Unraveling rift margin evolution and escarpment development ages along the Dead Sea fault using cosmogenic burial ages     

A. Matmon  D. Fink  M. Davis  S. Niedermann  D. Rood  A. Frumkin 《Quaternary Research》2014

The Dead Sea fault (DSF) is one of the most active plate boundaries in the world. Understanding the Quaternary history and sediments of the DSF requires investigation into the Neogene development of this plate boundary. DSF lateral motion preceded significant extension and rift morphology by ~ 10 Ma. Sediments of the Sedom Formation, dated here between 5.0 ± 0.5 Ma and 6.2_− 2.1^+ inf Ma, yielded extremely low ¹⁰Be concentrations and ²⁶Al is absent. These reflect the antiquity of the sediments, deposited in the Sedom Lagoon, which evolved in a subdued landscape and was connected to the Mediterranean Sea. The base of the overlying Amora Formation, deposited in the terminal Amora Lake which developed under increasing relief that promoted escarpment incision, was dated at 3.3_− 0.8^+ 0.9 Ma. Burial ages of fluvial sediments within caves (3.4 ± 0.2 Ma and 3.6 ± 0.4 Ma) represent the timing of initial incision. Initial DSF topography coincides with the earliest Red Sea MORB's and the East Anatolian fault initiation. These suggest a change in the relative Arabian–African plate motion. This change introduced the rifting component to the DSF followed by a significant subsidence, margin uplift, and a reorganization of relief and drainage pattern in the region resulting in the topographic framework observed today.  相似文献   

Holocene rockfalls in the southern Negev Desert,Israel and their relation to Dead Sea fault earthquakes     

Yair Rinat  Ari Matmon  Maurice Arnold  Georges Aumaître  Didier Bourlès  Karim Keddadouche  Naomi Porat  Efrat Morin  Robert C. Finkel 《Quaternary Research》2014

Rockfall ages in tectonically active regions provide information regarding frequency and magnitude of earthquakes. In the hyper-arid environment of the Dead Sea fault (DSF), southern Israel, rockfalls are most probably triggered by earthquakes. We dated rockfalls along the western margin of the DSF using terrestrial cosmogenic nuclides (TCN). At each rockfall site, samples were collected from simultaneously exposed conjugate boulders and cliff surfaces. Such conjugate samples initially had identical pre-fall (“inherited”) TCN concentrations. After boulder detachment, these surfaces were dosed by different production rates due to differences in post-fall shielding and geometry. However, in our study area, pre-rockfall inheritance and post-rockfall production rates of TCN cannot be evaluated. Therefore, we developed a numerical approach and demonstrated a way to overcome the above-mentioned problems. This approach can be applied in other settings where rockfalls cannot be dated by simple exposure dating. Results suggest rockfall ages between 3.6 ± 0.8 and 4.7 ± 0.7 ka. OSL ages of sediment accumulated behind the boulders range between 0.6 ± 0.1 and 3.4 ± 1.4 ka and support the TCN results. Our ages agree with dated earthquakes determined in paleoseismic studies along the entire length of the DSF and support the observation of intensive earthquake activity around 4–5 ka.  相似文献   

Near-field effects of Cherenkov radiation induced by ultra high energy cosmic neutrinos     

Chia-Yu Hu  Chih-Ching Chen  Pisin Chen 《Astroparticle Physics》2012,35(7):421-434

The radio approach based on the Askaryan effect for detecting the ultra-high energy cosmic neutrinos has become a mature experimental technique. So far the existing calculations of the Cherenkov radiation associated with the Askaryan effect has been mostly based on the far-field approximation, whose validity maybe challenged when the detector is close to the event. In this paper we present an alternative approach to calculate the Cherenkov pulse by a numerical code based on the finite difference time-domain (FDTD) method. This approach has the advantage of providing the solution everywhere in space, contrary to other methods that rely on the far-field approximation. We also present a one-dimensional theoretical model for the shower with analytical solution, which helps to elucidate our nonzero-width simulation results. We show that for a shower with symmetric longitudinal development, the resulting near-field waveform would be asymmetric in time. In addition, we demonstrate that for a shower elongated by the LPM (Landau-Pomeranchuk-Migdal) effect and thus with a multi-peak structure, a bipolar, asymmetric waveform is still preserved in the near-field regime irrespective of the specific variations of the multi-peak structure, which makes it a generic, distinctive feature. This should provide an important characteristic signature for the identification of ultra-high energy cosmogenic neutrinos.  相似文献   

沉积盆地中恢复地层剥蚀量的新方法   总被引：33，自引：0，他引：33  

王毅  金之钧 《地球科学进展》1999,14(5):482-486

主要介绍了磷灰石裂变径迹分析法,沉积波动过程分析法和宇宙成因核素分析法等３种恢复和计算地层剥蚀量的新方法。它们的优点是不但给出一个剥蚀面造成的地层总的剥蚀量,还能详细刻画整个剥蚀过程,从而能计算出每一期构造抬升引起的地层剥蚀量。  相似文献   

