Quaternary Geochronology最新文献

We present the results of the first dating study of site P13 at Pirro Nord, Italy, which documents some of the earliest evidence for hominin presence in western Europe. Our multi-technique dating approach is based on a combination of palaeomagnetism, electron spin resonance (ESR), thermally-transferred optically stimulated luminescence (TT-OSL) and combined U-series/ESR applied to both fossil material and host sediment. It provides ages ranging from 627 ± 59 to 1006 ± 126 ka and clustering around 0.8 Ma. One additional fossil tooth collected from the nearby P10 site also returns an age within this range. Ordinarily, this outcome would naturally lend itself to the straightforward conclusion that Pirro Nord has a late Early Pleistocene age of ∼0.8 Ma. However, this interpretation is complicated by the fact that these numerical dating results are in contradiction with the biochronological evidence, which suggests a much older age on the order of 1.3–1.7 Ma. Consequently, we explore the various potential sources of bias that could have influenced the numerical dating methods and the biochronological inferences. In particular, the critical evaluation of the palaeomagnetic data available for various sites belonging to the younger Colle Curti Faunal Unit (FU) indicates that there is non-negligible age uncertainty on the allegedly minimum age of ∼1.1 Ma traditionally assigned to the Pirro FU. Moreover, while the combined U-series/ESR dataset could accommodate an older age for the fossil remains if uranium uptake in the dental tissues occurred relatively rapidly before the closure of the system (CSUS model), the ages obtained from the two semi-independent quartz dating methods (ESR and TT-OSL) both appear to indicate that the sediment was last exposed to sunlight about 0.8 Ma. This disparity opens up the possibility that the sediment and fossil assemblage may not be coeval. In other words, it is possible that the fossil remains may have been reworked into younger deposits that entered the karst about 0.8 Ma. Though feasible from a karst sedimentary dynamics perspective, this hypothesis is not consistent with previous taphonomic studies that indicate an absence of evidence for fossil reworking after entering the karst. At the very least, our dating results indicate that site formation processes at Pirro Nord site P13 are more complex than previously considered.

Conditions of sediment transport and deposition in highly dynamic fluvio-glacial environments enhance incomplete bleaching of luminescence signals during sunlight exposure. Whatever the geomorphic context or application, partial bleaching has been widely reported and remains a methodological limitation for application of Optically Stimulated Luminescence (OSL) dating methods, potentially resulting in sediment-burial age overestimation. This study focuses on the highly dynamic Séveraisse River (SW French Alps) where modern-day alluvial sands of a braided reach were sampled to assess the degree of quartz-OSL partial bleaching associated with superficial pre- and post-deposition geomorphic processes. Our original approach combines (i) a photogrammetry-based survey, (ii) sediment grain-size analysis, and (iii) measurements of both portable OSL luminescence signals and conventional quartz OSL equivalent doses in modern superficial (from 0.1 to 1 cm) and sub-surface (up to 30 cm) alluvial sands exposed to sunlight for at least 19 days. Our results show high but spatially variable residual luminescence signals at the surface, measured in all grain-size fractions with both the portable luminescence reader (≥5 x10⁶ cts/g) and conventional quartz-OSL doses (≥80 Gy), even within the uppermost millimetres of the exposed alluvial surface. Our data thus highlight poor luminescence bleaching in the Séveraisse's modern sands, during both pre-depositional transport and post-depositional exposure. In addition, our study reveals, for the first time, the significant sunlight attenuation over a few millimetres within modern alluvial sediments, perhaps conditioned by dark sand grains, and/or by superficial blanketing by silts (i.e. waning flow stage) that leads to a porosity decrease and very low sunlight penetration. We suggest the occurrence of a critical sediment layer (i.e. only a few mm thick) that could play a key role in bleaching processes for alluvial surfaces, with strong implications for our understanding of residual doses in braided systems' sandy deposits and the dynamics of such alluvial surfaces.

The Mas des Caves site at Lunel-Viel, Southern France, is a complex of several caves, developed in Miocene limestone, that have yielded a rich archaeo-palaeontological sequence attributed to the Middle Pleistocene with abundant vertebrates and lithic artefacts. The first caves (LVI, II and III), discovered in 1800, were excavated at the beginning of the 19th century (Serres et al., 1828) before falling into oblivion for over a century. The main cavity is LVI, when LVII and III are smaller subparallel galleries not connected to LVI. In the early 1970s, research was conducted in the main gallery by E. Bonifay who discovered an extension named LVIV and the natural entrance (sinkhole, doline) both completely closed now.

