Minimum Age Model Research Articles

Preservation of probable MIS 7 deglacial and nonglacial deposits near the edge of the Hudson Bay Lowland in Manitoba, Canada

The stratigraphic principle of superposition assumes that sediments at surface are youngest. And yet, patches of older preserved landscapes continue to be identified in the regions formerly covered by the Laurentide Ice Sheet. Two gravel pits, at the edge of the western Hudson Bay Lowland near the geographic centre of the North American Ice Sheet Complex, reveal additional patches where older glacial and nonglacial sediment is preserved. These sites expose 1–4 m of a darker, highly overconsolidated, clayier till, and 0–2 m of a lighter, less consolidated, sandier till over glaciofluvial and post-glacial gravels and sands; the waning stages of deposition occurred at 214 ± 22 ka (1σ minimum age model quartz grain optical age estimates, n = 2). This was during the latter end of the cool Marine Isotope Stage (MIS) 7-d (within 1σ range) or near the end of MIS-8 (within 2σ range). Next followed a warmer period similar to, or warmer than, present day with higher precipitation; inferred from pollen and macrofossils deposited in nonglacial low-energy floodplain or pond sediments. Our study highlights the need to accurately date Quaternary sediments, given that the shallowest nonglacial sediments at both gravel pits were deposited during an old (MIS 7) interglacial; there is likely no record of the youngest interglacial (MIS 5). Preservation of older sediment also means that in Quaternary stratigraphy, disjoint regional nonglacial “organic marker beds” should not automatically be considered correlative. Identification of similar “old” patches, together with till stratigraphy and composition, is essential to accurately model glacial sediment transport over time.

Single grain pIRIR dating of glacigenic deposits in the Yuzhu Peak area of Kunlun Mountains of Tibetan Plateau revealed the glaciations during Holocene period

The variations of glaciers in the Kunlun Mountains of the northern Tibetan Plateau are influenced by the complex interaction of the East Asia summer monsoon (EASM), Indian summer monsoon (ISM) and Westerlies, as well as human activity during the Holocene period. Consequently there is ongoing debates regarding the evolution of glaciers and the factors driving their changes. The reconstruction of glacial evolutions in these regions has been hindered by insufficient chronological data for moraines and other glacial landforms. In this study, glacial sediment samples were collected from five moraine sequences located on the southern and northern slopes of the Yuzhu Peak in the Kunlun Mountains. These poorly bleached moraine samples were dated using the single-grain quartz optically stimulated luminescence (OSL) and K-feldspar post-infrared infrared stimulated luminescence (pIRIR) dating methods. The luminescence characteristics analysis of quartz grains shows that single grain quartz OSL dating cannot be used to date Holocene moraine samples due to the low brightness of quartz OSL signals. Various tests were conducted to assess the reliability of K-feldspar pIR50IR170 dating, including anomalous fading tests, dose recovery, and residual dose tests. The K-feldspar pIR50IR170 ages, determined using the Minimum Age Model (MAM), indicate that during the early Holocene, glaciations have expanded by ∼800 m in length at ∼ 8 ka, and during the end of the Neoglacial period, they extended by ∼200 m in length at ∼ 1 ka. The strengthened ISM precipitation and northward movement of ISM boundary likely contributed to the glacial expansion in the early Holocene. During the end of the Neoglacial period, the increase in westerlies precipitation and cold events may have played a role in the advancement of glaciers.

Holocene lake shrinkage on the northwestern Tibetan Plateau revealed by K-feldspar single-grain pIRIR dating of paleo-shorelines

