Reliable radiocarbon dating of fossil pollen grains: It is truly possible     

《Quaternary Geochronology》2023

Radiocarbon dating of fossil pollen concentrates has the potential to reduce limitations for sample selection in chronological studies of sedimentary archives. The recent development of the technology for rapidly preparing highly purified fossil pollen concentrates using a cell sorter makes it realistic to turn this dream into reality. Before utilizing pollen as a material for dating with confidence, however, it is necessary to understand the factors that may affect the result of the measurements, and to establish criteria to assess the reliability of the radiocarbon ages produced. In this study, peat soils which are commercially available in large quantities, and are hence used as our laboratory standard, as well as the varved lacustrine sediments from Lake Suigetsu, which has one of the best terrestrial radiocarbon stratigraphies in the world, were used to assess the accuracy of radiocarbon ages of pollen concentrates and to establish an appropriate protocol for sample preparation. A pollen-rich fraction prepared by a recently proposed combined method of physio-chemical pre-treatment and cell sorter (Yamada et al. 2021) was submitted to a range of different posterior treatments and radiocarbon measurement. The results were also compared with SEM (Scanning Electron Microscoic) and Fourier Transform Infrared Spectroscopic observations. It was discovered that the sample prepared by the initial pre-treatment and cell sorter were not sufficiently pure and did not yield radiocarbon ages that were consistent with the terrestrial leaf fossils. Instead, the Acid-Base-Acid treatment with ultrafiltration following on from the cell sorter step proved to be highly effective in the removal of contaminants and improve the measured ages. The comparison with Suigetsu's terrestrial radiocarbon dataset also indicated that accuracy could be improved through closer assessment using the pollen taxa composition, carbon content (%C), and stable isotope ratios (δ¹³C) of the pollen concentrates. The age-depth models established by the radiocarbon dating of fossil pollen grains extracted from the Suigetsu sediments agree very well with that of plant macrofossils, and even improve the precision of the combined model. As long as handling was appropriate, the pollen concentrates prepared by the cell sorter provide reliable radiocarbon ages and the method can significantly contribute to Quaternary sciences in the future.  相似文献   

Optical properties of inhomogeneous media: T-matrix approach (Review)     

P. Bussemer 《Astronomische Nachrichten》1989,310(4):311-314

In der vorliegenden Arbeit wird eine Übersicht darüber geben, wie man die effektive dielektrische Funktion, welche die optischen Eigenschaften heterogener Medien charakterisiert, berechnet. Für Inhomogenitäten kleiner als die Lichtwellenlange kann das entsprechende quasielektrostatische Problem in eine Integralgleichung umgeformt werden, welche die Anwendung des von der Festkörpertheorie her bekannten T-Matrix-Formalismus zur Berechnung von gestattet. Es werden unterschiedliche Näherungen für die T-Matrix diskutiert, die zu unterschiedlichen Effektiv-Medium-Theorien wie die Näherung der mittleren T-Matrix (ATA) oder die Näherung des kohärenten Potentials (CPA) führen.  相似文献   

Organic models of interstellar grains     

K. Wada  T. Inagaki  S. Yabushita 《Celestial Mechanics and Dynamical Astronomy》1992,54(1-3):275-277

A number of experimental studies have been carried out to verify the claim that interstellar grains largely consist of organic material, including biological cells. Our spectroscopic studies on biological cells and organic extracts from carbonaceous compounds have failed to identify the well-known 2200 Å interstellar extinction peak with the organic material.  相似文献   

河北宣龙地区铁质包壳粒及其形成的微生物作用   总被引：1，自引：0，他引：1  

刘敏 《沉积学报》1998,16(2):24-29

通过对宣龙地区“鲕状矿石”的详细镜下切片观察,与叠层石结构、形态和成分的对比,以及稳定同位素和有机地球化学特征分析研究,提出“鲕状矿石”实际上均为微生物成因的铁质包壳粒,并按其形态分为核形石,微生物鲕石、微生物豆石三种类型。对铁质包壳粒的微生物矿化作用也作了初步探讨。  相似文献   

    

D. Y. Gezari  M. D. Thornley  F. Varosi 《Astrophysics and Space Science》1995,224(1-2):465

Images of mid-infrared (5 - 20µm) circumstellar dust sources have been obtained with a new 58 × 62 pixel infrared array camera system. A seven-color imaging study of the bright planetary nebula NGC 7027 challenges the assertion that polycyclic aromatic hydrocarbons (PAH) may extend further from the center of the nebula than the continuum emission from silicate dust grains. It appears that the overall distributions are nearly identical, ruling out differences in intensity between the PAH emission and the general silicate dust material. A rigorous comparison between the infrared image data and new visible CCD images of NGC 7027 is made.  相似文献   

苏南江阴-嘉定断裂带断层泥扫描电镜研究及其地震地质意义   总被引：2，自引：0，他引：2       下载免费PDF全文

周积元  段光贤 《地震地质》1989,11(4):55-62

本文在分析苏南江阴-嘉定北西向断裂带宏观构造特征的基础上,对断层泥中石英碎砾表面溶蚀结构进行了扫描电子显微镜研究,并与郯-庐断裂带山东段断层泥进行了电镜图象的对比分析,从而确定了江阴-嘉定断裂带的相对(最新)活动年代及其地震活动性;此外,就江阴-嘉定断裂带不同区段活动年代差异及其纵向迁移模式、断层泥石英碎砾表面结构电镜图象聚类的概率分布特征及其地震地质意义等有关问题展开了讨论  相似文献   

Great new insights from failed experiments,unanticipated results and embracing controversial observations     

