Nordic Laboratory for Luminescence Dating

<strong class="journal-contentHeaderColor">Abstract.</strong> Infrared radiofluorescence (IR-RF) is an alternative dating technique for potassium feldspar grains, offering a higher signal stability and based on a simpler underlying mechanism than more common luminescence dating approaches. However, its accuracy when tested on known-age samples has so far shown inconsistent results. In this study, we present a refined accuracy assessment using samples that have previously produced unreliable IR-RF ages. Our approach incorporates two major methodological advancements developed over the past decade: elevated temperature measurements using the IR-RF₇₀ protocol and sensitivity change correction by vertical sliding. To expand the dose range comparison, we included two additional samples: one expected to be in saturation and another of modern age. Additionally, we evaluated the effect of using a narrower bandpass filter to exclude any signal contributions from potentially contaminating shorter wavelength emissions. Our results following the IR-RF₇₀ protocol with sensitivity corrections show an improvement over the original room temperature results. For four out of the seven tested known-age samples spanning 20&ndash;130 ka, we obtained results in keeping with the expected doses. Two additional modern samples, however, yielded slight age underestimations. Introduction of a multiple-aliquot regenerative dose (MAR) protocol improved the accuracy of two out of three samples with large sensitivity changes. Finally, we also compared the new IR-RF equivalent doses (D_e) to those obtained with the newer trap-specific dating method infrared-photoluminescence (IRPL) for the same samples, including previously published values and new measurements. We observe that with the new improvements the success rate of IR-RF is comparable to that of IRPL.

Abstract Alluvial fans are hypothesised to record signals of past hydroclimate changes in their depositional chronologies and slopes. However, direct tests of this hypothesis have been limited due to challenges in precisely dating the responses of alluvial fans to past climate forcing. Here, we present a new chronology of alluvial‐fan deposition at the Sierra de Aconquija in the southern Central Andes (27°S) spanning ~300 kyr and based on 35 cosmogenic 10Be‐derived exposure ages and eight infrared‐stimulated (IRSL) and optically stimulated luminescence (OSL) ages. The ages reveal that fan deposition was phased with past climate changes. Orbitally‐forced weakening and strengthening of the South American Summer Monsoon coincided with fan aggradation during dry episodes and incision during wetter episodes, consistent with predictions from alluvial‐channel models. These results are in precise agreement with independent palaeoclimate constraints spanning timescales of 103 to 105 years. Fan aggradation‐incision cycles record a predominant influence of precession‐induced variations in precipitation, although climate shifts as rapid as 1 kyr also triggered incision, and fan architecture appears to be further modulated by orbital eccentricity cycles. Incision events on the fans coincide with the ages of moraines in the headwater catchments, including those formed during the Younger Dryas and Last Glacial Maximum. Furthermore, the fan chronology indicates dry conditions in the southern Central Andes during Heinrich Stadial 1, suggesting that enhanced precipitation during this episode was limited to more northerly latitudes. Our results demonstrate that climate change exerts a primary control on simple, source‐to‐sink sedimentary systems and show that alluvial fans can, in some cases, be utilised as terrestrial palaeoclimate archives with which the spatio‐temporal variability of past climate changes can be constrained.

In 2017 part of an ancient stone causeway was uncovered at Karlslunde on the island of Sjælland, Denmark. With no artefacts found at the site, optically stimulated luminescence dating of coarse grains, grains derived from disaggregated rocks, and surficial rock chips obtained directly from granitic road cobbles were used to determine the time of construction. Some granitic road cobbles were visibly disaggregating at the time of excavation, and laboratory measurements revealed surprising strong fast component dominated quartz sensitivity from these samples. It was concluded that some of the rocks used in the causeway had been heated, presumably prior to incorporation in the structure. Dose recovery plateau experiments using sedimentary quartz and quartz grains recovered by gently disaggregating heated rocks suggested the use of a 220/180 °C preheat/cut-heat combination (DR ratio 0.999 ± 0.018; n = 40); this reduced the risk of thermal transfer in these young samples. IRSL signals were used for rocks that could not be disaggregated. The L/T burial profiles obtained from two unheated rocks (1 granite, 1 felsic gneiss) indicated they had been exposed for sufficient time for us to be confident of obtaining accurate IRSL ages. The post-IR IRSL180 signals were also measured in these two cobbles; the bleaching front was shallow and the signal was only sufficiently reset to allow accurate determination of De on one rock. After subtracting a residual, the dose recovery ratio results for the unheated rocks post-IR IRSL180 and IR50 were 1.006 ± 0.012 (n = 10) and 0.937 ± 0.007 (n = 10), respectively. In total 8 ages were accepted; 4 coarse grained sediment quartz ages from an unexcavated part of the road surface, 2 fading corrected IR50 ages from surface slices from non-disaggregated cobbles, and 2 quartz ages from disaggregated (apparently heated) cobbles. IRSL signals from the sedimentary and heated samples were used primarily to assess the degree of resetting of the quartz blue-stimulated OSL; both the post-IR IRSL and IR50 signals significantly over-estimated the quartz age. However, the sedimentary quartz ages, the heated cobble quartz ages and the fading corrected IR50 ages from the unheated road cobbles, are consistent and likely reflect a construction age of ∼2ka ago.