As a vital component of the “Asian water tower”, lakes on the Tibetan Plateau (TP) significantly influence the regional ecosystems and economies and they are also an effective sentinel of climate change. However, the temporal and spatial patterns of lakes and the related hydroclimatic evolution on the northwestern TP (NWTP) remain unclear. We reconstructed the lake level variations of a non-glacier-fed lake, Longjue Co, on the NWTP, using optical dating of paleo-shorelines. The optically stimulated luminescence signals of quartz grains were unsuitable for dating due to high contributions of the medium component, and thus the post-infrared infrared stimulated luminescence signals (pIR50IR170, pIR50IR225) of K-feldspar single grains were used. Internal checks including dose recovery tests, residual dose tests, and anomalous fading tests showed that the pIR50IR170 signal was suitable for paleo-shoreline dating in Longjue Co. However, some of the samples were affected by the incomplete bleaching of pIRIR signals before deposition, and in this case the Minimum Age Model was used to constrain the ages. We also examined the dependence of the K-feldspar equivalent dose (De) on grain brightness and explored the possible mechanisms, and the brightest grains were then used for De calculations. The results show that Longjue Co reached its maximum Holocene level (+34 m) during the early Holocene (10.06 ± 1.39 ka), and then after ∼5 ka it commenced a shrinking trend, punctuated by two rapid lake level decreases. Reference to independent paleoclimate records suggests that the Holocene lake level variations of Longjue Co and the regional hydroclimate were mainly controlled by the Indian summer monsoon.

Geological study of an outburst flood event in the upper Yangtze River and risk of similar extreme events

Outburst flood sediments are studied on the upper course of the Yangtze River (known as the Jinsha River) where is a key region for the development of hydroelectric power. As the history and magnitude of outburst flooding in this stretch of the Jinsha River during historic times has remained largely undocumented, we have endeavored as part of this study to conduct field investigations into, and provide numerical dating (using OSL and 14C dating techniques) of outburst flood evidence found in the First Bend area of the Yangtze River. Carbonized nutshells and charcoal from the ancient settlement yielded 14C ages that precisely pinpointed an outburst flood event ∼1200–1300 cal yr BP, during China's Tang Dynasty (618–907 CE). However, OSL ages using the minimum age model for all outburst flood samples ranged from 9.1 to 1.8 ka, which was ∼0.5–7.8 ka older than the 14C-dated outburst flood. This discrepancy suggests a potential overestimation of quartz age when dating outburst flood sediments from the Holocene period. Furthermore, using 2D hydraulic modeling, we estimated the magnitude of the aforementioned outburst flood, revealing a reconstructed peak flow discharge of 51,000–55,300 m3/s. This discharge was three times greater than the 10,000-year flood for the hydroelectric power station nearest to the study area. Our study underscores the significant role of combining archaeological and geological evidence in enhancing paleoflood hydrology research. Through a multidisciplinary approach, our findings emphasize the importance of paleoflood hydrology studies in comprehending both the latent and catastrophic flood risks in alpine mountain areas amid the context of global warming. Key points•A series of outburst flood sediments was identified in the First Bend area of the Yangtze River, with a maximum flood water surface ∼86 m high above modern river level.•The obtained 14C ages would suggest that the outburst flood occurred at ∼1200–1300 cal yr BP in the Tang Dynasty (618–907 CE) of China.•The reconstructed peak flow discharge (51,000–55,300 m3/s) is larger than the three times of the 10,000-yr flood for the nearest hydropower station to the study site.

Luminescence dating of adobe from monumental architecture in north coastal Peru

Luminescence dating was applied to adobe bricks from temples at several archaeological sites in coastal Peru. Resulting dates, ranging from BCE 100 to CE 920, are generally in agreement with associated radiocarbon assays, ca. 350–950 CE. Luminescence dates the last time bricks were exposed to sunlight. Because the bricks were likely made in molds, not all grains in the bricks were likely exposed to sufficient sun at time of manufacture. Use of single-grain dating is essential. Luminescence was measured on 180–212 µm potassium feldspar using infrared stimulated luminescence with correction for anomalous fading. A minimum age model was applied to isolate those grains most likely to have been fully exposed. Some dates were also derived for associated sediments.

Luminescence dating of tsunami deposits from the algarve shelf, Portugal

Offshore tsunami deposits have the potential to substantially improve our understanding of long-term tsunami hazard. This may be particularly true for the Portuguese Algarve coast, where onshore sediment records are restricted to the last 3000 years due to scarcity of sediment archives suitable for identifying tsunami deposits. This study investigates the potential of optically stimulated luminescence (OSL) for dating offshore tsunami layers from the Portuguese shelf and its background sedimentation cored during METEOR cruise M-152, by comparing luminescence ages with radiocarbon chronologies. Accurate luminescence ages for both offshore tsunami deposits and constraining shelf sediments can be achieved by using single grains of quartz in combination with the minimum age model. However, even single grain ages significantly over-estimate by several thousand years for some very poorly bleached tsunami deposits and underlying shelf sediments affected by erosion during the event. This demonstrates the necessity of using chronologies that are based on a large number of ages, as well as a combination of direct tsunami ages and limiting ages for background sedimentation. The combination of luminescence ages from this study with radiocarbon ages using a Bayesian approach yields an age of 3600–3800 years for a predecessor event of the 1755 CE Lisbon tsunami, formerly radiocarbon dated in the same offshore sediment cores to ca. 3600 cal years BP.

