Nature 2015;522:85–88) of an 26Al/10Be burial isochron age of 3.67±0.16 Ma for the sediments encasing hominin fossil StW573 (‘Little Foot’), we consider data on chert samples presented in that publication to explore alternative age interpretations. 10Be and 26Al concentrations determined on individual chert fragments within the sediments were calculated back in time, and data from one of these fragments point to a maximum age of 2.8 Ma for the sediment package and therefore also for the fossil. An alternative hypothesis is explored, which involves re-deposition and mixing of sediment that had previously collected over time in an upper chamber, which has since been eroded. We show that it is possible for such a scenario to yield ultimately an isochron indicating an apparent age much older than the depositional age of the sediments around the fossil. A possible scenario for deposition of StW573 in Member 2 would involve the formation of an opening between the Silberberg Grotto and an upper chamber. Not only could such an opening have acted as a death trap, but it could also have disturbed the sedimentological balance in the cave, allowing unconsolidated sediment to be washed into the Silberberg Grotto. This two-staged burial model would thus allow a younger age for the fossil, consistent with the sedimentology of the deposit. This alternative age is also not in contradiction to available faunal and palaeomagnetic data. Significance: • Data on chert samples taken close to StW573 impose a maximum age for the fossil of 2.8 Ma – younger than the 3.67 Ma originally reported. We propose and explore a two-stage burial scenario to resolve the inconsistency and to reopen the discussion on the age of fossil StW573.

Although the OSL signal sourced from quartz is expected to be more stable and bleached more rapidly than the IRSL signal sourced from feldspar in a general sense, the former is much less investigated than the latter for rock surface related luminescence dating. It is mainly due to the difficulty in isolating quartz-dominated OSL signals from rock slices, and the low sensitivity and non-fast component dominated OSL signals for quartz in most of rocks. In merit of the sub-conduction band transition of trapped electrons of feldspar under both green light stimulation and IR stimulation at elevated temperature (Jain and Ankjӕrgaard, 2011), it is expected that the contribution of feldspars to the green light stimulated luminescence could be substantially reduced by a prior IR stimulation at elevated temperature. Meanwhile, more fast-component dominated quartz OSL signal (if there is any) could be obtained by green light stimulation (Bailey et al., 2011). Therefore, in this study, we investigated the feasibility of using the post-IR pulsed green stimulation, which is performed at 25 °C (PGLSL 25) following two IR stimulations (IR 50 IR 225), to isolate the quartz-dominated OSL signals from rock slices of granite cobbles for burial dating. The decay characteristics of stimulation curve, characteristic saturation dose and thermal stability of the pIR 50 IR 225 PGLSL 25 signal suggest that this signal is quartz-dominated, but still not fast-component dominated. We tentatively validated the equivalent dose (D e) measurement protocol by dose recovery experiment. The luminescence-depth profiles show that the bleaching depths of pIR 50 IR 225 PGLSL 25 signals are slightly smaller than or close to that of the IR 50 signals, while they are much shallower for the pIR 50 IR 225 signals. The pIR 50 IR 225 PGLSL 25 procedure enables multiple D e values determined from luminescence signals, with different bleachabilities and stabilities, from both feldspars and quartz in one measurement, which is of potential for buried age dating of cobbles. • The pIR 50 IR 225 PGLSL 25 method could be used to isolate the quartz-dominated signal from rock slice. • The bleaching depth of the pIR 50 IR 225 PGLSL 25 signalis slightly less than or close to that of the IR 50 signal. • The pIR 50 IR 225 and the pIR 50 IR 225 PGLSL 25 D e values could be obtained in one measurement. [ABSTRACT FROM AUTHOR]

