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91.
Meteoritic and bedrock constraints on the glacial history of Frontier Mountain in northern Victoria Land, Antarctica 总被引:2,自引:0,他引:2
K.C. Welten L. Folco K. Nishiizumi M.W. Caffee A. Grimberg M.M.M. Meier F. Kober 《Earth and Planetary Science Letters》2008,270(3-4):308-315
In 2001, a small H4 chondrite, Frontier Mountain (FRO) 01149, was found on a glacially eroded surface near the top of Frontier Mountain, Antarctica, about 600 m above the present ice level. The metal and sulphides are almost completely oxidized due to terrestrial weathering. We used a chemical leaching procedure to remove weathering products, which contained atmospheric 10Be and 36Cl in a ratio similar to that found in Antarctic ice. The FRO 01149 meteorite has a terrestrial age of 3.0 ± 0.3 Myr based on the concentrations of the cosmogenic radionuclides 10Be, 26Al and 36Cl. This age implies that FRO 01149 is the oldest stony meteorite (fossil meteorites excluded) discovered on Earth. The noble gas cosmic ray exposure age of FRO 01149 is ~ 30 Myr. The meteorite thus belongs to the 33 Myr exposure age peak of H-chondrites.The bedrock surface on which FRO 01149 was found has wet-based glacial erosional features recording a former high-stand of the East Antarctic ice sheet. This ice sheet evidently overrode the highest peaks (> 2800 m a.s.l.) of the inland sector of the Transantarctic Mountains in northern Victoria Land. We argue that FRO 01149 was a local fall and that its survival on a glacially eroded bedrock surface constrains the age of the last overriding event to be older than ~ 3 Myr. The concentrations of in-situ produced cosmogenic 10Be, 26Al and 21Ne in a glacially eroded bedrock sample taken from near the summit of Frontier Mountain yield a surface exposure age of 4.4 Myr and indicate that the bedrock was covered by several meters of snow. The exposure age is also consistent with bedrock exposure ages of other summit plateaus in northern Victoria Land. 相似文献
92.
The upland planation surface in the Piedmont of central New Jersey consists of summit flats, as much as 130 km2 in area, that truncate bedding and structure in diabase, basalt, sandstone, mudstone and gneiss. These flats define a low‐relief regional surface that corresponds in elevation to residual hills in the adjacent Coastal Plain capped by a fluvial gravel of late Miocene age. A Pliocene fluvial sand is inset 50 m below the upland features. These associations suggest a late Miocene or early Pliocene age for the surface. To assess exposure age and erosional history, a 4·4 m core of clayey diabase saprolite on a 3 km2 remnant of the surface was sampled at six depths for atmospherically produced cosmogenic 10Be. The measured inventory, assuming a deposition rate of 1·3 × 106 atoms cm−2 a−1, yields a minimum exposure age of 227 000 years, or, assuming continuous surface erosion, a constant erosion rate of 10 m Ma−1. Because the sample site lies about 60 m above the aggradation surface of the Pliocene fluvial deposit, and itself supports a pre‐Pliocene fluvial gravel lag, this erosion rate is too high. Rather, episodic surface erosion and runoff bypassing probably have produced an inventory deficit. Reasonable estimates of surface erosion (up to 10 m) and bypassing (up to 50 per cent of total precipitation) yield exposure ages of as much as 6·4 Ma. These results indicate that (1) the surface is probably of pre‐Pleistocene age and has been modified by Pleistocene erosion, and (2) exposure ages based on 10Be inventories are highly sensitive to surface erosion and runoff bypassing. Copyright © 2000 John Wiley & Sons, Ltd. 相似文献
93.
基于宇宙成因核素~(10)Be的青藏高原东南部地区末次间冰期以来地表岩石剥蚀速率研究 总被引:1,自引:0,他引:1
地表剥蚀速率是衡量地貌演变的一个重要因子.本研究利用原地生成宇宙成因核素10Be对青藏高原东南部地区地表岩石剥蚀速率进行了首次测定.结果显示,自末次间冰期以来,青藏高原东南部地区的地表岩石剥蚀速率不超过60 mm/ka,平均剥蚀速率值约为27.1±10.2 mm/ka,这一结果与其他高海拔地区基岩剥蚀速率值一致.高原东南部地区地表岩石剥蚀率同时受构造活动和气候尤其降水量等因素的制约.与高原内部干旱、半干旱地区相比,青藏高原东南部地区的剥蚀速率偏大,但均在同一个数量级范围内.高原东南部地区较高原内部干旱区剥蚀速率大的原因主要是由于降水量的差异所致. 相似文献
94.