Insight into the dynamics of a long-runout mass movement using single-grain feldspar luminescence in the Pokhara Valley, Nepal

Abstract. Mass movements play an important role in landscape evolution of high mountain areas such as the Himalayas. Yet, establishing numerical age control and reconstructing transport dynamics of past events is challenging. To fill this research gap, we bring luminescence dating to the test in an extremely challenging environment: the Pokhara Valley in Nepal. This is challenging for two reasons: (i) the optically stimulated luminescence (OSL) sensitivity of quartz, typically the mineral of choice for dating sediments younger than 100 ka, is poor, and (ii) highly rapid and turbid conditions during mass movement transport hamper sufficient OSL signal resetting prior to deposition, which eventually results in age overestimation. Here, we first assess the applicability of single-grain feldspar dating of medieval mass movement deposits catastrophically emplaced in the Pokhara Valley. Second, we exploit the poor bleaching mechanisms to get insight into the sediment dynamics of this paleo-mass movement through bleaching proxies. The Pokhara Valley is a unique setting for our case study, considering the availability of an extensive independent radiocarbon dataset as a geochronological benchmark. Single-grain infrared stimulated luminescence (IRSL) signals were measured at 50 ∘C (IRSL-50) and post-infrared infrared stimulated luminescence signals at 150 ∘C (pIRIR-150). Our results show that the IRSL-50 signal is better bleached than the pIRIR-150 signal. A bootstrapped minimum age model (bMAM) is applied to retrieve the youngest subpopulation to estimate the paleodose. However, burial ages calculated with this paleodose overestimate the radiocarbon ages by an average factor of ∼23 (IRSL-50) and ∼72 (pIRIR-150), showing that dating of the Pokhara Formation with a single-grain approach was not successful for most samples. Some samples, however, only slightly overestimate the true emplacement age and thus could be used for a rough age estimation. Large inheritances in combination with the scatter in the single-grain dose distributions show that the sediments have been transported under extremely limited light exposure prior to deposition, which is consistent with the highly turbid nature of the sediment-laden flood and debris flows depositing the Pokhara gravels. To investigate the sediment transport dynamics in more detail, we studied three bleaching proxies: the percentage of grains in saturation 2D0 criteria, the percentage of best-bleached grains (2σ range of bMAM-De) and the overdispersion (OD). None of the three bleaching proxies indicate a spatial relationship with runout distance of the mass movement deposits. We interpret this as evidence for the lack of bleaching during transport, which reflects the catastrophic nature of the event. While not providing reliable burial ages of the Pokhara mass movement deposits, single-grain feldspar dating can potentially be used as an age range finder method. Our approach shows the potential of luminescence techniques to provide insights in sediment transport dynamics of extreme and rare mass movement events in mountainous regions.

OPTICALLY STIMULATED LUMINESCENCE (OSL) MORTAR DATING INTER-COMPARISON STUDY. THE SECOND ROUND OF MODIS, MORTAR DATING INTER-COMPARISON STUDY

ABSTRACT After an intercomparison age experiment carried out in the framework of the first MODIS (MOrtar Dating Inter-comparison Study) project, the results showed general agreement both between optically stimulated luminescence (OSL) dating laboratories and with radiocarbon (14C) dating results. As the needs for the selection of samples convenient for an inter-comparison are not the same between 14C and OSL, for the second running, it has been decided to choose two different sample sets, one to share between the radiocarbon labs and one for the OSL dating ones. The results obtained by applying different experimental protocols (multigrain and single grain techniques) and different statistical models (weighted mean, central age mode, average dose model, minimum age model and exponential exposure dose) are discussed in this work.