《Chemie der Erde / Geochemistry》2016,76(1):1-12

Experimental data and observations, whether telescopic or analytical, are never wrong, though data derived from such sources can be misinterpreted or applied inappropriately to derive conclusions that are incorrect. Given that nature always behaves according to the laws of physics and chemistry, rather than according to currently popular models and theories, experimental results should always be considered correct even when the results are far from those that one might initially expect. We discuss a number of cases where the results of experiments, even one carried out as a simple calibration measure, produced wildly different results that generally required many years of effort or contemplation to understand. On the positive side, exploration of the circumstances that produced the “errant” results often led to new and interesting insights concerning processes that might occur in natural environments and that were well worth the effort involved.Specifically, we show how an experiment that “failed” due to a broken conductor led to experiments that made the first refractory oxide solids containing mass independently fractionated oxygen isotopes and to 1998 predictions of the oxygen isotopic composition of the sun that were confirmed by the analysis of Genesis samples in 2011. We describe a calibration experiment that unexpectedly produced single magnetic domain iron particles. We discuss how tracking down a persistent source of “contamination” in experiments intended to produce amorphous iron and magnesium silicate smokes led to a series of studies on the synthesis of carbonaceous grain coatings that turn out to be very efficient Fischer–Tropsch catalysts and have great potential for trapping the planetary noble gases found in meteorites. We describe how models predicting the instability of silicate grains in circumstellar environments spurred new measurements of the vapor pressure of SiO partially based on previous experiments showing unexpected but systematic non-equilibrium behavior instead of the anticipated equilibrium products resembling meteoritic minerals. We trace the process that led from observations of the presence of crystalline minerals detected in the comae of some comets to the 1999 prediction of large-scale circulation of materials from the hot, innermost regions of the solar nebula out to the cold dark nebular environments where comets form. This large-scale circulation was ultimately confirmed by analyses of highly refractory Stardust samples collected from the Kuiper Belt Comet Wild 2. Finally we discuss a modern and still unresolved conflict between the assumptions built into three well known processes: the CO Self Shielding Model for mass independent isotopic fractionation of oxygen in solar system solids, rapid and thorough mixing within the solar nebula, and the efficient conversion of CO into organic coatings and volatiles on the surfaces of nebular grains via Fischer–Tropsch-type processes.  相似文献   

云南西北部丽江—剑川地区古近纪宝相寺组石英砂颗粒表面特征     

崔晓庄  江新胜  伍皓  熊国庆 《中国区域地质》2011,(8):1238-1244

石英砂具有丰富的颗粒表面特征,是判别沉积环境的重要标志。利用扫描电镜对云南丽江—剑川地区宝相寺组（E2b）的石英砂颗粒表面特征进行了系统分析：下部样品具水成特征,中部样品具风成特征,上部样品则具经水流改造后的风成特征。结合野外观察结果,从宝相寺组石英砂颗粒表面特征的变化规律可以看出,下部为近源洪积环境、中部为风成沙丘环境、上部为湖泊环境。其中中部样品的石英砂磨圆、分选极好,普遍具有标准的碟形、新月形撞击坑和毛玻璃化表面,是典型的沙漠砂沉积。  相似文献   

云南西北部丽江—剑川地区古近纪宝相寺组 石英砂颗粒表面特征   总被引：1，自引：0，他引：1  

崔晓庄  江新胜  伍皓  熊国庆 《地质通报》2011,30(8):1238-1244

石英砂具有丰富的颗粒表面特征,是判别沉积环境的重要标志。利用扫描电镜对云南丽江—剑川地区宝相寺组(E2b)的石英砂颗粒表面特征进行了系统分析:下部样品具水成特征,中部样品具风成特征,上部样品则具经水流改造后的风成特征。结合野外观察结果,从宝相寺组石英砂颗粒表面特征的变化规律可以看出,下部为近源洪积环境、中部为风成沙丘环境、上部为湖泊环境。其中中部样品的石英砂磨圆、分选极好,普遍具有标准的碟形、新月形撞击坑和毛玻璃化表面,是典型的沙漠砂沉积。  相似文献   

加速溶剂萃取-气相色谱法测定谷物中有机氯农药和多氯联苯   总被引：1，自引：0，他引：1  

杨佳佳  佟玲  吴淑琪  阎妮 《岩矿测试》2013,32(3):487-494

针对大米、小麦、玉米和黄豆等谷物样品中有机氯农药(OCPs)和多氯联苯(PCBs)检测的前处理过程较为复杂,消耗溶剂多,易导致部分挥发性化合物损失而影响分析的准确度,本文优化了加速溶剂萃取(ASE)提取大米、小麦、玉米和黄豆等谷物样品中OCPs和PCBs的条件,比较了凝胶渗透色谱(GPC)和固相萃取柱(SPE)两种净化方式净化样品的效果,采用气相色谱-电子捕获检测器实现了样品中17种OCPs和8种PCBs单体的系统分析.结果表明,选择二氯甲烷-丙酮混合溶剂(体积比1∶1),采用ASE萃取,同时加入弗罗里硅土在线净化,可满足样品提取需求;除了黄豆和黑豆等豆制品样品需采用GPC结合SPE的净化方法外,大米、小麦、玉米等大部分谷物样品采用SPE净化即可满足测定需求.采用弗罗里硅土SPE净化,仅用9 mL正己烷-乙酸乙酯淋洗液(体积比1∶1)即可将所有目标物回收,克服了有机试剂用量大、同时使用多种试剂及试剂毒性大的问题.添加低、高两个浓度水平0.69 μg/kg和5.52μg/kg,OCPs和PCBs单体的平均回收率为71.0％ ～ 112.0％,相对标准偏差为3.6％～16.7％(n=7);方法检出限为0.07 ～0.30μg/kg,低于国家标准方法的检出限.该方法净化效率高,操作简单,分析成本较低,适用于大批量谷物样品中多种OCPs和PCBs的快速分析.  相似文献