Coherent slumping of early postglacial lake sediments at Hall Lake, Ontario, Canada     

KEITH DAVID BENNETT 《Boreas: An International Journal of Quaternary Research》1986,15(3):209-215

Cores of organic postglacial sediment from Hall Lake, southern Ontario, Canada, are described. The laminated, calcareous sediments deposited between 9,000 and 8,000 B.P. have coherently slumped into the deep part of the lake, causing overturning and replication of parts of the sequence. This process may be considered as a mechanism for sediment focusing, since it involves reworking of marginal sediments into deeper areas. Unlike previously described mechanisms, it may be a source of error in the interpretation of diagrams of pollen percentages as well as accumulation rates. The slumping has only been recognized through the distortion of the laminae. It might not be possible to recognize slumping in unstratified sequences.  相似文献   

High-resolution stratigraphy of the northernmost concentric raised bog in Europe: Sellevollmyra, Andøya, northern Norway     

KARL-DAG VORREN  MAARTEN BLAAUW  STEFAN WASTEGÅRD  JOHANNES VAN DER PLICHT  CHRISTIN JENSEN 《Boreas: An International Journal of Quaternary Research》2007,36(3):253-277

From the Sellevollmyra bog at Andøya, northern Norway, a 440‐cm long peat core covering the last c. 7000 calendar years was examined for humification, loss‐on‐ignition, microfossils, macrofossils and tephra. The age model was based on a Bayesian wiggle‐match of 35 ¹⁴C dates and two historically anchored tephra layers. Based on changes in lithology and biostratigraphical climate proxies, several climatic changes were identified (periods of the most fundamental changes in italics): 6410–6380, 6230–6050, 5730–5640, 5470–5430, 5340–5310, 5270–5100, 4790–4710, 4890–4820, 4380–4320, 4220–4120, 4000–3810, 3610–3580, 3370–3340 (regionally 2850–2750; in Sellevollmyra a hiatus between 2960–2520), 2330–2220, 1950, 1530–1450, 1150–840, 730? and c. 600? cal. yr BP. Most of these climate changes are known from other investigations of different palaeoclimate proxies in northern and middle Europe. Some volcanic eruptions seemingly coincide with vegetation changes recorded in the peat, e.g. about 5760 cal. yr BP; however, the known climatic deterioration at the time of the Hekla‐4 tephra layer started some decades before the eruption event.  相似文献   

Anomalous luminescence of subglacial sediment at Haut Glacier d'Arolla,Switzerland – a consequence of resetting at the glacier bed?     

DARREL A. SWIFT  DAVID C. W. SANDERSON  PETER W. NIENOW  ROBERT G. BINGHAM  IAN C. COCHRANE 《Boreas: An International Journal of Quaternary Research》2011,40(3):446-458

Swift, D. A., Sanderson, D. C. W., Nienow, P. W., Bingham, R. G. & Cochrane, I. C. 2010: Anomalous luminescence of subglacial sediment at Haut Glacier d'Arolla, Switzerland – a consequence of resetting at the glacier bed? Boreas, Vol. 40, pp. 446–458. 10.1111/j.1502‐3885.2010.00196.x. ISSN 0300‐9483. Luminescence has the potential to elucidate glacial geomorphic processes because primary glacial sediment sources and transport pathways are associated with contrasting degrees of exposure to light. Most notably, sediment entrained from extraglacial sources should be at least partially reset, whereas sediment produced by glacial erosion of subglacial bedrock should retain substantial luminescence commensurate with a geological irradiation history. We set out to test the validity of this assumption at Haut Glacier d'Arolla, Switzerland using sediment sampled extraglacially and from the glacier bed. Contrary to our expectations, the subglacial samples exhibited natural signals that were substantially lower than those of other sample groups, and further (albeit limited) analyses have indicated no obvious differences in sample‐group luminescence characteristics or behaviour that could account for this observation. For glaciological reasons, we can eliminate the possibilities that the subglacial sediment has been extraglacially reset or exposed in situ to heat or light. We therefore advocate investigation of possible resetting processes related to subglacial crushing and grinding, and speculate that such processes, if more generally present, may enable the dating of subglacially deposited tills using luminescence‐based techniques.  相似文献   

Stegosaur tracks and the persistence of facies — the Lower Cretaceous of Western Australia     

DAVID PAGE 《Geology Today》1998,14(2):71-74

Sometimes between January and June 1996, the only known stegosaur tracks were stolen from Broome in north-western Australia (Fig. 1). Vandalism or loss of any type material is always to be lamented, yet there is good cause to suspect that the trackmaker at Broome was not a stegosaur. The reasons why this should be so relate to some of the factors involved in the formation of dinosaur trace fossils and the difficulties encountered in their interpretation. The stratigraphy at Broome is notable for preserving evidence of potential Wealden-type deposition in Australia.  相似文献   