Analysis probes and statistical parameters affecting the OSL ages of mortar samples; a case study from Italy

Mortars stand among the very few materials that theoretically cannot be reused due to irreversible hardening processes. Among the various dating techniques, radiocarbon and Optically Stimulated Luminescence (OSL) struggle for being selected as the most robust and reliable dating technique for the specific material. The principle of mortar OSL dating depends on the bleaching of the quartz grains of the sandy aggregate while mixing and laying the mortar to daylight. Thus, the OSL ages strongly depend on the effective bleaching of the quartz. Here, we deal with OSL ages from the old Roman Theatre of Padua. Preliminary OSL results based on Single Aliquot Regeneration (SAR) protocol using three regenerated doses to multigrain (MG) quartz aliquots, indicated distributions of ED (Equivalent Dose) leading to significant mismatch of these results compared to the expected ages. The present work attempts to discuss the influence of various data analysis approaches such as (a) exclusion criteria like recycling ratio and recuperation values, (b) selection of the suitable region of interest in the signal's integral along with the correct background (late or early) subtraction technique and (c) appropriate statistical analysis by selecting the suitable age model (descriptive statistics, Central Age Model, Minimum Age Model) on the final distribution as well as both value and precision of the ED, enabling thus to obtain ages that are not only more accurate, but also closer to what was expected. Alternative statistical indicators of either the symmetry of the ED distributions (like skewness, kurtosis, etc) or the OSL signal itself (residual distribution analysis, kinetic parameters and percentage contribution of each OSL component to the overall signal) will be assessed in an effort to investigate possible correlations.

Tending to tradition: Dating stone arrangement maintenance in northwest Australia using optical methods

Despite the ubiquity of Aboriginal stone arrangements around the Australian continent, there is very little data-driven information about the antiquity or development of these sites. The lack of chronological controls for these sites has limited our understanding of the timing, development, and functions of stone arrangement culture. Here, we present geochronological investigations of a stone arrangement complex near the Packsaddle Valley in the Pilbara region of Western Australia using optically stimulated luminescence (OSL) dating. Sedimentary OSL samples were collected from directly beneath the boulders that comprise the stone arrangements to estimate the timing of their emplacement. The process of boulder erection by Aboriginal people involved partial removal of the topsoil, which would only have provided the sediments with brief periods of sunlight exposure. Hence, the OSL signals of our samples were not expected to have been fully bleached during boulder erection. Consequently, the single-grain OSL equivalent dose (De) data were modelled using the unlogged Minimum Age Model to identify those grains that reflect boulder emplacement. The OSL characteristics (proportion of zero-dose grains, skewness of De distribution, and Central Age Model De) from the stone arrangement OSL samples were compared to those from natural soil samples taken adjacent to the boulders, and results show that the stone arrangement samples retain a record of boulder emplacement and do not simply reflect natural soil processes. Consequently, ages for all samples were calculated to generate a chronology for boulder emplacement at the site.Boulder emplacement proceeded from ∼1,410 years ago until ∼420 years ago, with data from four recumbent boulders indicating they collapsed ∼380 years ago. The data clearly clusters into three discrete, self-consistent phases of boulder emplacement occurring at 1,360 ± 90 years ago, 800 ± 30 years ago, and 480 ± 20 years ago. We conclude that (i) the stone arrangement complex was constructed at least 1,360 years ago, (ii) the boulders tend to fall down by natural processes and, thus, the site was subsequently visited and maintained at least twice (800 and 480 years ago) when the fallen boulders were re-emplaced, and (iii) this process ended ca. 380 years ago after which the site has not been maintained. The maintenance of the stone arrangement complex over at least 900 years demonstrates a strong connection between people, the landscape, and their imprint on the landscape.

Single-grain K-feldspar pIRIR dating of the Shalongka archeological site revealed the relationship between monsoon, overbank flooding, and human occupation during the Holocene on the northeastern Tibetan Plateau

