Quaternary Geochronology最新文献

Here we report luminescence dating results on exhumed fault rocks from the North Tehran Fault (NTF, Iran), including the fault gouges. The NTF is an oblique-dip thrust fault expanding from west to east at the northern fringe of the megacity of Tehran. Although the fault is known to be active and a major threat to the city, only little is known about its earthquake history. We present first data on the timing of past fault motion using dating of fault rocks. Three sites have been selected for this study in which the fault damage zone is associated with Eocene volcaniclastic rocks (Karaj Formation). The fault gouge, transitional and damage zone were sampled for which we observed slip planes in the field. The fault rocks are composed of quartz and alkali feldspar favourable for luminescence dating. However, our study reveals that the quartz optically stimulated luminescence (OSL) signal of the Karaj Formation does not seem to have a measurable fast decaying signal component. Instead, the post-infrared stimulated luminescence at 225 °C (pIRIRSL₂₂₅) of polymineral fine-grain fraction appears to be the most feasible signal for these samples. The first luminescence-based results presented here comprise an age range from 45 ± 5 ka to 72 ± 13 ka for fault gouges and transitional zone. Since dating the transitional zone close to the fault gouge led to a younger age than the fault gouge at one site, we conclude that the sampling location plays a crucial role in dating exhumed fault rock using luminescence dating. The obtained ages are far older than those of the previous palaeoseismological studies that dated earthquake-related sedimentary features in the region. Therefore, more research is required to shed light on the resetting mechanism and condition of these fault rocks due to the recent activity of the NTF.

Quartz optically stimulated luminescence (OSL) sensitivity is varied and related to Earth surface processes and, thus, it has been shown to be a useful tool for appraising sediment recycling and provenance investigations. These investigations are mainly based on OSL data purposely measured for sensitivity calculations. However, it has been recently shown that the relative sensitivity of the quartz OSL fast component (%BOSL_F) from the first test dose (T_n) signal from an OSL dating measurement using the Single Aliquot Regenerative-dose (SAR) protocol can be used to discriminate sediment sources. Here, we investigate the possibility of characterizing %BOSL_F for provenance purposes using not only T_n signals but all other OSL signals obtained over SAR protocol cycles from OSL dating measurements. We address the %BOSL_F behaviour over SAR cycles (if conservative or not), the %BOSL_F dependency on dose-size, differences between %BOSL_F values given by natural/regenerative and test dose signals, and %BOSL_F application for provenance studies. Quartz sand grains data from twenty Late Quaternary sediment samples, representing orogenic and cratonic sources and diverse depositional contexts from South America, Africa, and Asia, are included in the analysis. All calculations were performed using data that have been previously obtained for equivalent dose estimation. The key finding is that the averaged %BOSL_F of all SAR signals was representative of the samples' characteristic sensitivity and could satisfactorily discriminate samples from known sources, mainly in the case of high-sensitivity samples. We could distinguish sediment source areas by averaging the %BOSL_F of OSL signals from SAR natural/regenerative and test doses together. Likewise, laboratories worldwide could produce regional/global sediment provenance fingerprinting reference data using their dating measurements accumulated throughout the last decade.

