New insights into Late Pleistocene glacial and postglacial history of northernmost Ungava (Canada) from Pingualuit Crater Lake sediments     

Hervé Guyard  Guillaume St-Onge  Reinhard Pienitz  Pierre Francus  Bernd Zolitschka  Garry K.C. Clarke  Sonja Hausmann  Veli-Pekka Salonen  Patrick Lajeunesse  Grégoire Ledoux  Michel Lamothe 《Quaternary Science Reviews》2011,30(27-28):3892-3907

The Pingualuit Crater was formed by a meteoritic impact ca. 1.4 million years ago in northernmost Ungava (Canada). Due to its geographical position near the center of successive North American ice sheets and its favorable morphometry, the Pingualuit Crater Lake (water depth = 246 m) promises to yield a unique continuous sedimentary sequence covering several glacial/interglacial cycles in the terrestrial Canadian Arctic. In this paper, we suggest the existence of a subglacial lake at least during the Last Glacial Maximum (LGM) by hydraulic potential modeling using LGM ice-surface elevation and bed topography derived from a digital elevation model. These results support the hypothesis that the bottom sediments of the Crater Lake escaped glacial erosion and may contain a long-term continental sedimentary sequence. We also present the stratigraphy of a 9 m-long core retrieved from the deep basin of the lake as well as a multiproxy reconstruction of its deglacial and postglacial history. The base of the core is formed by very dense diamicton reflecting basal melt-out environments marking the end of subglacial conditions at the coring site. The overlying finely laminated silt are related to the onset of proglacial conditions characterized by extremely low lacustrine productivity. Infra Red Stimulated Luminescence and AMS ¹⁴C dating, as well as biostratigraphic data indicate sediment mixing between recent (e.g. Holocene) and much older (pre- to mid-Wisconsinan) material reworked by glacier activity. This process prevents the precise dating of these sediments that we interpret as being deposited just before the final deglaciation of the lake. Two finer grained and organic-rich intervals reflect the inception of lacustrine productivity resulting from the cessation of glacial meltwater inputs and ice-free periods. The lower organic interval corresponds to the early postglacial period (6850–5750 cal BP) and marks the transition between proglacial and postglacial conditions during the Holocene Thermal Maximum, while the uppermost organic-rich core section represents late Holocene sediments (～4200–600 cal BP). The organic intervals are separated by a basin-scale erosive slide occurring around 4200 cal BP and likely related to 1) a seismic event due to the glacio-isostatic rebound following the last deglaciation or 2) slope instabilities associated with rapid discharge events of the lake.  相似文献   

Interpreting Auckland’s volcanic governance through an institutional lens     

Catherine Murray  Garry McDonald  Shane Cronin 《Natural Hazards》2015,75(1):441-464

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Evaluation of the hydrology of the IBIS land surface model in a semi‐arid catchment          下载免费PDF全文

Min Chen  Garry R. Willgoose  Patricia M. Saco 《水文研究》2015,29(5):653-670

This paper evaluates the Integrated BIosphere Simulator (IBIS) land surface model using daily soil moisture data over a 3‐year period (2005–2007) at a semi‐arid site in southeastern Australia, the Stanley catchment, using the Monte Carlo generalized likelihood uncertainty estimation (GLUE) approach. The model was satisfactorily calibrated for both the surface 30 cm and full profile 90 cm. However, full‐profile calibration was not as good as that for the surface, which results from some deficiencies in the evapotranspiration component in IBIS. Relatively small differences in simulated soil moisture were associated with large discrepancies in the predictions of surface runoff, drainage and evapotranspiration. We conclude that while land surface schemes may be effective at simulating heat fluxes, they may be ineffective for prediction of hydrology unless the soil moisture is accurately estimated. Sensitivity analyses indicated that the soil moisture simulations were most sensitive to soil parameters, and the wilting point was the most identifiable parameter. Significant interactions existed between three soils parameters: porosity, saturated hydraulic conductivity and Campbell ‘b’ exponent, so they could not be identified independent of each other. There were no significant differences in parameter sensitivity and interaction for different hydroclimatic years. Even though the data record contained a very dry year and another year with a very large rainfall event, this indicated that the soil model could be calibrated without the data needing to explore the extreme range of dry and wet conditions. IBIS was much less sensitive to vegetation parameters. The leaf area index (LAI) could affect the mean of daily soil moisture time series when LAI < 1, while the variance of the soil moisture time series was sensitive to LAI > 1. IBIS was insensitive to the Jackson rooting parameter, suggesting that the effect of the rooting depth distribution on predictions of hydrology was insignificant. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献   

A microseismic experiment in Abu Dhabi,United Arab Emirates: implications for carbonate reservoir monitoring     

Sumana Basu  Mohammed Y. Ali  Asam Farid  Karl A. Berteussen  Garry Mercado 《Arabian Journal of Geosciences》2014,7(9):3815-3827

