共查询到20条相似文献，搜索用时 31 毫秒
1.
K. Nishiizumi J.R. Arnold M.W. Caffee J. Masarik 《Geochimica et cosmochimica acta》2009,73(7):2163-449
Cosmic ray produced 10Be (half-life = 1.36 × 106 yr), 26Al (7.05 × 105 yr), and 36Cl (3.01 × 105 yr) were measured in a depth profile of 19 carefully-ground samples from the glass-coated lunar surface rock 64455. The solar cosmic ray (SCR) produced 26Al and 36Cl in this rock are present in high concentrations, which in combination with the low observed erosion rate, <0.5 mm/Myr, provide well defined depth profiles characterizing the SCR component of the cosmic rays. In conjunction with new experimentally determined excitation functions, the 36Cl concentrations suggest a softer solar-proton spectral shape than that derived from most previous measurements. The fact that no SCR-produced 10Be activity could be detected in 64455 is in good agreement with observations in 68815 and also indicates a softer SCR spectrum. Comparison of observed SCR profiles in 64455 with theoretical calculations indicates that the average solar-proton spectrum over the past 2 Myr (based on 26Al) has an exponential rigidity parameter (R0) of about 90 MV with a proton flux (J) of 73 protons/cm2/s·4π above 10 MeV. Over the last ∼0.5 Myr (based on 36Cl) R0 is about 70 MV with a flux of ∼196 protons/cm2/s·4π above 10 MeV. These SCR fluxes are consistent with most previous work. 相似文献
2.
We have determined the production rate of in situ-produced 10Be in calcite through measurements of 10Be and 36Cl concentrations in the same calcite samples and of 10Be concentrations in depth profiles of flint from the same erosional surface. This yields a 10Be production rate in calcite of 37.9 ± 6.0 at/g/yr at sea level and high latitude, approximately sixfold higher than production in the coexisting flint. We propose that this higher rate of production may be due to high production cross sections for C spallation by cosmic rays with energies below 50 MeV. These results also open the possibility of dating burial events in carbonate-rich environments by differential radioactive decay of 10Be and 36Cl. 相似文献
3.
Cosmogenic Ne isotopes are stable and are routinely used for constraining the timing of events and the rate of surface change beyond the limit that can be studied with radionuclides 10Be, 26Al, and 36Cl. Cosmogenic Ne analysis can be used in quartz and in a range of other minerals. Analysis typically requires significantly less material than do cosmogenic 10Be and 26Al, opening up the technique for small samples—individual pebbles in river sediments, for example. Analysis is easier and faster than for radionuclides, not least because Ne measurements do not require significant chemical procedures. However, the presence of other sources of Ne in minerals tends to restrict the use of cosmogenic 21Ne to old landscapes and long exposure durations. In this review we briefly outline the background of cosmogenic Ne production in rocks and minerals at the Earth’s surface, then document the key uses of the technique by highlighting some earlier studies, and finish with a short perspective on the future of the technique. 相似文献
4.
