Quaternary Geochronology最新文献

In this study we apply optically stimulated luminescence and infra-red stimulated luminescence to the sediments from the interfluve dividing three river basins: the Pechora, the Kama and the Severnaya Dvina, hoping to gather new age data on glaciofluvial sediment. We also studied the valley of the Berezovka, a medium-scale river cutting through this interfluve. We obtained a chronology from 17 quartz and 15 feldspar ages. Sedimentological analyses and luminescence dating show that most of the sediments examined here are water-transported (gully alluvium, slopewash deposits), and their ages mark a period of accumulation during MIS 2. Some of these sediments were reworked by aeolian processes; these took place over a time span consistent with such processes in other parts of the East European Plain (19-12 ka). The Berezovka river experienced incision before ∼22 ka and another erosion event with extremely high floods at 15–16 ka. Its terrace formed in MIS 5, constraining the minimum age of the valley. In the bottom part of the sections, much older, possible MIS 8, glaciofluvial sediments were found; the apparent absence of MIS 6 sediments may argue for moving the MIS 6 ice sheet limit further to the north of the study area.

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 (D_e) on grain brightness and explored the possible mechanisms, and the brightest grains were then used for D_e 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.

Differing from the classic fine silt-dominated loess on the southern and central Chinese Loess Plateau (CLP), sandy loess is extensively distributed along the southern bank of the middle Yellow River and reaches thickness of up to ∼ 200 m. However, its deposition time and formation processes remain unclear. In this study, we dated three representative sandy loess sections along the middle Yellow River using single-aliquot regenerative-dose optically stimulated luminescence (OSL) and multiple-aliquot regenerative-dose recuperated OSL (ReOSL) dating protocols on fine quartz grains (4–11 μm). The reliability of these methods was robustly verified through traditional luminescence dating checks. Our dating results showed that the sandy loess was predominantly deposited during the last glacial period and exhibited an exceptionally high dust accumulation rate surpassing that of the classic loess on the southern and central CLP. By considering atmospheric circulation, geomorphology, and proxy data from both the sandy loess and the Yellow River fluvial sediments, we propose that the sandy loess primarily originated from the proximal riverbeds and fluvial plains of the middle Yellow River, transported by northerly East Asian winter monsoon (EAWM) winds. During the last glacial period, weakened East Asian summer monsoon (EASM) in central and northern China resulted in reduced runoff and vegetation cover in the middle Yellow River region. Consequently, the riverbeds and fluvial plains served as main sources of dust material. Subsequently, the strengthened EAWM winds carried and deposited the dust along the southern bank of the middle Yellow River, culminating in the formation of the sandy loess. Our study underscores the importance of aeolian and fluvial processes interactions in contributing to the formation of the sandy loess along the middle Yellow River and suggests that the investigated sandy loess holds potential for high-resolution paleoclimate reconstruction.

The optically stimulated luminescence (OSL) sensitivity of the fast component in quartz has been increasingly used in provenance analysis of Quaternary sediments. Quartz OSL natural sensitization is thought to be mainly controlled by the formation conditions of the source bedrock and surface processes occurring mainly in sediment source areas. Thus, quartz OSL sensitivity can be linked to distinct sediment source regions, based on their tectonic setting and erosion conditions. In this way, changes in quartz OSL sensitivity within siliciclastic successions would track variations in sediment provenance. So far, few works evaluated how the OSL sensitivity of quartz sand grains varies in sedimentary successions that experienced long-term cycles of deep burial, exhumation, and erosion. Therefore, this work aims to characterize the sensitivity of the fast OSL component of quartz sand grains retrieved from the Cenozoic sedimentary rocks of the Northern Andes basins and assess its spatiotemporal changes. We found that quartz grains with the lowest OSL sensitivity are sourced by crystalline and volcanic rocks related to the Andean Continental Arc emplaced in the Colombian Central Cordillera, reflecting the onset of denudation in orogenic sources during the Paleocene. Subsequently, increasing trends in OSL sensitivity are related to the sedimentary recycling during the Andean orogeny, reaching maximum values as a result of the progressive unroofing of Cretaceous rocks in the Colombian Eastern Cordillera, originally sourced from the low-relief Amazon Craton. Changes in quartz OSL sensitivity measured in the Cenozoic sedimentary basin-fill sequences of the Northern Andes vary according to the shifts in sediment provenance related to the orogenic construction and sediment recycling of the Andean range.

The Galería karstic complex, situated within the Atapuerca Multilevel Karst system (Burgos, Spain), records an impressive sedimentary sequence from the Early to Middle Pleistocene period. One of the notable features of this complex is the presence of thick fluvial deposits (waterlain facies), providing a detailed record of the transitional moment between the formation of the middle and lower Atapuerca karst levels. Examining these sediments, barely dated thus far, is crucial for gaining a comprehensive understanding of fluvio-karstic dynamics at the Atapuerca site. In our study, we conducted dating analyses on sediment samples from different areas of the Galería complex using Electron Spin Resonance (ESR) on quartz grains (4 samples from Covacha de los Zarpazos and 1 from Tres Simas Norte outcrops) and paleomagnetism (12 samples). The aim was to refine the chronological framework of the Galería complex, providing ages for the formation of these passages. Considering the geological context, our results revealed underestimated Aluminium (Al) ESR ages ranging from 372 ± 78 to 569 ± 80 ka in Covacha de los Zarpazos, along with consistent dates of 1184 ± 120 and 1001 ± 302 ka in Covacha de los Zarpazos and Tres Simas Central, respectively. Our results agree with previous estimates obtained through luminescence dating methods, indicating Middle Pleistocene ages for the samples. In contrast, reverse polarity estimates disagree with those from radiometric dating methods, except for samples ZAR1501 and TSC1501. Caution should be taken when interpreting these ages, as various geological factors including leaching processes from upper zones, post-sedimentary structures, and lithological variations may indicate alterations in the primitive geochemical composition of the sediment. Consequently, these factors can potentially affect the total Dose rate parameter and introduce uncertainties into the age calculations.