Parts of Central Asia have been dominated by high dust flux since the start of the Quaternary. The resulting loess-palaeosol deposits are important archives for landscape and climate changes, but there is a lack of chronological data for the subaerial deposits of Southern Tajikistan. Our study presents a high-resolution luminescence chronology for the Khonako II section in the Khovaling region. Thirty-seven samples were collected from the first ∼8 m of the section, corresponding to the Holocene soil and the upper part of the Loess 1 (L1) unit. We applied quartz OSL dating to the coarse-silt fraction (40–63 μm) and polymineral pIRIR_200,290 dating to the very fine sand fraction (63–90 μm). The polymineral pIRIR_200,290 signal has satisfactory characteristics. The quartz dose response curve displays a non-single exponential growth above ∼100 Gy, thus, the D_e values were estimated by fitting a single exponential function plus linear component to the dose response data. To assess the pIRIR_200,290 residual dose at deposition, we used the offset between our quartz and polymineral chronologies from Khonako II and equivalent doses measured on modern dust samples from Tajikistan and Uzbekistan. The resulting 9.2 ± 0.4 Gy dose was then subtracted from the pIRIR_200,290 doses for final age calculation. The quartz OSL and pIRIR ages are then generally consistent. The obtained high-resolution luminescence chronology shows that the upper part of the L1 unit accumulated during the end of marine isotope stage (MIS) 3 and through MIS 2 (39–20 ka). The average dust accumulation rates (DAR) increased from ∼31 cm ka⁻¹ to 41 cm ka⁻¹ between MIS 3 and MIS 2. The DAR reached a peak of ∼71 cm ka⁻¹ at 21 ka. A hiatus of ∼7–9 ka was then identified between the end of the last glacial maximum (LGM) and the beginning of the Holocene, and the average DAR decreased during the Holocene. Our results indicate a continuous high dust flux in the Khovaling plateau over the last 39 ka, but reworking processes and potential deflation events mark the LGM-Holocene transition. High-resolution luminescence dating studies in Tajikistan are therefore important to detect potential discontinuities in the sequences and provide an independent timescale for interpreting the climate proxies and calculating dust accumulation rates.

The emergence of ‘standing stone’ monuments within the European Late Prehistoric landscape is considered to be associated with a pivotal human cultural transition from hunting and gathering to agriculture and permanent settlement, being the earliest monuments currently dated by radiocarbon to the 5th millennium BCE. However, many standing stones were first erected, subsequently collapsed, and then re-erected during the following three millennia. The excavation of the site of an apparently in situ statue-menhir at Cruz de Cepos in NE Portugal provided the rare opportunity in Iberian prehistory to apply radiocarbon and luminescence techniques to establish the date of construction. On the basis of the iconography, the standing stone was assigned to a sculptural tradition of north-western and western Iberia, loosely dated to the Early/Middle Bronze Age (ca. 2000/1900–1250 BCE). The optically stimulated luminescence (OSL) and dosimetry characteristics of quartz extracted from sediment samples taken from locations associated with the socket pit and surrounding backfilling deposits were examined, producing OSL single grain ages at eight locations. Comparison of the OSL and calibrated radiocarbon ages shows very good agreement, with the mid-3rd millennium BCE dates confirming original erection during the Copper Age and not a much later transformation of the monument. These encouraging results indicate that OSL has the potential to provide reliable dating of depositional processes related to the construction process and is suitable for wider application to megalithic monuments of this type.

Assessing the adequate bleaching of quartz Electron Spin Resonance (ESR) signals at the time of deposition is essential for sediment ESR dating. In this study, we focus on the Datong volcanic group is situated in Datong City, Shanxi Province, and is among the most renowned volcanic groups in China. The eruption within the Datong volcanoes during a geological period resulted in extensive high-temperature lava flow that directly overlaid Quaternary lacustrine deposits and subjected the underlying lacustrine layers to high-temperature heating. Thus, an investigation of the field profile in the Yujiazhai area, southeast of the Datong Volcanic Group, shows a novel approach for assessing the bleaching extent of ESR centers. This is accomplished by comparison of the D_E values of the Al and the Ti–Li centers in partly-heated layer sample. The result reveals that quartz Al and Ti–Li centers in the lacustrine sediments appear to undergo sufficient bleached during transportation and natural bleaching processes in the study area. Furthermore, this study provides insight into the chronology of volcanic eruption in the Yujiazhai area, estimating an eruption age of approximately 300 ka. This volcanic activity most likely corresponds to the third volcanic activity period in the Datong region.

