浓酸熟化——一种有效的硬岩铀矿浸出方法

本文通过对某中生代火山岩型铀矿床矿石进行铀浸出试验研究,认为浓酸熟化浸出法是处理硬岩铀矿石、提高其铀浸出率的一种有效方法。本文所研究的铀矿石,在浸出条件相同的情况下,浓酸熟化法的铀浸出率比常规酸浸法高20％左右。     

华北基性岩墙群的古地磁极及其哥伦比亚超大陆重建意义

从华北克拉通的中西部和东部发育的基性岩墙群获得三个精确定年的实际古地磁极位置(VGPs)。华北克拉通中西部恒山GU岩墙的斜锆石U-Pb年龄为1769±3Ma,该岩墙的古地磁给出古地磁极位置在北纬36°,东经247° (dp=2, dm=4); 华北克拉通东部DY岩墙的斜锆石U-Pb年龄为1620.8±6.9Ma, 获得的古地磁极位置为北纬6.9°东经81.9°(dp=4.31, dm=6.09); 东部另一条岩墙LW4的SHRIMP U-Pb 年龄为1157±18Ma, 获得的古地磁极位置为北纬27.1°东经162°(dp=15.8, dm=18.7)。通过将这三个从基性岩墙获得的华北克拉通古地磁极位置与加拿大地盾的中元古代视极移曲线对比,在中元古代早期（1800~1600Ma）,华北克拉通与加拿大地盾一起同属哥伦比亚超大陆,而在中元古代晚期（1600~1200Ma）,华北克拉通与加拿大地盾分离,响应哥伦比亚超大陆的最终裂解事件。     

Forestal Arauco experimental research catchments; daily rainfall-runoff for 10 catchments with different forest types in Central-Southern Chile

Forestal Arauco (FA), a global manufacturer of forest products, manages more than 1 million ha of forest plantations and oversees the conservation of more than half a million hectares of native forest and vegetation in Brazil, Argentina and Chile. In 2008, FA responded to local concerns about the effect of plantations on water resources and commenced streamflow monitoring in catchments in the coastal range of central-southern Chile between 35° and 39° of latitude south. This data note presents an overview of daily streamflow and rainfall records for 10 small catchments (18–112 ha) from 2008 to 2018. The catchments are covered by three different forest types, namely native forest (2), pine plantations of different ages (6) and eucalypt plantations (2). All of these catchments share similar metamorphic geology. A 90° V notch weir was built at each catchment outlet and data collected at 5 min interval using a pressure transducer that was calibrated monthly. The dataset is part of a research programme aiming to improve our understanding about the role of forest plantations on water balance at a stand and catchment level. It also includes the rainfall data from these catchments estimated using a combination of local rain gauges and data from the longer term records of the Chilean Directorate of Water. This dataset can be used in hydrological modelling and in a wide range of research questions and water management issues regarding forest plantations in a Mediterranean climate.     

Photosynthetic responses of selected Antarctic plants to solar radiation in the southern maritime Antarctic

The effects of UV-B exclusion and enhancement of solar radiation on photosynthesis of the two phanerogams which occur in the maritime Antarctic, Deschampsia antarctica and Colobanthus quitensis , and the moss Sanionia uncinats were investigated. Data on air temperature and solar radiation illustrate a drastic seasonal variation. Daily O₃ column mean values and UV-B measured at ground level document the occurrence of the O₃"hole" in the spring of 1997, with a concomitant increase in UV-B. The grass, D. antarctica , exhibited a broad temperature optimum for photosynthesis between 10–25°C while photosynthesis did not saturate even at high irradiance. The high water use efficiencies measured in the grass may be one of the features explaining the presence of this species in the maritime Antarctic. The net photosynthesis response to intercellular CO₂ (A/c_i) for D. antarctica was typical of a C₃ plant. Exposure to a biologically effective UV-B irradiance of 0.74 W M^-2 did not result in any significant change in either the maximum rate of photosynthesis at saturating CO₂ and light, or in the initial carboxylation efficiency of Rubisco. (V_c,max). Furthermore while ambient (or enhanced) solar UV-B did not affect photochemical yield, measured in the field, of C. quitensis and D. antarctica , UV-B enhancement did affect negatively photochemical yield in S. uncinata . In D. antarctica plants, exposure to UV-B at low irradiances elicited increased flavonoid synthesis. The observed effects of UV-B enhancement on the moss (decreased photochemical yield) and the grass (increase in flavonoids) require further, separate investigation.     