Here, we provide evidence suggesting that marine (diatom) opal contains not only a high fidelity record of dissolved oceanic concentrations of cosmic ray-produced radionuclides, 10Be and 26Al, but also a record of temporal variations in a large number of trace elements such as Ti, Fe, Zn and Mn. This finding is derived from measurements in purified biogenic opal that can be separated from detrital materials using a newly developed technique based on surface charge characteristics. Initial results from a sediment core taken near the present-day position of the Antarctic Polar Front (ODP Site 1093) show dramatic changes in the intrinsic concentrations of, Be, Al, Ti, Fe, Mn and Zn in the opal assemblages during the past ∼140 kyr BP. The results imply appreciable climatically controlled fluctuations in the level of bioreactive trace elements. The time series of total Be, Al, Ti, Fe and 10Be in the sediment core are all well correlated with each other and with dust records in the polar ice cores. The observations suggest that a significant flux of these trace metals to oceans is contributed by the aeolian dust, in this case, presumably from the Patagonia. This observation also allows determination of fluxes of dust-contributed 10Be to the Antarctica ice sheets. However, our data show that the relationships among the various metals are not perfectly linear. During periods of higher dissolved concentrations of trace elements (indicated by Fe and Ti) the relative concentrations of bioreactive elements, Be, Al, Mn and Zn are decreased. By contrast, the Fe/Zn and Fe/Mn ratios decrease significantly during each transition from cold to warm periods. The relative behavior could be consistent with any of the following processes: (i) enhanced biological productivity due to greater supply of the bioreactive elements (e.g. Zn) during cold periods (ii) increased biological and inorganic scavenging of particle active elements (e.g. Be and Al) during early interglacial periods (iii) differential uptake/removal of the metals by the various diatom taxa whose relative productivity or growth rate changes with large scale climate. In any case, with one sedimentary phase and in single sedimentary sections, we now have the potential to compare directly a proxy for aeolian input of micronutrients (e.g. Fe or Ti), with a proxy for production (e.g. 26Al/Al ratios). We expect that studies of the temporal records of trace elements and cosmogenic nuclides in contrasting regions of upwelling and productivity, which exhibit different sensitivities to global climate fluctuations and micronutrient inputs, would lead to a direct and comprehensive test of ideas such as the hypothesis of iron control of atmospheric carbon dioxide [Martin, J.H., 1990. Glacial-interglacial CO2 change: the iron hypothesis. Paleoceanography5, 1-13]. Our present data from a single site do not show that increases in dissolved Fe concentrations, per se, were responsible for increased biological productivity. However, a much clearer picture of the effect of increased dust fluxes should emerge when we have data for trace elements and the cosmogenic nuclides, 10Be and 26Al from various oceanic provinces. 相似文献
5.
长期暴露于地表的石英砂被快速搬入洞穴或埋藏,不再接受宇宙射线辐射,埋藏前所积累的陆地宇生核素26 Al 和10 Be 随时间指数衰减。据此用加速器质谱计测定沉积物中石英样品现存的26 Al /10 Be可计算其埋藏年代。用此方法本文对周口店第一地点的下部地层年代作了初探。此次研究表明自第10层以下的沉积物其年代很可能≥ 1 Ma。 相似文献
6.
We have searched for excesses of 36S derived from the decay of extinct 36Cl in sodalite, a secondary Cl-rich mineral, in Ca-Al-rich inclusions (CAIs) from the Vigarano and Allende CV3 chondrites and in a chondrule from the Ningqiang carbonaceous chondrite. The presence of sodalite in two CAIs from Vigarano and its absence from surrounding CAI fragments suggests sodalite formation after CAI fragmentation. As for sodalite in the Allende Pink Angel CAI, oxygen isotopic compositions have been interpreted as indicative of high temperature interactions, thus suggesting formation prior to accretion to the parent body, probably in a nebular setting. Sodalite in the Ningqiang chondrule is considered to have formed via alkali-Ca exchange, which is believed to have occurred before accretion to the parent body.Sodalites in the Vigarano CAIs and in the Ningqiang chondrule show no clear evidence for the presence of radiogenic 36S. The inferred 2σ upper limits for 36Cl/35Cl at the time of sodalite formation are 1.6 × 10−6 (Vigarano CAIs) and 3.3 × 10−6 (Ningqiang chondrule), respectively. In the Pink