Minimum Age Model Research Articles

Reconstructing the tsunami record in Tirúa, Central Chile beyond the historical record with quartz-based SAR-OSL

The most recent high magnitude seismic events, e.g. the Mw 8.2 Iquique earthquake (April 1st, 2014) and the Mw 8.8 Maule earthquake (February 27th, 2010) are reminders of the pronounced vulnerability of the Chilean coast to the impact of natural hazards like earthquakes and tsunamis. Therefore it is crucial to understand the complex tsunami history of Chile which can be deciphered by studying the geological record of former tsunamis in the form of tsunami deposits.At the coastal locality of Tirúa (Central Chile) six distinct, successive tsunamigenic sand layers are intercalated in fine grained floodplain sediments. We present the optically stimulated luminescence (OSL) analysis of quartz from samples of this sedimentological river marsh profile of 1.5 m depth.After the assessment of the applicability of OSL to these samples, it could be noted that despite of an expected low OSL sensitivity of the quartz from the South American Cordillera, most of the sampled quartz yielded a detectable natural signal. After performance tests according to the SAR-protocol, the measurements of the different tsunami sand layers were conducted with small (2.5 mm) aliquots of quartz with the preheat temperature 180 °C. The calculation of De was provided by applying both the central age and minimum age models. All samples are heterogeneous in their De distributions due to incomplete or absent significant bleaching during transport by tsunami. The resulting ages of the tsunami sediments yield an offset of nearly 200 years for CAM ages and less than 50 years for MAM ages, consequently favouring MAM ages for true burial age determination. In some tsunami sand layers and their surrounding river marsh sediments age inversions occur. They were caused by the initial deposition of well bleached sediments derived from beach and dunes followed by older sediments redeposited from beach and intertidal environments during tsunami flow. Despite the offset and age inversion six different tsunami events were dated in the Tirúa profile. Three of these events extend the historical record to pre-Columbian time with the oldest tsunami dated to over 1500 years before present.

Application of single-grain OSL dating to ice-proximal deposits, glacial Lake Benson, west-central Minnesota, USA

Glacial Lake Benson formed in west-central Minnesota as the Des Moines lobe of the Laurentide ice sheet retreated north of a small moraine in the Minnesota River lowland. Although previous research has constrained the timing of glacial Lake Agassiz immediately to the north, little age control is available for the formation of glacial Lake Benson and ice-marginal positions to the south. In order to constrain the age of glacial Lake Benson and test the application of single-grain optically stimulated luminescence (OSL) dating to ice-marginal deposits, seven OSL samples were collected from a variety of depositional settings. These included deltaic deposits linked to specific lake levels, pro-glacial fluvial, ice-contact and supra-glacial deposits. Single-grain OSL results indicate evidence for incomplete resetting (partial bleaching) of the luminescence signal, as expected for glacial environments, and therefore ages were calculated using a minimum age model. OSL results constrain the timing of ice-margin retreat and lake formation to 14.4–14.8 ka. Analysis of single-grain equivalent dose distributions indicates that deposits created by glacial-dominated processes typically had higher over-dispersion (>50%) and greater positive skew (>0.9) than deposits originating from fluvial processes. These results suggest that water-lain deposits should be targeted for OSL sampling over those created by glacial processes when dating ice-proximal settings.

Testing and refining the timing of hydrologic evolution during the latest Pleistocene regressive phase of Lake Bonneville

Lacustrine, fluvial, and wetland landforms present in the now desertified regions of Dugway Proving Ground (DPG) and the Sevier Desert in western Utah, record a fascinating history of falling lake level, river development, and establishment of wetland habitats in the Lake Bonneville basin between ∼13 and 9ka. This was not only a time of rapid climate change but also of human occupation into suitable habitats made available by decline of the large lake. Using optically stimulated luminescence (OSL) dating methods we have determined depositional ages for sediment samples from bar features (reworked deltaic sands), braided fluvial channels, and topographically inverted fluvial channels collected from DPG. All samples analyzed showed good luminescence characteristics. An uncertainty estimate incorporated into Minimum Age Model analysis increased confidence in the equivalent dose (De) estimate for the majority of samples. OSL ages for five of six samples studied support the previously constructed model of overflow from the Sevier basin northwards to the Great Salt Lake basin at ∼12–13ka and rapid regression of Lake Bonneville at this time.

