SCHMIDT‐HAMMER EXPOSURE AGES FROM PERIGLACIAL PATTERNED GROUND (SORTED CIRCLES) IN JOTUNHEIMEN,NORWAY, AND THEIR INTERPRETATIVE PROBLEMS          下载免费PDF全文

STEFAN WINKLER  JOHN A. MATTHEWS  RICHARD W. MOURNE  PETER WILSON 《Geografiska Annaler: Series A, Physical Geography》2016,98(3):265-285

Periglacial patterned ground (sorted circles and polygons) along an altitudinal profile at Juvflya in central Jotunheimen, southern Norway, is investigated using Schmidt‐hammer exposure‐age dating (SHD). The patterned ground surfaces exhibit R‐value distributions with platycurtic modes, broad plateaus, narrow tails, and a negative skew. Sample sites located between 1500 and 1925 m a.s.l. indicate a distinct altitudinal gradient of increasing mean R‐values towards higher altitudes interpreted as a chronological function. An established regional SHD calibration curve for Jotunheimen yielded mean boulder exposure ages in the range 6910 ± 510 to 8240 ± 495 years ago. These SHD ages are indicative of the timing of patterned ground formation, representing minimum ages for active boulder upfreezing and maximum ages for the stabilization of boulders in the encircling gutters. Despite uncertainties associated with the calibration curve and the age distribution of the boulders, the early‐Holocene age of the patterned ground surfaces, the apparent cessation of major activity during the Holocene Thermal Maximum (HTM) and continuing lack of late‐Holocene activity clarify existing understanding of the process dynamics and palaeoclimatic significance of large‐scale sorted patterned ground as an indicator of a permafrost environment. The interpretation of SHD ages from patterned ground surfaces remains challenging, however, owing to their diachronous nature, the potential for a complex history of formation, and the influence of local, non‐climatic factors.  相似文献   

The generation of available potential energy, according to Lorenz' exact and approximate equations   总被引：1，自引：0，他引：1  

PETER SIEGMUND 《地球，A辑:动力气象学与海洋学》1994,46(5):566-582

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Surface exposure dating (36Cl and 10Be) of post‐Last Glacial Maximum valley moraines,Lake District,northwest England: some issues and implications     

PETER WILSON  CHRISTOPH SCHNABEL  KLAUS M. WILCKEN  PETER J. VINCENT 《第四纪科学杂志》2013,28(5):536-536

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Context of relict Wisconsinan glacial ice at Angus Lake, SW Banks Island, western Canadian Arctic and stratigraphic implications     

PETER WORSLEY 《Boreas: An International Journal of Quaternary Research》1999,28(4):543-550

Massive ice incorporating till beds and scattered erratic clasts exposed in a bimodal thaw slide displayed an association with the surrounding fluvioglacial and flow-till facies indicative of a consanguineous relationship. The massive ice cores a low ridge interpreted as a recessional moraine feature paralleling the Last Glacial Maximum advance limit. Both ice and sand wedges penetrate the massive ice and their tops are truncated by a thaw unconformity overlain by a diamicton. In a permafrost environment, relict glacial ice can persist for many millennia, and the timing of the thaw is largely determined by the vagaries of erosional processes. The age of related kettle landforms can display considerable diachronism.  相似文献   

Timing of the last deglaciation in Belarus     

VINCENT R. RINTERKNECHT  IRINA E. PAVLOVSKAYA  PETER U. CLARK  GRANT M. RAISBECK  FRANCOISE YIOU  EDWARD J. BROOK 《Boreas: An International Journal of Quaternary Research》2007,36(3):307-313

We measured ¹⁰Be concentrations in boulders collected from the Orsha and Braslav moraines, associated with the Last Glacial Maximum extent and a recessional stage of the Scandinavian Ice Sheet (SIS), respectively, providing a direct dating of the southeastern sector of the ice-sheet margin in Belarus. By combining these data with selected existing radiocarbon ages, we developed a chronology for the last deglaciation of Belarus. The northeastern part of the country remained ice free until at least 19.2±0.2 cal. kyr BP, whereas the northwestern part of the country was ice free until 22.3±1.5 cal. kyr BP. A lobate ice margin subsequently advanced to its maximum extent and deposited the Orsha Moraine. The ice margin retreated from this moraine at 17.7±2.0 ¹⁰Be kyr to a position in the northern part of the country, where it deposited the Braslav Moraine. Subsequent ice-margin retreat from that moraine at 13.1±0.5 ¹⁰Be kyr represented the final deglaciation of Belarus. Direct dating of these moraines better constrains the relation of ice-margin positions in Belarus to those in adjacent countries as well as the SIS response to climate change.  相似文献   

Early Holocene drowned lagoonal deposits from the Kattegat, southern Scandinavia     

OLE BENNIKE  JØRN BO JENSEN  PETER B. KONRADI  WOLFRAM LEMKE  JAN HEINEMEIER 《Boreas: An International Journal of Quaternary Research》2000,29(4):272-286