Recently, a multidisciplinary approach has been set up (DRAC-SRA Occitanie) to contextualize the ancient collections with the recent ones and to allow a better understanding of the site formation, palaeoenvironmental and behavioral history of the animals and humans who lived there (Brugal et al., 2021). The previous chronology based on faunal evidence yields important biomarkers (including new genus and species/subspecies) making Lunel-Viel a major Middle Pleistocene site in the European record. Among various dating techniques used in this study, trapped-charged methods such as combined ESR/U-series and pIR-IR₂₉₀ were applied on fossil tooth enamel and on K-feldspars, respectively. The results obtained by both methods are in agreement and suggest a period of human occupation between 300 and 200 ka. This age range matches well with the composition of the faunal assemblage attributed to the second part of the Middle Pleistocene (biochronology) and which constrains the occupation to a cool/temperate and humid period which could be contemporaneous with the MIS7 (Lisiecki and Raymo, 2005) cited in figure 5 legend.

We report a detailed rock-magnetic, archaeomagnetic and absolute intensity investigation on burned in situ remains of the Plazuelas archaeological site (Northern Border of Mesoamerica). Fifty-six specimens were subjected to step-wise alternating field demagnetizations to retrieve characteristic remanence directions. All samples yielded evidence of stable, single-component magnetization carried by magnetite or Ti-poor titanomagnetite. Sixty-four specimens were selected for paleointensity experiments following the Thellier double heating technique, including remanence anisotropy correction. The archaeomagnetic dating, based on full geomagnetic vectors, was performed using the global geomagnetic models and the regional Paleosecular Variation Curves available for Mesoamerica. The most probable age intervals obtained for the burned floor of Site 1 (Casas Tapadas North) are within the interval 972AD – 744 AD. In the case of the burned floor of Site 2 (Casas Tapadas West), the ages obtained fall within 971 AD - 752 AD. In the case of the burned floor of Site 3 (South Sector), the ages obtained fall within the interval 752 AD – 969 AD. The calculation of the most probable age intervals, carried out using the Bootstrap resampling method, provided the dates of 940 ± 6 AD, 896 ± 14 AD and 883 ± 14 AD, respectively. These ages agree well with various archaeological hypotheses on the sudden collapse of Plazuelas as a result of intentional destruction, mutilation and generalized firing due to the local war and/or social unrest.

The Middle Paleolithic site of Mutzig-Rain, discovered in 1992, has been studied through several pits (called M1 to M15) and excavation area since 2009, evidencing several localities and delivering more than 5000 lithic artifacts and 12,000 well preserved paleontological remains. The main excavation M2 sequence corresponds to a collapsed rock shelter, containing several levels of Middle Paleolithic occupation. The faunal assemblage of the main archaeological levels (l.7a to 7c) from this sequence includes woolly mammoth, reindeer, horse, bison and woolly rhinoceros, reflecting both cold climate and a steppe context for the whole sequence, while microfauna from the lower levels (l.7d and l.10) indicate the occasional presence of forests that could correspond to a cooler climate. In 1995, U-series analyses on bones from M8 were attempted but the obtained results did not follow the sample stratigraphic order. Later, an OSL dating study has placed the M2 archaeological sequence as coeval to the onset of the Weichselian glacial stage (MIS5d-5a), between 100 and 80 ka.

The good preservation of the abundant faunal remains at Mutzig-Rain has allowed their use for ESR/U-series dating studies and the results obtained on Mutzig horse teeth are given in the present paper. A first set of analyses of teeth carried out from the M2 excavation provided ages around 106-96 ka for levels M2 l.7, in agreement with the OSL data, despite quite systematic evidence of U-leaching from the dental tissues and the consequent use of the Accelerating Uptake (AU) model for the age calculation. A second set of analyses on teeth from the M2 and M8 localities confirms this uranium leaching trend, placing the deposition of these levels ca 133 -122 ka.

Taking the whole set of ESR/U-series ages, which are slightly older than the OSL dates, would suggest that the stratigraphic sequence was deposited between ca 130 ka (M8 l. 6 and M2 l.10) and ca 100 ka (M2 l.7), i.e. on a time range covering the Eemian Interglacial (MIS5e) and the subsequent Early Weichselian Glacial stage (MIS5d-5a). However, as the faunal record indicates a cool climate and an open steppe-like environment for the whole archaeological sequence, the ESR/U-series dating to the Eemian Interglacial in the Mutzig-Rain sequence seems unlikely. In order to check the quality of the paleodosimetric reconstruction of the ESR/U-series analyses, an additional isochron study was performed for the two levels for which several teeth were analyzed: M2 l.7 (n = 4) and M8 l.6 (n = 3). This isochron study validates the proposed reconstruction and confirms the Early Weichselian age of these two levels. These results confirm the chronology established previously with OSL and places Mutzig-Rain as a reference site for the understanding of the Neanderthal Middle Palaeolithic occupation in Eastern France.