Angel CAI sodalite exhibits small 36S excesses which weakly correlate with 35Cl/34S ratios. The inferred 36Cl/35Cl ratio of (1.8 ± 2.2) × 10−6 (2σ error) is lower than that found by Hsu et al. [Hsu, W., Guan, Y., Leshin, L. A., Ushikubo, T. and Wasserburg, G. J. (2006) A late episode of irradiation in the early solar system: Evidence from extinct 36Cl and 26Al in meteorites. Astrophys. J. 640, 525-529], thus indicative of heterogeneous distribution of 36Cl in this CAI. Spallation reactions induced by energetic particles from the young Sun are suggested for the origin of 36Cl, similar to the case of 10Be. While 10Be appears to be present in roughly equal abundance in all studied CAIs, our study indicates the level of 36Cl abundances to be variable so that there seems to be no simple relationship between 10Be and 36Cl. This would be expected if trapped cosmic rays rather than Early Solar System spallation were the dominant source of 10Be in the Early Solar System, since their contribution to 36Cl would have been tiny.If the variability of 36Cl abundances is caused by temporal differences in the alteration that formed sodalite, sodalite in the Vigarano CAIs and in the Ningqiang chondrule may have formed ?0.5 and ?0.2 Ma after formation of the sodalite in the Ningqiang CAI analyzed by Lin et al. [Lin, Y., Guan, Y., Leshin, L. A., Ouyang, Z. and Wang, D. (2005) Short-lived chlorine-36 in a Ca- and Al-rich inclusion from the Ningqiang carbonaceous chondrite. Proc. Natl. Acad. Sci. USA 102, 1306-1311]. The Pink Angel sodalite that we analyzed may have formed ∼0.3 Ma after formation of the sodalite in the Pink Angel analyzed by Hsu et al. [Hsu, W., Guan, Y., Leshin, L. A., Ushikubo, T. and Wasserburg G. J. (2006) A late episode of irradiation in the early solar system: Evidence from extinct 36Cl and 26Al in meteorites. Astrophys. J. 640, 525-529]. The estimated temporal differences suggest that alteration extended over at least 0.5 Ma. If previous works showing very low initial 36Cl/35Cl in the Allende CAIs and a H3 chondrite CAI are also considered, then alteration processes may have been more than 1.7 Ma. 相似文献
7.
Weiquan Dong Devendra Lal Barbara Ransom Wolfgang Berger Marc W Caffee 《Journal of Earth System Science》2001,110(2):95-102
The geochemical behaviors of Be and Al in ocean waters have been successfully studied in recent years using natural, cosmogenic,
radioactive10Be and26Al as tracers. The present day dissolved concentrations and distribution of the stable and radioactive isotopes of Be and
Al in ocean waters have revealed their short residence times and appreciable effects of exchange fluxes at the coastal and
ocean-sediment interfaces. It follows that concentrations of these particle-active elements must have varied in the past with
temporal changes in climate, biological productivity and aeolian flux of continental detritus to the oceans. We therefore
investigated the feasibility of extending the measurements of Be and Al isotope concentrations in marine systems to the 103–106 y BP time scale. We report here the discovery of significant amounts of intrinsic Be and Al in marine foraminiferal calcite
and coral aragonite, and of Al in opal (radiolarians) and aragonite (coral), which makes it possible to determine10Be/Be and26Al/Al in oceans in the past. We also report measured10Be/9Be in foraminiferal calcite in Pacific Ocean cores, which reveal that the concentrations and ratios of the stable and cosmogenic
isotopes of Be and Al have varied significantly in the past 30 ky. The implications of these results are discussed. 相似文献
8.
9.
We have found clear evidence of live 10Be in five normal Type A Calcium-aluminum-rich inclusions (CAIs), one normal Type B CAI, and one FUN Type A CAI, all from CV3 chondrites. The (10Be/9Be)0 ratios range from ∼0.36 × 10-3 to ∼0.77 × 10-3 and are similar to those found by previous workers. The (10Be/9Be)0 ratios do not correlate in a temporal fashion with (26Al/27Al)0, suggesting that 10Be and 26Al were produced by different mechanisms. An examination of possible sources for the short-lived radionuclides indicates that production of 10Be was almost certainly by particle irradiation, possibly within the solar system, and was probably accompanied by significant production of 41Ca and 53Mn. In contrast, all of the 60Fe, most of the 26Al, and some of the 53Mn were probably produced in stars and were imported into the solar system within presolar dust grains. 相似文献
10.