A microseismic experiment utilizing a single downhole array of eight 3-component receivers was conducted in an offshore oilfield in the emirate of Abu Dhabi in the United Arab Emirates. The Lower Cretaceous Thamama Group is the major carbonate reservoir in the field producing from six zones. Microseismic data was acquired in conjunction with gas injections that took place in the Thamama IV A and IV B reservoirs during 9 days of acquisition. The aim of the experiment was to monitor the microseismic activity arising in the carbonate reservoirs as a result of gas injection. A total of 103 microseismic events were detected from two of the receivers. For the majority of these events, there were no well-defined P wave arrivals, probably due to the presence of strong background noise and the very weak microseismic signals. The results from this experiment indicate that the detected events are probably related to the microseismic activities caused by the gas injection within the Thamama IV B reservoir. Therefore, downhole microseismic monitoring methods can potentially provide valuable information about the fracture systems within the carbonate reservoirs of Abu Dhabi's oilfields.  相似文献   

Study by MOA of extrasolar planets in gravitational microlensing events of high magnification     

I. A. Bond  N. J. Rattenbury  J. Skuljan  F. Abe  R. J. Dodd  J. B. Hearnshaw  M. Honda  J. Jugaku  P. M. Kilmartin  A. Marles  K. Masuda  Y. Matsubara  Y. Muraki  T. Nakamura  G. Nankivell  S. Noda  C. Noguchi  K. Ohnishi  M. Reid  To. Saito  H. Sato  M. Sekiguchi  D. J. Sullivan  T. Sumi  M. Takeuti  Y. Watase  S. Wilkinson  R. Yamada  T. Yanagisawa  P. C. M. Yock 《Monthly notices of the Royal Astronomical Society》2002,333(1):71-83

A search for extrasolar planets was carried out in three gravitational microlensing events of high magnification, MACHO  98–BLG–35  , MACHO  99–LMC–2  and OGLE  00–BUL–12  . Photometry was derived from observational images by the MOA and OGLE groups using an image subtraction technique. For MACHO  98–BLG–35  , additional photometry derived from the MPS and PLANET groups was included. Planetary modelling of the three events was carried out in a supercluster computing environment. The estimated probability for explaining the data on MACHO  98–BLG–35  without a planet is <1 per cent. The best planetary model has a planet of mass ∼(0.4–1.5)× M _Earth at a projected radius of either ∼1.5 or ∼2.3 au. We show how multiplanet models can be applied to the data. We calculate exclusion regions for the three events and find that Jupiter-mass planets can be excluded with projected radii from as wide as about 30 au to as close as around 0.5 au for MACHO  98–BLG–35  and OGLE  00–BUL–12  . For MACHO  99–LMC–2  , the exclusion region extends out to around 10 au and constitutes the first limit placed on a planetary companion to an extragalactic star. We derive a particularly high peak magnification of ∼160 for OGLE  00–BUL–12  . We discuss the detectability of planets with masses as low as Mercury in this and similar events.  相似文献   

The effects of Martian near surface conditions on the photochemistry of amino acids     

Inge Loes ten Kate  James R.C. Garry  Bernard Foing 《Planetary and Space Science》2006,54(3):296-302

In order to understand the complex multi-parameter system of destruction of organic material on the surface of Mars, step-by-step laboratory simulations of processes occurring on the surface of Mars are necessary. This paper describes the measured effects of two parameters, a CO₂ atmosphere and low temperature, on the destruction rate of amino acids when irradiated with Mars-like ultraviolet light (UV). The results show that the presence of a 7 mbar CO₂ atmosphere does not affect the destruction rate of glycine, and that cooling the sample to 210 K (average Mars temperature) lowers the destruction rate by a factor of 7. The decrease in the destruction rate of glycine by cooling the sample is thought to be predominantly caused by the slower reaction kinetics. When these results are scaled to Martian lighting conditions, cold thin films of glycine are assumed to have half-lives of 250 h under noontime peak illumination. It has been hypothesised that the absence of detectable native organic material in the Martian regolith points to the presence of oxidising agents. Some of these agents might form via the interaction of UV with compounds in the atmosphere. Water, although a trace component of Mars’ atmosphere, is suggested to be a significant source of oxidising species. However, gaseous CO₂ or adsorbed H₂O layers do not influence the photodestruction of amino acids significantly in the absence of reactive soil. Other mechanisms such as chemical processes in the Martian regolith need to be effective for rapid organic destruction.  相似文献   

Active microwave remote sensing for soil moisture measurement: a field evaluation using ERS‐2     

Jeffrey P. Walker  Paul R. Houser  Garry R. Willgoose 《水文研究》2004,18(11):1975-1997

