Statistical detection of the mid-Pleistocene transition   总被引：12，自引：0，他引：12  

KA Maasch 《Climate Dynamics》1988,2(3):133-143

Using statistical methods we have shown quantitatively that the transition in mean and variance observed in ¹⁸O records during the middle of the Pleistocene was abrupt. By applying these methods to all of the available records spanning the entire Pleistocene it appears that this jump was global and primarily represents an increase in ice mass. At roughly the same time an abrupt decrease in sea surface temperature also occurred, indicative of sudden global cooling. This kind of evidence suggests a possible bifurcation of the climate system that must be accounted for in a complete explanation of the ice ages. Theoretical models including internal dynamics are capable of exhibiting this kind of rapid transition.  相似文献   

The strontium and oxygen isotopic record of hydrothermal alteration of syenites from the Abu Khruq complex,Egypt     

Timothy M. Lutz  Kenneth A. Foland  Henry Faul  LeeAnn Srogi 《Contributions to Mineralogy and Petrology》1988,98(2):212-223

Hydrothermal convection initiated by emplacement of the gabbro-syenite complex of Abu Khruq into the Egyptian basement 89 Ma ago systematically altered the trace element and isotopic compositions of the syenites. The scale of Sr transport in migrating solutions was far larger than the scale of Sr isotopic equilibration within rocks. As a result, Sr exchange was heterogeneous in the syenites, an effect which can be observed on three different scales. Within grains of a single mineral species, heterogeneities are related to grain boundaries and microfractures through which fluids migrated. Among minerals within rock samples, heterogeneities are related to differences in susceptibility to Sr alteration. Among samples within a single unit, heterogeneous alteration is apparently related to differences in permeability close to fracture zones.During the early stages of alteration radiogenic Sr derived from the country rocks was added to the syenites, causing small net changes in concentration (5 ppm ave.). Some Rb-Sr mineral isochrons from single rock samples yield the emplacement age because isotopic equilibration of this added Sr sometimes occurred within rock specimens. However, regressions of the whole-rock Rb-Sr data yield apparent ages that are about 10 Ma too old. Later stage alteration involved larger changes in whole-rock Sr concentration (45 ppm ave.) but had little further effect on the isotopic relationships because the Sr was derived from cogenetic gabbros rather than the country rocks.Alterations of Rb, Sr, and Sr isotopic compositions are not well correlated with changes in ¹⁸O/¹⁶O ratio because mineralogy played an important role in decoupling trace element and oxygen isotopic alteration. In general, the absence of such correlations for whole-rock data is not diagnostic of rocks with unaltered trace element and isotopic compositions. Mineral-scale Sr isotopic heterogeneities associated with grain boundaries and microfractures may be the most unambiguous evidence of trace element mobility.Deceased on 9/81  相似文献   

The spatio-temporal distribution and population structure of green turtles (Chelonia mydas) in New Zealand     

DA Godoy  ANH Smith  C Limpus  KA Stockin 《新西兰海洋与淡水研究杂志》2016,50(4):549-565

Despite being endangered internationally and protected nationally, little consideration has been given to the occurrence of green turtles (Chelonia mydas) in New Zealand. New Zealand lies on the southern boundary of the distributional range of green turtles in the southwestern Pacific, with individuals found within these waters historically considered to be occasional visitors or stragglers incidentally carried by ocean currents. However, the present work shows that green turtles are present year round in New Zealand’s northern waters (c. 34°–38° S). A review of sighting, stranding and incidental capture data collected between 1895 and 2013 illustrate New Zealand’s green turtle population comprises post-pelagic immature juveniles to large subadults. The female:male sex ratio of 1.7:1 is similar to those reported from warm temperate foraging grounds in eastern Australia. A subsample of new recruits indicates green turtles recruit to neritic habitats at approximately 40.8?cm curved carapace length. This study suggests that New Zealand’s neritic habitats constitute a transitional developmental ground for post-pelagic immature green turtles. We observed an exponential increase in the number of documented records over time, though whether this is due to increased numbers of turtles or increased reporting rates, or both, is unclear and warrants further investigation. More broadly, this work provides a baseline understanding of the ecology of green turtles at the edge of their range, providing opportunities to investigate regional niche modelling and connectivity of this highly mobile species, while also monitoring broad-scale effects of climate-induced environmental change.  相似文献   

Analysis of instrumental observations of the Jesenice meteorite fall on April 9, 2009     

Pavel SPURNÝ  Jiří BOROVIČKA  Javor KAC  Pavel KALENDA  Jure ATANACKOV  Gregor KLADNIK  Dieter HEINLEIN  Thomas GRAU 《Meteoritics & planetary science》2010,45(8):1392-1407

