The compositional classification of chondrites: II The enstatite chondrite groups     

Derek W. Sears  Gregory W. Kallemeyn  John T. Wasson 《Geochimica et cosmochimica acta》1982,46(4):597-608

We present new data from a neutron activation analysis of four enstatite chondrites including the taxonomically important St. Sauveur, and discuss the classification of enstatite chondrites. The enstatite chondrites can be divided into two compositionally distinct sets; in one set abundances of nonrefractory siderophiles and moderately volatile chalcophiles and alkalis are 1.5–2.0× higher than in the other. A well-resolved compositional hiatus separates these two sets. The differences in composition are as great as those between the groups of ordinary chondrites, and therefore it appears best to treat these sets as separate groups. By analogy with the symbols used for ordinary chondrites we propose to designate the high-Fe, high siderophile group EH and the low-Fe, low-siderophile group EL. Known members of the EH group belong to petrologic types 4 and 5, whereas all EL members are petrologic type 6. Within the EH group no correlation is observed between petrologic type and abundance of nonrefractory siderophiles or moderately volatiles or alkalis.Two physical properties show only modest overlap between the EH and EL groups. Cosmic-ray ages for EH chondrites are 0.5–7 Ma, while those for EL chondrites are 4–18 Ma. Relative to Bjurböle, I-Xe formation intervals are $\text{?1.3 ± 0.6}$ Ma for EH chondrites and $\text{2.9 ± 0.5}$ Ma for EL chondrites. The weight of the chemical and physical evidence indicates that the EH and EL groups formed separate bodies at similar distances from the Sun.The available evidence for Shallowater and Happy Canyon, two strongly recrystallized silicate-rich meteorites containing > 40 mg/g Fe-Ni, indicates that the former is an enstatite-clan chondrite altered by loss of sulfide- and plagioclase-rich melts, whereas the latter is intermediate in composition between EL chondrites and the chondritic silicates in the Pine River IAB-anomalous meteorite.  相似文献   

Late Pleistocene sea level history of Bermuda     

Russell S. Harmon  Henry P. Schwarcz  Derek C. Ford 《Quaternary Research》1978,9(2):205-218

The timing of eustatic sea level fluctuations over the vertical range + 15 to ?11 m has been deduced from ${}^{230}\text{Th}{}^{234}\text{U}$ dating of Bermudan corals and speleothems. On this tectonically stable carbonate island, interglacial periods are characterized by platform submergence, development of patch reefs, and the deposition of littoral and eolian carbonates, whereas glacial periods are times of platform emergence, carbonate diagenesis, soil development, and the deposition of speleothems in caves extending below present sea level. Interglacial periods are observed at about 200,000, 130,000 to 90,000, and 10,000 yr BP to present. The sea level history of the last interglacial period (130,000 to 90,000 yr BP) is complex, consisting of at least two short, distinct episodes of high sea stand (at 125,000 and 97,000 yr BP) superimposed on a longer period of general platform submergence. The sea level data derived from this study are compatible with those from other stable areas such as the Bahamas, but in addition suggest that eustatic sea level changes can be rapid, on the order of 5 to 10 m/1000 yr.  相似文献   

Instructing engineers     

Derek Ellis 《Marine pollution bulletin》1975,6(4):51-52

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Cell parameter correlations in the aluminosilicate-sodalites     

Derek Taylor 《Contributions to Mineralogy and Petrology》1975,51(1):39-47

Cell parameters, ranging from 8.447 to 9.331 Å, are given for 13 synthetic aluminosilicate-sodalites. Correlations between the cell edge of aluminosilicate-sodalites and the sizes of the cavity ions are established and discussed. The principal infrared absorption bands for 6 synthetic and 4 natural aluminosilicate-sodalites are also correlated with the cell edge and discussed in terms of the bonding theory of linked TO₄ tetrahedra (T=Si, Al).  相似文献   

Biomagnification     

Fisk AT  Hoekstra PF  Borgå K  Muir DC 《Marine pollution bulletin》2003,46(4):522-4; author reply 525-6

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The concept of "sustainable ecological succession"; and its value in assessing the recovery of sediment seabed biodiversity from environmental impact     

Ellis DV 《Marine pollution bulletin》2003,46(1):39-41

The problem of determining whether the biodiversity of an impacted muddy seabed is recovering can be resolved by drawing on a concept termed "sustainable ecological succession". At a site impacted by discharge of mine tailings, a suite of approximately 6 primary opportunist species (mostly polychaete worms) had started to sustain itself within 1-2 years after discharge ceased (1995), within the mix of 100+ other species which were not sustaining themselves. The start of a sustaining ecological succession is easily measurable by repeat surveys, and requires only the services of one taxonomic identifier to demonstrate the consistent presence and numbers of a limited range of species. At the assessed site, by 2000, some secondary opportunist species had entered the succession, and the species richness of the impacted area had come to equal that of the reference areas.  相似文献   

For the love of pipes and cables: a response to Deborah Thien   总被引：2，自引：0，他引：2  

Derek McCormack 《Area》2006,38(3):330-332

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Rural diversification in Albania     

Derek R. Hall 《GeoJournal》1998,46(3):283-287

This paper examines the prospects for Albanian rural diversification with particular reference to rural tourism. In the early 1990s, tourism was identified by the Albanian government and Western development consultants as a likely vehicle for an appropriate and sustainable development strategy, given the relative wealth generated by international tourism in neighbouring Greece, Italy and Croatia. Pressure has been exerted by commercial developers for mass coastal tourism and permission for around 40 new tourist development has been granted. But Albania embraces a considerable wealth of natural and cultural heritage, which provides opportunities for the development of small scale rural tourism carefully integrated into the local economy with respect to organic farming, quality wine production and sustainable fishing. But sensitive social integration is vital where it is difficult to identify rural communities where there is a conspicuous absence of local consensus. The resurgence of traditional social systems and the empowerment of local actors in cases where organised crime has taken root pose major problems for rural diversification. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

New Associate Editors     

Derek Sears 《Meteoritics & planetary science》1998,33(3):383-383

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Measuring Rates of Biodegradation in a Contaminated Aquifer Using Field and Laboratory Methods   总被引：5，自引：0，他引：5  

Francis H. Chapelle  Paul M. Bradley  Derek R. Lovley  Don A. Vroblesky 《Ground water》1996,34(4):691-698

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