Cross dating (Th/U-C) of calcite covering prehistoric paintings in Borneo     

Valérie Plagnes  Christiane CausseMichel Fontugne  Hélène ValladasJean-Michel Chazine  Luc-Henri Fage 《Quaternary Research》2003,60(2):172-179

We present the first application of cross-dating (Th/U measured by thermo-ionization mass spectrometry (TIMS) and ¹⁴C measured by accelerator mass spectrometry (AMS)) of calcite covering prehistoric paintings. Th/U age estimates of cave drapery range from 9800 to 27,300 yr B.P. while conventional ¹⁴C age is estimated between 9900 and 7610 yr B.P. depending on the dead carbon correction. The age discrepancy is attributed to a disturbance of Th/U and/or ¹⁴C geochemical systems, showing the limits of the geochronological approach applied to this kind of material. For the Th/U system, the poor consistency of U data (U content, ²³⁴U/²³⁸U activity ratios) and apparent ages argue for open system conditions. For ¹⁴C system, variation of the dead carbon fraction (dcf) and a possible mixing of successive generations of calcite could account for age discrepancy. Nevertheless, one sample shows concordant ages for the two methods. Compatible ages through corrections for open system conditions are assumed for other samples. Then, the cross-dating suggests 9900 yr as the minimum age of the piece of drapery; the underlying painting must be older. This study of rock art demonstrates the presence of a Pleistocene population before 9900 yr in the southeast of Borneo, whereas previously the only population in evidence in this area was of Austronesian type from ∼5000 to 6000 yrs ago.  相似文献   

有关翡翠A、B、C货鉴定问题的讨论   总被引：1，自引：0，他引：1  

施加辛 《上海国土资源》2002,(2):61-63

翡翠A、B、C货的鉴定需要综合性的考虑，单一方法易出差错，翡翠鉴定首要任务是确定矿物组成，从而确定是否翡翠及翡翠的类型；其次确定是否有人工充填物及人工加色，从而区别A、B、C货。  相似文献   

天然、优化、处理翡翠玉件常规仪器鉴别(一)     

苏文宁 《云南地质》2003,22(3):229-249

多年系统研究和大量样品检测证明：正确鉴别天然(A)、优化(B)翡翠玉件，比重、荧光是指示，结构是基础，识别充填物是关键，拉曼、红外作验证，综合分析下结论。而在常规仪器检测过程中，特别抓住结构(基础)、充填物(关键)，即：用岩矿显微镜细致观察翡翠玉件结构，辅以针探和微区组分鉴别法区分各种充填物，结合比重、荧光检测结果，可以准确、快捷、经济地鉴别翡翠玉件A货、B货，而不需使用红外、拉曼。借助色源类型鉴别可正确鉴别处理翡翠玉件(C货)。  相似文献   

Crust-Mantle Interaction in Dabie Orogenic Belt, Central China： Geochemical Evidence from Late Cretaceous Basalts     

匡少平  张本仁 《中国地球化学学报》2003,22(3):231-243

It has been suggested that eclogites in the Dabie orogenic belt are exhumation prod-ucts, which had subducted into the deep-seated mantle and undergone ultra-high pressure meta-morphism during the Triassic. But no direct evidence supports this process except the calculated p-T conditions from mineral thermobarometem. The Late Cretaceous basalts studied in the pres-ent paper, however, have provided some geochemical evidence for crust-mantle interaction in the area. These basalts are distributed in Mesozoic faulted basins in central and southern Dabieorogenic belt. Since little obvious contamination from continental crust and differentiation-crys-tallization were observed, it is suggested, based on a study of trace elements, that the basaltsare alkaline and resultant from batch partial melting of the regional mantle rocks, and share thesame or similar geochemical features with respect to their magma source. In the spider diagram normalized by the primitive mantle, trace element geochemistry data show that their mantle sources are enriched in certain elements concentrated in the continental crust, such as Pb, K,Rb and Ba, and slightly depleted in some HFSE such as Hf, P and Nb. Pb-Sr-Nd isotopic com-positions further suggest the mantle is the mixture of depleted mantle (DM) and enriched one(EMI EMII). This interaction can .explain the trace element characteristics of basaltic mag-mas, i.e.,the enrichment of Pb and the depletion of Hf, P and Nb in basalts can be interpre-ted by the blending of the eclogites in DOB (enriched in Pb and depleted in Hf, P and Nd)with the East China depleted mantle (As compared to the primitive mantle, it is neither en-riched in Pb nor depleted in Hf, P and Nb). It is also indicated that the eclogites in the Dahieorogenic belt were surely derived from the exhumation materials, which had delaminated into thedeep-seated mantle. Moreover, the process subsequently resulted in compositional variation of the mantle (especially in trace elements and isotopes) , as revealed by the late mantle-derivedbasalts in the Dabie orogenic belt.  相似文献   

地震活动的三维动画演示系统     

肖立萍 《地震地磁观测与研究》2004,(Z1)

详细介绍了辽宁数字遥测地震台网利用C语言、3DSMAX软件开发的地震活动的三维动画演示系统。  相似文献   

丘陵红壤区决明属牧草品系的适应性筛选   总被引：12，自引：0，他引：12  

黄毅斌  应朝阳  黄金煌  庄绍东  翁伯奇 《山地学报》2004,22(6):742-749

针对占全国总面积22％的南方红壤区有机质含量低、酸性强、水土流失严重等生态问题，及福建省当家豆科草种少等问题。引进40个豆科决明属(Chamaecrista spp．)牧草，在福建省不同气候带的红壤山地进行多年适应性筛选和验证试验。通过聚类分析和建立综合指标评价体系，筛选出适宜荒山荒坡地种植的直立型品种C．nictitans ATF2217、ATF2219，适宜于果园套种的匍匐型品种C．rotundifolia CPI34721、CPI92985和适宜保持水土改良土壤的C．rotundifolia CPI86134、CPI86178等6个品系进行推广利用。其中Chamaecrista nictitans cv．ATF2217已通过全国牧草品种审定，定名为“闽引羽叶决明”。  相似文献   

