Revised palaeoclimatic significance of Mueller Glacier moraines,Southern Alps,New Zealand          下载免费PDF全文

Natalya V. Reznichenko  Tim R. H. Davies  Stefan Winkler 《地球表面变化过程与地形》2016,41(2):196-207

A sequence of Late Holocene moraines on the foreland of the Mueller Glacier, Southern Alps, New Zealand, forms part of a local moraine‐age database used to establish a regional glacier chronology and subsequently to investigate potential intra‐hemispheric and global climate forcing mechanisms. We present new sedimentological and geomorphological evidence that a set of these moraine ridges, previously considered to represent individual advances, constitutes a single moraine complex (the ‘Mueller Memorial Moraine’) formed by supraglacial transport of a large volume of landslide debris to the glacier terminus. Because a moraine formed in this way is not necessarily associated with an advance triggered by a climate event, we question the palaeoclimatic significance of the Mueller Memorial Moraine, as well as that of other moraines in comparable settings. Our findings suggest that the mode of formation and glacio‐dynamical context of moraines whose ages contribute to existing palaeoclimate reconstructions need to be re‐examined in order to assess the reliability of these reconstructions. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   

Combining compositional zoning and foliation intersection axes (FIAs) in garnet to quantitatively determine early P-T-t paths in multiply deformed and metamorphosed schists: north central Massachusetts,USA     

Hyeong?Soo?KimEmail author  Tim?H.?Bell 《Contributions to Mineralogy and Petrology》2005,149(2):141-163

Quantitative compositional and microstructural analysis of garnet porphyroblasts in kyanite–staurolite–garnet grade rocks from the northeastern flank of the Pelham dome, north central Massachusetts, distinguishes the effects of Acadian deformation and metamorphism from extensive overprinting Alleghanian shearing. The P–T conditions and the metamorphic path during the Acadian were determined using samples preserving well defined stages in a lengthy tectonic history revealed by a succession of five foliation intersection axis trends preserved within porphyroblasts (FIAs). This Acadian succession extends at least 120 km to the north into rocks where no evidence has been found of an Alleghanian overprint. For each sample where garnet first nucleated during one of these stages in the tectonic history, the PT of core growth was determined by plotting the intersection of the Mn, Fe and Ca isopleths calculated for the core composition on a P–T pseudosection for that sample using THERMOCALC. Combining the PT data from all these samples indicates that the temperature and pressure increased throughout Acadian orogenesis, causing episodic garnet growth. During the Alleghanian, locally intense shearing, especially against the margin of the Pelham dome, formed the dominant schistosity, which truncated all foliations defined by inclusion trails in porphyroblasts and obliterated all remains of Acadian deformation and metamorphism in the rock matrix. Shearing was accompanied by near complete homogenization of the compositional zoning in garnet porphyroblasts and an associated apparent increase in the temperature of the matrix to 700°C in those rocks lying directly adjacent to the Pelham dome, and resulted from the rocks of the Northfield syncline being thrust a large distance southwards over the gneisses in the dome.  相似文献   

STARE Results on a Single Field: Tens of New Pulsating Stars     

Roi Alonso  Juan Antonio Belmonte  Tim Brown 《Astrophysics and Space Science》2003,284(1):13-16

We present preliminary results on variable stars of aSTARE's three month observational run centered at the Cygnus constellation.A total amount of aprox. 14000 stars with 9^2 FOV, have been analyzed to obtainlightcurves for each of these stars.The data spans for 90 nights.In this single field, we detect more that 40 stars withpulsation modes between 5 and 40 c/d, the vast mayoritypreviously unknown to be variables.  相似文献   

Membership, binarity and accretion among very low-mass stars and brown dwarfs of the σ Orionis cluster     

M. J. Kenyon  R. D. Jeffries  Tim Naylor  J. M. Oliveira  P. F. L. Maxted 《Monthly notices of the Royal Astronomical Society》2005,356(1):89-106

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THE DECLINE OF PARTY VOTING: A GEOGRAPHICAL ANALYSIS OF THE 1978 MASSACHUSETTS ELECTION     

Bruce Downing  Tim Hudson  Peter Taylor  Peter Bland  Nancy Villanueva 《The Professional geographer》1980,32(4):454-461

A factor analysis of the 1978 Massachusetts election is undertaken to investigate whether the alleged decline of political parties in the United States can be distinguished at the state scale. Four factors are identified, two of which relate to the voting patterns of state-wide candidates. The main factor is easily seen to represent a “party voting”pattern and the fourth factor suggests a nonparty pattern of support associated with the Democratic candidate for governor, Edward King. It is suggested that this separation of the voting pattern for Democratic candidates may possibly reflect party decomposition in Massachusetts.  相似文献   

The global 2000 report to the President: A report prepared by the Council on Environmental Quality and the Department of State. London: Penguin, 1982. 751 pp. £7.95 paperback; £14.95 hardback (Allen Lane)     

