南京直立人的U/Th和U/Pa年代   总被引：2，自引：0，他引：2  

程海  艾思本  汪永进 《高校地质学报》2003,9(4):667-677

中国直立人化石的准确定年对于研究人类演化有着极为重要的意义。1993～1994年在南京汤山葫芦洞发现的两个直立人头盖骨化石和一枚牙化石被称为“南京直立人”。其中1号头盖骨化石之上的方解石钙板的U/Th年龄为53.3_(-1.2)~(+1.5)万年;但考虑到定年的准确性,则为53.3_(-3.0)~(+3.5)万年。其~(231)Pa/~(235)U活度比值为0.998±0.006。这表明“南京直立人”的年代应该大于50万年。与”南京直立人”伴生的动物牙化石U/Th年代为18.5～29.0万年;U/Pa年代为13.7～17.2万年。此外,对于同一颗牙化石,牙釉的年龄小于牙本质的年龄。同一样品的U/Pa年龄也显著小于其U/Th年龄。因此,牙化石的U摄取过程并不符合U早期摄取模式。多数牙化石分析点在~(234)U/~(238)U-~(230)Th/~(238)U图上落在位于U早期摄取和线性摄取模式曲线之间,指示牙化石的U摄取过程很可能介于上述两种模式之间。如果这一假设成立,那么牙化石的U/Th和U/Pa线性摄取模式年龄则为其年代的上限。因为不受U摄取过程~(234)U/~(238)U变化的影响,U/Pa线性摄取模式年龄比U/Th较为可靠。最小的U/Pa线性摄取模式年龄为1Ma,这是”南京直立人”上限年龄的估计。从定年结果看,”南京直立人”可能生活在海洋同位素(MIS)16阶段,但这不是最终结论。  相似文献   

A rooftop tuned mass damper frame     

Jerod G. Johnson  Lawrence D. Reaveley  Chris Pantelides 《地震工程与结构动力学》2003,32(6):965-984

This article documents the analytical study and feasibility of placing a tuned mass damper in the form of a limber rooftop moment frame atop relatively stiff structures to reduce seismic acceleration response. Six existing structures were analytically studied using a suite of time history and response spectra records. The analyses indicate that adding mass in conjunction with a limber frame results in an increase in the fundamental period of each structure. The fundamental period increase generally results in a decrease in seismic acceleration response for the same time history and response spectra records. Owing to the limber nature of the rooftop frames, non‐linear analysis methods were required to evaluate the stability of the rooftop tuned mass damper frame. The results indicate the addition of a rooftop tuned mass damper frame reduces the seismic acceleration response for most cases although acceleration response can increase if the rooftop frame is not tuned to accommodate the specific structure's dynamic behaviour and localized soil conditions. Appropriate design of the rooftop tuned mass damper frame can result in decreased seismic acceleration response. This translates to safer structures if used as a retrofit measure or a more economical design if used for new construction. Copyright © 2003 John Wiley & Sons, Ltd.  相似文献   

Phytolith analysis from the archaeological site of Kush, Ras al-Khaimah, United Arab Emirates   总被引：1，自引：0，他引：1  

Sachiko Ishida  Adrian G. Parker  Derek Kennet  Martin J. Hodson   《Quaternary Research》2003,59(3):310-321

Despite the wealth of archaeological sites and excellent conditions for preservation, few phytolith investigations have been undertaken from the Arabian Gulf region. The results from the Sasanian and Islamic archaeological tell of Kush, Ras al-Khaimah, United Arab Emirates, are presented. Kush is situated just inside the Gulf on an important trade route. The occupation sequence dates from the 4^th century A.D. until the 13^th century A.D., recording the development of the site in the Sasanian period, followed by the arrival of Islam in the 7^th century A.D. and the final abandonment of the site in the late 13^th century when the nearby site of al-Mataf (Julfar) began to develop closer to the present day coastline. All the samples analyzed contained abundant phytoliths (short cells, elongated cells, and groups of elongated cells) of various types. They included date palm (Phoenix dactylifera), papillae (possibly from barley (Hordeum)), and hair cells possibly from species of canary grass (Phalaris spp.). Some researchers have suggested that groups of elongated cells may indicate the presence of irrigation in semiarid environments. The present results for this class of phytoliths appeared to imply that intensive irrigation was unlikely to have taken place around Kush.  相似文献   

Strontium in coral aragonite: 2. Sr coordination and the long-term stability of coral environmental records     

Adrian A. Finch  Nicola Allison 《Geochimica et cosmochimica acta》2003,67(23):4519-4527

We have used X-ray Diffraction (XRD) and Sr K-edge Extended X-ray Absorption Fine Structure (EXAFS) to determine the structural state of Sr in a suite of coral aragonite samples. Our samples encompassed a selection of coral species (Porites lobata, Porites lutea, Pocillopora eydouxi, Montastrea annularis, Pavona gigantea and Pavona clavus) including some commonly used for palaeoenvironmental reconstruction. Aragonite was the only carbonate observed by XRD. We refined the isolated EXAFS against structural models for Sr in aragonite and two-phase strontianite/aragonite mixes. Our data are indistinguishable from Sr ideally substituted in aragonite and strontianite was present below detection levels (estimated at <5% of Sr present). Comparisons of recent and ancient coral aragonite show no sign of exsolution, either by spinodal decomposition or by the direct nucleation of strontianite domains. Published diffusion rates of Sr in ionic solids support the view that exsolution would occur prohibitively slowly. Coral aragonites are metastable materials with slow diffusion kinetics that have the potential to encode environments over timescales of millions of years.  相似文献   