Abstract– We report an analysis of instrumental observations of a very bright fireball which terminated with a meteorite fall near the town of Jesenice in Slovenia on April 9, 2009, at 0h59m46s UT. The fireball designated EN090409 was recorded photographically and photoelectrically by two southern stations of the Czech part of the European Fireball Network (EN). Simultaneously, a part of the luminous trajectory was also captured by two all‐sky CCD systems and one video camera of the Slovenian meteor network. In addition to these optical recordings, the sonic booms produced by the Jesenice fireball were detected at 16 seismic stations located within 150 km of the trajectory. From all these records, we reconstructed the fireball’s atmospheric trajectory, basic geophysical data, the possible impact area, and the original heliocentric orbit of the meteoroid. Using a detailed fireball light curve, we modeled the atmospheric fragmentation of the meteoroid. Both the atmospheric behavior and the heliocentric orbit proved to be quite normal in comparison with other observed meteorite falls. The Jesenice orbit is markedly different from the P?íbram and Neuschwanstein orbital meteorite pair, which fell on similar dates (April 7, 1959, and April 6, 2002, respectively). Three meteorites with a total weight of 3.6 kg (until April 2010) were found in a high mountain area near the town of Jesenice. They are classified as L6 ordinary chondrites ( Bischoff et al. 2010 ).  相似文献   

A 1300‐year multi‐proxy,high‐resolution record from a rich fen in northern Poland: reconstructing hydrology,land use and climate change     

M. LAMENTOWICZ  M. GAŁKA  K. MILECKA  K. TOBOLSKI  Ł. LAMENTOWICZ  B. FIAŁKIEWICZ‐KOZIEŁ  M. BLAAUW 《第四纪科学杂志》2013,28(6):582-594

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Nd isotopes demonstrate the role of contamination in the formation of coexisting quartz and nepheline syenites at the Abu Khruq Complex,Egypt     

J. D. Landoll  K. A. Foland  C. M. B. Henderson 《Contributions to Mineralogy and Petrology》1994,117(3):305-329

The petrogenesis of Abu Khruq, an 89 Ma alkaline ring complex of eastern Egypt which is composed of alkali gabbros and both silica over- and undersaturated syenites, has been investigated. Major and trace element relationships and Nd and Sr isotope data are consistent with formation of the gabbros from an alkaline mafic magma that experienced extensive fractionation, and all syenites from a felsic derivative of this melt. The parental magma had an ⁸⁷Sr/⁸⁶Sr of 0.7030 and an ¹⁴³Nd/¹⁴⁴Nd of 0.512750 (_Nd = +4.4) indicating derivation from a depeleted mantle source. The initial ¹⁴³Nd/¹⁴⁴Nd ratios are: 0.512721 to 0.512748 for the gabbros, 0.512739 to 0.512750 for the alkali syenites and trachytes, 0.512717 to 0.512755 for the nepheline syenites, and, 0.512706 to 0.512732 for the quartz syenites. In contrast, analyzed Precambrian granites from eastern Egypt have generally lower ¹⁴³Nd/¹⁴⁴Nd ratios (ranging from 0.51247 to 0.51261 or _Nd = -0.8 to 1.7, for 89Ma); their Nd model ages range from 775 to 935 Ma and suggest there was no significant input of pre-Pan-African crust in their formation. Among Abu Khruq rocks, ¹⁴³Nd/¹⁴⁴Nd ratios indicate that the quartz syenites formed by open-system, crustal contamination processes whereas the nepheline syenites experienced little or no contamination. Modeling shows that contamination occurred at various stages, affecting both mafic and more evolved compositions with input of about 20% crustal Nd for the most contaminated samples. The degree of contamination is related to the silica saturation of the quartz syenites. Simplified modeling of magma evolution within Petrogeny's Residua System demonstrates the ability of AFC processes to cause a critically undersaturated magma to evolve across the feldspar join and produce oversaturated rocks. The oversaturated syenites at Abu Khruq were produced in this manner whereas the nepheline syenites formed by fractionation without similarly large degrees of contamination. The results have broad implications for the formation of subvolcanic complexes in continental settings beyond the important production of silica oversaturated compositions from crustal interaction. They underscore the importance of crustal interactions in the formation of the various lithologies. Such interactions occur at various stages in the evolution of the magmas and, as such, are not strictly coupled with fractional crystallization. While previous study of Abu Khruq has demonstrated extensive hydrothermal alteration of O and Sr isotopes, the present work shows that the Nd isotope ratios were not significantly affected and thus reflect magmatic signatures. This feature combined with relatively small corrections for initial ratios emphasizes the utility of Nd isotopes for petrogenetic studies.  相似文献   

The age of the Lugar sill and a discussion of the Late-Carboniferous/Early-Permian sill complex of S.W. Scotland     

C. M. B. Henderson  K. A. Foland  F. G. F. Gibb 《Geological Journal》1987,22(1):43-52

The incremental heating ⁴⁰Ar/³⁹Ar method has been used to date a kaersutite separate from the main theralite-picrite unit of the Lugar sill. Ar-release spectra show discordance mainly due to the presence of excess Ar in alteration phases intimately associated with the primary kaersutite. Plateaus in the spectra allow an emplacement age of 288 ± 6 Ma (2γ) to be assigned to the sill. The results are used to discuss the age relations of the alkaline Permo-Carboniferous sill complex of southwest Scotland. It is concluded that these sills could have been emplaced over a shorter period of time than implied by the available conventional K/Ar data. The classification of the alkaline sills into kylite and teschenite types has little petrogenetic significance.  相似文献   

On the origin of an amphibole-rich vein in a peridotite inclusion from the Lunar Crater Volcanic Field,Nevada, U.S.A.     