The present study aims at testing the possibility of using the in-situ cosmogenic burial dating technique on deltaic deposits. The sequence analyzed is exposed along the Ligurian coast (north-west Italy) and is made of proximal marine and continental deposits previously considered Pliocene or Plio-Quaternary in age. In the study area two allostratigraphic units were recognized. The lower unit represents the evolution of a small coarse-grained delta developed in a fjord or embayment environment. The coarsening/shallowing upward trend observed within the sections, from bottom to top, suggests that the delta prograded rapidly in the landward portion of the canyon placed opposite to the paleo-river outlet. Within the deltaic sequence the transgressive and highstand system tracts were recognized. The unit 2 is composed by several alluvial fan systems deposited in small incised valleys developed within the previously, uplifted deltaic deposits and successively incised by a braided river system. In-situ produced cosmogenic nuclides were used in order to date the age of the deposition of the deltaic deposits. Results suggest that the studied deltaic sediments belonging to the unit 1 were deposited between 1,300,000 and 200,000 year ago thus during the Lower to Middle Pleistocene, whereas the unit 2 was deposited during the Middle Pleistocene as a consequence of a tectonically driven uplift phase. Furthermore samples collected within the prograding part of the delta show the higher denudation rates. The obtained results demonstrate that burial ages and related erosion rates inferred from cosmogenic nuclides concentrations can be considered as a very useful tool to reconstruct the sea level changes over the past 1 million year. [ABSTRACT FROM AUTHOR]

The Central Anatolian Plateau (CAP) in Turkey is a relatively small plateau (300 × 400 km) with moderate average elevations of ∼1 km situated between the Pontide and Tauride orogenic mountain belts. Kızılırmak, which is the longest river (1355 km) within the borders of Turkey, flows within the CAP and slowly incises into lacustrine and volcaniclastic units before finally reaching the Black Sea. We dated the Cappadocia section of the Kızılırmak terraces in the CAP by using cosmogenic burial and isochron-burial dating methods with 10 Be and 26 Al as their absolute dating can provide insight into long-term incision rates, uplift and climatic changes. Terraces at 13, 20, 75 and 100 m above the current river indicate an average incision rate of 0.051 ± 0.01 mm/yr (51 ± 1 m/Ma) since ∼1.9 Ma. Using the base of a basalt fill above the modern course of the Kızılırmak, we also calculated 0.05–0.06 mm/yr mean incision and hence rock uplift rate for the last 2 Ma. Although this rate might be underestimated due to normal faulting along the valley sides, it perfectly matches our results obtained from the Kızılırmak terraces. Although up to 5–10 times slower, the Quaternary uplift of the CAP is closely related to the uplift of the northern and southern plateau margins respectively. [ABSTRACT FROM AUTHOR]

Abstract: Since its discovery within a travertine quarry, the fragmentary cranium of the only known Turkish Homo erectus, the Kocabaş hominid, has led to conflicting biochronological estimations. First estimated to be old, the partial skull presents a combination of archaic and evolved features that puts it as an intermediate specimen between the Dmanisi fossils (Homo georgicus) and the Chinese Zhoukoudian skulls (Homo erectus) respectively dated to 1.8 to . Here we present a multidisciplinary study combining sedimentological, paleontological and paleoanthropological observations together with cosmogenic nuclide concentration and paleomagnetic measurements to provide an absolute chronological framework for the Upper fossiliferous Travertine unit where the Kocabaş hominid and fauna were discovered. The 26Al/10Be burial ages determined on pebbles from conglomeratic levels framing the Upper fossiliferous Travertine unit, which exhibits an inverse polarity, constrains its deposition to before the Cobb Mountain sub-chron, that is between 1.22 and . The alternative match of the normal polarity recorded above the travertine with the Jaramillo subchron (lower limit 1.07 Ma) may also be marginally compatible with cosmogenic nuclides interpretation, thus the proposed minimum age of 1.1 Ma for the end of massive travertine deposition. The actual age of the fossils is likely to be in the 1.1–1.3 Ma range. This absolute date is in close agreement with the paleoanthropological conclusions based on morphometric comparisons implying that Kocabaş hominid belongs to the Homo erectus s.l. group that includes Chinese and African fossils, and is different from Middle and Upper Pleistocene specimens. Furthermore, this date is confirmed by the large mammal assemblage, typical of the late Villafranchian. Because it attests to the antiquity of human occupation of the Anatolian Peninsula and one of the waves of settlements out of Africa, this work challenges the current knowledge of the Homo erectus dispersal over Eurasia. [Copyright &y& Elsevier]