Over the past two decades, stepped-terrace systems within the Loire River basin's tributaries have undergone comprehensive multidisciplinary studies, encompassing Quaternary geology, prehistory and geochronology. Surprisingly, the geochronological exploration of the Loire River itself, the longest river in France, and its fossil stepped terraces system has been relatively limited, especially in the middle section near Orléans. However, for about fifty years, this region has been pivotal in providing evidence of the historical confluence of two ancient rivers, shaping the current Loire Valley. Researchers have suggested the existence of a Plio-Pleistocene Loire paleo-river, flowing northward from the Massif Central to the Seine valley and eventually reaching the English Channel. Subsequently, this Loire River would have underwent a reorientation of its flow westward, from the Blois area to the Atlantic Ocean, after being disconnected from its previous course.

The absence of alluvial deposits in the area between the current Loire valley and the Seine valley, attributed to substantial erosion, prevents direct exploration of evidence related to the south-north paleo-river. To address this challenge, the hypothesis suggests that the preserved alluvial terraces in the intermediate sector were established post-capture, offering an opportunity to determine when this significant geological event occurred. Through the application of Electron Spin Resonance (ESR) quartz dating, a chronological model for the Middle Loire has been then constructed. This model identifies five distinct phases in the evolution of the Middle Loire system, spanning from 800 ka to the present day. These phases indicate a gradual capture process, initiating between 900 and 800 ka, resulting in alterations to fluvial dynamics and ultimately leading to the establishment of the current course approximately 250 ka.

Northern Germany is famous for its numerous Neanderthal (Middle Palaeolithic) archaeological sites and well-preserved palaeoclimate records. Nevertheless, our understanding of how hominins responded to climate fluctuations and adapted to changing environments in this region remains limited because there are only a few reliable, highly-resolved chronological frameworks of long stratigraphic successions. Most of the Middle Palaeolithic sites in this region lack a reliable chronostratigraphy beyond the radiocarbon dating range. In this study, we present a high-resolution optically stimulated luminescence (OSL) chronology derived from a ∼21 m long sediment core (Li-BPa) that was drilled in close proximity to the known Neanderthal site of Lichtenberg. Quartz OSL dating was applied to the upper 6.5 m of the core. Subsequently, the obtained quartz OSL ages were compared with feldspar post-infrared (IR) IRSL (pIRIR) measured at 290 °C (pIRIR₂₉₀), pulsed IR₅₀ (pre-pIRIR₂₂₅), and pulsed pIRIR₂₂₅ ages to select a suitable feldspar signal to date older samples. A comparison of the quartz and feldspar ages indicates that only fading-corrected pulsed IR₅₀ (pre-pIRIR₂₂₅) and pIRIR₂₂₅ ages agree well with quartz OSL ages. Finally, the age framework of the sediment sequence was established based on the 11 quartz OSL ages and 23 fading-corrected pulsed IR₅₀ (pre-pIRIR₂₂₅) and pulsed pIRIR₂₂₅ ages. The resulting Bacon age-depth model agrees with litho- and biostratigraphic designations, indicating that the whole sequence was deposited between ca. 275 ka and ca. 24 ka, corresponding to the Saalian to Weichselian periods.

Central Yakutia is a large region in northeastern Siberia characterized by extensive permafrost, large river valleys, mountain glaciers, and large massifs of aeolian sands; the geological history of the region is complex and, at present, poorly constrained. In recent years, it has been shown that aeolian sands cover up to 60% of large parts of Central Yakutia. This paper presents the results of luminescence dating of aeolian sedimentation at the Diring Yuriakh Palaeolithic site located in the middle reaches of the Lena River. Field studies identified several thick units of aeolian sand, which cover an old deflation surface with Late (Duktai culture) and Early Palaeolithic (Diring culture) artefacts. The reliability of the OSL chronology was assessed by comparison of ages based on the optically stimulated luminescence from quartz and the infra-red stimulated luminescence from potassium-rich feldspars; these age pairs are in good agreement, implying that at least the quartz grains were sufficiently bleached before sedimentation. We obtained OSL ages that reflect three periods of accumulation between the LGM and the Holocene: ∼21 ka, 15-14 ka, and 12.5–10 ka. These periods of accumulation broadly coincide with global cooling episodes during the Last Glacial Maximum, the Older Dryas, and the Younger Dryas, with some extension into subsequent warmer intervals, whereas the intervening intervals without preserved sediments are taken to reflect dune stability during warmer periods. The sand on the terraces, sourced from alluvial bars in the river channel, was blown up the valley slope during cold and dry periods when the vegetation cover was sparse. When the climate warmed, the vegetation took some time to spread, and so the accumulation of aeolian sand on the high terraces continued into the warm periods. We also infer periods of deflation (wind erosion) that occurred before 21 ka and between 20 and 15 ka, presumably due to increased aeolian activity and localized remobilization of sediment. The new OSL chronology shows that the younger artefacts located at the cape of Diring Yuriakh, belonging to the Late Palaeolithic Duktai culture, are older than 15 ka. The new ages also show that the post-LGM aeolian sand sequences at Diring Yuriakh are correlated with the regionally developed subaerial Dolkuma Formation.