Merging chironomid training sets: implications for palaeoclimate reconstructions     

Naomi Holmes  Peter G. Langdon  Chris Caseldine  Stephen J. Brooks  H. John B. Birks 《Quaternary Science Reviews》2011,30(19-20):2793-2804

Icelandic and Norwegian chironomid calibration or training sets were merged to investigate whether a larger combined training set would be useful to apply to subfossil chironomid data from Iceland for periods such as the early Holocene, the Holocene Thermal Maximum and the Little Ice Age, when temperatures can be expected to be outside the current temperature range of the Icelandic training set. Following taxonomic harmonisation, the Icelandic and Norwegian data sets were compared before being merged to form a combined Norwegian-Icelandic training set. Analyses showed that it was biologically and statistically valid to merge the two data sets. The resulting combined inference model for mean July air temperature had improved performance statistics (r²_jack = 0.87; RMSEP_jack = 1.13) when compared to the best performing Icelandic model (r²_jack = 0.61; RMSEP_jack = 0.83), due to the longer environmental gradient covered (Icelandic 6–11 °C; combined 3.5–16 °C), and to the increased number of samples (Icelandic = 53 lakes; combined = 207 lakes) and taxa (Icelandic = 47 taxa; combined = 133 taxa) present within the combined training set. The inference models were applied to an early Holocene chironomid sequence from Vatnamýri, north Iceland, and a 450-year recent record from Myfluguvatn, north-west Iceland, to compare the reconstructions produced. The various inference models produced similar trends and patterns of temperature reconstruction, but the inference model based on the combined training set produced a larger range of reconstructed temperatures than the Icelandic model. It was found that different inference models produced more variation in the reconstruction than when different training sets were used. A comparison of the Myfluguvatn reconstructions with meteorological observations showed that the combined Norwegian–Icelandic inference model produced more reliable results than the Icelandic or Norwegian inference models alone.  相似文献   

The magmatic oxygen fugacity of an ultrabasic dyke     

F. G. F. Gibb  C. M. B. Henderson 《Contributions to Mineralogy and Petrology》1971,30(2):119-124

The magmatic oxygen fugacity (fO₂) of a thirty foot wide feldspathic peridotite dyke has been determined using the experimental method of Fudali (1965). Determinations were made on samples from both the marginal and central portions of the dyke and a difference of approximately one order of magnitude in fO₂ was observed. This difference is attributed to the increase in the H₂O content of the liquid as crystallization proceeded and to diffusion of hydrogen out of the dyke. It is concluded that the dyke was emplaced with an fO₂ between 10^–8 and 10^–9 atmospheres. Data on the absorbtion of Fe by the silver/palladium sample containers during the experiments are given in an appendix.  相似文献   

Seismicity in north-eastern Brazil: fractal clustering and the evolution of the b value     

Jeremy Henderson  Ian G. Main  Robert G. Pearce  Mario Takeya 《Geophysical Journal International》1994,116(1):217-226

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Distribution of attached algae in estuaries     

Martin Wilkinson  Anne R. Henderson  Christine Wilkinson 《Marine pollution bulletin》1976,7(10):183-184

Preliminary studies on distributions of attached algae in British estuaries suggest that the estuaries might be classified on the basis of the flora in the upper reaches. This could contribute to biological assessment of water quality in estuaries.  相似文献   

Lithium tracer-diffusion in an alkali-basaltic melt — An ion-microprobe determination     

R.K. Lowry  S.J.B. Reed  J. Nolan  P. Henderson  J.V.P. Long 《Earth and Planetary Science Letters》1981,53(1):36-40

An ion-microprobe-based technique has been used to measure lithium tracer-diffusion coefficients (D_Li) in an alkali-basaltic melt at 1300, 1350 and 1400°C. The results can be expressed in the form:D_Li=7.5 ×10^?2exp(?27,600/RT)cm²S^?1The results show significantly faster diffusion rates than those previously recorded for other monovalent, divalent and trivalent cations in a tholeiitic melt. Consequently, diffusive transport of ions acting over a given time in a basaltic melt can produce a wider range of transport distance values than hitherto supposed. Hence, it is concluded that great care should be exercised when applying diffusion data to petrological problems.  相似文献   

Lithium diffusion in silicate melts     

G.J. Cunningham  P. Henderson  R.K. Lowry  J. Nolan  S.J.B. Reed  J.V.P. Long 《Earth and Planetary Science Letters》1983,65(1):203-205

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Tracer diffusion of some alkali,alkaline-earth and transition element ions in a basaltic and an andesitic melt,and the implications concerning melt structure     

Roy K. Lowry  Paul Henderson  John Nolan 《Contributions to Mineralogy and Petrology》1982,80(3):254-261