We applied both single-sample and isochron methods of cosmogenic-nuclide burial dating to determine the age of the sedimentary fill in Unaweep Canyon, western Colorado, USA. This stratigraphic sequence is of interest because it documents capture and diversion of the ancestral Gunnison River by the Colorado River during late Cenozoic incision of the Colorado Plateau. Seven 26Al–10Be burial ages from sedimentary infill penetrated by a borehole in central Unaweep Canyon, as well as a 26Al–10Be burial isochron age formed by multiple clasts and grain-size separates in a sample from the stratigraphically lower Gateway gravels, indicate that canyon blockage, initiation of lacustrine sediment accumulation, and presumed river capture, took place 1.41 ± 0.19 Ma. Lacustrine sedimentation ceased 1.34 ± 0.13 Ma. [ABSTRACT FROM AUTHOR]

The Guizhou Plateau represents a geomorphic transition between the Tibetan Plateau and the Yangtze River Plain. It likely formed in response to the propagation of surface uplift in southeastern Tibet during India-Eurasia continental collision. However, the uplift history of the region is unclear largely due to a lack of datable material. The bedrock geology is dominated by carbonate rocks, which contains numerous multi-level caves in the main river valleys that are linked to the river incision history. Cosmogenic 26Al and 10Be burial dating of sediments in caves and river terraces from the northwestern and southern plateau reveals the fluvial chronology and provides the first direct determination of long-term river incision rates. The caves and terraces on the Liuchong River in NW Guizhou yield burial ages of between 0.41 ± 0.12 Ma and 2.85 ± 0.21 Ma, indicating an average incision rate of 57 ± 3 m/Ma. Four level caves at Libo in southern Guizhou yield burial ages of between 0.56 ± 0.16 Ma and 3.54 (+0.25/-0.22) Ma, indicating slightly slower incision rate (47 ± 5 m/Ma). These new results imply that the high elevation of the Guizhou Plateau had developed before the Late Pliocene, and that surface uplift during the Late Cenozoic was largely uniform across the region. [ABSTRACT FROM AUTHOR]

Constraining the ages of fluvial terraces is essential to understanding fluvial responses to climate and sea-level changes and estimating uplift/incision. Luminescence dating of sand or silt grains from fluvial terrace deposits in Japan is difficult because sand layers are often absent from gravelly deposits, quartz grains are typically dominated by medium/slow components and/or contaminated by feldspars, and short transport distances and short residence times in riverbeds result in poor bleaching of luminescence signals. Luminescence dating of cobbles may overcome these difficulties, but few studies have applied this technique to fluvial terrace deposits. Here, we examine the utility of luminescence dating applied to three granodiorite cobbles from a late Pleistocene fluvial terrace deposit of the Ara River, Japan. We investigated variations of the infrared stimulated luminescence (IRSL) and post-IR IRSL signals with depth in each cobble. The IRSL and post-IR IRSL signals generally increase with depth, indicating that the cobbles were not completely bleached before deposition. Nonetheless, the IRSL ages of the cobble surfaces (19–17 ka) are consistent with the age of a tephra layer (16–15 ka) at the base of loess deposits overlying the terrace. In contrast, IRSL ages of sand-sized feldspar grains overestimate the depositional age because of incomplete bleaching, whereas silt-sized quartz grains greatly underestimate the depositional age, likely because of the thermal instability of the medium component. Our results demonstrate that luminescence dating of cobbles could provide a better understanding of fluvial systems in which luminescence dating of sand grains is difficult. [ABSTRACT FROM AUTHOR]

Abstract: The Klondike gravel is a widespread glaciofluvial gravel marking the earliest and most extensive Cordilleran Ice Sheet (CIS) in NW North America. New terrestrial cosmogenic nuclide (TCN) burial ages indicate this gravel was emplaced 2.64+0.20/−0.18 Ma (1σ). Coupled with previously interpreted paleomagnetic stratigraphy, this numerical age constrains the timing of the earliest CIS to the late Gauss Chron and provides a minimum age for the Upper White Channel gravel, a significant placer gold source in the Yukon. This implies the first CIS glacial maximum pre-dates the maximum extent of the Laurentide Ice Sheet, indicating that during the initial stages of northern hemisphere glaciation, the most extensive glaciers were present in the relatively cold and high elevation northern Cordillera. Our results verify the CIS as a likely source of persistent coeval ice-rafted debris in the northern Pacific, and suggest that the first CIS formed as a response to the establishment of the northern Pacific halocline and emergence of the 41 ka obliquity cycle during the Plio-Pliocene transition. [Copyright &y& Elsevier]