Special issue on quantitative estimates of the geology of large regions and their application to mineralresource assessment     

Richard B. McCammon  W. David Menzie  Lawrence J. Drew  Janet S. Sachs 《Natural Resources Research》1997,6(3):155-155

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Matchboxes and dice     

Lawrence J. Drew 《Natural Resources Research》1997,6(3):151-153

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Fingerprinting the Origin of Fluvial Suspended Sediment in Larger River Basins: Combining Assessment of Spatial Provenance and Source Type   总被引：3，自引：0，他引：3  

Adrian L. Collins  Desmond E. Walling  & Graham J.L. Leeks 《Geografiska Annaler: Series A, Physical Geography》1997,79(4):239-254

Investigation of the potential for using sediment fingerprinting to integrate both spatial provenance and source type information for larger drainage basins appears to be desirable. This contribution presents the results of adopting a composite fingerprinting procedure incorporating statistically verified multicomponent signatures and a multivariate mixing model to provide a preliminary integration of spatial provenance and source type information for the upper and middle reaches of the drainage basins of the Rivers Exe (601 km²) and Severn (4325 km²), UK. A nested approach is employed, whereby spatial provenance is addressed in terms of the distinct sub-basin zones constituting each study area as an entirety, and source type is then characterised within each of these distinct spatial zones in terms of surface (woodland, pasture, cultivated) and subsurface (channel bank) materials. The results demonstrate that the fingerprinting approach possesses considerable potential for integrating spatial provenance and source type information, and hence for improving the resolution of existing sediment source information for larger drainage basins.  相似文献   

A calderas field at the Marifil Formation, new volcanogenic interpretation, Norpatagonian Massif, Argentina     

Eugenio Aragn  Adrian Mario Iiguez Rodriguez  Alfredo Benialgo 《Journal of South American Earth Sciences》1996,9(5-6)

Major volcanogenic structures within the Marifil Formation allowed to determine the location of a claderas field that spreads along 400 kilometers. This field has at least three large calderas with diameters near to 100 kilometers, recognizable by regional distribution of associated dikes and rhyolite lava flows present at the caldera border that separates a monotonous ignimbritic plateau from a depressed (150 meters) inner volcanic collapsed caldera. The Marifil ignimbritic plateau cover more than 50,000 square kilometers with thicknesses that reach 800 meters. Associated with these plateau ignimbrites there is an important fluorite mineralization.  相似文献   

Automated AF-demagnetization on the 2G-Enterprises through-bore,cryogenic magnetometer     

Giddings  John W.  Klootwijk  Chris  Rees  John  Groenewoud  Adrian 《Geologie en Mijnbouw》1997,76(1-2):35-44

Since the early sixties, alternating field demagnetization (AFD) has been a standard laboratory technique for demagnetizing rocks to expose the multicomponent structure of their natural remanent magnetization (NRM). In the majority of AFD implementations, however, the procedure remains as labour-intensive as ever. The implementation that we have developed at the Australian Geological Survey Organisation, automates the procedure for AFD based on the static method, and results in significant productivity and efficiency gains without compromising data quality. A properly formulated procedure for static AFD may be the only method of retrieving higher-coercivity components of natural remanence in samples prone to developing gyroremanence at higher alternating fields (AFs). Our AFD environment comprises: a 2G-Enterprises through-bore, cryogenic magnetometer; 2G AF-coils and control equipment; and personal computer software, developed by us, to control all procedural aspects for a complete AFD of a sample including, importantly, a counteracting procedure to neutralize the effects of gyroremanence build-up at higher AFs. With our system, AFD of 8 samples/day, each of 20+ steps, requires only 20 min of user attention compared with a full day for conventional systems.  相似文献   

Trough structures in the Western syenite of Kûngnât, S Greenland: mineralogy and mechanism of formation     

M. E. Hodson  Adrian A. Finch 《Contributions to Mineralogy and Petrology》1997,127(1-2):46-56

In the Western layered syenite stock of the Kûngnât complex, close to the intrusion wall, there are two groups of regularly spaced, horizontally aligned, stacks of infilled troughs. These features resemble, to some extent, the trough layering within the UZa trough zone of the gabbroic Skaergaard¹ intrusion. Such features have never before been described in syenitic rocks. The lower group comprises six stacks of infilled troughs; the upper group comprises seven. The two groups are vertically separated by about 10 m of sparsely layered syenite. The infilled troughs in the upper group are stacked vertically; those in the lower group gradually shift laterally and appear to converge over an antiformal structure. It is not possible to measure the plunge of the troughs due to outcrop geometry. Troughs are up to about 80 cm deep. The material filling the troughs is more melanocratic than the syenite that surrounds them. Individual troughs exhibit normal grading. The syenite within the troughs contains large amphibole and biotite oikocrysts. Faintly layered syenite occurs laterally between stacks. Minerals in the host syenite are more ferroan than those in the troughs, this is thought to represent re-equilibration with residual melt. Feldspar textures, irregular pyroxene and apatite zoning, and the presence of irregular shaped amphibole patches within pyroxene grains all imply alteration by a pervasive deuteric fluid in both troughs and host syenite. We suggest the following hypothesis for the formation of the troughs. A mafic crystal sheath which grows on the walls of the magma chamber becomes detached and flows downwards. The descending slurry forms a series of regularly spaced streams which erode trough shaped channels into the crystal pile at the base of the chamber. Uneroded crystal material separates the channels. Crystals are deposited from these streams. Successive streams flow over each other to generate stacks of troughs.  相似文献