The diffusion properties of Na, Cs, Sr, Ba, Co, Mn, Fe and Sc ions in a basaltic and an andesitic melt have been determined experimentally using the radiotracer residual-activity method, and narrow platinum capillaries, over the temperature range 1,300–1,400° C. Diffusion of all cations follows an Arrhenius relationship; the values of the activation energies range from 24 kcal mol^–1 for Na to 67 kcal mol^–1 for Co in the andesitic melt, and from 39 kcal mol^–1 for Na to 65 kcal mol^–1 for Cs in the basaltic melt. Relative diffusivities in the basaltic melt, but not in the andesitic melt, correlate with assumed ionic radii values. Each cation, except Na⁺, diffuses faster in the basaltic melt than in the andesitic melt over the studied temperature range. Sodium shows similar diffusivity in the two melts.Compensation diagrams incorporating new and some previously-published data indicate that Cs probably diffuses by different mechanisms in different silicate glass and melt systems. Iron has a relatively high activation energy which is consistent with its part occupancy of tetrahedral co-ordination polyhedra.  相似文献   

The mobility of the rare earth elements: Evidence and implications from selected terrains affected by burial metamorphism   总被引：1，自引：0，他引：1  

Phillip L. Hellman  Raymond E. Smith  Paul Henderson 《Contributions to Mineralogy and Petrology》1979,71(1):23-44

The mobility of the rare earth element (REE) during hydrous burial metamorphism is described from three localities. Comparison of REE abundances in relict domains and metadomains from flood lavas in the Maddina Volcanics, Fortescue Group, Western Australia shows that, relative to the relict domains, REE may be strongly depleted in certain metadomains. Strong variations in La/Yb, La/Sm and Eu may also occur due to postcrystallization secondary processes. Similar comparisons in flood lavas from Mamainse Point in the Canadian Keweenawan Series show that REE are mobile and increase in abundance in metadomains. Spilites from U.S. Virgin Islands also show evidence for REE mobility during low grade burial metamorphism. In this case light REE (LREE) have been preferentially mobilized with heavy REE (HREE) remaining parallel or sub-parallel on chondrite normalized plots.REE analyses from these locations together with an evaluation of published work suggests that the mobility of REE can be described by: 1. gross REE and selective LREE enrichment; 2. REE movement around a primary mean; 3. gross REE depletion; 4. selective REE mobility. Failure to take into account REE mobility may lead to incorrect conclusions concerning petrogenetic models based on altered basic sequences. The coherence of REE with other key trace elements during alteration is also discussed.  相似文献   

The thermal expansion of synthetic aluminosilicate-sodalites,M 8(Al6Si6O24)X 2     

C. M. B. Henderson  D. Taylor 《Physics and Chemistry of Minerals》1978,2(4):337-347

Thermal expansion data, determined by powder X-ray diffraction methods are presented for 11 members of the (Li,Na,K,Rb)₈(Al₆Si₆O₂₄)Cl₂ solid solution series, 3 members of the (Na,K)₈(Al₆Si₆O₂₄)Br₂ solid solution series and Na₈(Al₆Si₆O₂₄)I₂. Only the latter showed a discontinuity in its expansion curve at 810° C wigh a mean linear expansion coefficient of 22.0×10^?6 °C^?1 below and 7.7×10^?6 °C^?1 above the discontinuity. The mean expansion coefficients from 0° to 500° C decrease gradually over the range of room temperature cell edges from 8.4 to 8.89 Å, then increase up to a cell edge of 9.01 Å above which they decrease sharply and extrapolate to a zero coefficient at 9.4 Å. These variations may be related to the expansion characteristics of the bonds between the cavity cations and cavity anions in different sodalites. The aluminosilicate-sodalites which show a discontinuity in their thermal expansion curves are those with large cavity anions, I^? or SO ₄ ^2? ; the discontinuity is believed to occur at the point when the x-coordinate of the cavity cation becomes 0.25.  相似文献   

Archean chemical weathering at three localities on the Canadian Shield     

Mikkel Schau  John B. Henderson 《Precambrian Research》1983,20(2-4)

Sapropelite developed on a granodiorite basement below the Archean Steeprock Group in the western Superior Structural Province of Canada, weathered materials from a 3.15 Ga granitic basement to the Archean Yellowknife Supergroup in the Slave Structural Province, and weathered detritus from contemporaneous komatiites and gneissic basement of the Archean Prince Albert Group in northern Churchill Structural Province, have been analysed. The deviation of the weakly metamorphosed weathered material from the chemical composition of their precursors is comparable to that seen in more recent weathered profiles from similar source materials. This includes the enhancement of ferric to ferrous iron ratios, and potash to soda, lime and magnesia ratios. There is also an increase in lighter REE and a depletion of heavier REE. Quartz rich sediments immediately above the unconformity, derived from the basement granitoids, may be enriched in aluminum and iron, and yield chloritoid under proper metamorphic conditions. Sediments formed from mixed sources, such as weathered gneissic basement and contemporaneous komatiitic volcanics, yield anomalous resistate sedimentary mixtures such as chromiferous quartzites. Based on the data given here, there is no need to postulate that different weathering and/or ground water systems were operative during the Archean, compared to more recent times. On the other hand the complicated weathering and diagenetic history that altered material undergoes below a subsiding unconformity, relies as much or more on the buffering capacity of the enclosed rock mass as on the atmospheric conditions prevalent at the time of weathering. Hence weathering profiles, old and new, are more a response to local environmental conditions within the rock than the composition of the atmosphere.  相似文献