Abstract: The radionuclides 26Al and 10Be in situ produced in quartz near the ground surface by secondary cosmic rays can be used for dating the sediment burial. This paper introduces the principles, preconditions and limitations of the recently established dating method. In China its first trial application is to the site of Peking man. The weighted mean of six significant results of samples from layers 7–10 is 770±80 ka. This date provides strong support to an earlier and longer human presence at the site than once estimated. This method has also been applied for the first time to two Lower Paleolithic sites in the Cher Valley, central France, Lunery “la Terre-des-Sablons” and Brinay “la Noira”. The preliminary results attribute ages of 750±240 and 730±210 ka to the two sites, largely consistent with the previous age estimates based on geological and geomorphological studies and on ESR dating. With its well-founded basis in physics, its independence from other dating methods and its timescale filling a “blank period” in radioisotopic dating, the 26Al/10Be burial dating will be widely applied and contribute substantially to the establishment of a reliable timescale for the earliest human occurrence and evolution in China and in Europe. [Copyright &y& Elsevier]

Abstract: The Whippoorwill Formation is a gleyed diamicton that is present locally within bedrock depressions beneath the oldest glacial till in northern Missouri, USA. Stratigraphy, paleomagnetism, and cosmogenic–nuclide burial ages show that it was deposited between the Matuyama–Gauss magnetostratigraphic boundary at 2.58 Ma and the first advance of the Laurentide ice sheet into Missouri at 2.47 ± 0.19 Ma. High cosmogenic–nuclide concentrations also show that the constituents of the Whippoorwill Formation experienced long exposure at a stable landscape surface with erosion rates of 1–2 m/Ma. However, cosmogenic–nuclide concentrations are invariant with depth below the Whippoorwill Formation surface, indicating active mixing of the soil profile shortly before burial by till. The Whippoorwill Formation retains numerous features indicative of cryoturbation. Therefore, we interpret it as a buried Gelisol, a soil formed under periglacial conditions in the presence of permafrost. At the onset of Northern Hemisphere glaciation, climate cooling established permafrost conditions and accelerated erosion by inducing landscape instability. Thus, weathered regolith materials were mobilized and redeposited by gelifluction shortly before the ice sheet overrode the landscape. [Copyright &y& Elsevier]

Abstract: Cosmogenic-nuclide burial dating relies on a pair of cosmic-ray-produced nuclides that are produced in the same rock or mineral target at a fixed ratio, but have different half-lives. For example, 26Al and 10Be are produced in quartz at 26Al:10Be=6.75:1. If a sample of quartz is exposed at the surface for a time, 26Al and 10Be concentrations reflect this ratio; if it is then buried below the penetration depth of cosmic rays, production stops and both nuclides decay. The half-life of 26Al is half that of 10Be, so the 26Al/10Be ratio decreases over time and can be used to date the burial event. Because quartz derived from surface erosion and then buried by sediment accumulation is common, the method is widely applicable for dating Plio-Pleistocene clastic sediments. All (terrestrial) applications of burial dating so far have used the 26Al–10Be pair. Here we show that coupling cosmogenic 21Ne, which is also produced in quartz, with 26Al or 10Be should improve upon both the age range and accuracy of 26Al–10Be burial dating. We establish the feasibility of this approach by 21Ne measurements at two sites that have already been dated using 26Al–10Be burial dating. Burial ages from all three nuclide pairs agree at both sites, which shows that currently accepted values for decay constants and production ratios are internally consistent. Thus, it is possible at present to increase the useful range of cosmogenic-nuclide burial dating by incorporating 21Ne. Fully realizing the potential improvements in accuracy would benefit from additional estimates of 21Ne/26Al and 21Ne/10Be production ratios that are independent of the 26Al and 10Be decay constants. [Copyright &y& Elsevier]