Sources of uncertainties in OSL dating of archaeological mortars: The case study of the Roman amphitheatre “Palais-Gallien” in Bordeaux

Archaeological mortars are more convenient and much more representative for the chronology of buildings than brick or wood constructions that can be re-used from older buildings. Before dating unknown samples of mortars, further investigation of OSL from mortars is required and the most efficient methodology needs to be established. In this study we compared the ages obtained by OSL dating of quartz extracted from mortars of the Roman amphitheatre Palais-Gallien in Bordeaux with independent age information.Resetting of the OSL signal occurred during the preparation of mortar when grains of sand (quartz) were extracted and mixed with lime and water. The mortar was subsequently hidden from light by embedding within the structure which is the event to be dated.Various factors contribute to uncertainties in the age determination. The frequency of measured equivalent doses reveals a large scattering. Optical bleaching of certain grains can be partial due to the short duration of the exposure to light. We worked with the single grain technique in order to find and select the grains that were sufficiently exposed to daylight. To determine the average equivalent dose, we tried three different approaches: a calculation of an arithmetic mean and one following either the central age model or the 3-parameter minimum age model, the latter turned out to be the only relevant way to evaluate the experimental data. The proportion of grains included in the calculation of the average equivalent dose represents 2.7–4.7 % of the overall analysed grains. The results obtained for the three out of four samples are approaching the expected age, however, the minimum doses and the corresponding ages are significantly over-estimated in case of two samples.The studied material is very coarse, which causes heterogeneity of irradiation at the single grain scale, and contributes to a dispersion of equivalent doses. Different analytical methods (scanning electron microscopy with energy dispersive X-ray spectroscopy cartography, Beta-radiography imaging, inductively coupled plasma mass spectrometry) were employed to demonstrate the presence of this phenomenon.Despite the extremely large proportion of high equivalent doses in equivalent dose distributions, there is an apparent presence of well-bleached grains at the beginning of equivalent dose distributions. The study shows the potential of dating mortars by single grain OSL.

수렴단층노두 해안단구 퇴적층의 OSL 연대에 대한 재고찰: 단일입자 OSL 연대측정 연구

이 논문에서는 경주시 양남면에 분포하는 해발고도 약 45 m의 수렴단층 노두 해안단구 퇴적층의 형성시기를 추정하기 위하여, 퇴적층을 구성하고 있는 석영에 대한 단일입자 OSL(Single Grain Optically Stimulated Luminescence) 연대측정을 실시하였다. 실험에 사용된 총 1200개의 석영입자 중, 93개의 입자가 연대측정에 적합한 OSL 신호특성을 보였으며, 이들의 등가선량은 50-610 Gy까지 넓은 분포를 보인다. 이 자료를 중심연대모델(Central Age Model)과 최소연대모델(Minimum Age Model)을 이용하여 분석하면, 각각 <TEX>$83{\pm}4ka$</TEX>와 <TEX>$60^{+3}{_{-7}}ka$</TEX>의 연대가 도출되지만, 이들 연대는 MIS 5a시기로 보고된 기존의 제2해안단구의 OSL 연대와 층서적으로 불일치한다. 단일입자 OSL 분석결과들을 혼합연대모델(Finite Mixture Model)에 적용하면, 분석된 입자들 중 <TEX>$6{\pm}4%$</TEX>의 석영입자가 MIS 7의 퇴적시기 <TEX>$194{\pm}24ka$</TEX>)를 지시함을 알 수 있다. 결론적으로, 수렴단층 노두 해안단구 퇴적층이 MIS 7 시기에 형성되었을 가능성을 배제할 수 없으며, 이 퇴적층은 일반적으로 적용되는 다입자 OSL(multiple grain OSL) 연대측정법을 적용하기에 적합하지 않은 시료로 판단된다. In this paper, we report new OSL ages of the marine terrace sediments at Suryum fault site, using single grains of quartz, and briefly discuss their chronological implications on the timing of terrace formation along the southeastern coast of Korea. Of 1200 grains measured, 93 quartz grains were found to have OSL properties suitable for dating, the equivalent dose (<TEX>$D_e$</TEX>) values of which varied significantly, ranging from 50 Gy to 610 Gy with the overdispersion of <TEX>$30{\pm}4%$</TEX>. Applied to the Central Age Model (CAM) and Minimum Age Model (MAM), these quartz grains showed the OSL ages of <TEX>$83{\pm}4ka$</TEX> and <TEX>$60^{+3}{_{-7}}ka$</TEX>, respectively, both of which are stratigraphically inconsistent with the previously reported OSL ages of lower <TEX>$2^{nd}$</TEX> terrace (MIS 5a; ~80 ka). However, Finite Mixture Model (FMM) revealed that a small fraction of the measured quartz grains (<TEX>$6{\pm}4%$</TEX>) were of the ages (<TEX>$194{\pm}24ka$</TEX>) corresponding to MIS 7. Conclusively, based on single grain OSL ages, it would be prudent not to exclude the possibility that the marine terrace sediments at Suryum fault site have formed during MIS 7. Further, our single grain OSL ages imply that multiple grain(single aliquot) OSL dating methods are not applicable to the marine sediments at Suryum fault site.