Steven C. Bergman  Kenneth A. Foland  Frank J. Spera 《Earth and Planetary Science Letters》1981

Late Cenozoic alkali basaltic lavas of the Lunar Crater Volcanic Field (LCVF), located in the center of the Great Basin of the Western U.S.A., contain a diverse suite of nodule samples of the lower crust and upper mantle. This paper documents a composite nodule from the Marcath flow in which an amphibole-bearing wehrlite (59% olivine, 30% clinopyroxene, 6% amphibole) is cut by a 6–9 mm wide vein of andesine-amphibolite (80% kaersutite, 15% andesine, 3% ilmenite). Aside from nodule-basalt reaction at the nodule exterior, there is little chemical variation either within or between individual grains of hydrous and anhydrous phases in the vein and host wehrlite. Furthermore, there is no systematic compositional zoning in the wehrlite relative to vein proximity. The whole-rock major and trace element composition of the vein is similar to a primitive (Mg/(Mg+Fe)=0.692) basaltic liquid and has Al, Fe, Mg, Ca, Mn, Na, K, Zr, Y and Sr contents similar to basalts observed in the LCVF. In contrast to the Sr isotopic equilibrium displayed by vein feldspar and vein amphibole, Sr isotopic disequilibrium is exhibited between the vein (0.70318(4)), wehrlite (0.70322(4)), and host basalt (0.70357(5) n=3). However, the Sr isotopic ratios of older LCVF basalts (0.7030–0.7038; n=14) overlap those of the vein and wehrlite, and the magmatic activity leading to vein and wehrlite formation could be related to this older phase of LCVF volcanism. Petrographic and geochemical evidence is not consistent with a metasomatic origin for the vein and instead supports the view that the vein originated by the intrusion into a wehrlite mass and subsequent crystallization of a relatively primitive alkali basaltic magma in the lower crust or upper mantle. The wehrlite contains olivine of FO₇₁ and probably originated by crystal separation and accumulation from a relatively differentiated basaltic magma in the lower crust or upper mantle.  相似文献   

Timing of volcanic, plutonic and geothermal activity at Ngatamariki, New Zealand     

G. B. Arehart  B. W. Christenson  C. P. Wood  K. A. Foland  P. R. L. Browne 《Journal of Volcanology and Geothermal Research》2002,116(3-4)

Four ⁴⁰Ar/³⁹Ar dates on mineral separates from fresh and hydrothermally altered volcanic and plutonic rocks from the Ngatamariki geothermal field indicate that andesitic volcanism took place in the eastern portion of the Taupo Volcanic Zone (TVZ) prior to 1.2 Ma and probably considerably earlier. These data significantly extend the onset and duration of andesitic volcanism in the east-central TVZ over previous estimates. Intrusive activity is represented at Ngatamariki by a dioritic pluton, the only such pluton yet recognized in the entire TVZ. Hornblende from the pluton yields a crystallization age of near 550 ka. Hydrothermal alteration spatially associated with the pluton produced sericite of a similar age. Overlying and postdating the most intense hydrothermal alteration zone is the Whakamaru Ignimbrite (or its equivalent) which was emplaced at 330 ka. Two distinct geothermal systems may have been active at nearly the same site from 550 ka to present. The most intense activity occurred before 330 ka and was associated with emplacement of the Ngatamariki diorite. This was followed by the less intense system that is currently active. The geothermal regime at Ngatamariki has, therefore, probably been active intermittently for at least 550 ka.  相似文献   

40Ar/39Ar and Rb-Sr geochronology of the Qingyang batholith,Anhui Province,China     

Jiangfeng Chen  Taixi Zhou  K. A. Foland 《中国地球化学学报》1985,4(3):220-235

The geochronology and genesis of the Qingyang batholith were investigated using⁴⁰Ar/³⁹Ar and Rb-Sr isotopic techniques. The Qingyang is a composite batholith consisting of two major rock types granodiorite and granite in the Yangtze fold belt.⁴⁰Ar/³⁹Ar spectra for biotite and amphibole separates are internally concordant. The concordance of the minerals and spectra indicate no thermal disturbance of the ages, and rapid cooling of the rocks. The granodiorite has an age of 137.6±1.4 m.y. and the granite 122.7±1.2 m.y. Whole-rock Rb-Sr analysis yields ages consistent with the⁴⁰Ar/³⁹Ar dates. Thus, the Qingyang batholith was formed in two major stages in the late Jurassic and early Cretaceous. The batholith is not Triassic as was previously proposed. Special⁴⁰Ar/³⁹Ar analysis of two granodiorite samples has precisely documented a 1.0 m.y. apparent age difference between these samples. Several factors could account for this difference, but different emplacement times seem most convincible. The granodiorite and granite show little variation in initial⁸⁷Sr/⁸⁶Sr ratio (about 0.7085). The high initial Sr ratios suggest that the magmas were formed by anatexis of older crustal materials.  相似文献