The slope of isentropes constituting a frontal zone     

AARNOUT VAN DELDEN 《地球，A辑:动力气象学与海洋学》1999,51(5):603-611

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Intermediate time error growth and predictability: tropics versus mid-latitudes     

By DAVID M. STRAUS  DAN PAOLINO 《地球，A辑:动力气象学与海洋学》2009,61(5):579-586

The evolution of identical twin errors from an atmospheric general circulation model is studied in the linear range (small errors) through intermediate times and the approach to saturation. Between forecast day 1 and 7, the normalized error variance in the tropics is similar to that at higher latitudes. After that, tropical errors grow more slowly. The predictability time τ taken for tropical errors to reach half their saturation values is larger than that for mid-latitudes, especially for the planetary waves, thus implying greater potential predictability in the tropics.
The discrepancy between mid-latitude and tropical τ is more pronounced at 850 hPa than at 200 hPa, is largest for the planetary waves, and is more pronounced for errors arising from wave phase differences (than from wave amplitude differences).
The spectra of the error in 200 hPa zonal wind show that for forecast times up to about 5 d, the tropical error peaks at much shorter scales than the mid-latitude errors, but that subsequently tropical and mid-latitude error spectra look increasingly similar.
The difference between upper and lower level tropical τ may be due to the greater influence of mid-latitudes at the upper levels.  相似文献   

The ice-dammed lakes of Ossian Sarsfjellet (Svalbard): their geomorphology and significance     

MATTHEW R. BENNETT  MICHAEL J. HAMBREY  DAVID HUDDART  NEIL F. GLASSER  KEVIN CRAWFORD 《Boreas: An International Journal of Quaternary Research》1998,27(1):25-43

The tidewater glacier complex of Kongsvegen/Kronebreen, at the head of Kongsfjorden in north-west Spitsbergen, has advanced rapidly several times since its Neoglacial maximum. Two such advances, 1869 and 1948, are well constrained in time and space and are widely interpreted as glacier surges. During the 1869 advance an ice-dammed lake formed on the western side of Ossian Sarsfjellet. This ice-dammed lake is associated with a thrust moraine complex. Four lake levels are identified, two of which are associated with rock-cut shorelines implying a degree of lake stability. The history of this lake, the nature of the ice dam and its relationship to the thrust moraine complex are discussed. The lake history spanning 28 to 35 years is used to assess the ice-marginal dynamics of the Kongsvegen/Kronebreen glacier. It is concluded that, contrary to previous suggestions, the rapid advance of this tidewater glacier may simply be an example of a non-climatic ice-marginal fluctuation, of the type common to tidewater glacier, as opposed to a glacier surge. A second ice-dammed lake, to the east of Ossian Sarsfjellet, formed sometime after 1869 as the ice retreated, and still exists today. This largely supraglacial lake is associated with a very different geomorphological assemblage, which has a poor long-term preservation potential. The geomorphological characteristics of the two lakes on Ossian Sarsfjellet are compared and used to discuss the problems associated with the recognition of ice-dammed lakes within the Pleistocene record. On the basis of the evidence presented here, ice-dammed lakes may be more common during deglaciation than currently suggested.  相似文献   

John MacCulloch: precursor of the British 'Geological Survey'     

DAVID A. CUMMING 《Geology Today》1985,1(4):124-125

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Mössbauer study of Meridiani Planum,the first iron‐nickel meteorite found on the surface of Mars by the MER Opportunity     

C. VAN CROMPHAUT  V. G. DE RESENDE  E. DE GRAVE  R. E. VANDENBERGHE 《Meteoritics & planetary science》2007,42(12):2119-2123

Abstract— –Meridiani Planum is the first iron meteorite found on Mars. It was discovered in 2005 by the Mars Exploration Rover Opportunity (MER‐B). Mössbauer spectra (MS) of the unbrushed and brushed meteorite species were acquired in 10 degrees temperature windows in the range of 210–260 K. Earlier examinations of these MS have led to the conclusion that the meteorite, which contains ～～7 wt% Ni, belongs to the IAB meteorite group. Here, making use of a recently developed calibration/folding procedure for MER MS, we report the results of the MS analyses for the single temperature windows m5 (210–220 K), m6 (220–230 K), m7 (230–240 K), and m89 (240–260 K). All spectra consist of a sextet and a ferric doublet. The hyperfine field of the sextet, extrapolated to room temperature, is ～～34.5 T, which is, based on Mössbauer studies of meteorites found on Earth, indeed consistent with the presence of kamacite. The fractional spectral area of the sextet is ～～0.96 of the total spectrum. The ferric doublet has an average quadrupole splitting of 0.70 mm/s and is not diagnostic of any specific Fe mineral.  相似文献   

Non-methane volatile organic compound flux from a subarctic mire in Northern Sweden     

KRISTINA BÄCKSTRAND  PATRICK M. CRILL  MIKHAIL MASTEPANOV  TORBEN R. CHRISTENSEN  DAVID BASTVIKEN 《Tellus. Series B, Chemical and physical meteorology》2008,60(2):226-237

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