Experimental characterization,design and modelling of the RBRL seismic‐isolation system for lightweight structures

The Rolling‐Ball Rubber‐Layer (RBRL) system was developed to enable seismic isolation of lightweight structures, such as special equipment or works of art, and is very versatile, a great range of equivalent natural frequencies and coefficients of damping being achievable through choice of the system parameters. The necessity to have a simple and effective design procedure has led to a new parametric experimentation at Tun Abdul Razak Research Centre (TARRC) on the rolling behaviour of the RBRL system and load–deflection behaviour of the recentering springs. The experimental results, together with theories for the rolling resistance of a loaded steel ball on a thin rubber layer and the lateral load–deflection behaviour of cylindrical rubber springs, are used to develop a general design method for the RBRL system, which allows the system to be tailored to the specific application. Sinusoidal test results are presented for the small‐deflection behaviour of the system, influenced by the presence of a viscoelastic depression on the rubber tracks beneath each ball, and an amplitude‐dependent time‐domain model is proposed, based on these results and on the steady‐state behaviour of the system. The model is validated through comparison with previously performed shaking‐table tests. Attention is here restricted to uniaxial behaviour. Copyright © 2016 John Wiley & Sons, Ltd.     

Evaluation of the Global Mean Sea Level Budget between 1993 and 2014

Evaluating global mean sea level (GMSL) in terms of its components—mass and steric—is useful for both quantifying the accuracy of the measurements and understanding the processes that contribute to GMSL rise. In this paper, we review the GMSL budget over two periods—1993 to 2014 and 2005 to 2014—using multiple data sets of both total GMSL and the components (mass and steric). In addition to comparing linear trends, we also compare the level of agreement of the time series. For the longer period (1993–2014), we find closure in terms of the long-term trend but not for year-to-year variations, consistent with other studies. This is due to the lack of sufficient estimates of the amount of natural water mass cycling between the oceans and hydrosphere. For the more recent period (2005–2014), we find closure in both the long-term trend and for month-to-month variations. This is also consistent with previous studies.     

Gravel sources of knappable alibates silicified dolomite

Alibates silicified dolomite is one of the principal knappable lithic materials indigenous to the Southern High Plains. Prehistorically, this material was extensively quarried along the Canadian River in Potter County, Texas. Some of these quarries are preserved in what is now the Alibates National Monument. Archaeologists working in Oklahoma traditionally interpret artifacts of Alibates silicified dolomite as evidence for long distance trade. However, a survey of three transects across the Canadian's valley in western Oklahoma reveals the persistent, but minor, presence of Alibates clasts in gravel deposits. Thirty-nine gravel exposures yielded 1365 clasts of the dolomite. The abundance, size, shape, and knappability of this material is comparable to most flakes and implements found on western Oklahoma archaeological sites, especially those of prehistoric and protohistoric Plains Villagers. © 1993 John Wiley & Sons, Inc.     

Early to Middle Devonian granitic and volcanic rocks from the central Gulf of Maine

Cashes Ledge igneous suite in the central Gulf of Maine is represented by 10 granitic and two felsic tuff samples collected from bedrock outcrops using the submersible Alvin in 1971–1972 and archived at the Woods Hole Oceanographic Institute. Laser ablation ICP-MS analyses of zircon grains yielded crystallization ages of 414.9 ± 1.1 Ma and 399.7 ± 1.5 Ma for two alkali feldspar granite samples, 407.0 ± 1.9 Ma for a syenogranite sample, and 384.4 ± 2.3 Ma and 383.9 ± 1.6 Ma for two felsic tuff samples. The samples contain iron-rich mafic minerals, including aegirine-augite, grunerite/ferroedenite, and annite. Most of the samples are alkaline to slightly peralkaline, with high concentrations of SiO₂, Y, Zr, Nb, and REE, strong negative Eu anomalies, and positive epsilon Nd values (1.8 to 3.7). The suite resembles part of a belt of similar Silurian–Devonian rocks with ages between 426 and 370 Ma now recognized in the central part of Avalonia in southeastern New England. They formed in a long-lived, likely extensional regime linked to subduction and subsequent complex transcurrent motions among Ganderia, Avalonia, and Meguma, culminating in the closure of the Rheic Ocean.     

