吉林陨石的热释光剖面与母体宇宙暴露历史示踪

对３个已知取样浓度和３个未知取样部位的吉林陨石样品的热释光研究表明,其自然热释光值具有宇宙成因核素含量相似的性质即浓度分布效应,随着样品距离表面位置的增大而降低,这表征了母体暴露期间宇宙射线的分布状况。诱导热释光数据表明,母体表面部分的样品的峰温和峰宽高于较深部位样品,说明这些样品中发光体矿物由有序态向无序态转化趋势明显。表面位置样品明显高的热释光数据说明在母体暴露过程中,除了银河宇宙射线外,太阳     

Quantitative evaluation of soil processes using in situ-produced cosmogenic nuclides

In situ-produced cosmogenic nuclides provide a means for quantitative evaluation of a wide range of weathering and sediment transport processes. Although these nuclides have received attention for their power as geochronometers of surface exposure, it may be argued that they are more broadly suited for study of surface processes. In many environments, they may be used to evaluate collapse, erosion, burial, bioturbation, and creep, as well as providing a qualitative basis for distinguishing allochthonous from autochthonous materials. In addition, these nuclides can provide quantitative information on rates of erosion on scales of landforms and drainage basins. Here, we review the systematics of cosmogenic nuclide production within the Earth's surface, and present field examples demonstrating the utilization of in situ-produced cosmogenic nuclides distributions for evaluation of a range of soil evolution processes. To cite this article: E.T. Brown et al., C. R. Geoscience 335 (2003).     

Geomagnetic field variations and the accumulation of in-situ cosmogenic nuclides in an eroding landform

The analysis of cosmogenic nuclides in an eroding surface yields information concerning erosion rates and exposure times. Such analysis requires accurate knowledge of the nuclide production rate at the site in question. Here we develop a relatively simple analytic model for the time variation of the production rate caused by fluctuations in the geomagnetic field. This model contains three parameters, which have a clear physical meaning and which provide a convenient way to quantify information on the production rate variations. We use this model to compute the buildup of nuclides in an eroding surface, and derive an analytic formula for the nuclide concentration as a function of the exposure time and the erosion rate. Several representative applications of our results are presented.     

Interpretation of cosmogenic nuclides in meteorites on the basis of accelerator experiments and physical model calculations

Cosmogenic nuclides in extraterrestrial matter provide a wealth of information on the exposure and collision histories of small objects in space and on the history of the solar and galactic cosmic radiation. The interpretation of the observed abundances of cosmogenic nuclides requires detailed and accurate knowledge of their production rates. Accelerator experiments provide a quantitative basis and the ground truth for modeling cosmogenic nuclide production by measurements of the relevant cross sections and by realistic simulations of the interaction of galactic protons with meteoroids under completely controlled conditions, respectively. We review the establishment of physical model calculations of cosmogenic nuclide production in extraterrestrial matter on the basis of such accelerator experiments and exemplify this approach by presenting new experimental and theoretical results for the cosmogenic nuclide⁴⁴Ti. The model calculations describe all aspects of cosmogenic nuclide production and allow the determination of long-term solar and galactic cosmic ray spectra and a consistent interpretation of cosmogenic nuclides in extraterrestrial matter.     

原地生成宇宙成因核素暴露和埋藏年龄计算方法的统一

原地生成宇宙成因核素测年技术计算暴露和埋藏年龄以往分属于不同的计算方法体系,采用的计算等式不同。实际上,无论是暴露过程还是埋藏过程,都涉及了核素的新生和已生成核素的减少,其浓度计算方法原理上有相通之处。考察被研究样品历史上某时点的状态,侵蚀使样品距地表深度不断减小,埋藏使样品距地表深度不断增加,刚好是一种相反的过程,而原地生成宇宙成因核素的生成速率与距地表深度呈指数函数形式相关。本文按照原地生成宇宙成因核素浓度与暴露时间、侵蚀速率间关系的计算原理,推导出在匀速埋藏过程中,计算被测试样品的浓度随时间的变化时,以样品目前生成速率为标准,可将埋藏速率(β)视为负侵蚀速率(-ε),从而将暴露年龄和埋藏年龄的计算等式统一起来。非匀速埋藏情况,通过求导计算,仍可视埋藏为负侵蚀。在埋藏速率和侵蚀速率用同一参数指代,埋藏速率可视为负侵蚀速率的基础上,推导出不同埋藏(侵蚀)模式下样品的核素浓度计算等式。理论上根据不同埋藏(侵蚀)模式,可计算复杂地表演化过程样品的埋藏(暴露)年龄。