The increased frequency of flooding on the Tibetan Plateau as a result of global warming has affected the lives of millions of people along the river valleys. The relationship between human settlement, climate change, and the frequency of flooding at long time scales is still unclear primarily due to the lack of a robust chronology for flooding deposits. In this study, AMS 14C dating, single-grain quartz OSL dating, and single-grain K-feldspar pIRIR dating using pIR50IR170 and pIR200IR290 signals were applied to the fluvial-paleosol sequence at the archaeology site Shalongka (SLK20) in the upper Yellow River valley on the northeastern Tibetan Plateau, where Paleolithic, Neolithic, and Bronze Age cultural layers were found. Utilizing luminescence characteristics analysis and a comparison of quartz OSL ages, K-feldspar pIRIR ages, and charcoal 14C ages, the reliability of single-grain quartz OSL and K-feldspar pIRIR ages was tested. Our results indicate that single-grain K-feldspar pIRIR170 dating with the minimum age model (MAM) can be used to date Holocene fluvial deposit that have been poorly bleached. Based on the age-depth model, proxy data of the SLK20 grain size and magnetic susceptibility demonstrate that Yellow River overbank flooding increased during the periods 9.9–9.1, ∼8.0, 7.6–6.3 and 5.0-3.4 kyr BP; during the intervals between these periods, Yellow River overbank decreased and paleosols developed. Human occupations, as indicated by the appearance of cultural layers at the SLK20 site during the ∼8.1, ∼7.8, 6.3–5.0 and 3.4–2.0 kyr BP periods, occurred when paleosol developed. The variation in East Asian summer monsoon (EASM) intensities caused a moist and warm mid-Holocene climate at the SLK20 site, which was conducive to human settlement. Flood events caused by EASM precipitation changes during the mid-Holocene significantly influenced human settlement at the SLK20 site. During the middle to late Holocene, as EASM decreased in the region, the improvement of subsistence strategies likely dominated human settlement on the northeastern Tibetan Plateau.

Testing the accuracy of OSL and pIR IRSL dating of young geoarchaeological sediments in coastal Peru

Luminescence dating of late Quaternary sediments in Peru is challenging, especially on the Peruvian coast. Earlier studies have shown that quartz grains often exhibit a thermally unstable, medium signal that caused the underestimation of Optically Stimulated Luminescence (OSL) ages. InfraRed Stimulated Luminescence (IRSL) dating has shown to produce more reliable ages, depending, amongst other factors, on the age model (Central or Minimum Age Model), and the IRSL signal. IRSL dating of geoarchaeological sediments has, however, hardly been carried out, let along validated, against an independent age dataset. This dating approach is, nonetheless, the only promising way to date the geological substrate in which many of Peru's archaeological sites are buried. Peru contains some of the oldest and most important archaeological heritage sites, yet not much is known of the environmental context in which many of its early civilizations prospered. A better understanding of which luminescence method works best could therefore help in a better understanding of the geological-stratigraphical context of many of Peru's sites. To investigate this matter more fully, we compared the luminescence dating results of seven sediment samples from the top layer of the Lima alluvial fan and from geoarchaeological layers of the Maranga Complex (San Miguel, Lima), with an independent dataset of sixteen 14 C ages. Our results showed that the quartz OSL ages always underestimated the expected ages due to a signal dominated by medium and slow components, and that the post-IR IRSL 225 (pIR IRSL 225 ) and IRSL 50 ages of K-feldspars, on basis of the Central Age Model (CAM), always overestimated the expected ages. The Minimum Age Model (MAM) on the other hand, correctly predicted the expected ages for the early Holocene, Lima alluvial fan sediments using the pIR IRSL 225 signal of K-feldspars, and the late Holocene, geoarchaeological ages using the IRSL 50 signal.

Dose dependency of aliquot sizes and age models from modern alluvial fan deposits of Helan Mountain, China

Alluvial fan deposits are identified as evidence of regional climatic variations and tectonic events; therefore, it is crucial to establish absolute time series by dating alluvial fan deposits. Limited exposure to light poses a challenge to accurately estimating the buried ages for alluvial deposits with optically stimulated luminescence (OSL). This challenge has been positively developed by controlling the number of grains on each disk to measure and choosing suitable statistical models for the equivalence dose (De) distribution to analyze. In this research, three modern alluvial samples and one modern loess-like sample were collected from the Dashuigou alluvial fan of Helan Mountain, China. The De distributions of these four samples were studied by the application of small aliquots (1-, 3-, and 5-mm aliquots) of quartz OSL with the average dose model, central age model, unlogged minimum age model (MAM), lowest 5%, internal/external consistency criterion minimum age model (IEU), and finite mixture model. It is concluded that an overestimation of De lower than 1 Gy can be obtained using quartz OSL dating of 1-mm aliquots (∼50 grains) with MAM and IEU for the alluvial sediments. The lowest 5% method may underestimate the De values of the 1-mm aliquots for young samples. This research makes the dose dependency of aliquot sizes and age models more definite and opens up the possibility of dating paleoalluvial deposits to establish a chronological framework to decipher the implications of paleoclimates and tectonics.