Digging your own grave: OSL signatures in experimental graves

Excavation of mock graves in sediments of aeolian and fluvial origin were conducted to test the bleaching efficiency of grave digging in materials that commonly host ancient burials in Australia. Grave-size pits were dug into Pleistocene aeolian sediments at Willandra Lakes and younger fluvial sediments on the Lachlan River, backfilled, and re-excavated. Samples for optical dating were taken from sediment infilling the mock graves and from the adjacent, undisturbed substrate, and analysed using the single aliquot-regenerative dose (SAR) protocol applied to single quartz grains. The resulting equivalent dose (De) distributions revealed that ≤1% of grains had been fully zeroed in both settings, and an additional 1–6% of poorly bleached grains were apparent in the fluvial sediments. Insufficient and heterogeneous bleaching of sediments during excavation and backfilling produced a decrease in the central dose of between 3 and 6 Gy, and an increase in over-dispersion values of between 5 and 10%. These differences were insufficient to clearly distinguish the disturbance event from the effects of bioturbation, biological mixing, or other sources of De variation. The use of the Minimum Age Model substantially over-estimated the burial age (zero years) in both depositional environments, with the degree of over-estimation increasing with the age of the host sediments. These results suggest that optically stimulated luminescence (OSL) techniques will not produce accurate ages for grave infill in a number of forensic and archaeological settings. Further study of the bleaching susceptibility of grains within grave infills, as well as the effectiveness of grave-digging as a bleaching mechanism is required. In other archaeological and geomorphological applications of OSL dating we recommend routine checks on the effective zeroing of sediments in modern equivalent situations.

Reliability of equivalent-dose determination and age-models in the OSL dating of historical and modern palaeoflood sediments

The challenge of accurately estimating the deposition age of incompletely-bleached samples in luminescence dating has motivated developments in the analysis of single grain dose distributions, and a number of statistical approaches have been proposed over the last few years. In this study, we compare the behaviour of the arithmetic average, so-called ‘robust statistics’, the Central Age Model (CAM), the Minimum Age Model (MAM) and the Internal–External Consistency Criterion (IEU) and lowest 5% method, when applied to single-grain dose distributions from a sequence of eight recent (40–1000 years) flash-flood deposits. These sediments are expected to be incompletely bleached, but all have age control from historical records. Modifications were made to allow the use of the standard CAM and MAM models with dose distributions containing near zero and negative dose values. An assessment of minimum over-dispersion (OD) is based on dose recovery tests based on gamma-irradiated samples. We then present a detailed analysis of the effect of an additional uncertainty added to the individual dose estimates on the burial dose estimates from the MAM and the IEU approach. The results of the various models are discussed in terms of the accuracy of the resulting age, and we conclude that, overall, the IEU approach generates the most accurate ages. We also demonstrate that accurate doses can be obtained for those older samples for which uncertainties of ∼40 years are unimportant by applying the IEU model to small aliquot (∼30 grains) dose distributions. From our study we conclude that these and similar young slack-water flood deposits can be accurately dated using quartz OSL, opening up the possibility of establishing time series of flood discharge in catchments for which no instrumental or historical record exists.

