北美西部陆相白垩系-古近系界线孢粉学特征简介―兼评中国东部白垩系-古近系界线研究     

刘耕武  Dennis R.Braman  李伟同  Don Brinkman 《地层学杂志》2009,33(1)

已经报道的北美西部陆相白垩系-古近系界线剖面已达近百处,这些剖面分布在阿拉斯加南部向南经加拿大直到美国南部的新墨西哥州北部的广大北美西部内陆地区,其中很多属迄今所知全球很好的陆相白垩系-古近系界线剖面.这些剖面常有标志性的界线黏土,并伴有其他地球化学、生物地层学特征.因为这些剖面所在地当时都在湿润或半干旱地区内,有利于生物化石,特别是孢粉化石的保存,易于开展孢粉学研究.经过近四十年不懈努力,孢粉学已经成为北美精确确定陆相白垩系-古近系界线最重要的、也是迄今为止所知最为有效的古生物学工具.孢粉植物群在界线上下特征差别显著,容易区分.界线之下含有大量主要繁盛于白垩纪的被子植物花粉,而在临近界线时则突然消失或仅零星出现,界线附近则以一层孢子异常丰富层为古近系底部特征.进入古近纪之后,虽然被子植物花粉有所恢复,但是繁盛于白垩纪的成分却很少出现.北美和新西兰、日本白要系-古近系界线附近在沉积岩和孢粉学方面的相似性表明这一事件可能是全球性事件.简要回顾和讨论了我国与孢粉学相关的几个热点地区陆相白垩系-古近系界线的研究概况,我国东北及江苏北部和北美西部大部分地区白垩系-古近系界线附近的孢粉植物群及其沉积环境比较类似,在苏北到东北地区范围内首次发现陆相白垩系-古近系界线地层的可能性比其他地区大.  相似文献   

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   总被引：5，自引：4，他引：1  

侯贵廷  Henry HALLS  Don DAVIS  黄宝玲  杨默函  王传成 《岩石学报》2009,25(3):650-658

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。  相似文献   

Projected risks to groundwater‐dependent terrestrial vegetation caused by changing climate and groundwater abstraction in the Central Perth Basin,Western Australia          下载免费PDF全文

Olga Barron  Ray Froend  Geoff Hodgson  Riasat Ali  Warrick Dawes  Phil Davies  Don McFarlane 《水文研究》2014,28(22):5513-5529

The effect of potential climate change on groundwater‐dependent vegetation largely depends on the nature of the climate change (drying or wetting) and the level of current ecosystem dependence on groundwater resources. In south‐western Australia, climate projections suggest a high likelihood of a warmer and drier climate. The paper examines the potential environmental impacts by 2030 at the regional scale on groundwater‐dependent terrestrial vegetation (GDTV) adapted to various watertable depths, on the basis of the combined consideration of groundwater modelling results and the framework for GDTV risk assessment. The methodology was tested for the historical period from 1984 to 2007, allowing validation of the groundwater model results' applicability to such an assessment. Climate change effects on GDTV were evaluated using nine global climate models under three greenhouse gas emission scenarios by applying the climate projections to groundwater models. It was estimated that under dry climate scenarios, GDTV is likely to be under high and severe risk over more than 20% of its current habitat area. The risk is also likely to be higher under an increase in groundwater abstraction above current volumes. The significance of climate change risk varied across the region, depending on both the intensity of the change in water regime and the sensitivity of the GDTV to such change. Greater effects were projected for terrestrial vegetation dependent on deeper groundwater (6–10 m). Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

Quantifying household social resilience: a place-based approach in a rapidly transforming community     

Sarah Henly-Shepard  Cheryl Anderson  Kimberly Burnett  Linda J. Cox  John N. Kittinger  Maka‘ala Ka‘aumoana 《Natural Hazards》2015,75(1):343-363

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Argon, krypton, and xenon in the bulk solar wind as collected by the Genesis mission     

Nadia Vogel  Veronika S. Heber  Donald S. Burnett 《Geochimica et cosmochimica acta》2011,75(11):3057-3071