Charles D. Walcott in England and Wales (1888): A crucial visit in the resolution of Taconic-Cambrian-Ordovician questions     

Michael G. Bassett 《Proceedings of the Geologists' Association. Geologists' Association》2004,115(1):63-75

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Late Holocene climatic changes in Tierra del Fuego based on multiproxy analyses of peat deposits     

Dmitri Mauquoy  Maarten Blaauw  Ana Borromei  Frank M. Chambers 《Quaternary Research》2004,61(2):148-158

A ca. 1400-yr record from a raised bog in Isla Grande, Tierra del Fuego, Argentina, registers climate fluctuations, including a Medieval Warm Period, although evidence for the ‘Little Ice Age’ is less clear. Changes in temperature and/or precipitation were inferred from plant macrofossils, pollen, fungal spores, testate amebae, and peat humification. The chronology was established using a ¹⁴C wiggle-matching technique that provides improved age control for at least part of the record compared to other sites. These new data are presented and compared with other lines of evidence from the Southern and Northern Hemispheres. A period of low local water tables occurred in the bog between A.D. 960-1020, which may correspond to the Medieval Warm Period date range of A.D. 950-1045 generated from Northern Hemisphere tree-ring data. A period of cooler and/or wetter conditions was detected between ca. A.D. 1030 and 1100 and a later period of cooler/wetter conditions estimated at ca. cal A.D. 1800-1930, which may correspond to a cooling episode inferred from Law Dome, Antarctica.  相似文献   

Phytolith evidence for C4-dominated grassland since the early Holocene at Long Pocket, northeast Queensland, Australia   总被引：1，自引：0，他引：1  

Vanessa C. Thorn 《Quaternary Research》2004,61(2):168-180

Preliminary phytolith analysis of ephemeral lake fill sediment at Long Pocket, near Toomba, northeast Queensland, Australia, indicates that a C4-dominated grassland with a minor woody component has been present in the region since ca. 8000 cal yr B.P. Based on the modern distribution of C4 and C3 native grasses in Australia, this suggests that mean summer temperatures of at least 14°C (ca. 10°C cooler than present) were maintained since the early Holocene. This interpretation is comparable with previous studies, which together imply that the establishment of C4-dominated grasses in central and northeast Australia occurred between the last glacial maximum (most likely after ca. 16,000 ¹⁴C yr B.P.) and ca. 7200 ¹⁴C yr B.P. (ca. 8000 cal yr B.P.). Taxonomic composition of the grassland appears relatively consistent since the early Holocene at Long Pocket and includes phytoliths comparable with those from modern Arundinoideae, Panicoideae, and Chloridoideae. Rare non-grass phytoliths are also present. A gradual decrease in abundance of saddle phytolith forms (attributed to Chloridoideae grasses) from the base of the record at ca. 6500-7000 cal yr B.P. suggests decreasing aridity throughout the Holocene. This trend could reflect a locally drawn out effect of the end of the postglacial arid period due to the well-drained basalt flow catchment maintaining a local arid habitat for the Chloridoideae grasses.  相似文献   

Chemical, biological and hydrological controls on the C content of cold seep carbonate crusts: numerical modeling and implications for convection at cold seeps     

G. Aloisi  K. Wallmann  J.-F. Saliège 《Chemical Geology》2004,213(4):359-383

Understanding the hydrology of cold seep environments is crucial to perform accurate estimates of fluid and chemical fluxes at sedimentary wedges. Shallow convection processes may affect fluid flux estimates and could favor the destabilization of gas hydrate accumulations, increasing the sediment-ocean methane flux. Evidence for the occurrence of convection at cold seeps, however, is still limited. We use the concentration of ¹⁴C (D¹⁴C) in carbonate crusts formed at cold seeps of the eastern Mediterranean Sea as a tracer for convective recirculation of seawater-derived fluids. A numerical model is applied to investigate the controls on ¹⁴C incorporation in cold seep carbonates. Our simulations show that increased amounts of CH₄ in the expelled fluids result in elevated crust D¹⁴C, while high Ca²⁺ and HCO₃⁻ concentrations produce the opposite effect. Convection is the only transport process that can significantly increase crust D¹⁴C. Advection, bioirrigation, eddy diffusion and bioturbation instead, have little effect on, or produce a decrease of, crust D¹⁴C. In addition, the presence of old or modern carbon (MC) in host sediments prior to cementation and the ¹⁴C-decay associated to the time needed to form the crust contribute in defining the D¹⁴C of carbonate crusts. We then use the model to reproduce the ¹⁴C content of the eastern Mediterranean Sea crusts to constrain the chemical and hydrological conditions that led to their formation. Some crusts contain relatively low amounts of ¹⁴C (−945.0<D¹⁴C ‰<−930.2) which, assuming no ageing after crust formation, can be reproduced without considering convection. Other crusts from two sites (the Amsterdam and Napoli mud volcanoes), instead, have a very high ¹⁴C-content (−899.0<D¹⁴C ‰<−838.4) which can only be reproduced by the model if convection mixes deep fluids with seawater. Order-of-magnitude calculations using the Rayleigh criterion for convection suggest that the slow seepage (about 10 cm year⁻¹) of low salinity (20‰) fluids at the Amsterdam sites could trigger haline convection there. On the Napoli mud volcano, where high-density brines are expelled, density-driven convection cannot take place and other processes, possibly involving the rapid movement of free gas in the sediment, could be important.  相似文献