超灵敏加速器质谱技术进展及应用 总被引：5，自引：1，他引：4
加速器质谱(AMS)是一门发展非常迅速的核分析技术,诞生于20世纪70年代末,是基于加速器和离子探测器的一种高能质谱,它克服了传统质谱存在的分子本底和同量异位素本底干扰的限制,对同位素丰度灵敏度的测量可以达到10-16。经过的30多年发展,AMS以其多方的优势,日益受到人们的重视与青睐。在地学领域,通过测26Al、10Be等核素,可以实现地表暴露年龄、侵蚀速率测定和地貌演变研究;在海洋学领域,通过测量129I、10Be等核素,可以研究海洋沉积物、锰结核、锰结壳等生长速率和沉积速率;在考古学领域,通过测量14C、10Be等核素,可以实现珍贵样品的年代测定和第四纪人类进化的年代学研究;在环境科学领域,通过测量129I、14C等核素,可以对核污染、城市环境污染、全球气候变化进行监测与研究。目前,AMS从技术和应用研究两个方面都在迅速发展。文章对AMS的工作原理、设备和技术发展,以及在地学、海洋科学、考古学、环境科学等领域的应用进行详细阐述。 相似文献
11.
G.J. Wasserburg J. Aléon A.N. Krot K. Nagashima 《Geochimica et cosmochimica acta》2011,75(17):4752-4770
We report on a study of Al3509, a large Na- and Cl-rich, radially-zoned object from the oxidized CV carbonaceous chondrite Allende. Al3509 consists of fine-grained ferroan olivine, ferroan Al-diopside, nepheline, sodalite, and andradite, and is crosscut by numerous veins of nepheline, sodalite, and ferroan Al-diopside. Some poorly-characterized phases of fine-grained material are also present; these phases contain no significant H2O. The minerals listed above are commonly found in Allende CAIs and chondrules and are attributed to late-stage iron-alkali-halogen metasomatic alteration of primary high-temperature minerals. Textural observations indicate that Al3509 is an igneous object. However, no residual crystals that might be relicts of pre-existing CAI or chondrule minerals were identified. To establish the levels of 26Al and 36Cl originally present, 26Al-26Mg and 36Cl-36S isotopic systematics in sodalite were investigated. Al3509 shows no evidence of radiogenic 26Mg∗, establishing an upper limit of the initial 26Al/27Al ratio of 3 × 10−6. All sodalite grains measured show large but variable excesses of 36S, which, however, do not correlate with 35Cl/34S ratio. If these excesses are due to decay of 36Cl, local redistribution of radiogenic 36S∗ after 36Cl had decayed is required. The oxygen-isotope pattern in Al3509 is the same as found in secondary minerals resulting from iron-alkali-halogen metasomatic alteration of Allende CAIs and chondrules and in melilite and anorthite of most CAIs in Allende. The oxygen-isotope data suggest that the secondary minerals precipitated from or equilibrated with a fluid of similar oxygen-isotope composition. These observations suggest that the formation of Al3509 and alteration products in CAIs and chondrules in Allende requires a very similar fluid phase, greatly enriched in volatiles (e.g., Na and Cl) and with Δ17O ∼ −3‰. We infer that internal heating of planetesimals by 26Al would efficiently transfer volatiles to their outer portions and enhance the formation of volatile-enriched minerals there. We conclude that the site for the production of Na- and Cl-rich fluids responsible for the formation of Al3509 and the alteration of the Allende CAIs and chondrules must have been on a protoplanetary body prior to incorporation into the Allende meteorite. Galactic cosmic rays cannot be the source of the inferred initial 36Cl in Allende. The problem of 36Cl production by solar energetic particle (SEP) bombardment and the possibility that 36Cl and 41Ca might be the product of neutron capture resulting from SEP bombardment of protoplanetary surfaces are discussed. This hypothesis can be tested comparing inferred “initial” 36Cl with neutron fluencies measured on the same samples and on phases showing 36S∗ by Sm and Gd isotopic measurements. 相似文献
12.