     

原地宇宙成因核素(TCN)测年靶标制备

自20世纪80年代以来,得益于高能加速器质谱的发展及其分析精度的提高,TCN测年技术得到了快速发展,并被成功应用于解决诸多领域关键性的年代学问题研究中,对地学的发展也起到了革命性的推动作用。TCN测年由测年靶标制备、AMS测量及数据分析等步骤组成。其中测年靶标制备直接影响AMS的测量结果,进而影响可靠年代学框架的建立与古气候环境的重建。测年靶标制备首先是代表性样品的采集,继而是所用靶标矿物的提纯,再者是所测元素的分离提取,最后是靶标压制。此处以第四纪冰川研究中应用较为广泛的TCN放射性核素¹⁰Be与²⁶Al为例,结合冰川侵蚀与沉积地貌的分布及其特征,从样品采集、石英提纯、¹⁰Be与²⁶Al核素的分离提取及最后的靶标压制等方面展开论述,以期为初涉第四纪冰川研究的学者提供TCN测年靶标制备的理论指导,同时也为地学其他研究领域该测年技术的应用提供参考。     

Multiple cosmogenic nuclides document complex Pleistocene exposure history of glacial drifts in Terra Nova Bay (northern Victoria Land, Antarctica)

Geomorphological and glacial geological surveys and multiple cosmogenic nuclide analyses (¹⁰Be, ²⁶Al, and ²¹Ne) allowed us to reconstruct the chronology of variations prior to the last glacial maximum of the East Antarctic Ice Sheet (EAIS) and valley glaciers in the Terra Nova Bay region. Glacially scoured coastal piedmonts with round-topped mountains occur below the highest local erosional trimline. They represent relict landscape features eroded by extensive ice overriding the whole coastal area before at least 6 Ma (pre-dating the build-up of the Mt. Melbourne volcanic field). Since then, summit surfaces were continuously exposed and well preserved under polar condition with negligible erosion rates on the order of 17 cm/Ma. Complex older drifts rest on deglaciated areas above the younger late-Pleistocene glacial drift and below the previously overridden summits. The combination of stable and radionuclide isotopes documents complex exposure histories with substantial periods of burial combined with minimal erosion. The areas below rounded summits were repeatedly exposed and buried by ice from local and outlet glaciers. The exposure ages of the older drift(s) indicate multiple Pleistocene glacial cycles, which did not significantly modify the pre-existing landscape.     

Long-term rates of chemical weathering and physical erosion from cosmogenic nuclides and geochemical mass balance

Quantifying long-term rates of chemical weathering and physical erosion is important for understanding the long-term evolution of soils, landscapes, and Earth's climate. Here we describe how long-term chemical weathering rates can be measured for actively eroding landscapes using cosmogenic nuclides together with a geochemical mass balance of weathered soil and parent rock. We tested this approach in the Rio Icacos watershed, Puerto Rico, where independent studies have estimated weathering rates over both short and long timescales. Results from the cosmogenic/mass balance method are consistent with three independent sets of weathering rate estimates, thus confirming that this approach yields realistic measurements of long-term weathering rates. This approach can separately quantify weathering rates from saprolite and from overlying soil as components of the total. At Rio Icacos, nearly 50% of Si weathering occurs as rock is converted to saprolite; in contrast, nearly 100% of Al weathering occurs in the soil. Physical erosion rates are measured as part of our mass balance approach, making it particularly useful for studying interrelationships between chemical weathering and physical erosion. Our data show that chemical weathering rates are tightly coupled with physical erosion rates, such that the relationship between climate and chemical weathering rates may be obscured by site-to-site differences in the rate that minerals are supplied to soil by physical erosion of rock. One can normalize for variations in physical erosion rates using the “chemical depletion fraction,” which measures the fraction of total denudation that is accounted for by chemical weathering. This measure of chemical weathering intensity increases with increasing average temperature and precipitation in data from climatically diverse granitic sites, including tropical Rio Icacos and six temperate sites in the Sierra Nevada, California. Hence, across a wide range of climate regimes, analysis of chemical depletion fractions appears to effectively account for site-to-site differences in physical erosion rates, which would otherwise obscure climatic effects on chemical weathering rates. Our results show that by quantifying rates of physical erosion and chemical weathering together, our mass balance approach can be used to determine the relative importance of climatic and nonclimatic factors in regulating long-term chemical weathering rates.     