Testing the potential of using coarse-grain feldspars for post-IR IRSL dating of calcium sulphate-wedge growth in the Atacama Desert

The growth of vertically laminated calcium-sulphate wedges in the Atacama Desert is assumed to be driven by the interaction of moisture supply and salt dynamics in the subsurface. Geochronological data of these wedge laminations is yet sparse but indispensable to resolve wedge-growth phases and episodes of moisture supply and to use these deposits as a palaeoclimate archive in the hyperarid environment. Our pilot study presents a first approach of dating a calcium-sulphate wedge from the Atacama Desert using coarse-grain feldspar luminescence dating. Our results show a widespread and clustered equivalent-dose distribution of two wedge samples from ∼20 Gy up to saturation. Optically stimulated luminescence (OSL) of quartz revealed unsuitable properties for dating wedge deposits. Consequently, we applied post-infrared infrared stimulated luminescence (post-IR IRSL) to coarse-grained feldspars. Since feldspar single-grain measurements yielded a low number of luminescent grains, we used 1 mm aliquots as reliable single-grain proxies for genuine single-grain measurements. Data from energy-dispersive x-ray spectroscopy (EDX) showed that the feldspar single grains have large differences in their internal K content, resulting in an averaged internal K content of 3.9 ± 1.0 % for all luminescent grains. This result was subsequently used for dose rate and age calculations. Our results of equivalent-dose distributions and palaeodoses derived from the minimum age model reveal most recent wedge-growth activities at 10.6 ± 2.2 ka and 7.9 ± 1.8 ka for the two wedge samples.

Getting the right age? Testing luminescence dating of both quartz and feldspars against independent age controls

When luminescence dating was being developed much scientific effort was invested in showing it could achieve the correct ages, but this is now not routinely carried out for established protocols. This paper focussed on known age deposits from two case studies to explore whether correct ages were achieved. Case study 1 used the Storegga tsunami deposit dated to 8.2 ka sampled both horizontally and vertically and measured with OSL, IRSL and pIRIR. All results, for both quartz and feldspars, returned the correct age for the horizontal sample. Results from the vertical sample were more problematic with issues attributed to ongoing feldspar contamination of quartz and to beta heterogeneity. To agree with the independent age control single aliquot results required combination of >400 palaeodose replicates and in the case of IRSL the use of minimum age models. Measurements of feldspars at the single grain level using pIRIR measurements showed much improvement. Case study 2 used a barchan dune on the Tibet Plateau, China known to have been in position ∼10 years. Both quartz and feldspars returned young ages close to the true age, but the feldspar ages with brighter luminescence signal were more accurate once the luminescence signal to background ratio was optimised. On the basis of this study we advise against sampling vertically. We also recommend measuring feldspars with single grain pIRIR where possible, measuring >150 palaeodose replicates per sample and choosing feldspars rather than quartz for very young samples.

Optical Dating of Quartz Grains From the Minjiang Fluvial Terraces in the Sonpan Area on the Eastern Margin of the Tibetan Plateau

The fluvial terraces along the banks of the Minjiang River are very important for understanding the tectonic activities of the eastern margin of the Tibetan Plateau and have been widely investigated. However, the reliability of the ages previously reported for the terraces needs further evaluation. In this study, the Minjiang River terraces in the Sonpan area from Hongqiaoguan to the Songpan town were investigated and dated using optically stimulated luminescence (OSL) techniques on quartz grains. Seven strath terraces (T1–T7) were recognized based on the exposures of fluvial sediment and the elevation of bedrock strath, and two of them have been reported by previous studies. The terrace deposits and overlying loess were sampled for OSL dating. The samples exhibited a large scatter in De, even for loess samples, which could be attributed to poor bleaching at deposition. However, the OSL ages obtained using the minimum age model were underestimated, and those obtained using the central age model are considered relatively reliable based on stratigraphic and geomorphological consistency and the comparison of the ages between stratigraphically parallel samples. The results show that the loess samples overlying fluvial terrace sediments were deposited later than terrace formation and their OSL ages cannot represent the terrace formation ages. The T1, T3, T4, T5, and T6 terraces were dated to 13.5 ± 0.6, 29.0 ± 1.7, 48.0 ± 3.3, 44.3 ± 5.2 and 63.8 ± 4.7 ka, respectively. The T4 and T5 terraces may be the same terrace with a weighted mean age of 46.9 ± 2.8 ka. The ages of the T2 and T7 terraces were inferred to be ∼20 and ∼80 ka, respectively, based on the relationship between strath ages and elevations of the other terraces. The mean bedrock river incision rates were calculated to be 1.2 ± 0.1 mm/a for the time period of 64 ka for the T6 terrace—14 ka for the T1 terrace, and 0.15 mm/a for the past 14 ka.