Abstract This study uses quartz‐based optically stimulated luminescence dating to determine when a massive fortification wall (W11186) was constructed in the archaeological site of Tall Zarʿa in the Jordan Valley. A total of 11 samples of sediments were taken from a trench on the north side of the wall (extramuros). The extracted quartz grains had good luminescence characteristics and were identified as well bleached by comparison with feldspar infrared‐stimulated luminescence (IRSL) ages. The optical ages showed that the deposition against the wall occurred in two different periods. The first was around 3.20 ± 0.07 ka ago (Iron Age), and the second was around 2.28 ± 0.08 ka (Hellenistic period). Human activity was evident because of the intermixing of cultural material with the presumed naturally deposited units.

&amp;lt;p&amp;gt;The Western Iberian passive margin is under compressive tectonic reactivation resulting in spatial and temporal variations in surface uplift. This uplift can be quantified in coastal settings using staircases of wave-cut platforms developed onto rocky headlands. This study focuses on two marine terrace staircases of central Portugal: Cape Raso (west of Lisbon) and Cape Espichel (western Arr&amp;amp;#225;bida mountain chain). Geomorphic and stratigraphic analyses identified four marine terraces above sea level at Cape Raso area and twelve at Cape Espichel. ESR and pIRIR dating were used to develop a chronological framework for the staircases, from which uplift rates were calculated.&amp;lt;/p&amp;gt;&amp;lt;p&amp;gt;Using the interaction between the global mean sea-level elevations in the Quaternary and the local uplift rate (Roberts et al., 2013) the marine terraces were correlated with Marine Isotope Stages (MIS). At Cape Raso, Tm1 (+38 m) corresponds to MIS 17 (712-676 ka), Tm2 (+34 m) corresponds to the MIS 15 (621-563 ka) and was reworked during the MIS 11 (399-408 ka), Tm3 (+ 22 m) correlates with MIS 13 (533-478 ka) and was reworked during the highstand of MIS 9 (330-316 ka) and Tm4 (+9 m) correlates with MIS 7 (243 -191 ka). At Cape Espichel, a correlation was found between the relative sea-level elevations of the eight lowest terraces with several MISs (MIS 5 until MIS 17). The correlation becomes unclear for terraces older than MIS 17, translating into an apparent decrease in uplift rate towards older times. Either in Cape Raso or Espichel, the terrace staircases do not correlate in all cases with sea level high stands sequentially. For instance, the palaeoshoreline elevation of MIS 11 is higher than the palaeoshoreline of MIS 13. This suggests that marine terraces have been formed by superposition of multiple sea-level fluctuations in a long-term uplift context, but with an uplift rate low enough to allow the reworking of older shorelines during subsequent MISs.&amp;lt;/p&amp;gt;&amp;lt;p&amp;gt;At Cape Raso, the dating of Tm2 correlated with MIS 15 allows for an estimation of an uplift rate of ~0.07 m/ka for this coast, seemingly decreasing over the last ~125 ka. At Cape Espichel, the chronological framework of Tm5 and Tm6 allows associations with MIS 15 and MIS 11, respectively. The estimated mean uplift rate from MIS 5e to MIS 17 was ~0.14m/ka. For times older than MIS 17 (up to ca. 3.7 Ma) the uplift rate was lower than during the last ~125 ka (~0.04 m/ka). The present elevations of the late Zanclean wave-cut platform, represented by the Raso Cape Platform (~100 m) and the Cape Espichel (up to ~220 m) platforms, further express the differential uplift between the study areas for the last ~3.7 Ma.&amp;lt;/p&amp;gt;&amp;lt;p&amp;gt;&amp;amp;#160;&amp;lt;/p&amp;gt;&amp;lt;p&amp;gt;