暴露测年样品中26Al和10Be分离及其加速器质谱测定 总被引：4，自引：4，他引：0
在已有实验流程基础上,建立并优化了石英样品中Be和Al提取、纯化等实验流程,设计的流程条件实验包括实验试剂、器皿和离子交换柱选择、离子交换树脂分离Be和Al时酸浓度选择等。结果表明,选择钢铁研究总院研制的9Be标准溶液作为10Be样品制备的载体;使用一次性实验器皿;选用4 cm规格的离子交换柱;用0.05 mol/L草酸和0.75 mol/L盐酸混合溶液洗脱吸附于阴离子树脂上的Al,可有效提取、纯化样品中的Be和Al。加速器质谱(AMS)测量结果显示,13组化学空白的10Be/9Be和26Al/27Al比值平均值分别为7.48×10-15和1.96×10-15,与国内已有宇宙成因核素实验室的结果(5×10-15~8×10-15)具有可比性。电感耦合等离子体发射光谱(ICP-AES)的测量结果表明,Be、Al回收率分别达90%和60%。基于新建立的实验流程分析了祁连山北侧金佛寺的一个岩石样品,获得了10Be和26Al的暴露年代分别为(10.7±1.0) ka和(10.0±1.2) ka,与前人研究结果一致。 相似文献
13.
The concentrations of the radionuclides, 10Be, 230Th and 232Th have been measured in four gravity cores from the Pacific and one piston core from the Indian Ocean. Three of the Pacific Ocean cores were studied for the presence of magnetic reversals. Accumulation rates based on the nuclear and magnetic methods fall in the range of 1–6 mm/103 yr and except in one case, are in fair agreement with each other. This result leads to the conclusion that the constants used in the 10Be-dating equation are approximately correct (within + 30 per cent) and the usefulness of the cosmic ray produced nuclei 10Be for dating Pliocene and recent sediments seems to be established, considering the underlying assumptions in the Be10-dating method. 相似文献
14.
《Quaternary Science Reviews》2005,24(1-2):49-65
New cosmogenic surface-exposure ages of moraine-crest boulders from southwestern Colorado are compared with published surface-exposure ages of boulders from moraine complexes in north-central Colorado and in west-central (Fremont Lake basin) Wyoming. 10Be data sets from the three areas were scaled to a single 10Be production rate of 5.4 at/g/yr at sea level and high latitude (SLHL), which represents the average 10Be production rate for two high-altitude, mid-latitude sites in the western United States (US) and Austria. Multiple nuclide ages on single boulders indicate that this 10Be production rate yields ages comparable to those calculated with a commonly used 36Cl production scheme. The average age and age range of moraine-crest boulders on terminal moraines at the southwestern Colorado and Wyoming sites are similar, indicating a retreat from their positions ∼16.8 36Cl ka (Cosmogenic ages in this paper are labeled 10Be or 36Cl ka or just ka when both 10Be or 36Cl ages are being discussed; radiocarbon ages are labeled 14C ka, calibrated radiocarbon are labeled cal ka, and calendar ages are labeled calendar ka. Errors (±1σ) associated with ages are shown in tables. Radiocarbon ages were calibrated using the data of Hughen et al. (Science 303 (2004) 202). This suggests a near-synchronous retreat of Pinedale glaciers across a 470-km latitudinal range in the Middle and Southern Rocky Mountains. Hypothetical corrections for snow shielding and rock-surface erosion shifts the time of retreat to between 17.2 and 17.5 10Be ka at Pinedale, Wyoming, and between 16.3 and 17.3 36Cl ka at Hogback Mountain, Colorado. 相似文献
15.