The distribution of equivalent dose (D_e) values of individual feldspar grains is affected by a range of variables, including internal and external dose rates, residual doses, and uncertainties associated with luminescence behaviours and measurement errors. The distributions of these variables may be non-Gaussian, resulting in a complex D_e distribution pattern that may be challenging to interpret and analyse using conventional statistical models. To address this problem, we present an empirical Bayesian hierarchical age model for feldspar (BHAM-F), which integrates all key components involved in the optical dating of individual feldspar grains. The model is based on application of the standardised growth curve and L_nT_n methods to obtain a full distribution of single-grain D_e values, and use of prior information about major sources of uncertainty that can be obtained experimentally or theoretically. A Bayesian outlier model is also adopted to detect and deal with outliers. We test and validate the BHAM-F using an experimentally gathered dataset obtained from a sediment sample and various simulated datasets. Our results show that the BHAM-F provides a robust and flexible way to hierarchically deal with data obtained in single-grain optical dating of feldspars.

This article presents the first age model built with a combination of paleomagnetic data and radiocarbon dating for the Las Brusquillas 4 archaeological site (Pampas region, Argentina). The sedimentary sequence represents fluvio-lacustrine deposits where faunal remains and lithic artefacts were found in two archaeological layers separated by culturally sterile sediments. Our age model is fundamental to date the human occupation in the area during the Holocene and determine when paleoenvironmental changes occurred at a local scale. Paleomagnetic secular variations (PSV) recorded in 129 cm of this sedimentary sequence were compared to four global geomagnetic field models. Rock magnetic results suggest that the magnetic signal is carried by low-coercivity magnetic minerals like magnetite with an important contribution of antiferromagnetic minerals (hematite-type). The PSV of Las Brusquillas 4 compare well with other natural archives from different regions of Argentina but some differences were found in the declination data, showing the importance of further records from this region to better constrain the secular variation of the geomagnetic field.

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.

Well-preserved shorelines, situated at elevations ranging from tens to hundreds of meters above the current lake levels, are commonly found in the lake basins across the Tibetan Plateau (TP). These shorelines offer a valuable opportunity to reconstruct past hydroclimate changes, contingent upon precise age determination of palaeoshorelines. While single-aliquot luminescence methods have been extensively employed for dating palaeoshoreline sediments, both quartz and K-feldspar fractions, the application of single-grain (SG) dating techniques has been relatively limited, particularly in the case of water-lain sediments where partial bleaching must be taken into account. In this study, we applied the single-grain K-feldspar dating technique using the post-IR IRSL (pIRIR) protocol to a selection of palaeoshorelines from Qinghai Lake, the largest lake on the TP. Our primary objectives were to investigate the behavior of single-grain K-feldspar pIRIR signals and to establish precise timing for late Quaternary lake level fluctuations based on SG data. Our findings reveal a clear correlation between the D_e (equivalent dose) values of single grains and their fading rates. The higher fading rates observed in dim grains constitute the primary reason for the underestimation of D_e values. However, it appears that the internal K content of the grains cannot explain the relationship between fading rates and grain brightness. Finally, we utilized the 30% brightest grains for SG pIRIR D_e determinations, allowing us to reconstruct the historical water level fluctuations of Qinghai Lake. Our results indicate a pronounced decline in lake levels during the last interglacial-glacial transition, approximately 90,000 to 75,000 years ago. This decline can be attributed to the response of regional hydroclimate patterns to global environmental changes.

With the aim of dating the early salt production at Puntone di Scarlino (Central Tuscany, Italy) and establishing the environmental history of this coastal site, a sediment core was studied, taken from the lagoon next to the archaeological site. Diachronic radiocarbon dating of terrestrial plant macro remains and Loripes orbiculatus (Poli, 1795) shells, a burrowing lucinid bivalve occurring throughout the sediment cored, revealed a Marine Reservoir Effect (MRE) that varied markedly over time. Between ca. 4000 and 2500 cal BP, the △R values ranged between −50 and + 500 ¹⁴Cyears, thus rendering the Loripes shells truly unsuited for independent radiocarbon dating. Extensive geochemical and palaeoecological study of the core and its environment showed that none of the ubiquitous explanations for this highly variable MRE, such as ‘hard water’ or ‘upwelling old seawater’, can be valid. We attribute the phenomenon to the uptake by this lucinid mollusc of ‘old carbon’ from the sediment column into which it had burrowed, released by diagenetic microbial decomposition processes such as methanogenesis. The age of this inorganic carbon varied, being linked to the sedimentation rate: with decreasing sedimentation rate its impact will increase, whereas at high sedimentation rates its impact will likely be minimal. Our results raise serious doubts about the suitability for radiocarbon dating of benthic fauna from shallow coastal environments and point at these diagenetic processes as potentially important sources of ‘old carbon’.