&amp;lt;p&amp;gt;We demonstrate how assumptions about strath terrace formation affect the interpretation of climatic control on landscapes, calculation of incision and rock uplift rates, and recommend strategies for geochronological sampling and interpretation. An innovative approach to OSL dating terrace gravels allows us to produce a detailed ~200 kyr history of punctuated river incision and strath terrace formation spanning two stratigraphic landform levels in the High Atlas Mountains (NW Africa). Extensive preservation and exposure of strath-top gravels, within a post-orogenic setting unaffected by eustatic influences, enables the derivation of rates of base-level fall, integrated over periods of strath-top deposition, metastable equilibrium, and incision, that are consistent with independently constrained regional rock uplift rates. Combining a punctuated river incision model with our well-constrained terrace formation history allows us to demonstrate how assumptions concerning Quaternary river incision and deposition can lead to the problematic Sadler Effect, an apparent dependence of incision rates on measured time interval. Subsequently, we demonstrate that an approach to reinterpreting previously published data using the punctuated incision model, even when combined with limited terrace age data, results in more consistent and parsimonious conclusions about rates of river incision, rock uplift and base-level lowering across the mountain belt. Our recommendations for sampling strategies to constrain rock uplift rates require samples to be taken just above the strath surface, and in addition towards the top of the deposit for river incision rates. In a setting with punctuated river incision and strath terrace formation, both rock uplift and incision rates require burial dates, as exclusive use of abandonment ages will not yield constraints on accurate rates of rock uplift or incision. Furthermore, we find that only with multiple along-stream locations and multiple burial dates in each terrace deposit, could a reliable climatic signal be extracted; this signal would not have shown up in terrace abandonment ages such as those derived from cosmogenic exposure dates. The demonstrated effects of assumptions about strath terrace formation, and the recommended approaches for sampling and interpretation, have implications for those attempting to constrain palaeoclimatic, tectonic, and geomorphic histories from strath terrace records in regions exhibiting punctuated river incision.&amp;lt;/p&amp;gt;

Permafrost region subsurface organic carbon (OC) pools are a major component of the terrestrial carbon cycle and vulnerable to a warming climate. Thermokarst lagoons are an important transition stage with complex depositional histories during which permafrost and lacustrine carbon pools are transformed along eroding Arctic coasts. The effects of temperature and salinity changes during thermokarst lake to lagoon transitions on thaw history and lagoon deposits are understudied. We analyzed two 30-m-long sediment cores from two thermokarst lagoons on the Bykovsky Peninsula, Northeast Siberia, using sedimentological, geochronological, hydrochemical, and biogeochemical techniques. Using remote sensing we distinguished between a semi-closed and a nearly closed lagoon. We (1) characterized the depositional history, (2) studied the impact of marine inundation on ice-bearing permafrost and taliks, and (3) quantified the OC pools for different stages of thermokarst lagoons. Fluvial and former Yedoma deposits were found at depth between 30 and 8.5 m, while lake and lagoon deposits formed the upper layers. The electrical conductivity of the pore water indicated hypersaline conditions for the semi-closed lagoon (max: 108 mS/cm), while fresh to brackish conditions were observed beneath a 5 m-thick surface saline layer at the nearly closed lagoon. The deposits had a mean OC content of 15 ± 2 kg/m3, with higher values in the semi-closed lagoon. Based on the cores we estimated a total OC pool of 5.7 Mt-C for the first 30 m of sediment below five mapped lagoons on the Bykovsky Peninsula. Our results suggest that paleo river branches shaped the middle Pleistocene landscape followed by late Pleistocene Yedoma permafrost accumulation and early Holocene lake development. Afterward, lake drainage, marine flooding, and bedfast ice formation caused the saline enrichment of pore water, which led to cryotic talik development. We find that the OC-pool of Arctic lagoons may comprise a substantial inventory of partially thawed and partially refrozen OC, which is available for microbial degradation processes at the Arctic terrestrial-marine interface. Climate change in the Arctic leading to sea level rise, permafrost thaw, coastal erosion, and sea ice loss may increase the rate of thermokarst lagoon formation and thus increase the importance of lagoons as biogeochemical processors of former permafrost OC.

Previous experiments and modelling suggest that quartz and feldspar grains receive a net negative charge when irradiated with electrons. Here we used silt-sized grains of quartz and feldspar to investigate the behaviour of luminescence at very high electron doses, when electrostatic effects become possible. Both quartz and feldspar show an increasing luminescence response up to 700 kGy, after which we observe a non-linear decrease in luminescence with dose which eventually stabilises, in contrast to modelling predictions using charge imbalance. The presence of an electric field on the grains is investigated as a possible explanation for the non-linear decrease, using several electron energies. Charge leakage and de-stabilisation of the electron trap at high doses is also discussed.