《Quaternary Science Reviews》2007,26(11-12):1547-1556
A new method of permafrost dating with the cosmogenic radionuclide 36Cl is presented. In the first application, syngenetic ice wedges are dated using the ratio of 36Cl and Cl concentrations in ice as the signal. 36Cl is produced in the atmosphere by nuclear reactions of cosmic rays on argon. Stable chlorine enters the atmosphere from the oceans. Their ratio does not depend on chloride concentration in precipitations and on sublimation of snow. In situ production of 36Cl in permafrost ice via cosmic ray-induced reactions and neutron capture are calculated and the dating age limit is estimated as 3 million years. 36Cl/Cl ratios in permafrost samples from cape Svyatoy Nos (Laptev Sea coast), North-Eastern Siberia, are measured by accelerator mass spectrometry. Analysis of the first results and the calculated dates support the feasibility of the 36Cl permafrost dating method 相似文献
16.
《Geochimica et cosmochimica acta》1996,60(1):109-119
We report the development of a NaOH-leaching technique to extract the authigenic Al and Be in marine sediments, which should allow the sedimentary signals of cosmogenic 26Al and 10Be to be more effectively studied as geochemical/geophysical tracers. The technique has been applied to the study of 26Al and 10Be in opal-rich sediments from the North Pacific. The 26Al/27Al and 10Be/9Be ratios of ~3 × 10−14 and 1 × 10−7 leached from the sediments are higher than those in the total sediments by factors of 3–10 and 2–3, respectively. The authigenic 10Be/9Be ratios are similar to those in deep waters at the study site, pointing to the potential usefulness of the ratios in paleoceanographic studies. The fractions of total Be and Al in the sediment studied that are of authigenic origin average about 40 and 17%, respectively. Estimated 26AL/27A1 ratios in detrital sediments are ≤ 10−15, low enough to indicate that the source of 26Al in the ocean mainly comes from atmospheric production. In the study area, the deposition flux of 26Al is comparable to its atmospheric supply. However, the deposition flux of 10Be is about threefold higher than the atmospheric input, signifying lateral transport of 10Be from the open ocean to this area of relatively high particle flux. The 26Al/10Be ratio, being insensitive to the oceanic influx of lithogenic particles, may serve as a valuable proxy for paleoproductivity. Both the authigenic and total-sediment 26Al/27Al and 10Be/ 9Be ratios decreased significantly at ~6 ka, which could reflect an enhanced input of windblown lithogenic particles to the North Pacific. While the enhanced dust input did not significantly alter the deep-water 9Be concentration, it contributed to the observed increase of authigenic 9Be flux to the sediment. 相似文献
17.
宇宙成因核素10 Be(半衰期1.5Ma)不但是古环境变化的示踪剂,而且具有确定地质年龄的能力。80个全岩样品的10 Be和化学分析数据表明,黄土高原约6Ma以来的红粘土和黄土序列中年龄校正的10 Be浓度与沉积物粒度和风化程度的化学指标具有显著的关系。根据这种关系建立的10 Be浓度与化学指标的经验回归线性模型,可以估计红粘土和黄土形成时的10 Be浓度,确定红粘土和黄土形成的10 Be放射性年龄。 相似文献
18.