We present bulk solar wind isotopic and elemental ratios for Ar, Kr, and Xe averaged from up to 14 individual analyses on silicon targets exposed to the solar wind for ∼2.3 years during NASA’s Genesis mission. All averages are given with 1σ standard errors of the means and include the uncertainties of our absolute calibrations. The isotopic ratios ⁸⁶Kr/⁸⁴Kr and ¹²⁹Xe/¹³²Xe are 0.303 ± 0.001 and 1.06 ± 0.01, respectively. The elemental ratios ³⁶Ar/⁸⁴Kr and ⁸⁴Kr/¹³²Xe are 2390 ± 120 and 9.9 ± 0.3, respectively. Average fluxes of ⁸⁴Kr and ¹³²Xe in the bulk solar wind in atoms/(cm² s) are 0.166 ± 0.009 and 0.017 ± 0.001, respectively. The flux uncertainties also include a 2% uncertainty for the determination of the extracted areas. The bulk solar wind ³⁶Ar/³⁸Ar ratio of 5.50 ± 0.01 and the ³⁶Ar flux of 397 ± 11 atoms/(cm² s) determined from silicon targets agree well with the ³⁶Ar/³⁸Ar ratio and the ³⁶Ar flux determined earlier on a different type of target by Heber et al. (2009). A comparison of the solar wind noble gas/oxygen abundance ratios with those in the solar photosphere revealed a slight enrichment of Xe and, within uncertainties a roughly uniform depletion of Kr-He in the solar wind, possibly related to the first ionization potentials of the studied elements. Thus, the solar wind elemental abundances He-Kr display within uncertainties roughly photospheric compositions relative to each other. A comparison of the Genesis data with solar wind heavy noble gas data deduced from lunar regolith samples irradiated with solar wind at different times in the past reveals uniform ³⁶Ar/⁸⁴Kr ratios over the last 1-2 Ga but an increase of the ⁸⁴Kr/¹³²Xe ratio of about a factor of 2 during the same time span. The reason for this change in the solar wind composition remains unknown.  相似文献   

Using three-dimensional geological mapping methods to inform sustainable groundwater development in a volcanic landscape, Victoria, Australia   总被引：1，自引：1，他引：0  

Bruce Gill  Don Cherry  Michael Adelana  Xiang Cheng  Mark Reid 《Hydrogeology Journal》2011,19(7):1349-1365

This study investigated the use of three-dimensional (3D) geological methods to provide better groundwater resource estimates for the Spring Hill area in central Victoria, Australia. Geological data were gathered in 3D geological software, which was utilised to derive fundamental dimensional parameters of the groundwater system in the study area. Mining industry software and hydrogeological methods were combined to give volumetric determinations of the basalt aquifer that were used to improve estimates of the groundwater resource. The methods reduce uncertainty about the physical attributes of the aquifer systems and greatly improve conceptual understanding of their behaviour. A simple numerical water-balance model was developed to refine the estimates of aquifer volume and fluxes to approximate observed water-level behaviour in the area. This enabled a much better comparison of groundwater resource use to the natural inputs and outputs for the area. A key conclusion was that the main issues for sustainable development and use in the study area are more to do with the physical aspects of the aquifer system, rather than simply the volume of water pumped. Visualisations of the area’s hydrogeology also provide improved hydrogeological understanding and communication for groundwater users and administrators.  相似文献   

Coastal eutrophication, land use changes and Ceratium furca (Dinophyceae) blooms in Pago Pago Harbor, American Samoa 2007-2009     

Steve L. MORTON  Andrew SHULER  Jeff PATERNOSTER  Sharon FANOLUA  Don VARGO 《中国海洋湖沼学报》2011,(4)

The bloom forming dinoflagellate, Ceratium furca, has been linked with coastal eutrophication worldwide in tropical and subtropical locations. During the summer of 2007, an unusual 6-month long bloom of C. furca was observed in Pago Pago Harbor, Tutuila Island, American Samoa. Incidents of dinoflagellate blooms in this area have not been previously reported. The bloom was first reported in May and dissipated in November 2007. In February-March 2009, a similar C. furca bloom was observed. During both blooms,...  相似文献   