Small aliquot and single grain IRSL and post-IR IRSL dating of fluvial and alluvial sediments from the Pativilca valley, Peru

Infrared stimulated luminescence (IRSL) and post-IR IRSL are applied to small aliquots and single grains to determine the equivalent dose (De) of eleven alluvial and fluvial sediment samples collected in the Pativilca valley, Central Peru at ca. 10°S latitude. Small aliquot De distributions are rather symmetric and display over-dispersion values between 15 and 46%. Small aliquot g-values range between 4 and 8% per decade for the IRSL and 1 and 2% per decade for the post-IR IRSL signal. The single grain De distributions are highly over-dispersed with some of them skewed to higher doses, implying partial bleaching; this is especially true for the post-IR IRSL. Measurements of a modern analog reveal that residuals due to partial bleaching are present in both the IRSL as well as the post-IR IRSL signal. The g-values of individual grains exhibit a wide range with high individual uncertainties and might contribute significantly to the spread of the single grain De values, at least for the IRSL data. Electron Microprobe Analysis performed on single grains reveal that a varying K-content can be excluded as the origin of over-dispersion. Final ages for the different approaches are calculated using the Central Age Model and the Minimum Age Model (MAM). The samples are grouped into well-beached, potentially well-bleached and partially bleached according to the evaluation of the single grain distributions and the agreement of age estimates between methods. The application of the MAM to the single grain data resulted in consistent age estimates for both the fading corrected IRSL and the post-IR IRSL ages, and suggests that both approaches are suitable for dating these samples.

Quartz OSL dating of lake shoreline ridge sediments:A case study of Lake Xingkai, Northeast China

古湖岸堤是湖面波动的地貌证据,可以用来重建古湖泊演化.古湖岸堤沉积物的准确测年是应用此地貌学证据重建湖泊演化的关键.以我国兴凯湖最低一级湖岸堤——大湖岗为研究对象,采用石英小片技术,应用单片再生剂量法(SAR)对大湖岗2个不同位置的剖面风成砂质沉积物(共13个样品)进行了光释光(OSL)测年.样品石英组分的光释光衰减曲线特征表明,样品的释光信号以快组分为主,预热坪和实验室剂量恢复实验结果表明,SAR法可以用来测量兴凯湖古湖岸堤样品的等效剂量.通过分析样品等效剂量分布情况和比较3种年龄模型(平均值模型、中值模型和最小值模型),认为大湖岗湖滨砂质沉积物在沉积埋藏前石英光释光信号晒退完全,获得的OSL年龄是可信的.年代结果表明,大湖岗采自不同位置的2个剖面的年代范围一致,且各个剖面中所有年代均随地层顺序变化;另外,2个样品的OSL年龄与同层位的炭屑样品的¹⁴C年代结果在误差范围内一致,进一步表明OSL测年技术可以获得可靠的兴凯湖岸堤沉积物的年龄.尽管与前人使用热释光(TL)测年方法研究大湖岗形成年代有较大差别,本文认为兴凯湖最低一级古湖岸堤——大湖岗形成于距今约1.24-0.50 ka.;Positions of lake shoreline ridges are indicative of the fluctuations in lake level and can be used for reconstruction of palaeolake evolution history. Reliable and accurate chronology is necessary for using lake shoreline ridge sediments to infer lake geomorphologic variations. This paper selected the Dahugang (DHG) shoreline ridge of Lake Xingkai (Northeast China) to demonstrate the potential of optically stimulated luminescence (OSL) dating technique in sandy shoreline sediments. Thirteen sedimentary samples were collected from two profiles (DHG1 and DHG2) of DHG shoreline ridge. Using single-aliquot regenerative dose (SAR) procedure, equivalent dose (D_e) of all samples was measured in small aliquot. The OSL signals of our samples decay very quickly, indicating that the OSL signal is dominated by fast component; preheat plateau tests and dose recovery tests were carried out to select suitable preheat temperature (220℃) for SAR procedure measurement. We analyzed the distributions of D_e for each sample, and compared the D_es derived from three models (Mean age model, Central age model, and Minimum age model). The results suggested that the sandy sediments from DHG shoreline ridge were well bleached prior to deposition and they are appropriate for OSL dating. The resultant OSL ages are stratigraphically ordered at each of the profiles of DHG1 and DHG2, and both have shown that the DHG shoreline was likely to be formed during~1.24-0.50 ka. Furthermore, the robustness and reliability of our OSL ages are validated by two ¹⁴C ages of charcoals. Although our results seem different from previous researches we propose that the DHG shoreline ridge in the Lake Xingkai was formed at around 1.24-0.50 ka based on the present OSL dating results.