Narendra Bhandari 《Journal of Earth System Science》1981,90(3):359-382
Recent results on cosmic ray interactions in lunar samples and meteorites resulting in production of stable and radionuclides, particle tracks and thermoluminescence are reviewed. A critical examination of26A1 depth profiles in lunar rocks and soil cores, together with particle track data, enables us to determine the long term average fluxes of energetic solar protons (>10 MeV) which can be represented by (J s,R o)=(125, 125). The lunar rock data indicate that this flux has remained constant for 5×105 to 2×106 years. Production rates of stable and radionuclides produced by galactic cosmic rays is given as a function of size and depth of the meteoroid. Radionuclide (53Mn,28Al) depth profiles in meteorite cores, whose preatmospheric depths are deduced from track density profiles are used to develop a general procedure for calculating isotope production rates as a function of meteoroid size. Based on the track density and22Ne/21Ne production rates, a criterion is developed to identify meteorites with multiple exposure history.22Ne/21Ne ratio <1·06 is usually indicative of deep shielded exposure. An examination of the available data suggests that the frequency of meteorites with multiple exposure history is high, at least 15% for LL, 27% for L and 31% for H chondrites. The epi-thermal and the thermal neutron density profiles in different meteorites are deduced from60Co and track density data in Dhajala, Kirin and Allende chondrites. The data show that the production profile depends sensitively on the size and the chemical composition of the meteoroid. Cosmic ray-induced thermoluminescence in meteorites of known preatmospheric sizes has been measured which indicates that its production profile is nearly flat and insensitive to the size of the meteoroid. Some new possibilities in studying cosmic ray implanted radionuclides in meteorites and lunar samples using resonance ionisation spectroscopy are discussed. 相似文献
19.
经历反复埋藏暴露演化过程的河流阶地样品,难以用常规方法将原生宇宙核素10Be、26Al有效分离。本文在前人实验方法基础上,使用人工挑选、磁选仪分选及酸洗方法,分离样品中碳酸盐、含铁矿物及大气生成的10Be,进一步优化了石英提纯实验流程。结果表明:长度为9 cm、内径为1 cm的阴离子交换树脂装置匹配4 mol/L氢氟酸淋滤液,可将B、Mg、Ca、Cr、Fe、Mn、Ni、Ti和Be、Al有效分离,Be、Al回收率分别可达95.7%、85.7%。阳离子交换树脂能有效分离Be、Al,两元素回收率均达到85%。获得10Be/9Be和26Al/27Al流程空白分别为2.19×10-15和1.63×10-15。优化后的实验方法显著提高了河流阶地样品中原生宇宙核素10Be、26Al的纯化效率,且10Be/9Be和26Al/27Al流程空白数值与国内外实验室具有可比性。采用本方法获得了成都平原冲积物10Be、26Al暴露年龄分别是76.36±9.51 ka和69.44±14.13 ka,为评价龙门山前缘隐伏断裂构造特征和活动性提供了年代学依据。 相似文献
20.
Neil F. Glasser Philip D. Hughes Cassandra Fenton Christoph Schnabel Henrik Rother 《第四纪科学杂志》2012,27(1):97-104
This paper presents results of the analysis of paired cosmogenic isotopes (10Be and 26Al) from eight quartz‐rich samples collected from ice‐moulded bedrock on the Aran ridge, the highest land in the British Isles south of Snowdon. On the Aran ridge, comprising the summits of Aran Fawddwy (905 m a.s.l.) and Aran Benllyn (885 m a.s.l.), 26Al and 10Be ages indicate complete ice coverage and glacial erosion at the global Last Glacial Maximum (LGM). Six samples from the summit ridge above 750–800 m a.s.l. yielded paired 10Be and 26Al ages ranging from 17.2 to 34.4 ka, respectively. Four of these samples are very close in age (10Be ages of 17.5 ± 0.6, 17.5 ± 0.7, 19.7 ± 0.8 and 20.0 ± 0.7 ka) and are interpreted as representing the exposure age of the summit ridge. Two other summit samples are much older (10Be ages of 27.5 ± 1.0 and 33.9 ± 1.2 ka) and these results may indicate nuclide inheritance. The 26Al/10Be ratios for all samples are indistinguishable within one‐sigma uncertainty from the production rate ratio line, indicating that there is no evidence for a complex exposure history. These results indicate that the last Welsh Ice Cap was thick enough to completely cover the Aran ridge and achieve glacial erosion at the LGM. However, between c. 20 and 17 ka ridge summits were exposed as nunataks at a time when glacial erosion at lower elevations (below 750–800 m a.s.l.) was achieved by large outlet glaciers in the valleys surrounding the mountains. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献