A microstructural study of the Tishomingo meteorite

Metallography, electron microscopy and X-ray diffraction techniques were employed to study a fragment of the Tishomingo iron meteorite. The results suggest the following thermal-mechanical history: The fragment was originally a large crystal of taenite (γ). Cooling through the α + γ phase boundary did not result in accompanying precipitation of kamacite (α). Transformation to a martensitic structure initiated between ? 25 and ?65°C. Transformation continued as the temperature fell to ? 75 to ? 115°C, resulting in approx 80% martensite (α′). Subsequent shock deformation and thermal aging processes substantially modified the taenite and martensite microstructures. Twins in the retained taenite phase are attributed to shock deformation at a pressure estimated for a single event at ~170 kbar. The existing complex, altered martensite structure containing both taenite and kamacite (3–15% Ni) particles was apparently the product of both shock deformation and thermal aging processes. The maximum temperature reached during thermal aging is estimated to be less than 400°C, and perhaps below 310°C.     

试论吉林省天然矿泉水资源及其价值

吉林省天然矿泉水资源十分丰富 ,在全国占有重要地位。本文根据大量的实际资料 ,从理论上对矿泉水的形成机制和分布规律进行了探讨。同时从矿泉水的资源属性出发 ,对其价值问题提出了新的认识。     

宁绍平原中全新世火历史与影响因素研究

宁绍平原是研究全新世火事件、气候环境以及人类活动之间复杂关系的理想场所。本研究选取宁绍平原田螺山遗址(30°01′20″N,121°22′38″E)和井头山遗址(30°01′28.45″N,121°21′40.69″E)两钻孔(长度分别为18.17 m和19.8 m)进行炭屑分析,并结合孢粉记录,旨在研究宁绍平原中全新世(9000~5700 cal.a B.P.)火历史、气候环境变化与人类活动的变化规律。结果表明：1)2个钻孔炭屑浓度在早中全新世都很低,田螺山钻孔 < 50 μm(细粒)、50~100 μm(中粒)和>100 μm(粗粒)这3种粒径的炭屑浓度均为钻孔最低值,反映当时火事件发生频率低;此时正值全新世大暖期,亚洲夏季风强劲,降水丰沛,孢粉记录也显示此时的植被类型为亚热带阔叶林,温暖湿润的气候不利于火事件发生。2)随着研究区水文环境的稳定,人类被丰富的资源吸引前来定居,人类活动的加强可能导致火事件频发,炭屑浓度升高。7900 cal.a B.P. 左右,随着海平面上升速度减缓,人类先民选择井头山区域定居,并开始了早期稻作农业的尝试,炭屑浓度随着人类在此定居出现了高值。在7000 cal.a B.P. 之后,研究区淡水湿地广泛分布,河姆渡文化兴起,炭屑浓度再次上升。田螺山钻孔炭屑浓度在6300 cal.a B.P. 左右出现最大值,但此时研究区环境尚未稳定,仍会受到海水影响,7000~6000 cal.a B.P. 期间田螺山钻孔炭屑浓度多次出现低值都与海水入侵有关;5900 cal.a B.P. 之后研究区完全成陆,稻作农业也开始了蓬勃发展,炭屑浓度也出现了明显上升。本研究探讨了中全新世宁绍平原火事件、气候环境以及人类活动之间的相互关系,揭示了气候与人类活动对该区域火事件的影响,为该区域的相关研究提供了一个新的视角。

     