Shallow seismic profiling indicated the presence of a drowned lagoon-barrier system formed during the transgression of the southern Kattegat, and investigations of core material have confirmed this. Studies of plant and animal macrofossils show that the lagoonal sediments contain a mixture of marine, brackish, lacustrine, telmatic and terrestrial taxa, and analyses of foraminifers indicate brackish-water conditions. Low oxygen isotope values obtained on shells of marine molluscs also point to lowered salinity. The lagoonal sediments are situated at depths between 24 and 35 m below present sea level. They are dated to between c. 10.5 cal. ka BP and c. 9.5 cal. ka BP, and reflect a period characterized by a moderate relative sea level rise. The lagoonal sediments are underlain by lateglacial glaciomarine clay and silt, which are separated from the Holocene deposits by an unconformity. The earliest Holocene sediments consist of littoral sand with gravel, stones and shells; these sediments were formed during the transgression of the area before the barrier island-lagoon system was developed. The lagoonal sediments are overlain by mud, which contains animal remains that indicate increasing water depths.  相似文献   

Three-dimensional transport and concentration of SF₆     

A. SCOTT DENNING  MARK. HOLZER  KEVIN R. GURNEY  MARTIN HEIMANN  RACHEL M. LAW  PETER J. RAYNER  INEZ Y. FUNG  SONG-MIAO FAN  SHOICHI TAGUCHI  PIERRE FRIEDLINGSTEIN  YVES BALKANSKI  JOHN TAYLOR  MANFRED MAISS  INGEBORG LEVIN 《Tellus. Series B, Chemical and physical meteorology》1999,51(2):266-297

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Magmatic Evolution and Ascent History of the Aries Micaceous Kimberlite, Central Kimberley Basin, Western Australia: Evidence from Zoned Phlogopite Phenocrysts, and UV Laser 40Ar/39Ar Analysis of Phlogopite-Biotite     

DOWNES  PETER J.; WARTHO  JO-ANNE; GRIFFIN  BRENDAN J. 《Journal of Petrology》2006,47(9):1751-1783

The Neoproterozoic Aries kimberlite was emplaced in the centralKimberley Basin, Western Australia, as a N–NNE-trendingseries of three diatremes infilled by lithic-rich kimberlitebreccias. The breccias are intruded by hypabyssal macrocrysticphlogopite kimberlite dykes that exhibit differentiation toa minor, high-Na–Si, olivine–phlogopite–richteritekimberlite, and late-stage macrocrystic serpentine–diopsideultramafic dykes. Mineralogical and geochemical evidence suggeststhat the high-Na–Si, olivine–phlogopite–richteritekimberlite was derived from the macrocrystic phlogopite kimberliteas a residual liquid following extended phlogopite crystallizationand the assimilation of country rock sandstone, and that themacrocrystic serpentine–diopside ultramafic dykes formedas mafic cumulates from a macrocrystic phlogopite kimberlite.Chemical zonation of phlogopite–biotite phenocrysts indicatesa complex magmatic history for the Aries kimberlite, with theearly inheritance of a range of high-Ti phlogopite–biotitexenocrysts from metasomatized mantle lithologies, followed bythe crystallization of a population of high-Cr phlogopite phenocrystswithin the spinel facies lithospheric mantle. A further oneto two phlogopite–biotite overgrowth rims of distinctcomposition formed on the phlogopite phenocrysts at higher levelsduring ascent to the surface. Ultra-violet laser ⁴⁰Ar/³⁹Ar datingof mica grain rims yielded a kimberlite eruption age of 815·4± 4·3 Ma (95% confidence). ⁴⁰Ar/³⁹Ar laser profilingof one high-Ti phlogopite-biotite macrocryst revealed a radiogenic⁴⁰Ar diffusive loss profile, from which a kimberlite magma ascentduration from the spinel facies lithospheric mantle was estimated(assuming an average kimberlite magma temperature of 1000°C),yielding a value of 0·23–2·32 days for thenorth extension lobe of the Aries kimberlite. KEY WORDS: ⁴⁰Ar/³⁹Ar; diamond; kimberlite; mantle metasomatism; phlogopite–biotite  相似文献   

Observed climate change constrains the likelihood of extreme future global warming     

PETER A. STOTT  CHRIS HUNTINGFORD  CHRIS D. JONES  JAMIE A. KETTLEBOROUGH 《Tellus. Series B, Chemical and physical meteorology》2008,60(1):76-81

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Assessment of dispersive pressure as a beach placer mechanism     

MATT R. TOMKINS  PETER NIELSEN  TOM E. BALDOCK 《Sedimentology》2010,57(2):408-417

The concept of sediment sorting extending from the Bagnold constitutive relationship for sediment under shear is examined in the context of beach placer formation. The traditional interpretation of shear sorting is found to be inconsistent with data from new granular flow experiments. A binary mixture satisfying the shear equivalence relationship displayed pronounced segregation during shear. This observation is contrary to shear sorting as applied in the literature where no such segregation for this pairing of mineral species is expected. Further experiments minimizing the potential of grain percolation of smaller grains or kinetic sieving also demonstrated sorting patterns inconsistent with the existing shear sorting interpretation. Consequently, the shear sorting process, as currently formulated, may not be an appropriate means to describe beach placer formation. Kinetic sieving appears to be a more likely mechanism in this context, enhanced by the shearing and dilation of the granular‐fluid flow.  相似文献