Active microwave remote sensing observations of backscattering, such as C‐band vertically polarized synthetic aperture radar (SAR) observations from the second European remote sensing (ERS‐2) satellite, have the potential to measure moisture content in a near‐surface layer of soil. However, SAR backscattering observations are highly dependent on topography, soil texture, surface roughness and soil moisture, meaning that soil moisture inversion from single frequency and polarization SAR observations is difficult. In this paper, the potential for measuring near‐surface soil moisture with the ERS‐2 satellite is explored by comparing model estimates of backscattering with ERS‐2 SAR observations. This comparison was made for two ERS‐2 overpasses coincident with near‐surface soil moisture measurements in a 6 ha catchment using 15‐cm time domain reflectometry probes on a 20 m grid. In addition, 1‐cm soil moisture data were obtained from a calibrated soil moisture model. Using state‐of‐the‐art theoretical, semi‐empirical and empirical backscattering models, it was found that using measured soil moisture and roughness data there were root mean square (RMS) errors from 3·5 to 8·5 dB and r² values from 0·00 to 0·25, depending on the backscattering model and degree of filtering. Using model soil moisture in place of measured soil moisture reduced RMS errors slightly (0·5 to 2 dB) but did not improve r² values. Likewise, using the first day of ERS‐2 backscattering and soil moisture data to solve for RMS surface roughness reduced RMS errors in backscattering for the second day to between 0·9 and 2·8 dB, but did not improve r² values. Moreover, RMS differences were as large as 3·7 dB and r² values as low as 0·53 between the various backscattering models, even when using the same data as input. These results suggest that more research is required to improve the agreement between backscattering models, and that ERS‐2 SAR data may be useful for estimating fields‐scale average soil moisture but not variations at the hillslope scale. Copyright © 2004 John Wiley & Sons, Ltd.  相似文献   

The Hercules Échelle Spectrograph at Mt. John     

J. B. Hearnshaw  S. I. Barnes  G. M. Kershaw  N. Frost  G. Graham  R. Ritchie  G. R. Nankivell 《Experimental Astronomy》2002,13(2):59-76

The High Efficiency and Resolution Canterbury University Large échelle Spectrograph (HERCULES) a fibre-fed échelle spectrograph that was designed and built at the University of Canterbury and has been in operation at Mt. John University Observatory since April 2001.HERCULES receives light from the f/13.5 Cassegrain focus of the 1 m McLellan telescope. Resolving powers of R = 41 000, 70 000 and 82 000 are available. An R2 200 × 400 mm échelle grating provides dispersion and cross-dispersion uses a large BK7 prism in double pass. The wavelength coverage is designed to be 380–880 nm in a single exposure. The maximum detective quantum efficiency of the fibre, spectrograph and detector system is about 18% in 2 arc second seeing. High wavelength stability (to better than 10 ms^-1 in radial velocity) is achieved by installing the whole instrument in a large vacuum tank at 2–4 torr and by there being no moving parts. The tank is in a thermally isolated and insulated environment. The paper describes the design philosophy of HERCULES and its performance during the first year of operation. Now deceased; formerly at This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

The volcanoes and caldera of Talasea,New Britain: Mineralogy     

Garry G. Lowder 《Contributions to Mineralogy and Petrology》1970,26(4):324-340

The Talasea Peninsula is composed of a chain of Quaternary volcanoes whose lavas range from basalt to rhyolite. The peninsula is situated in an orogenic environment and the lavas, while essentially calc-alkaline, show some differences from other orogenic suites on the Pacific rim. The most distinctive feature of the Talasea series is absolute iron enrichment in some lavas. Mineralogically, the andesites are characterized by phenocrysts of plagioclase, orthopyroxene, clinopyroxene and titanomagnetite, while the basalts lack titanomagnetite phenocrysts but contain olivine. The acid rocks have a mineralogy similar to that of the andesites, but also contain quartz, amphibole, biotite and ilmenite. The compositions of coexisting titanomagnetite and ilmenite in the acid lavas indicate equilibration temperatures in the range 920° to 860° C and oxygen fugacities ( ) above those of the fayalitemagnetite-quartz buffer assemblage. The mineralogical evidence supports the hypothesis of a crystal fractionation origin for this series and there is a possibility that the was more or less constant during the early stages of its evolution. The iron enriched lavas may be an offshoot from the main line of descent, resulting from near-surface fractionation, with the dominance of plagioclase in the crystal residuum producing an iron-rich liquid.  相似文献   

Petrography of the Herrin (No. 11) coal in western Kentucky     

James C. Hower  Garry D. Wild 《International Journal of Coal Geology》1981,1(2):139-153

The Herrin (No. 11) coal in western Kentucky is in the upper part of the Pennsylvanian (Des Moinesian) Carbondale Formation. Samples were obtained from 13 mines in Kentucky and one mine in Illinois in three equal benches from two to three channels for a total of 93 samples. The rank of the coal (as vitrinite reflectance) is high volatile C bituminous in the Moorman Syncline and high volatile A bituminous in the Webster Syncline. Reflectance does not vary between mines in in the Moorman Syncline. The percentage of total vitrinite macerals for each mine is over 85% and the percentage of togal vitrinite plus liptinite maceralsis over 89% (average over 90%) (both on dry, mineral-free basis). The variation of the two maceral percentages is only significant at the betweenbench level, the middle bench generally having the lowest vitrinite and vitrinite plus liptinite percentages.  相似文献