We assess if variations in the in situ cosmogenic 26Al/10Be production ratio expected from nuclear physics are consistent with empirical data, knowledge critical for two-isotope studies. We do this using 313 samples from glacially transported boulders or scoured bedrock with presumed simple exposure histories in the Informal Cosmogenic-nuclide Exposure-age Database (ICE-D) from latitudes between 53°S to 70°N and altitudes up to 5000 m above sea level. Although there were small systematic differences in Al/Be ratios measured in different laboratories, these were not significant and are in part explained by differences in elevation distribution of samples analyzed by each laboratory. We observe a negative correlation between the 26Al/10Be production ratio and elevation (p = 0.0005), consistent with predictions based on the measured energy dependence of nuclear reaction cross-sections and the spatial variability in cosmic-ray energy spectra. We detect an increase in the production ratio with increasing latitude, but this correlation is significant only in a single variate model, and we attribute at least some of the correlation to sample elevation bias because lower latitude samples are typically from higher elevations (and vice versa). Using 6.75 as the 26Al/10Be production ratio globally will bias two-isotope results at higher elevations and perhaps higher latitudes. Data reported here support using production rate scaling that incorporates such ratio changes, such as the LSDn scheme, to minimize such biases. [ABSTRACT FROM AUTHOR]

Abstract: In geochronology it is increasingly common to apply several methods to a set of samples. The task then arises of combining different types of data, with perhaps qualitatively different types of uncertainty, into a coherent age estimate which makes optimum use of the available information. In this paper we discuss a method which uses Bayesian reasoning to combine radiometric, stratigraphic, and paleomagnetic information when dating sediment layers. After presenting a general formulation, we derive an analytic formula for the probability distribution of the age of a sediment layer. We then apply this methodology to refine previous cosmogenic nuclide burial dating results for the age of a sediment layer containing a hominin fossil at Sterkfontein, South Africa. [Copyright &y& Elsevier]

The Upland Complex is a widespread terrace of the ancestral Mississippi River. It has played a central role in studies of the Pliocene Mississippi River drainage, as well as uplift and seismicity in the central Mississippi River Valley. Previous efforts to date the Upland Complex have yielded a range of age estimates spanning the Miocene through Pleistocene. We dated gravels and Fe-oxide cements from quarries of the Upland Complex in Arkansas, Kentucky, Mississippi, and Tennessee using 26Al/10Be burial dating and (U-Th)/He geochronology. Our 26Al/10Be burial dates revealed possible Pliocene-to-Pleistocene depositional ages, while (U-Th)/He dating showed that the onset of weathering dates to at least the Pliocene. Taken together, the 26Al/10Be and (U-Th)/He age constraints demonstrate that the Upland Complex is at least Pliocene in age, and likely formed during a prolonged period of base level stability that preceded Pleistocene glaciations. • 26Al/10Be and (U-Th)/He dates provide a Pliocene minimum age for the Upland Complex. • The Upland Complex is likely mid-Pliocene and is no older than Late Miocene. • Formation of the Upland Complex may be related to widespread Pliocene aggradation. [ABSTRACT FROM AUTHOR]