Transport and exchange of U-series nuclides between suspended material,dissolved load and colloids in rivers draining basaltic terrains

This study presents uranium and thorium concentrations and activity ratios for all riverine phases (bedload, suspended load, dissolved load and colloids) from basaltic terrains in Iceland and the Azores. Small basaltic islands, such as these, are thought to account for ~ 25% of CO₂ consumed by global silicate weathering, and for ~ 45% of the flux of suspended material to the oceans. These data indicate that [U] and [Th] in the dissolved and colloidal fractions are strongly controlled by pH, and to a much lesser extent by levels of dissolved organic carbon (which are low in these environments). At high pH, basalt glass dissolution is enhanced, and secondary mineral formation (e.g. Fe-oxyhydroxides and allophane) is suppressed, resulting in high dissolved [U], and low colloidal [U] and [Th], indicating a direct chemical weathering control on elemental abundances. When the dissolved (²³⁴U/²³⁸U) activity ratio is >~1.3 (i.e. when physical weathering, groundwater contribution or soil formation are high), there is little isotope exchange between dissolved and colloidal fractions. At lower activity ratios, the dissolved load and colloids have indistinguishable activity ratios, suggesting that when chemical weathering rates are high, secondary clay formation is also high, and colloids rapidly adsorb dissolved U. Many of the suspended sediment samples have (²³⁴U/²³⁸U) activity ratios of > 1, which suggests that uptake of U onto the suspended load is important. Identical (²³⁰Th/²³²Th) in suspended, dissolved and colloidal samples suggests that Th, like U, is exchanged or sorbed rapidly between all riverine phases. This particle-reactivity, combined with poorly constrained contributions from groundwater and hydrothermal water, and short-term variations in input to soils (volcanic and glacial), suggests that U-series nuclides in riverine material from such basaltic terrains are unlikely to reflect steady state erosion processes.     

Fluctuations in late Neoproterozoic atmospheric oxidation — Cr isotope chemostratigraphy and iron speciation of the late Ediacaran lower Arroyo del Soldado Group (Uruguay)

Oxygenation of the Earth's atmosphere occurred in two major steps, near the beginning and near the end of the Proterozoic Eon (2500 to 542 Ma ago), but the details of this history are unclear. Chromium isotopes in iron-rich chemical sediments offer a potential to highlight fine-scale fluctuations in the oxygenation of the oceans and atmosphere and to add a further dimension in the use of redox-sensitive tracers to solve the question regarding fluctuations of atmospheric oxygen levels and their consequences for Earth's climate. We observe strong positive fractionations in Cr isotopes (δ⁵³Cr up to + 5.0‰) in iron-rich cherts and banded iron formation horizons within the Arroyo del Soldado Group (Ediacaran; Uruguay) that can be explained by rapid, effective oxidation of Fe(II)-rich surface waters. These fluctuations are correlated with variations in ratios of highly reactive iron (Fe_HR) to total iron (Fe_tot) which indicate a predominance of anoxic water columns (Fe_HR/Fe_tot > 0.38) during the onset of oxidation pulses. We favor the scenario by which isotopically heavy Cr(VI) entered the basin after pulses of oxidative weathering on land and in which Fe(II) accumulated in the water column. Neodymium isotopes reveal that these oxygenation pulses were followed by increased influxes to the basin of continental crust-derived detrital components of Paleoproterozoic (Nd T_DM model ages = 2.1–2.2 Ga) provenance typical of the Rio de la Plata Craton. The association of positive δ⁵³Cr–ferruginous (Fe_HR/Fe_tot > 0.38) stratigraphic intervals with low-diversity acritarch assemblages dominated by Bavlinella faveolata strongly support models postulating a stratified, eutrophic Neoproterozoic ocean. Thus, even within a few million years of the Precambrian–Cambrian boundary, paleoceanographic conditions resembled more those of Paleoproterozoic oceans than Phanerozoic and present oceans. This highlights the sheer magnitude of ecological changes at the Precambrian–Cambrian transition, changes which ultimately led to the demise of the Precambrian world and the birth of the metazoan-dominated Phanerozoic.