Luminescence dating of a megaflood event on a terrace of the Jinsha River, China

The numerical dating of megaflood sediments is a worldwide challenge, a fact that has impeded a full understanding of Late Quaternary dam-outburst flood processes that occurred along the river courses of the Tibetan Plateau. Optically stimulated luminescence (OSL) dating has been widely used on such sediments. Due to their short transportation distances prior to deposition, the OSL signals of megaflood sediments are often partially bleached, resulting in age overestimations. Here, we report on a comparison of OSL ages obtained using both quartz (4–11 μm FG; 90–125, 180–250 μm CG) and K-feldspar (180–250 μm CG) extracted from sediments taken from the Binghong-Bingnong Neolithic-Bronze Age site on the second Jinshan River terrace (T2), in Yunnan Province, southwestern China. Contrary to previous experience suggesting that CG fractions are usually better bleached than FG fractions prior to deposition, our results showed that the OSL ages for the FG quartz fraction were generally younger than those for the CG fraction. This would suggest that the two fractions may have come from different sources, and may have been subject to different geomorphological processes prior to deposition. FG quartz fractions may be suitable to define the maximum age of sediments located in alpine gorge regions. CG quartz fractions can be used by applying the minimum age model (MAM) to select relatively well-bleached grains yielded ages close to the ‘true’ burial ages of the sediments. The results showed that the post-IR IRSL225 ages of single grain K-feldspar were overestimated by > 3 ka, suggesting K-feldspar may not be suitable dating material for megaflood sediments <30 ka. The OSL dates suggest that the T2 terrace was formed ∼8.4 ka, that aeolian sediments were deposited during ∼2.6–1.5 ka, and that the megaflood event occurred after ∼1.5 ka.

Luminescence ages and new interpretations of the timing and deposition of Quaternary sediments at Natural Trap Cave, Wyoming

Natural Trap Cave, located in the Big Horn Mountains of north-central Wyoming, has a history of trapping and preserving a range of North American fauna that plummeted into the deep vertical entrance. These animal remains were buried and preserved within sediments of the main chamber and, in turn, have helped elucidate the procession of faunal dynamics during the latest glacial cycle. The cave location, south of the Laurentide and Cordilleran Ice Sheets, and proximal to Yellowstone, is at an ideal geographical juncture to provide insights to ecological changes in North America. The sediments that the animals are buried in inform us about transport and deposition both inside and outside of the cave that relate to catchment dynamics. We report on a series of optically stimulated luminescence (OSL) ages derived from samples obtained within the cave during excavation work in 2014 and in 2018. We also examine chronology produced by argon, tephrochronology, fission track, and luminescence techniques that have been used for understanding the infilling of the cave. The cave sediment ages and in situ measured gamma spectroscopy as measured in this study helped resolve an improved chronological age model when combined with previous data.The suite of OSL ages is interpreted through the stratigraphic relationships (and vertebrates contained within) which requires the use of an adequate age model; we use either the central age model or minimum age model where appropriate and with justification. Lowest sediments are dated to ∼150 ka with a hiatus at ∼130 to 52 ka. Above this, sediment deposition and entrainment of paleontological materials are representative of Pleistocene and early Holocene times, between 37 ± 6 ka and 7.6 ± 0.5 ka. The stratigraphic architecture suggests that deposition of materials into the cave is episodic and rapid, followed by quiescent periods where hydrologic scour, heavy overland flow, or possibly a cryo-hydrologic process may have altered unit relationships. Thus, the complementary geochronometers and the characteristics of quartz versus feldspar luminescence signals improve temporal interpretations of these complex deposits. This adapted understanding of mixing also sets the stage for future work with the aim to improve our understanding of ages and sources for ash units within these cave deposits. The three ash units recognized in the cave may represent an in-situ reworking of the same ash or may be representative of previously undocumented eruptions from the Yellowstone Caldera.