A quantitative assessment of snow shielding effects on surface exposure dating from a western North American 10Be data compilation     

《Quaternary Geochronology》2023

To better assess the spatiotemporal variations of the snow shielding effect on surface exposure dating, we compiled a dataset of 1341 ¹⁰Be ages from alpine moraines and glacially eroded valleys across western North America, and conducted a sensitivity test with both modern and time-integrated snow data covering the same region. Our analyses reveal significant differences in snow shielding both across our geographic domain and through time. In our time-integrated experiments we find snow-based exposure age corrections as low as 3.5% in the Great Basin region and high as 28.4% in the Pacific Northwest for samples dating to the Last Glacial Maximum (LGM) when no wind-sweeping is assumed. As demonstrated with our time-varying snow conditions with a global climate model and a positive degree day model, modern snow conditions across western North America cannot account for the varying snow patterns under large scale climate shifts since the LGM. The snow-based exposure age corrections from the modern data differ from those calculated by our time-varying model by up to 17% across our model domain. In addition, we find that the ¹⁰Be ages calculated under two end-member scenarios regarding wind-sweeping effects, specifically whether boulders were shielded only when the total snow accumulation exceeded boulder heights or were always shielded when the snow was present, can differ by ∼7.6% on average for LGM aged samples. Our analyses provide a model-based estimates of the spatiotemporal variability and complexity of snow shielding effects on surface exposure dates across western North America and highlight the need to consider snow depth variations both spatially and temporally when conducting surface exposure dating in terrains where snowfall accumulation is significant.  相似文献   

Cosmogenic 36Cl glacial chronologies of the Late Quaternary glaciers on Mount Geyikdağ in the Eastern Mediterranean     

《Quaternary Geochronology》2017

We report the timing of glaciations during the Late Quaternary in the central Taurus Mountains of Turkey in the Eastern Mediterranean. Forty moraine samples from three glacial valleys on Mount Geyikdağ (36.53°N, 32.10^°E, 2877 m), near the Eastern Mediterranean coast of Turkey, were dated with in-situ cosmogenic ³⁶Cl. These glacial valleys are located on the southern flank of the mountain and were filled with few km long glaciers that terminated at elevations of about 1750 m above sea level. Three glacial retreats/advances were determined in this study. During the Last Glacial Maximum (LGM), glaciers reached their maximum positions at 20.6 ± 0.6 ka ago (±1σ). This date is in accordance with the timing of local maximum ice extent, represented by piedmont glaciers in the northern side of the mountain. Glaciers started to retreat after the LGM and shortly stabilized or re-advanced two times before they completely vanished out. The first stage ended before 13.7 ± 0.8 ka ago during the Late-glacial. The last glaciation occurred during the Holocene and ended between 9.6 ± 1.4 ka and 5.9 ± 0.5 ka ago. Later, glaciers mostly vanished from the study area, but a few rock glaciers developed during the Late Holocene. Glacial chronologies of Mount Geyikdağ are mostly comparable with the globally observed advances elsewhere.  相似文献   

Cosmogenic nuclide burial dating of an alluvial conglomerate sequence: An example from the Hexi Corridor,NE Tibetan Plateau     

《Quaternary Geochronology》2017

The thick alluvial conglomerate sequences around the Tibetan Plateau have been notoriously difficult to date. Here we use the cosmogenic nuclide burial dating method to date the Yumen and Jiuquan formations, a ∼900 m thick fanglomerate found in the Hexi Corridor, the foredeep of the Qilian Shan, and exposed in the Laojunmiao anticline. We date 16 sites with simple burial dating and 2 sites with isochron burial dating, and use these dates to reinterpret the magnetostratigraphy of the section. We suggest that the bottom of the Yumen Formation, defined by a progressive unconformity, is around 5 My. Taking this timing as the initiation of anticline growth, the long-term crustal shortening rate at the ramp zone in western Qilian Shan is about 0.72 mm/yr, consistent with those obtained from middle and eastern Qilian Shan. The boundary between the Yumen and Jiuquan Formations is near ∼1.2 My. Three other angular unconformities are dated to ∼2.6–3.1, ∼2.2–2.5, and ∼1.2–1.7 My, respectively. Burial dating offers a robust chronology for these deposits, and when combined with paleomagnetic stratigraphy offers much tighter precision.  相似文献   

Clean quartz matters for cosmogenic nuclide analyses: An exploration of the importance of sample purity using the CRONUS-N reference material     

