Reply to L. M. Leslie and A. F. Bennett     

H. JEAN THIÉBAUX  LAUREN L. MORONE 《地球，A辑:动力气象学与海洋学》1992,44(3):272-272

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Composition and source of the clay-sized fraction of Saalian till in The Netherlands     

SYLVI HALDORSEN  PER JØRGENSEN  MARTIN RAPPOL  PETER A. RIEZEBOS 《Boreas: An International Journal of Quaternary Research》1989,18(2):89-97

The clay mineral composition of a number of Saalian till samples from The Netherlands shows a large variation in smectite and illite abundances. The samples were selected according to their source area, as inferred from coarse erratic components. Specimens containing primarily rock fragments indicative of East and East-Central Baltic areas are associated with no or low smectite percentages in their clay fractions. Those with mainly flint and rock fragments indicative of the West Baltic areas have high smectite contents in the clay. In general the smectite-rich material is found in the lower portions of the Saalian till bed, whereas the smectite-poor occurs in the upper portions. The linkage between very fine and coarse till components in the upper smectite-free parts of the till suggests that this entire till has been subjected to englacial transport over distances of at least 1000 km.  相似文献   

Breeding biology of dark-bellied brent geese Branta b. bernicla in Taimyr in 1990 in the absence of arctic foxes and under favourable weather conditions   总被引：1，自引：0，他引：1  

BERNARD SPAANS  MARTIN STOCK  REW ST. JOSEPH  HANS-HEINER BERGMANN  BARWOLT S. EBBINGE 《Polar research》1993,12(2):117-130

In combination with observations in spring staging and wintering grounds in western Europe, a detailed etho-ecological study of nesting dark-bellied brent geese Branta b. bernicla in western Taimyr, Krasnoyarsk, Russia, was made in 1990. Most brent geese arrived on the breeding grounds from 14–19 June and started nesting within a few days. In the study area 264 nests of breeding brent geese were found, mainly on islands but also along small rivers on the mainland. The mean clutch size was 3.0 and 80% of the eggs hatched. Time budget studies showed that incubating females spent on average 138 minutes per 24 hours on feeding. Despite favourable weather conditions and a low density of arctic foxes, only about one-third of the mature birds in the study area bred. In the autumn an intermediate breeding success of 20% juveniles was recorded in the wintering areas. This was probably due to the relatively poor condition in which the brent geese left their spring staging areas.  相似文献   

Downward longwave radiation in general circulation models: a case study at a semi‐arid continental site     

MARTIN WILD  ROBERT CECHET 《地球，A辑:动力气象学与海洋学》2002,54(4):330-337

The present case study evaluates the downward longwave radiation at the surface (DLR) in several high‐resolution (≈1°) general circulation models (GCMs) using surface observations from a semiarid continental site in New South Wales, Australia (Uardry, 34.39°S, 142.30°E). This site is located on a large grassland plain uniform in both its land use and landcover type, and is therefore particularly well suited for a comparison with GCM grid mean values. Monthly averages of newly constructed clear‐sky and all‐sky DLR climatologies and the resulting cloud‐radiative forcing are compared. It is shown that the GCMs exceed the observed DLR under cloud‐free conditions by 10–20 W m⁻² at this semiarid site on an annual basis, with a strong seasonal dependence. The calculated clear‐sky fluxes are overestimated during the warmer summer season, with large absolute values of DLR, while the biases are reduced in the colder and dryer winter season with smaller fluxes. This gives direct support for recent evidence that the DLR model biases depend systematically on the thermal and humidity structure of the cloudless atmosphere. Fluxes from strongly emitting atmospheres tend to be overestimated, but may be underestimated from atmospheres with smaller emission. This points to common problems inherent in the simulation of the emission from the cloudless atmosphere in current longwave radiation codes.
The comparisons of the all‐sky climatologies at Uardry show that the clear‐sky biases are partly masked in the models with an insufficient cloud‐radiative forcing, thereby counterbalancing the excessive DLR of the cloud‐free atmosphere. On the other hand, when the cloudradiative forcing is improved, the biases in the cloud‐free atmosphere become fully apparent in the all‐sky fluxes.  相似文献   

Ice-marginal debris-flow deposits in western Allgau, southern West Germany     

MAT G.G. DE JONG  MARTIN RAPPOL 《Boreas: An International Journal of Quaternary Research》1983,12(1):57-70

Ice-marginal debris-flow deposits (comparable to deposits elsewhere described as flow tills) are described from glacier-proximal sediments in an Alpine foreland area. Debris-flow deposits are characteristically interstratified with subaeric or subaquatie meltwater deposits, and occur in a wide variety of geomorpho-logical settings. The granulomctric composition of debris-flow deposits is more variable than that of subglacial tills. Within-flow variability may occur as a result of the formation of graded bedding, lateral as well as vertical. Clast fabrics show both random and preferred orientations; unequivocal interpretation of these is not possible. Debris-flow deposits are composed of material derived from various sources: sources from subglaeially-derived debris as well as from previously deposited tills and walerlain sediments can be demonstrated.  相似文献   