95.
Denudation rates on cratonic landscapes: comparison between suspended and dissolved fluxes,and 10Be analysis in the Nyong and Sanaga River basins,south Cameroon 下载免费PDF全文
Vincent Regard Sébastien Carretier Jean‐Loup Boeglin Jules‐Rémy Ndam Ngoupayou Jean‐Guy Dzana Jean‐Pierre Bedimo Bedimo Jean Riotte Jean‐Jacques Braun 《地球表面变化过程与地形》2016,41(12):1671-1683
South Cameroon is located in a tropical and tectonically quiescent region, with landscapes characterized by thick highly weathered regolith, indicative of the long‐term predominance of chemical weathering over erosion. Currently this region undergoes huge changes due to accelerated mutations related to a growing population and economical developments with associated needs and increasing pressures on land and natural resources. We analysed two of the main south Cameroon rivers: the Nyong River and Sanaga River. The Sanaga catchment undergoes a contrasted tropical climate from sub‐humid mountainous and humid climate and is impacted by deforestation, agriculture, damming, mining and urbanization, especially in the Mbam sub‐basin, draining the highly populated volcanic highlands. By contrast, the Nyong catchment, only under humid tropical climate, is preserved from anthropogenic disturbance with low population except in the region of Yaoundé (Méfou sub‐basin). Moreover the Nyong basin is dam‐free and less impacted by agriculture and logging. We explore both denudation temporal variability and the ratio between chemical and physical denudation through two catchment‐averaged erosion and denudation datasets. The first one consists of an 11‐year long gauging dataset, while the second one comes from cosmogenic radionuclides [CRNs, here beryllium‐10 (10Be)] from sand sampled in the river mainstreams (timescale of tens to hundreds of thousands of years). Modern fluxes estimated from gauging data range from 5 to 100 m/Ma (10 to 200 t/km2/yr); our calculations indicate that the usual relative contribution of chemical versus physical denudation is 60% and 40%, respectively, of the total denudation. Beryllium‐10 denudation rates and sediment fluxes range from 4.8 to 40.3 m/Ma or 13 to 109 t/km2/yr, respectively, after correction for quartz enrichment. These fluxes are slightly less than the modern fluxes observed in Cameroon and other stable tropical areas. The highest 10Be‐derived fluxes and the highest physical versus chemical denudation ratios are attributed to anthropogenic impact. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
96.
青藏高原是第四纪古冰川研究的理想区域也是宇宙成因核素(terrestrial cosmogenic nuclides,TCN)暴露测年技术应用的天然实验场所。然而,现有的TCN测年数据与先前学者基于其他测年手段的研究结果不一致,显得相对年轻。为了探索其原因,本文尝试对青藏高原1594个TCN测年数据进行统计分析。研究结果表明:1测年样品中97%的样品是漂砾样品,测年数据中约有93%的年代数据小于130 ka;2 280组(n≥3)漂砾样品年代数据中大约76%的漂砾组数据变异系数大于10%,而基岩和羊背石样品组测年数据变异系数较低、相对集中;3冰碛垄表面漂砾样品的不等时暴露与后期侵蚀可能是造成TCN年代数据结果偏年轻的主要原因。本研究可为青藏高原地区冰川地貌TCN暴露年代研究提供重要启示。 相似文献
97.