吉林省常见的农业地质灾害及其防治措施初探

吉林省是农业大省，是全国重要的商品粮基地，农业收成的好坏直接影响到国民经济的发展及人民生活水平的提高，对破坏和影响农业生产的因素加以预防和防治对农业的增产增收起着举足轻重的作用，这里笔者对影响农业生产的几种常见的农业地质灾害及其防治措施作了简要论述。     

The discovery and history of the Dalgaranga meteorite crater,Western Australia

The Dalgaranga meteorite crater, 100 km northeast of Yalgoo, Western Australia, was one of the first impact structures identified in Australia, the smallest isolated crater found in Australia, and the only confirmed crater in the world associated with a mesosiderite projectile. Seventeen years passed before the Dalgaranga meteorites were described in the scientific literature, and nearly 40 years passed before a survey of the structure was published. The reasons for the time gap were never explained and a number of factual errors about the discovery and early history remain uncorrected in the scientific literature. Using historical and archival documents, and discussions with people involved in Dalgaranga research, the reasons for this time gap are explained by a series of minor misidentifications and coincidences. The age of the crater has yet to be determined, but using published data, we estimate the projectile mass to be 500–1000 kg.     

吉林省水文地质环境地质问题研究

根据吉林省水文地质环境地质问题的现状,在全面、系统综合研究最新成果的基础上,首先论述了自然环境特点和区域地质背景,其次根据当前全省经济现状和国民经济发展对水文地质环境地质问题的需求,对全省进行了水文地质环境地质分区,同时重点地论述了全省存在的主要水文地质环境地质问题,最后有针对性地提出了今后水文地质环境地质问题战略规划和建议。     

Lithology, landscape dissection and glaciation controls on catchment erosion as determined by cosmogenic nuclides in river sediment (the Wutach Gorge, Black Forest)

Cosmogenic nuclides, measured in quartz from recent river bedload, provide a novel tool to quantify catchment‐wide erosion rates at geologically meaningful time scales. Here we present an analysis of the geomorphological evolution of the 350 km² Wutach catchment in the uplands of the south‐west German Black Forest. The robustness of the method is demonstrated by the fact that, although the area was affected by river capture at 18 kyr bp , the formed gorge is so narrow that spatially averaged erosion rates were not resolvably perturbed. However, because cosmogenic nuclides preserve an erosion memory of several thousand years, the only perturbation introduced was detected in the minor areas that have been subject to the last maximum glaciation. In unglaciated areas, an important relationship between lithology and erosion can by quantified: sandstone lithologies erode at 12–18 mm kyr^?1, granite lithologies at 35–47 mm kyr^?1 and limestone lithologies (as deduced from river load gauging) at 70–90 mm kyr^?1.     

Katol meteorite shower, Maharashtra: A preliminary study

A meteorite shower occurred in Katol (21° 15′ 30″ N; 78° 35′ 00″ E; at an elevation of 415 m above msl), Nagpur district of Maharashtra state, India on May 22, 2012 between 14:00 to 14:30 hrs (Indian Standard Time) with a presently observed strewn field of ～5.0 sq km area. The event was experienced by the hundreds of inhabitants with a loud noise and fire ball between Akola in the west to Nagpur in the east. The Geological Survey of India has so far collected 27 meteorite pieces with a total weight of 3500 gm. The locations, size, shape and surface features of the individual meteorite pieces have been recorded. Based on their physical properties, mineralogy, mineral chemical mapping and REE chemistry, the Katol meteorites have been classified as olivine-rich H5 type differentiated stony meteorite with reconstituted chondrules. The preliminary evidence suggests the presence of pre-solar grains in Katol meteorite.     

A study of chondrules in the Boxian meteorite from Anhui Province,China

The types of chondrules in the Boxian meteorite have been determined. Electron microprobe analysis of various textural types of chondrules in the meteorite has revealed the composition of glassy chondrules and of their glassy matrix. Also presented in this paper are the related explanations. In addition, the genesis, textural diversity and evolution of the chondrules as well as the olivine girdles observed in the chondrules are discussed.     

Paleo-ocean chemistry records in marine opal: Implications for fluxes of trace elements, cosmogenic nuclides (Be and Al), and biological productivity

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.