Tim O&#x;Riordan 《Applied geography (Sevenoaks, England)》1982,2(4):315-317

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Multiple Foliations Defined by Different Sillimanite Crystal Habits, Partial Melting and the Late Metamorphic Development of the Cannington Ag-Pb-Zn Deposit, Northeast Australia     

Hyeong Soo Kim  Tim H. Bell   《Gondwana Research》2005,8(4):493-509

A succession of foliations defined by different sillimanite-bearing structural fabrics suggests that the macroscopic, isoclinal synform that dominates the geometry of the Cannington Ag-Pb-Zn deposit, northwest Queensland, Australia formed during D₂. The five foliations in this succession, S₁ to S₅, are defined by aligned sillimanite with habits ranging from individual crystals in S₁ through S₄ to clusters of fibrolite in S₅ in both the matrix and as inclusion trails within garnet and gahnite (Zn-rich spinel) porphyroblasts. S₁, S₃ and S₅ formed as sub-horizontal foliations, whereas S_1a, S₂ and S₄ formed sub-vertically. Foliation intersection/inflexion axes (FIAs) within garnet and gahnite porphyroblasts preserve a succession of trends that shifts from W-E to N-S. This succession indicates that this region experienced N-S followed by W-E bulk crustal shortening. N-S shortening occurred during D₁and D_1a, and W-E shortening occurred from D₂ to D₅. Prismatic and rhombic sillimanite produced during D₁-D₄ accompanied prograde metamorphism to ca. 634 62°C and 4.8 1.3 kbar. The coexistence of fibrous, prismatic and rhombic sillimanite resulted from post peak metamorphic reactivation of the early foliations during D₅. The synformal D₂ fold was intensified during D₄ by W-E bulk shortening. Local partial melting occurred after D₁ in the appropriate bulk rock compositions, based on calculation of P-T pseudosections in the chemical systems KFMASH, KFMASHTO, NCKFMASH and MnNCKFMASH. Zn mineralization related to gahnite growth occurred during D₃ through D₄, and was redistributed by partial melting into structural and rheological sites during D₄ and D₅shearing.  相似文献   

The major-ion composition of Permian seawater   总被引：1，自引：0，他引：1  

Tim K. Lowenstein  Michael N. Timofeeff  Juske Horita 《Geochimica et cosmochimica acta》2005,69(7):1701-1719

The major-ion (Mg²⁺, Ca²⁺, Na⁺, K⁺, SO₄²⁻, and Cl⁻) composition of Permian seawater was determined from chemical analyses of fluid inclusions in marine halites. New data from the Upper Permian San Andres Formation of Texas (274-272 Ma) and Salado Formation of New Mexico (251 Ma), analyzed by the environmental scanning electron microscopy (ESEM) X-ray energy-dispersive spectrometry (EDS) method, along with published chemical compositions of fluid inclusions in Permian marine halites from North America (two formations of different ages) and the Central and Eastern European basins (eight formations of four different ages) show that Permian seawater shares chemical characteristics with modern seawater, including SO₄²⁻ > Ca²⁺ at the point of gypsum precipitation, evolution into Mg²⁺-Na⁺-K⁺-SO₄²⁻-Cl⁻ brines, and Mg²⁺/K⁺ ratios ∼5. Permian seawater, however, is slightly depleted in SO₄²⁻ and enriched in Ca²⁺, although modeling results do not rule out Ca²⁺ concentrations close to those in present-day seawater. Na⁺ and Mg²⁺ in Permian seawater are close to (slightly below) their concentrations in modern seawater. Permian and modern seawater are both classified as aragonite seas, with Mg²⁺/Ca²⁺ ratios >2, conditions favorable for precipitation of aragonite and magnesian calcite as ooids and cements.The chemistry of Permian seawater was modeled using the chemical composition of brine inclusions for three periods: Lower Permian Asselian-Sakmarian (296-283 Ma), Lower Permian Artinskian-Kungurian (283-274 Ma), and Upper Permian Tatarian (258-251 Ma). Parallel changes in the chemistry of brine inclusions from equivalent age evaporites in North America, Central Europe, and Eastern Europe show that seawater underwent secular variations in chemistry over the 50 million years of the Permian. Modeled SO₄²⁻ concentrations are 20 mmol per kg H₂O (mmolal) and 19 mmolal in the Asselian-Sakmarian and Artinskian-Kungurian, with higher concentrations in the Upper Permian Tatarian (23 mmolal). Modeled Ca²⁺ is at or above its concentration in modern seawater throughout the Permian. Mg²⁺ is close to (slightly below) its concentration in modern seawater (55 mmolal) in the Asselian-Sakmarian (52 mmolal), and Tatarian (52 mmolal), but slightly higher than modern seawater in the Artinskian-Kungurian (60 mmolal). Mg²⁺/Ca²⁺ ratios are 3.5 (total range = 2.7 to 5.5) in the Lower Permian and rose slightly to 3.7 (total range = 3.1 to 5.8) in the Upper Permian, primarily due to decreases in Ca²⁺. These results are consistent with models that predict oscillations in the major-ion composition of Phanerozoic seawater on the basis of changes in the midocean ridge/river water flux ratio driven by changes in the rate of midocean ridge crust production.The Permian was characterized by low sea levels, icehouse conditions, and southern hemisphere glaciation. Such conditions, analogous to the present ice age, and the similarities between Permian seawater and modern seawater, all suggest that general Phanerozoic supercycles, driven by mantle convection and global volcanicity, also control the major-ion chemistry of seawater.  相似文献   