Coastal eutrophication, land use changes and Ceratium furca (Dinophyceae) blooms in Pago Pago Harbor, American Samoa 2007�C2009     

Steve L. Morton  Andrew Shuler  Jeff Paternoster  Sharon Fanolua  Don Vargo 《中国海洋湖沼学报》2011,29(4):790-794

The bloom forming dinoflagellate, Ceratium furca, has been linked with coastal eutrophication worldwide in tropical and subtropical locations. During the summer of 2007, an unusual 6-month long bloom of C. furca was observed in Pago Pago Harbor, Tutuila Island, American Samoa. Incidents of dinoflagellate blooms in this area have not been previously reported. The bloom was first reported in May and dissipated in November 2007. In February?CMarch 2009, a similar C. furca bloom was observed. During both blooms, no fish mortality events were reported. Maximum cell counts were observed on September 20, 2007 at 9 200 cell/mL. At this time, total nitrogen was measured at 1.2 mg/L while total phosphate was below detection limits. Changes in land use practices may have been the primary driver of these blooms. Intense fertilization of athletic fields coupled with ineffective management strategies is hypothesized to have a direct link to the increase in nutrients found in the Pago Pago Harbor and may have been the trigger for the initialization of these blooms. During 2008, the fields were not used due to an infestation of the fire ant, Solenopsis geminata. Once controlled, the fields were opened again in 2009 and fertilizers were applied in January, a month before the bloom was observed.  相似文献   

How will climate change spatially affect agriculture production in Ethiopia? Case studies of important cereal crops   总被引：2，自引：0，他引：2  

Paul Evangelista  Nicholas Young  Jonathan Burnett 《Climatic change》2013,119(3-4):855-873

Nearly all of Ethiopia’s agriculture is dependent on rainfall, particularly the amount and seasonal occurrence. Future climate change predictions agree that changes in rainfall, temperature, and seasonality will impact Ethiopia with dramatic consequences. When, where, and how these changes will transpire has not been adequately addressed. The objective of our study was to model how projected climate change scenarios will spatially and temporally impact cereal production, a dietary staple for millions of Ethiopians. We used Maxent software fit with crop data collected from household surveys and bioclimatic variables from the WorldClim database to develop spatially explicit models of crop production in Ethiopia. Our results were extrapolated to three climate change projections (i.e., Canadian Centre for Climate Modeling and Analysis, Hadley Centre Coupled Model v3, and Commonwealth Scientific and Industrial Research Organization), each having two emission scenarios. Model evaluations indicated that our results had strong predictability for all four cereal crops with area under the curve values of 0.79, 0.81, 0.79, and 0.83 for teff, maize, sorghum, and barley, respectively. As expected, bioclimatic variables related to rainfall were the greatest predictors for all four cereal crops. All models showed similar decreasing spatial trends in cereal production. In addition, there were geographic shifts in land suitability which need to be accounted for when assessing overall vulnerability to climate change. The ability to adapt to climate change will be critical for Ethiopia’s agricultural system and food security. Spatially explicit models will be vital for developing early warning systems, adaptive strategies, and policy to minimize the negative impacts of climate change on food production.  相似文献   

Cosmic rays and other nonsense in astronomical CCD imagers     

Don Groom 《Experimental Astronomy》2002,14(1):45-55

Cosmic-ray muons make recognizable straight tracks in the new-generation CCD's with thick sensitive regions. Wandering tracks (‘worms’), which we identify with multiply-scattered low-energy electrons, are readily recognized as different from the muon tracks. These appear to be mostly recoils from Compton-scattered gamma rays, although worms are also produced directly by beta emitters in dewar windows and field lenses. The gamma rays are mostly byproducts of ⁴⁰K decay and the U and Th decay chains. Trace amounts of these elements are nearly always present in concrete and other materials. The direct betas can be eliminated and the Compton recoils can be reduced significantly by the judicious choice of materials and shielding. The cosmic-ray muon rate is irreducible. Our conclusions are supported by tests at the Lawrence Berkeley National Laboratory low-level counting facilities in Berkeley and 180 m underground at Oroville, California. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献