Performance of different luminescence approaches for the dating of known-age glaciofluvial deposits from northern Switzerland

Luminescence properties of two samples taken from sand lenses in proglacial outwash de-posits of a piedmont glacier that reached the Swiss midlands during the Last Glacial Maximum are investigated in detail. Deconvolution of CW-OSL decay curves shows that the fast component dominates the OSL signal of quartz. The chemistry of single feldspar grains, in particular the K content in different grains, is determined using wavelength dispersive spectrometry (electron microprobe), revealing an average 12.9 wt.% K of the grains contributing to the IRSL signal. D e distributions are investigated in order to gain insights into partial bleaching, and agreement is found for quartz OSL and feldspar IR50 and pIRIR225 ages for small aliquots and single grains when applying the Minimum Age Model. These ages are also consistent with independent age control. For one sample, ages determined using the Central Age Model result in highly overestimated ages for both feldspar and quartz.

Combining radiocarbon and single-grain optically stimulated luminescence methods to accurately date pre-ceramic irrigation canals, Tucson, Arizona

We present 12 accelerator mass spectrometry (AMS) 14C and five quartz single-grain optically stimulated luminescence (OSL) ages from three Early Agricultural period irrigation canals recently discovered in the floodplains of the Santa Cruz River and Rillito Creek in Tucson, Arizona. Significant discrepancies in the AMS 14C ages are associated with fluvial redeposition of charcoal, producing at times, age overestimates of ∼1000 years. Single-grain OSL ages on canal sediments and application of a minimum age model accurately date the final operation of the canals but have relatively large standard errors of several hundred years. Based on single-grain OSL, one canal dates 730–310 B.C. and the other two date 560–100 B.C. This corresponds with a period of predominant floodplain aggradation (∼500 B.C.–A.D. 1) conducive to water control and irrigation agriculture. Stratigraphic evidence of uncontrolled flooding and rapid sedimentation is present in all three canals and marks the abandonment of two canals. Determining the age of the earliest canals is important for understanding the origins of water management and the transition from foraging to intensive agriculture in the North American Southwest. Due to potential problems with reworked organic material for 14C dating and partial bleaching (resetting) of luminescence signals in fluvial settings, we recommend a combined AMS 14C and single-grain OSL approach for dating early canals.

