Abstract:
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 Optically Stimulated Luminescence (OSL) dating to the test in an extremely challenging environment: the Pokhara Valley in Nepal. This is challenging for two reasons: i) the 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 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 run-out 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 region.Keywords:
Thermoluminescence dating
Deposition
Optical dating
Optically stimulated luminescence
Optically stimulated luminescence
Optical dating
Thermoluminescence dating
Equivalent dose
Sample (material)
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Naturally accumulated doses after pottery manufacture were compared between optically stimulated luminescence (OSL) from quartz grains and infrared-stimulated luminescence (IRSL) from feldspar grains, together with a red-thermoluminescence (RTL) result from quartz grains. Quartz and feldspar extracts from nine Jomon pottery pieces, which were manufactured and used 3,500-6,000 years ago, were subjected to three kinds of luminescence measurements using a new automated luminescence measuring system. Since this system included a small X-ray irradiator, a single-aliquot regenerative-dose (SAR) protocol was applicable to each luminescence dosimetry. Naturally accumulated doses from RTL were higher than OSL- and IRSL-dose results. This is probably due to relatively easy-bleaching effects or unstable luminescence properties related to the OSL in quartz grains and well-known anomalous fading effects of feldspar grains. On the basis of these results, the RTL-luminescence ages, estimated using the accumulated doses and annual doses, are closer to the predicted archaeological ages. In conclusion, it was also confirmed here that the RTL-dating is most suitable dating-method when quartz extracts from burnt archaeological materials are available.
Optically stimulated luminescence
Thermoluminescence dating
Equivalent dose
Optical dating
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Luminescence techniques for dating both heated materials (e.g., pottery and burnt stone) and sediments have gone through three phases in the past 50 years. The first 22 years, from 1957 to 1979, were devoted to thermoluminescence (TL) techniques applied to heated material. In the next six years, from 1979 to 1985, it was found that TL dating could be applied to sediments. However, the TL signals of both quartz and feldspar grains observed for modern sediments were small, but were not zero, thus making them useful only for older sediments. A new luminescence signal that was totally zeroed by exposure to sunlight for a relatively short period of time, a few hours or less, was found; this led to the development of optically stimulated luminescence (OSL) dating techniques in 1985. Further developments have continued to the present day. Within the past 22 years, 1999 was also a year with major developments. A reliable procedure for single aliquots of quartz that have a rapidly bleached (‘fast’) OSL component was formalized and an instrument that allowed rapid measurement of equivalent doses for single grains was constructed. These developments have led to OSL becoming a major dating tool in Quaternary geology, at least for the past 100 000 years, and in archaeology, particularly as related to the dispersal of modern humans.
Thermoluminescence dating
Optically stimulated luminescence
Optical dating
Persistent luminescence
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Optically stimulated luminescence
Thermoluminescence dating
Optical dating
Chronology
Saturation (graph theory)
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Optically stimulated luminescence
Optical dating
Thermoluminescence dating
SIGNAL (programming language)
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Optical dating
Optically stimulated luminescence
Thermoluminescence dating
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Optically Stimulated Luminescence(OSL) method dates the last bleached or thermal event of the sediments. Since its development in the 1980 s,OSL dating has been improved significantly. Quartz and feldspar are mainly applied to conduct such dating.This paper aims to provide an overview of the OSL dating method for geoscientists who intend to use OSL dating for chronological control in which the sampling in the field can satisfy OSL chronologists. The general principles of the method are described,and the procedures of OSL dating from the field sampling to the age interpretation in the luminescence dating laboratory are recounted,which include sampling,pretreatment,equivalent dose(De) and dose rate determination. Recent methodical and technological progress and the development of new laboratory measurement procedures for obtaining the Dehave resulted in more widespread and more confident use of OSL for dating,and new luminescence signals are being investigated in order to extend the age range back by an order of magnitude from 100 ka to 1Ma.
Optical dating
Optically stimulated luminescence
Thermoluminescence dating
Radiometric dating
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Optically stimulated luminescence
Optical dating
Thermoluminescence dating
Equivalent dose
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제4기 퇴적층의 형성 시기 추정을 위해 적용할 수 있는 연대측정법들 중 석영의 OSL (Optically stimulated luminescence) 신호를 이용한 연대측정법은 시료의 제약이 적기 때문에 다양한 환경에 적용되고 있다. 석영 OSL 연대측정 가능상한(일반적으로, 약 10만 년 전후) 이상의 오래된 시료의 경우, 석영 OSL 신호보다 더 오래된 시기를 측정할 수 있는 K-장석 IRSL (InfraRed Stimulated Luminescence) 신호를 이용한 연구가 다수 보고되고 있다. 이번 연구에서는 K-장석 pIRIRSUB225/SUB 신호의 초기화 특성 및 연대측정 결과의 신뢰도를 확인해 보았다. 인공광원 노출시간에 따른 K-장석 pIRIRSUB225/SUB 신호를 측정한 결과 K-장석 IRSUB50/SUB 신호와 기존에 보고된 석영OSL 신호에 비해 초기화 속도가 느리게 나타남을 확인할 수 있었다. 이는 빛에 노출되었을 때 K-장석 pIRIRSUB225/SUB 신호의 느린 초기화 특성으로 인해 K-장석 pIRIRSUB225/SUB 연대측정 결과가 실제 퇴적연대를 과대평가할 가능성이 있음을 지시한다. 현생 홍수퇴적층 시료를 대상으로 중심연대모델(Central Age Model)을 적용한 단일입자 K-장석 pIRIRSUB225/SUB 연대측정결과는 8.8 ± 0.6 Gy로 측정된다. 육성 선상지 퇴적층에서 채취한 5개 시료에 대한 다입자 K-장석 pIRIRSUB225/SUB 연대측정 결과는 시료마다 차이는 있으나 석영 OSL 연대측정 결과에 비해 평균적으로 5.5 ± 2.9 ka 정도 오래된 결과를 보인다. 이러한 결과들은 K-장석 IRIRSUB225/SUB 신호가 느린 초기화 특성으로 인해 실제 퇴적연대를 과대평가할 수도 있으나 석영 OSL 연대측정 가능상한 이상의 오래된 시료(약 10만 년 이상)에서는 그 영향이 퇴적연대의 10% 미만이며, 루미네선스 연대측정 결과의 정밀도(1σ기준, 상대오차 ± 10% 내외)를 감안하면 퇴적층의 형성시기 추정에 효과적으로 적용될 수 있음을 의미한다.
Optically stimulated luminescence
Optical dating
Thermoluminescence dating
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