Pleistocene-Holocene deformation and seismic history of the Kalabagh Fault in Pakistan using OSL and post-IR IRSL dating

The Kalabagh Fault forms a lateral offset in the Main Frontal Thrust in the Sub-Himalayan area of Pakistan, forming a push-up block within the stepover zone of its segments. Deformed sediments along the frontal part of this push-up block have cross cutting relations with morphotectonic and paleoseismic features. These sediments are dated using luminescence dating methods. The post-infrared infrared stimulated luminescence (post-IR IRSL) of K-feldspar was used for samples representing these sedimentary units. For stratigraphically younger sediments with partially-bleached pIRIR signal, optically stimulated luminescence (OSL) of quartz was applied with the minimum age model (MAM). These ages are used to illustrate the timing of development of the push-up block, the westward diversion of the Indus River and Holocene earthquakes along the Kalabagh Fault (KBF). The deformed sediments from the mountain front at Larkakki are older than those of Khairabad and Ghundi. These age estimates are consistent with the chronological order of the tectonic deformations in the stepover zone of the Kalabagh Fault. Age estimates and correlation of the sedimentary units suggest the emergence of the push-up block in the stepover zone during the past ∼0.5 Ma. Active faulting and development of the ramp along the Kalabagh Fault has diverted the course of the Indus River towards the west at a displacement rate of 12–15 cm/a during last ∼140 ka. Luminescence data indicate Holocene timing for the earthquakes along the Kalabagh Fault, which are diachronous and suggest differential movements along the segments of the fault. The earthquake recurrence interval at Khairabad is 10 ± 2 ka on average. The younger earthquakes at the foreland in the south of the stepover indicate seismically active zone.

Multi-Method Luminescence Dating of Old Fluvial Sediments from Northern Tian Shan, China

At the eastern tip of Anjihai anticline on the northern piedmont of Tian Shan (northwest China), deformed fluvial deposits have recorded active folding since the Pleistocene, but the absence of accurate ages makes it difficult to evaluate the anticline's shortening rate. Geological studies ascribed the fluvial strata to the early Pleistocene, which poses potential challenges for luminescence dating. In this study, multi-methods luminescence dating was applied to a fluvial sand sample taken from the sandy bed of the deformed basal strata. Single grain post-Infrared Infrared Stimulated Luminescence (pIRIR) and multiple-aliquot-regenerative (MAR) dose along with multiple-elevated-temperature pIRIR (MET-pIRIR) procedures were applied to determine the paleodose of the sample. The methodological uncertainties, such as thermal transfer and initial sensitivity change, were treated by increasing the test dose and performing dose recovery test. With consideration of the potential partial bleaching and anomalous fading, various statistical metrics were applied to the D&lt;sub&gt;e&lt;/sub&gt; values determined by using the single grain pIRIR&lt;sub&gt;225&lt;/sub&gt;, single grain pIRIR&lt;sub&gt;290&lt;/sub&gt; and MAR-MET-pIRIR&lt;sub&gt;290&lt;/sub&gt; signals. The minimum age model (MAM) D&lt;sub&gt;e&lt;/sub&gt; values are 11% – 17% lower than the central age model (CAM) D&lt;sub&gt;e&lt;/sub&gt; values in general, and the MAM D&lt;sub&gt;e&lt;/sub&gt; values determined by the single grain pIRIR procedures are underestimated by more than 40% when compared with those determined by MAR-MET-pIRIR&lt;sub&gt;290&lt;/sub&gt; procedure. The MAM MAR-MET-pIRIR&lt;sub&gt;290&lt;/sub&gt; D&lt;sub&gt;e&lt;/sub&gt; of 811 ± 44 Gy results in a burial age of 284 ka for the basal deformed fluvial strata, which is much younger than the proposed early Pleistocene age.