Since its discovery, the Chauvet cave elaborate artwork called into question our understanding of Palaeolithic art evolution and challenged traditional chronological benchmarks Valladas H et al. ...(2001) Nature 413:419–479. Chronological approaches revealing human presences in the cavity during the Aurignacian and the Gravettian are indeed still debated on the basis of stylistic criteria Pettitt P (2008) J Hum Evol 55:908–917. The presented 36Cl Cosmic Ray Exposure ages demonstrate that the cliff overhanging the Chauvet cave has collapsed several times since 29 ka until the sealing of the cavity entrance prohibited access to the cave at least 21 ka ago. Remarkably agreeing with the radiocarbon dates of the human and animal occupancy, this study confirms that the Chauvet cave paintings are the oldest and the most elaborate ever discovered, challenging our current knowledge of human cognitive evolution.
The Longmen Shan range, located on the eastern margin of the Tibetan Plateau, is characterized by steep topography and a shortening rate of <3 mm/yr. This peculiar configuration is a source of ...controversy and questions about the topographic evolution and dynamics of this orogenic plateau margin. Investigating the variations in surface denudation over different spatial and temporal scales is important for a better understanding of topographic evolution, but there is still a lack of erosion‐rate data averaged over millennial timescales along the frontal range of the Longmen Shan, especially in its southern part. We present 25 new catchment‐wide denudation rates derived from 10Be concentrations in river sediments across the southern Longmen Shan. Our results show that average denudation rates increase from <0.15 mm/yr near Ya'an, located in the Sichuan Basin, northwestward to >0.50 mm/yr inside the southern Longmen Shan. The denudation rates correlate with slope gradient, relief, channel steepness, and specific stream power but exhibit a fair degree of scattering at high values. In combination with previous 10Be and low‐temperature thermochronology analyses, we found the denudation rates over kyr‐ to Myr‐timescales to be roughly consistent across the southern Longmen Shan, suggesting this part of the range is close to an exhumational steady state. In terms of spatial distribution, high rates of exhumation and denudation are localized in the hanging walls of major thrust faults, highlighting the role of tectonic structures in regulating the pattern of denudation and topography across the Longmen Shan. Our results favor the “brittle crustal shortening” model in which rock uplift pattern across the Longmen Shan is largely controlled by upper crustal shortening. Along‐strike variations in the distribution of denudation rates and topography can probably be attributed to segmentation of subsurface fault structures.
Key Points
10Be‐derived catchment‐wide denudation rates are positively correlated with topographic indices in the southern Longmen Shan
Erosion rates are consistent over short‐ and long‐term timescales across the Longmen Shan, suggesting an exhumational steady state
Rock uplift pattern and topographic evolution across the Longmen Shan have been largely controlled by upper crustal shortening and fault geometry
•The Aricota landslide dam is an enigmatic giant landslide of the hyper arid Andes•Its rock volume was 2km3, producing a dam of 600m height and a lake of 6km long•13 new 10Be exposure ages show two ...main events at 17.9±0.7 and 12.1±0.2 ka•This timing is consistent with periods of regional paleoprecipitation increases
The central part of the Western Andes holds an exceptional concentration of giant paleolandslides involving very large volumes of rock material (v>km3). While those gravitational slope failures are interpreted consensually as an erosional response to the geodynamic activity of the Andes (relief formation and tectonic activity), the question of their triggering mechanisms remains enigmatic. To clarify the respective roles of climatic versus seismic forcing on the Andean landslides, new temporal constraints on paleo movements are essential. Here, we focus on one of those giant slope failures, the Aricota giant rockslide that damned the Locumba valley in southern Peru. We conducted fieldwork, high-resolution DEM analysis and cosmogenic nuclide dating to decipher its development history and failure mechanisms. Our results point to the occurrence of two successive events. A giant failure mobilizing a rock volume of ca. 2km3 first produced a dam at 17.9±0.7 ka. Considering its height of ca. 600m, the Aricota rockslide dam is one of the three largest landslide dams worldwide. At 12.1±0.2 ka, a second event produced ca. 0.2 km3 of material, and the rock-avalanche debris spread out over the dam. As the chronology of those two events is pointing to the two main paleoclimatic pluvial periods in this region (Heinrich Stadial 1a and Younger Dryas), we favor the interpretation of a climatic forcing. At a regional scale, the concomitant aggradation of alluvial terraces and fan systems along the nearby valleys highlights higher regional erosion, sediments supply and mass-wasting events during those paleoprecipitation events and strengthens this conclusion.