• New cosmogenic nuclide burial-dating model to constrain the age of glacial sediments. • Higher Deckenschotter gravels in the northern Alpine Foreland deposited 1.0-0.9 Ma. • Onset of major glaciations in the Alps occurred during Middle Pleistocene Transition. A set of four outwash terraces in the northern Alpine Foreland motivated Penck and Brückner's classical scheme of four great Alpine ice ages: Günz, Mindel, Riss, and Würm. While it is now established that the Würm corresponds to marine isotope stages (MIS) 5d–2 (∼117–14 ka) and the Riss type locality to MIS 6 (∼191–130 ka), there is no consensus regarding the age of the older glaciations. The two oldest terraces, known as Höhere Deckenschotter (HDS) and Tiefere Deckenschotter (TDS) in Switzerland and neighbouring Germany, contain interbedded tills that directly indicate the first arrival of glaciers into the northern Alpine Foreland. Here, we set out to constrain the timing of the HDS, which signal the first major glaciations in the Alps. To achieve this goal, we devised a new burial-dating model tailored to glaciogenic sediments: P-PINI (Particle Pathway Inversion of Nuclide Inventories). The method applies a source-to-sink framework to a cosmogenic 10Be-26Al inversion model accounting for variable cosmic-ray exposure and non-steady erosion. Taking published 10Be-26Al data from five HDS sites (Feusi, Tromsberg, Siglistorf, Irchel Steig, and Irchel Hütz) and one TDS site (Iberig), we obtain age distributions (±1 σ) that are especially well constrained for Feusi (0.93 ± 0.13 Ma), Iberig (0.93 ± 0.17 Ma), and Tromsberg (0.88 ± 0.14 Ma), less well-constrained for Irchel Steig (0.69 ± 0.25 Ma) and Siglistorf (0.94 ± 0.27 Ma), and very poorly constrained for Irchel Hütz (1.39 ± 0.56 Ma). Consistent with the morphostratigraphy, which dictates that the TDS postdates the HDS, we implemented a Bayesian modelling framework, yielding an age of 0.69 ± 0.12 Ma for Iberig (TDS) and a combined age of 0.95 ± 0.07 Ma for the HDS sites. Based on the P-PINI burial ages as well as the combined, Bayesian burial age, we propose an age around 1.0–0.9 Ma for the onset of the large Alpine glaciations that triggered the accumulation of the HDS outwash sediments. This roughly accords with the first long glaciation of the Pleistocene (MIS 24–22), identified as a step-change to colder climate and larger glaciations towards the end of the Middle Pleistocene Transition. While our results challenge previously reported ages of ∼2 Ma or more for the HDS in Switzerland, they corroborate evidence from the southern Alpine retroforeland and provide quantitative support for the early hypothesis by G.J. Kukla, who ascribed the oldest glacial deposits in the northern Alpine Foreland to around MIS 22. Finally, we suggest that the source-to-sink approach of P-PINI offers a viable alternative to the established isochron burial-dating method in cases involving non-steady exposure and erosion. [ABSTRACT FROM AUTHOR]

Accelerator mass spectrometry (AMS) has a great potential for various geological applications. The precision and sensitivity is directly linked to technical developments. Therefore CologneAMS, the center for accelerator mass spectrometry of the University of Cologne (Dewald et al., 2013a, 2013b), does extensive work on method developments for isotopic ratio measurement, for new applications and to improve the precision. We present two important technical developments: (1) dating of sediments with 53Mn and (2) ultra-small 14CO 2 samples. (1) The age determination of discontinuously deposited sediments by measurement of cosmogenic 53Mn and 3He concentration in iron‑titaniumoxides (hematite, magnetite, titanomagnetite, ilmenite), where the measurement of the medium mass isotope 53Mn is difficult because of the interfering isobar 53Cr. It can be measured at only 2 laboratories worldwide. The new AMS system at the Cologne 10 MV FN tandem accelerator is therefore designed especially for the measurement of medium mass isotopes, e.g. 53Mn. It provides the opportunity to use several detector systems in different combinations: degrader foils with an electrostatic analyzer, a 4 m time-of-flight system, a new 135∘ gas-filled magnet, different gas ionization detectors and a projectile x-ray detector. With the implementation of the new 135∘ gas-filled magnet to the 10 MV FN-Tandem accelerator AMS beamline the first tests have shown an increase in transmission and reduction of blank value in comparrison to the measurement with the degrader foil technique (Schiffer et al. 2018). The background level was reduced by a factor of 3.3 and the error normalized sensitivity (Schiffer et al. 2018) was increased by a factor of 1.6. (2) For the measurement of extremely low carbon from cosmogenic in-situ produced 14C or from 14C content of bulk sediments, with 0.01% carbon, technical developments are required to measure low concentrations in terrestrial rocks of 100,000 atoms g−1 in quartz and to trace organic compounds with 10–50 μ g of 14CO 2 samples. It turned out, that the measurement of 14CO 2 micro-samples with the gas-ion source of the Cologne 6 MV AMS system in combination with a gas-handling system is an alternative to the development of a micro-scale graphitization. Modern 1 μ g CO 2 samples, (14C/12C) = 1.18×10−12, can be measured with this system with a precision of 2.8%. The overall efficiency is 4%–6% and the reproducibility of standard samples is 0.9% with a blank level of 3–6×10−15. • Technical developments for dating of sediments with 53Mn • Installation of new gas-filled magnet • Technical developments for ultra-small 14CO2 samples. • Modern 1 μg CO2 samples, (14C/12C) = 1.18x10-12, can be measured with a precision of 3% • Measurement of in-situ produced 14C. [ABSTRACT FROM AUTHOR]