Local inundation distances and regional tsunami recurrence in the Indian Ocean inferred from luminescence dating of sandy deposits in Thailand

Abstract. The Holocene beach-ridge plain of Phra Thong Island (Ko Phra Thong, SW Thailand) provides sedimentary evidence of several palaeotsunamis, in addition to the deposit of the 2004 Indian Ocean tsunami. Due to poor preservation conditions, these palaeoevent layers are restricted to swales. Correlation across beach ridges, which is important e.g. to reconstruct inundation distances, remains a major challenge. A primary tool for establishing a precisely confined correlation of the sand sheets is the use of chronological data. Since the application of radiocarbon dating is limited by the scarcity of appropriate material, this study utilised optically stimulated luminescence (OSL) dating of tsunamigenic quartz grains. Generally, the sediments showed favourable luminescence properties regarding signal intensity, dose recovery and thermal stability. Disturbances of the OSL signal due to partial bleaching were corrected using the minimum age model. At least three palaeoevents – being 490–550, 925–1035 and 1740–2000 yr old – were distinguished by dating the discontinuous sand sheets at four different sites. Besides this chronological framework, the OSL data provide the opportunity to correlate the discontinuous sand sheets between spatially separated sites within the same swale as well as across ridges. This allows for first estimates of inundation distances for the palaeotsunamis documented on Phra Thong Island. Furthermore, the two younger events overlap in age with contemporaneous tsunami and earthquake evidence from other coasts bordering the Indian Ocean.

Application of OSL dating to middle to late Holocene arroyo sediments in Kanab Creek, southern Utah, USA

Middle to late Holocene alluvium, identified as Quaternary alluvial unit 4 (Qa4), along Kanab Creek in southern Utah, USA was dated using optically stimulated luminescence (OSL) on quartz sand, and by radiocarbon dating of detrital charcoal. Entrenchment beginning in 1882 AD created arroyo walls that expose up to 35 m of the Qa4 alluvium. The stratigraphy and sedimentology suggest that fluvial aggradation along the study reach occurred rapidly. Due to the high sediment supply, short transport distances and semi-arid climate with flashy discharge, partial bleaching (zeroing) of the luminescence signal was expected to be a problem for OSL dating. We approached this problem by first using small-aliquot (∼20 grains) and single-grain dating of quartz sand to reduce the number of grains contributing to the OSL signal. Second, we used statistical parameters based on single-grain and small-aliquot equivalent dose (De) distributions of bleached sediment to help identify partial bleaching and to inform if a minimum age model (MAM) should be used for age calculation. Comparison of results with radiocarbon ages demonstrates the success of OSL dating on Kanab Creek arroyo-fill deposits, although careful attention should be paid to the sedimentary facies and stratigraphy of the targeted sample horizon to minimize the effects of partial bleaching. Thin, decimeter-scale plane-bedded and ripple cross-bedded sandy lithofacies were found to be the best target for OSL dating, as these sediments showed minimal evidence for incomplete solar resetting. Additionally, results generally indicate that better-bleached sediments are found in downstream reaches. Age control from these arroyo-fill deposits was acquired in order to fulfill larger research goals of understanding regional arroyo incision and aggradation cycles.

Timing of the deglaciation in southern Patagonia: Testing the applicability of K-Feldspar IRSL

The timing of the ice margin retreat of the Late Glacial Patagonian Ice Sheet (PIS) in southern Patagonia has been the object of discussion for many years. In order to resolve questions about the complex response of the PIS to past climate change, any geological interpretation and data modelling need evaluation against an absolute chronology. The aim of this project is to investigate the applicability of OSL dating to sediments from southern Patagonia; in particular, we examine the dating potential of K-feldspar IRSL signals. Samples were collected from landforms interpreted as being deposited during deglaciation of the PIS, with an expected age range of 17 and 22 ka, and from recently deposited sediment. We measure small aliquots and single grain distributions using an IR50 SAR protocol with IRSL stimulation at 50 °C following a preheat at 250 °C (held for 60 s). Uncertainties are assigned to our individual dose estimates based on the over-dispersion (OD) observed in laboratory gamma dose recovery experiments (22% for small aliquots and 18% for single grains). Then the possible effects of incomplete bleaching and differential fading are examined. For our natural samples we observe environmental ODs between 30 and 130% and mean residual doses between ∼30 and 80 Gy. Minimum age models are used to identify the part of the dose population that is most likely to have been well-bleached and results from these models are compared. The models give ages that are consistent with each other; this may imply that they successfully identified the fully-bleached grains in the distributions, although there are some discrepancies between our small aliquot and single grain data. We observe large fading rates (on average 7.9 ± 0.6%/decade for large aliquots) but nevertheless a comparison of our fading corrected ages with the expected age range shows that 2 out of 3 ages are consistent with geological interpretation and an established radiocarbon and cosmogenic nuclide chronology. We conclude that these investigations suggest that fading corrections can be based on laboratory average small aliquot/single grain fading rates. The third age is supported by an alternative geological interpretation, and the two ages consistent with the existing chronology imply that in the Strait of the Magellan the hills of the Brunswick peninsula (>70 m.a.s.l) were deglaciated at around 22 ka.