'This is like my comfort zone': Senses of place and belonging within Oruāmo/Beachhaven, New Zealand     

Tim McCreanor  Liane Penney  Victoria Jensen  Karen Witten  Robin Kearns  Helen Moewaka Barnes 《New Zealand geographer》2006,62(3):196-207

Abstract:  This paper examines the culturally specific experiences of belonging within Oruāmo/Beachhaven, a suburb in North Shore City. In-depth interviews with 32 caregivers of young children expose the fact that the ethnic groups represented – Māori, Samoan and Pākehā– vary in their uses and understandings of, as well as feelings for, residential neighbourhood. Examination of the themes of natural environment, social relations, continuity of residence, facilities, organisations and place transformation reveal that, while representatives of all groups had views on these matters, there was a variable degree of engagement with and priority afforded to these concerns.  相似文献   

Confronting hysteresis: Wood based river rehabilitation in highly altered riverine landscapes of south-eastern Australia   总被引：1，自引：1，他引：1  

Andrew P. Brooks  Timothy Howell  Tim B. Abbe  Angela H. Arthington 《Geomorphology》2006,79(3-4):395

This study evaluates an experiment in river rehabilitation which uses large wood to stimulate and emulate natural system processes in an effort to reverse channel degradation, excess sediment transport and habitat simplification that has resulted from two centuries of human induced disturbances, particularly desnagging. The experiment involved the reintroduction of 436 logs (350 t) within 20 engineered log jams (ELJs) over an 1100 m reach. Commencing in 1999, the experiment was set up as a standard BACI design, with a control reach 3 km upstream. In the 5 years since implementing the rehabilitation strategy, the study reach has experienced five floods greater than the mean annual, and a further five events capable of mobilising the gravel bed. Five surveys of channel terrain have been completed since treatment implementation, and the changes to net sediment storage and morphologic diversity assessed in comparison to the control reach. Seven surveys of the fish population in the reach have also been undertaken during the project to measure the ecological response to the introduced wood. The experiment has demonstrated the effectiveness of ELJ technology in achieving engineering and geomorphic goals. To date, the treatment has halted further degradation of the river and increased sediment storage, with the test reach now storing, on average, 40 m³/1000 m² more sediment than in the control. These values, it would appear, represent a new reach-scale dynamic equilibrium storage level over decadal timescales. Additional sediment storage amounts to 3.5 m³/m³ of wood added. At the reach scale this additional storage represents a reduction of just 2% or less of the post-European expansion in channel capacity, suggesting far greater efforts are required than those employed here to reverse the cumulative effects of 180 years of channel erosion and simplification.Pool and bar area in the test reach increased by around 5% and 3.5%, respectively, while the corresponding values in the control were around 1.5% and 1%, respectively. Two indices of morphologic diversity were measured for each bed survey: the standard deviation of 3D residuals of change compared with the baseline survey (SD_iΔ3D); and the standard deviation of thalweg residuals from the line of best fit (SD_iTR). The SD_iΔ3D index shows both reaches increased in complexity through the study with the treatment increasing more than the control (0.37 and 0.29, respectively). The SD_iTR index does not detect clear changes because of the low signal to noise ratio, however, it does suggest the test reach was more complex than the control at the outset. The observed increase in fish abundance after the first 12 months of monitoring, reported previously, is now far less distinct 4 years on — a pattern seemingly reflecting the relatively minor increases in critical pool habitat and habitat diversity over the same period. Although no significant differences were detectable in fish species richness or total abundance from the reach aggregate data after 4 years, analysis of individual structures show them to be high quality habitat for native fish compared to the rest of the reach and the upstream control.These results highlight the challenges river managers face in achieving measurable improvements in the health of aquatic ecosystems in highly altered rivers. Managers must confront hysteresis in a biophysical and institutional sense when attempting to reverse the degradation of rivers. The scale of treatment implemented in this experiment was at the upper end of the spectrum of rehabilitation efforts currently being undertaken in Australia, suggesting that far greater resources and longer timescales are required to achieve the levels of improvement in the diversity of stream habitat expected by the community. The study also highlights problems with the strategy of attempting to meet multiple objectives within a reach scale rehabilitation project. While this treatment successfully met some geomorphic study objectives, maximising the benefits for fish habitat would require a strategy focused primarily on the creation of complex woody habitat within deeper pools, particularly pools immediately below riffles.  相似文献