The middle reaches of Yarlung Tsangpo, situated on the southern Tibetan Plateau, have experienced extensive river damming events due to glacier advances, resulting in the formation of several ancient dammed lakes. These palaeolakes offer invaluable insights into past hydrological and geomorphological dynamics on the Tibetan Plateau. In this study, we reported a newly identified ancient dammed lake, named the Xiaru palaeolake, located upstream of the Ganglai Gorge in the uppermost segment of the middle reaches of Yarlung Tsangpo, and conducted a pioneer chronological investigation of the lake using K-feldspar post-IR IRSL (pIRIR) dating. Quartz minerals from most lacustrine and fluvial sediments can not provide reliable ages characterized with low intensity and large inter-aliquot scatter in equivalent doses (D_e). In contrast, the K-feldspar exhibited much greater luminescence intensity and narrower D_e distribution using the pIRIR₂₂₅ dating protocol. Residual, dose recovery, and fading tests demonstrated that the pIRIR₂₂₅ signals are well bleached with a relatively low fading rate, making it a more suitable dosimeter for dating applications in the study area. The pIRIR₂₂₅ ages, derived through single aliquots, standard growth curve (SGC), and single grain measurements, reveal a major phase of the Xiaru Lake between 24.1 ± 1.0 ka and 15.8 ± 1.1 ka, that commenced aligning with the global Last Glacial Maximum. Furthermore, one lacustrine sample dated to 29.9 ± 2.2 ka suggests the possibility of multiple damming events in Ganglai Gorge during the last glacial period, although further evidence is required for a comprehensive interpretation.

Gigantopithecus was a great ape once lived in Southeast Asia and China during the Pleistocene, and the northernmost evidence of its presence is presently known from the Longgupo and Jianshi Longgudong sites located in the West-Hubei and Three Gorges region in Southof China. Here, we report the first radiometric dating by ESR/U-series method on mammalian teeth of Jianshi Longgudong site which was found in 1970s, and renowned by the discovery of both possible hominin and Gigantopithecus fossils in association with undoubted stone artifacts. As the cave site was completely emptied by the successive excavations, the analyzed teeth were selected from museum collections while the dosimetry was established from reworked sediments sampled on the site. The results obtained on two fossil teeth from the lower layer 8 give a weighted mean age of 1512 ± 94 ka, while a mean age of 1044 ± 53 ka was obtained for two other teeth from the upper layer 4. These ESR/U-series dating results, in agreement with the fauna record, are younger than the previous paleomagnetic dating interpretation and suggest that Jianshi Longgudong sequence is younger than the Olduvai subchron and the neighboring Longgupo site dated by the same methods to ca 2.2–2.5 Ma.

Tephrochronology is a powerful tool used to synchronise and date stratigraphic records by accurate and precise geochemical analysis of deposited volcanic glass shards. However, in many distal stratigraphic records (e.g., polar ice cores) tephra shards are often extremely fine-grained (<10 μm). Geochemical characterisation of these shards is challenging because conventional preparation and analytical techniques require highly polished glass areas >5 μm for electron probe microanalysis (EPMA) to ensure high analytical totals and minimise alkali element loss. Recent method developments have put forward alternative approaches to accurately measure major oxides of small shards: a smaller 3 μm diameter beam, overlapping large (20 μm) beam areas onto supporting epoxy resin, and using scanning electron microscopy with energy dispersive spectrometry (SEM-EDS). However, there has been no direct intercomparison of these alternative techniques, which to date have only been tested on a limited range of glass compositions and tephras that are much larger than the extremely fine-grained material found in distal archives. These issues complicate decision making about the best analytical approach to take when faced with small shards. Here, we provide a new workflow protocol for the analysis of <10 μm tephra by determining the accuracy and precision of alternative SEM-EPMA methods. By analysing a variety of glass standards including those prepared to replicate fine-grained ice-core cryptotephras, we show that a 3 μm EPMA beam is suitable for use on all glass compositions provided the beam current is reduced to 1 nA. When glass areas are too small for a 3 μm beam we show that overlapping this small beam onto epoxy resin is preferable to SEM-EDS analysis. We also provide evidence confirming that using 3–0.2 μm polishes for <5 min increases analytical precision of the most abundant major oxides by up to three times, whilst, crucially, preserving the smallest shards in a sample. By directly applying these alternative methods to ice-core cryptotephra, we demonstrate the data are of suitable accuracy and precision to make robust geochemical correlations. This workflow can be applied to future tephrochronology studies, significantly increasing the quality and quantity of data that are obtained from cryptotephra horizons in distal records.