OSL dating of tsunami deposits from Phra Thong Island, Thailand

To evaluate the potential of optical dating (OSL) in establishing a proper tsunami chronology for Phra Thong Island (SW Thailand), the method was applied to a suite of tsunamigenic and littoral sandy deposits, for which independent age control was available. Small aliquots of coarse grained quartz were used for measurements, and processed statistically by means of appropriate age models. Based on the equivalent dose distributions, the well bleached littoral deposits were analysed with the central age model (CAM); the tsunamigenic samples revealed poor bleaching, thus, the minimum age model (MAM) was applied. The cross-check with independent age data showed good agreement between luminescence ages and the existing radiocarbon chronology for the littoral deposits. The poorly bleached deposits of the 2004 Indian Ocean tsunami revealed residuals of less than 40 years, which are insignificant for older deposits and demonstrate the general suitability of the dating technique for tsunamites on Phra Thong. Afterwards, the approach was extended to tsunamigenic and littoral sediments of unknown age. Since those revealed properties similar to their reference deposits, the procedures of statistical De determination were adopted. The resulting ages were in agreement with the stratigraphical position and (largely) with the wider chronological context.

Luminescence dating of an Upper Pleistocene alluvial fan and aeolian sandsheet complex: The Senne in the Münsterland Embayment, NW Germany

An up to 15 m thick alluvial fan and aeolian sandsheet complex is exposed in the upper Senne area, on the southern slope of the Teutoburger Wald Mountains (NW Germany). The origin and age of these deposits have been controversially discussed for many years, ranging from Saalian glaciofluvial to periglacial Weichselian deposits. In order to provide a high-resolution chronological framework for the deposits, we conducted luminescence dating of 12 samples from two localities (Oerlinghausen and Augustdorf pits). Both coarse-grain potassium-rich feldspar and quartz minerals were used for luminescence dating. Feldspar was measured using an elevated temperature post-IR infrared stimulated luminescence (IRSL). Quartz was measured using optically stimulated luminescence (OSL) with a conventional single aliquot regenerative dose (SAR) protocol. Feldspar results tend to overestimate quartz ages for the lower part of the sections (alluvial plain and alluvial fan facies) but are consistent with quartz ages for the upper part of the sections (aeolian facies). Quartz ages from both central and minimum age models suggest deposition during the Late Pleistocene Pleniglacial to Late Glacial.

Optical dating of young deltaic deposits on a decadal time scale

Modern Mississippi Delta sediments were analyzed to investigate quartz OSL signal resetting in large river deltas and test the accuracy of OSL dating on a decadal time scale with the early background subtraction and a recently proposed burial dose estimation procedure. Both fine silt-sized and sand-sized quartz were measured with a modified single-aliquot regenerative dose (SAR) protocol and equivalent dose (De) was calculated using different background subtraction methods. Evidence of insufficient bleaching was observed, but the residual signal is equivalent to ∼100a on average for both sandy quartz and fine silt-sized quartz. It is shown that dose distributions of sandy quartz are affected by the background subtraction. The proportion of aliquots that have De in agreement with expectation is significantly larger when an early background is subtracted compared to the late background subtraction. This is, in contrast, not observed for fine silt-sized quartz. Accurate OSL ages were obtained by employing the unlogged minimum age model to Des of sandy quartz obtained with the early background subtraction method.