Cosmic ray produced isotopes in terrestrial systems 总被引:2,自引:0,他引:2
D. Lal 《Journal of Earth System Science》1998,107(4):241-249
Continuing improvements in the sensitivity of measurement of cosmic ray produced isotopes in environmental samples have progressively
broadened the scope of their applications to characterise and quantify a wide variety of processes in earth and planetary
sciences. In this article, I will concentrate on the new developments in the field of nuclear geophysics, based on isotopic
changes produced by cosmic rays in the terrestrial systems. This field, which is best described as cosmic ray geophysics,
caught roots with the discovery of cosmogenic14C on the Earth by Willard Libby in 1948, and grew rapidly at first, but slowed down during the ’60s and ’70s. In the ’80s,
there was arenaissance in cosmic ray produced isotope studies, thanks mainly to the developments of the accelerator mass spectrometry technique
capable of measuring minute amounts of radioactivity in terrestrial samples. This technological advance has considerably enhanced
the applications of cosmic ray produced isotopes and today we find them being used to address diverse problems in earth and
planetary sciences
I discuss the present scope of the field of cosmic ray geophysics with an emphasis ongeomorphology. I must stress here that this is the decade in which this field, which has been studied passionately by geographers, geomorphologists
and geochemists for more than five decades, has at its service nuclear methods to introduce numeric time controls in the range
of centuries to millions of years. 相似文献
98.
陆地原位宇宙成因核素(TCN)在地表过程与构造活动关系研究中的应用 总被引:2,自引:0,他引:2
大地构造、气候变化和地表过程间的耦合作用被视为今后10年内六大地学新课题之一,而从事这一重大课题研究的有效途经便是陆地原位宇宙成因核素的研究和应用。从目前该领域的研究实践来看,经常使用的是^3He、^10Be、^14C、^21Ne、^26Al和^36Cl核素,其中石英的^26Al和^10Be的配合使用最为普遍。通过陆地原位宇宙成因核素(TCN)方法基本原理的阐释,并结合当今国际上该领域利用^10Be和^26Al在暴露年龄与侵蚀速率、沉积物埋藏年龄以及河流下切速率等方面的工作实例.介绍陆地原位宇宙成因核素在地表过程以及地表过程与构造活动相互关系研究上的应用。 相似文献
99.
《地球化学》2008,(2)
陨石离开其小行星母体直至降到地球表面期间,受到宇宙射线的照射,产生一系列包括10Be和26Al等的放射性核素。10Be和26Al的含量及其比值记录了宇宙射线辐照历史,而陨石降落到地球表面后,它们的衰变又提供了测定其降落时间,即居地年龄的方法。10Be和26Al由加速器质谱测定,样品需分离纯化。为此,开展了陨石样品Be和Al的分离纯化实验。通过模拟样品的条件实验,建立了Be和Al分离纯化的化学流程,其回收率分别达到89%和70%。在此基础上,分离并测定了一个降落型普通球粒陨石(吉林陨石)非磁性部分的10Be和26Al的含量。结果显示,吉林陨石26Al/10Be的比值为5.005,远大于两者的饱和比值(2.72),说明吉林陨石经历了短期的暴露辐射,这一结果与吉林陨石第二阶段的暴露年龄0.4Ma一致。整个化学流程的10Be/9Be和26Al/27Al空白分别为(4.33±0.46)×10-14和(6.59±4.66)×10-15,其中前者接近于该仪器的空白测量值,而后者则接近于仪器的检测限2.3×10-15。 相似文献
100.
Brent M. Goehring Meredith A. Kelly Joerg M. Schaefer Robert C. Finkel Thomas V. Lowell 《第四纪科学杂志》2010,25(6):865-874
Here we combine 10Be depth profile techniques applied to late glacial ice‐contact marine and lacustrine deltas, as well as boulder exposure dating of associated features in the Scoresby Sound region, east Greenland, to determine both the surface age and the magnitude of cosmogenic nuclide inheritance. Boulder ages from an ice‐contact delta in northern Scoresby Sund show scatter typical of polar regions and yield an average age of 12.8 ± 0.5 ka – about 2 ka older than both our average profile surface age of 10.9 ± 0.7 ka from three depth profiles and a radiocarbon‐based estimate. On the other hand, boulder exposure ages from a set of moraines in southern Scoresby Sund show excellent internal consistency for polar regions and yield an average age of 11.6 ± 0.2 ka. The profile surface age from a corresponding ice‐contact delta is 8.1 ± 0.9 ka, while a second delta yields an age of 10.0 ± 0.4 ka. Measured 10Be inheritance concentrations from all depth profiles are internally consistent and are between 10% and 20% of the surface concentrations, suggesting a regional cosmogenic inheritance signal for the Scoresby Sound landscape. Based on the profile inheritance concentrations, we explore the first‐order catchment‐averaged bedrock erosion under the Greenland ice sheet, yielding estimates of total erosion during the last glacial cycle of the order of 2–30 m. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献