Temporal Evolution of Magmatism in the Northern Volcanic Zone of the Andes: The Geology and Petrology of Cayambe Volcanic Complex (Ecuador)   总被引：4，自引：1，他引：3  

SAMANIEGO  PABLO; MARTIN  HERVE; MONZIER  MICHEL; ROBIN  CLAUDE; FORNARI  MICHEL; EISSEN  JEAN-PHILIPPE; COTTEN  JOSEPH 《Journal of Petrology》2005,46(11):2225-2252

In the Northern Volcanic Zone of the Andes, the Cayambe VolcanicComplex consists of: (1) a basal, mostly effusive volcano, theViejo Cayambe, whose lavas (andesites and subordinate dacitesand rhyolites) are typically calc-alkaline; and (2) a younger,essentially dacitic, composite edifice, the Nevado Cayambe,characterized by lavas with adakitic signatures and explosiveeruptive styles. The construction of Viejo Cayambe began >1·1Myr ago and ended at 1·0 Ma. The young and still activeNevado Cayambe grew after a period of quiescence of about 0·6Myr, from 0·4 Ma to Holocene. Its complex history isdivided into at least three large construction phases (Angurealcone, Main Summit cone and Secondary Summit cone) and compriseslarge pyroclastic events, debris avalanches, as well as periodsof dome activity. Geochemical data indicate that fractionalcrystallization and crustal assimilation processes have a limitedrole in the genesis of each suite. On the contrary, field observations,and mineralogical and geochemical data show the increasing importanceof magma mixing during the evolution of the volcanic complex.The adakitic signature of Nevado Cayambe magmas is related topartial melting of a basaltic source, which could be the lowercrust or the subducted slab. However, reliable geophysical andgeochemical evidence indicates that the source of adakitic componentis the subducted slab. Thus, the Viejo Cayambe magmas are inferredto come from a mantle wedge source metasomatized by slab-derivedmelts (adakites), whereas the Nevado Cayambe magmas indicatea greater involvement of adakitic melts in their petrogenesis.This temporal evolution can be related to the presence of thesubducted Carnegie Ridge, modifying the geothermal gradientalong the Wadati–Benioff zone and favouring slab partialmelting. KEY WORDS: adakites; ⁴⁰Ar/³⁹Ar dating; Cayambe volcano; Ecuador; mantle metasomatism; Andes  相似文献   

Diversity dynamics of the Late Cenozoic rodent community from south‐western Kansas: the influence of historical processes on community structure          下载免费PDF全文

ROBERT A. MARTIN  PABLO PELÁEZ‐CAMPOMANES 《第四纪科学杂志》2014,29(3):221-231

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Edge‐roundness of boulders of Torridonian Sandstone (northwest Scotland): applications for relative dating and implications for warm and cold climate weathering rates     

MARTIN P. KIRKBRIDE  CARA M. BELL 《Boreas: An International Journal of Quaternary Research》2010,39(2):187-198

Kirkbride, M.P. & Bell, C.M. 2009: Edge‐roundness of boulders of Torridonian Sandstone (northwest Scotland): applications for relative dating and implications for warm and cold climate weathering rates. Boreas, 10.1111/j. 1502‐3885.2009.00131.x. ISSN 0300‐9483. The relative ages of late Quaternary morainic and rock avalanche deposits on Late Precambrian Torridonian Sandstone are determined from the characteristic edge‐roundness of constituent boulders. Because weathering of sandstone is manifest as edge‐rounding by granular disintegration, a relative chronology can be derived by measuring the effective radii of curvature of a sample of boulder edges. Thirteen samples totalling 597 individual boulder edges fall into two statistically distinct groups. Moraines of inferred Younger Dryas age (12.9–11.5 kyr BP) are distinguished from moraines of the Wester Ross Re‐advance (≤14.0 kyr BP). One moraine previously assumed to be of Younger Dryas age is reassigned to the older group. The method allows spatial extrapolation of deposit ages from dated sites where lithological and sampling criteria are met. Calculated rates of edge‐rounding imply that granular disintegration was several times more rapid during cold stadial climates than during the Holocene. Used as a proxy for boulder ‘erosion rate’, this indicates that surface loss of grains in glacial climates exceeds that during interglacials by a factor of 2–5, with implications for the calculation of exposure ages from cosmogenic nuclides.  相似文献   

Earthworm calcite granules: a new tracker of millennial‐timescale environmental changes in Last Glacial loess deposits          下载免费PDF全文

PIERRE ANTOINE  OLIVIER MOINE  ELODIE TURPIN  LAURE HUGUENARD  VINCENT ROBERT  JEAN‐PHILIPPE DEGEAI 《第四纪科学杂志》2015,30(6):529-536

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Reply to the Discussion by Roger Higgs on ‘Hummocky cross‐stratification‐like structures in deep‐sea turbidites: Upper Cretaceous Basque basins (Western Pyrenees,France)’ by Mulder et al., Sedimentology, 56, 997–1015     

THIERRY MULDER  PHILIPPE RAZIN  JEAN‐CLAUDE FAUGÈRES  JEAN GÉRARD 《Sedimentology》2011,58(2):571-577

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