Optical dating of alluvial deposits at the orogenic front of the andean precordillera (Mendoza, Argentina)

Well constrained numerical ages of alluvial fan sediments are key to understanding the chronology of alluvial episodes and tectonic activity at the front of the Andean Precordillera. We tested the application of radiocarbon and optically stimulated luminescence (OSL) dating in the distal part of an alluvial fan five kilometers north of Mendoza. For OSL dating a large number of aliquots (n &gt; 70) — each composed of ∼50 quartz grains — were measured in order to obtain reliable burial ages despite scattered dose distributions. Owing to a feldspar contamination in all samples, an infrared stimulation was inserted before each OSL measurement, which reduced the feldspar OSL signal successfully. By using the minimum age model we obtained stratigraphically consistent burial ages of alluvial deposits in a depth profile. The uppermost ∼1 m of sediment is composed of debris flow deposits buried 770±76 years ago. Three plant remnants used for radiocarbon dating from the same layer, however, yielded ages younger than 350 years, which are interpreted to underestimate the depositional age. Underneath the debris flow, a major unconformity cuts a series of distal alluvial fan sediments with interstratified floodplain deposits, which are composed of sandy and calciterich silt layers, respectively. Three samples from this unit which were distributed over one meter of sediment thickness yielded statistically concordant OSL ages of 12.3±1.2 ka, 12.3±1.2 ka, and 11.7±1.1 ka. The deposition of these sediments during the latest Pleistocene coincides with a phase of cool and humid climate, which occurred before the alluvial fan propagated farther into the foreland. The overlying debris flow sediments are associated with alluvial fan incision during the arid Late Holocene.

Luminescence dating of anthropogenic rock structures in the northern Rockies and adjacent High Plains, North America: A progress report

Anthropogenic rock alignments, both circular and linear, are common in the northern Rockies and adjacent High Plains of North America. Their ages are largely unknown. Luminescence dating of single-grain feldspars is applied to sediment under the rocks on the assumption that prior to rock placement turbation processes zeroed sufficient number of grains and that these processes ended with the rock placement. Ages of single grains are corrected for anomalous fading and the age of placement is estimated using the minimum age model. Vertical distributions of ages show that youngest ages are clustered just under the rock, conforming to the turbation model. Low precision in fading corrections led to attempts to reduce fading with higher temperature stimulations. These did reduce fading but also recovered known doses poorly, suggesting possible age over-estimation. This uncertainty coupled with a problem of small sample sizes from material with generally low sensitivity resulted in overall low precision in ages, but still an improvement over the current lack of chronological information.

Geoarchaeological studies on Roman time harbour sediments in Cologne — comparison of different OSL dating techniques

Abstract Due to the construction of a new North-South subway in Cologne, Roman time harbour sediments were exposed and were sampled for luminescence dating. A very good independent age control was given by the precise knowledge of the chronology of Roman activity and by radiocarbon ages of charcoal samples. Hence, different methodological approaches within luminescence dating were applied for Holocene heterogeneously bleached fluvial samples and were compared to the known ages. For one sample, optically stimulated luminescence (OSL) dating was applied to coarse-grained quartz using a single aliquot regenerative-dose (SAR) protocol. After De-measurements, different statistical approaches were tested (i.e. arithmetic mean, median, minimum age model, finite mixture model, leading edge method and the Fuchs and Lang approach). It is demonstrated that the Fuchs and Lang approach along with the leading edge method yielded the best matching OSL ages with respect to the known ages. For the other sample which showed feldspar contamination within the quartz signal, the post-IR blue stimulated luminescence (double SAR protocol) was measured in three different ways to calculate the Devalue: with continuous wave (CW) stimulation with an IR-bleach at 50°C and at 225°C for 100 s prior to the OSL, and pulsed OSL (POSL). It was demonstrated that the IR-stimulation at 225°C has very good potential to remove the feldspar signal contribution as well as pulsed OSL, but the former might deplete parts of the quartz OSL signal.