We analyzed phytolith and diatom remains preserved at 45 Miocene and Pliocene localities dated between 8 and 1 Ma in northern Chad (16–17°N). Some of these localities yielded cranial remains, lower ...jaws, and teeth of the hominin species Australopithecus bahrelghazali (∼3.6 Ma) and Sahelanthropus tchadensis (∼7 Ma). Of the 111 sediment samples analyzed, 41 yielded phytoliths, 20 yielded diatoms, and seven yielded both phytoliths and diatoms. Freshwater planktonic and tychoplanktonic diatom species, indicative of lacustrine conditions, are dominant (>91%) in the samples. The phytolith assemblages indicate an opening of the vegetation and a general trend toward an expansion of grass-dominated environments during the time spanning the two hominin occurrences in Chad. The phytoliths suggest the presence of a mosaic environment, including closed forest patches, palm groves, and mixed/grassland formations, between 7.5 and 7 Ma, the replacement by palm grove-like vegetation at approximately 6.5–5 Ma, and the presence of exclusive grass-dominated formations after 4.5 Ma. The type-locality of S. tchadensis (TM266) was likely similar to modern palm grove formations with an arboreal cover percentage ≥40%. The type locality of A. bahrelghazali (KT12) was a grass-dominated ecosystem (likely savanna) with an unrated percentage of arboreal cover. Furthermore, the grass phytolith data support the existence of a (recurrent) Sahelian-like dry climate in northern Chad since at least 8 Ma. Therefore the local closed vegetation formations in the Djurab region at 7.5–7 Ma were sustained by aquatic systems (such as lakes or related rivers, marshes) rather than by extensive annual precipitation.
Following the installation and acceptance test of the French 5
MV AMS facility ASTER, the focus has been on improving the capability for routine measurements of
10Be and
26Al. Quality assurance has ...been established by the introduction of traceable AMS standards for each nuclide, by self-monitoring through participation in round-robin exercises and proficiency testing, and by surveillance of long- and short-time variability of blank and reference materials. A background level of 3
×
10
−14 makes ASTER well-suited for measuring
41Ca/
40Ca in the10
−12 region, which is sufficient for a wide range of applications. Routine AMS measurements of volatile elements like
36Cl and
129I will most likely become feasible in the very near future as the result of significant improvements in the ion source design.
We studied four marine sediment records of the Matuyama–Brunhes geomagnetic reversal from four sites located in the Indian, Atlantic and western Pacific oceans. The results combine paleomagnetic, ...cosmogenic nuclide beryllium (10Be) and oxygen isotope analyses that were performed on the same samples in order to avoid any stratigraphic bias. The three records from the equatorial Indian Ocean and North Atlantic Ocean did not reveal any offset between the authigenic 10Be/9Be ratio (Be-ratio) peak and the interval of low relative paleointensity (RPI) that characterizes the reversal. The lower and upper limits of transitional directions are also concomitant with the increased atmospheric 10Be production that accompanied the geomagnetic dipole intensity decrease. In contrast, the record from western equatorial Pacific Ocean sediments was found 18 cm below the Be-ratio changes as a result of late magnetization acquisition. At all four sites, maximum 10Be production occurred at the same period soon after the maximum of Marine Isotope Stage 19 (MIS 19) and, therefore, indicates its synchronous worldwide character. Such features are effectively observed from the Be-ratio signals and their relationship with the magnetic transition interval, which further confirms the synchronous character of the transition. Taking all dating uncertainties (1.6 ka between sites and 5 ka for the age model) into consideration, our records suggest a mean reversal age of 772.4 ± 6.6 ka. The age of the transition in the Atlantic Ocean record is closer to 774 ka but this difference is within the limit of significance.
•We present Be-ratio, paleomagnetic and δ18O records of four marine cores across the B/M reversal.•The maximum of 10Be production occurs soon after the maximum of Marine Isotope Stage 19.•Our astronomical age model indicates that the reversal occurred at 772.4±6.6 ka.
Investigation of Holocene extents of mountain glaciers along with the related naturally-driven climate conditions helps improve our understanding of glacier sensitivity to ongoing climate change. ...Here, we present the first Holocene glacial chronology in the Mont-Blanc massif (Argentière glacier) in the French Alps, based on 25 in situ-produced cosmogenic 10Be dates of moraines and glacial bedrocks. The obtained ages from mapped sequences of moraines at three locations reveal that the glacier retreated from its Lateglacial extent and oscillated several times between ∼11.7 ka and ∼10.4 ka, i.e. during the Younger Dryas/Early Holocene (YD/EH) transition, before substantially retreating at ∼10.4 ka. Climate conditions corresponding to the past extents of Argentière glacier during the YD/EH transition (∼11 ka) and the Little Ice Age (LIA) were modelled with two different approaches: by determining summer temperature differences from reconstructed ELA-rises and by using a Positive Degree Day (PDD) mass-balance model. The ELA-rise reconstructions yield a possible range of temperatures for the YD/EH transition that were lower by between 3.0 and 4.8 °C compared to the year 2008, depending on the choice of the ELA sensitivity to temperature. The results from the PDD model indicate temperatures lower by ∼3.6–5.5 °C during the YD/EH transition than during the 1979–2002 period. For the LIA, our findings highlight the role of local precipitation changes, superimposed on the dominant temperature signal, in the detailed evolution of the glacier. Overall, this study highlights the challenge that remains in accurately inferring paleoclimate conditions from past glacier extents.
•Argentière glacier oscillated 5 times between 11.7 ka and 10.5 ka.•Modeled Early Holocene temperature range is 3.6–5.5 °C below modern values.•Local precipitation changes explain detailed Little Ice Age glacier fluctuations.
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