《Quaternary Geochronology》2022

Reference materials are key for assessing inter-laboratory variability and measurement quality, and for placing analytical uncertainty bounds on sample analyses. Here, we investigate four years of data resulting from repeated processing of the CRONUS-N reference material for cosmogenic ¹⁰Be and ²⁶Al analyses. At University of Vermont, we prepared a CRONUS-N aliquot with most of our sample batches from 2013 to 2017; these reference material samples were then distributed to four different accelerator mass spectrometry facilities, yielding 73 ¹⁰Be analyses and 58 ²⁶Al analyses. We determine CRONUS-N ¹⁰Be concentrations of (2.26 ± 0.14) x 10⁵ atoms g⁻¹ (n = 73, mean, 1 SD) and ²⁶Al concentrations of (1.00 ± 0.08) x 10⁶ atoms g⁻¹ (n = 58, mean, 1 SD). We find a reproducibility of 6.3% for ¹⁰Be and 7.7% for ²⁶Al (relative standard deviations). We also document highly variable ²⁷Al and Mg concentrations and a ¹⁰Be dispersion twice as large as the mean AMS analytic uncertainty. Analyses of the CRONUS-N material with and without density separation demonstrate that non-quartz minerals are present in the material and have a large impact on measured concentrations of ²⁷Al, ¹⁰Be, and impurities; these non-quartz minerals represent only a very small portion of the total mass (0.6–0.8%) but have a disproportionally large effect on the resulting data. Our results highlight the importance of completely removing all non-quartz mineral phases from samples prior to Be/Al extraction for the determination of in situ cosmogenic ¹⁰Be and ²⁶Al concentrations.  相似文献   

Interlaboratory comparison of cosmogenic 21Ne in quartz     

《Quaternary Geochronology》2015

We performed an interlaboratory comparison study with the aim to determine the accuracy of cosmogenic ²¹Ne measurements in quartz. CREU-1 is a natural quartz standard prepared from amalgamated vein clasts which were crushed, thoroughly mixed, and sieved into 125–250 μm and 250–500 μm size fractions. 50 aliquots of CREU-1 were analyzed by five laboratories employing six different noble gas mass spectrometers. The released gas contained a mixture of 16–30% atmospheric and 70–84% non-atmospheric (predominantly cosmogenic) ²¹Ne, defining a linear array on the ²²Ne/²⁰Ne-²¹Ne/²⁰Ne three isotope diagram with a slope of 1.108 ± 0.014. The internal reproducibility of the measurements is in good agreement with the formal analytical precision for all participating labs. The external reproducibility of the ²¹Ne concentrations between labs, however, is significantly overdispersed with respect to the reported analytical precision. We report an average reference concentration for CREU-1 of 348 ± 10 × 10⁶ at [²¹Ne]/g[SiO₂], and suggest that the 7.1% (2σ) overdispersion of our measurements may be representative of the current accuracy of cosmogenic ²¹Ne in quartz. CREU-1 was tied to CRONUS-A, which is a second reference material prepared from a sample of Antarctic sandstone. We propose a reference value of 320 ± 11 × 10⁶ at/g for CRONUS-A. The CREU-1 and CRONUS-A intercalibration materials may be used to improve the consistency of cosmogenic ²¹Ne to the level of the analytical precision.  相似文献   

An inter-laboratory comparison of cosmogenic 3He and radiogenic 4He in the CRONUS-P pyroxene standard     

《Quaternary Geochronology》2015

This study reports an inter-laboratory comparison of the ³He and ⁴He concentrations measured in the pyroxene material CRONUS-P. This forms part of the CRONUS-Earth and CRONUS-EU programs, which also produced a series of natural reference materials for in situ produced ²⁶Al, ¹⁰Be, ¹⁴C, ²¹Ne and ³⁶Cl.Six laboratories (GFZ Potsdam, Caltech Pasadena, CRPG Nancy, SUERC Glasgow, BGC Berkeley, Lamont New York) participated in this intercomparison experiment, analyzing between 5 and 22 aliquots each. Intra-laboratory results yield ³He concentrations that are consistent with the reported analytical uncertainties, which suggests that ³He is homogeneous within CRONUS-P. The inter-laboratory dataset (66 determinations from the 6 different labs) is characterized by a global weighted mean of (5.02 ± 0.12) × 10⁹ at g⁻¹ with an overdispersion of 5.6% (2σ). ⁴He is characterized by a larger variability than ³He, and by an inter-lab global weighted mean of (3.60 ± 0.18) × 10¹³ at g⁻¹ (2σ) with an overdispersion of 10.4% (2σ).There are, however, some systematic differences between the six laboratories. More precisely, 2 laboratories obtained mean ³He concentrations that are about 6% higher than the clustered other 4 laboratories. This systematic bias is larger than the analytical uncertainty and not related to the CRONUS-P material (see Schaefer et al., 2015). Reasons for these inter-laboratory offsets are difficult to identify but are discussed below. To improve the precision of cosmogenic ³He dating, we suggest that future studies presenting cosmogenic ³He results also report the ³He concentration measured in the CRONUS-P material in the lab(s) used in a given study.  相似文献