MIGRATION IN THE PRESENCE OF NOISE*     

A.J. BERKHOUT  D.W. VAN WULFFTEN PALTHE 《Geophysical Prospecting》1980,28(3):372-383

It is shown that the so-called Kirchhoff-summation operator is of a very wide-band nature and even contains an evanescent part. As a consequence, discretization may cause serious aliasing errors, particularly for small extrapolation steps. It is proposed to use in all practical cases band-limited versions of the summation operator, the spatial cut-off frequency being determined by the spatial Fourier spectrum of the coherent noise.  相似文献   

A Silurian–Devonian acritarch flora from Saalian till in The Netherlands     

JAAP J. M. VAN DER  MEER REED WICANDER 《Boreas: An International Journal of Quaternary Research》1992,21(2):153-158

Micropaleontological analysis of a silt intraclast in till exposed near Steenwijk in the northern Netherlands revealed an acritarch flora of Late Silurian–Early Devonian age, of southeastern Baltic Basin origin. The age of this assemblage contrasts with what is known about the palynomorph content of Dutch tills. Petrologic analysis of the silt intraclast provides further insight in the direction and mode of Saalian glacier transport.  相似文献   

Plagioclase porphyroblast growth and its relation to deformation in the Alhamilla unit (Sierra Alhamilla, Betic Cordilleras, SE Spain)     

B. VAN DEN EECKHOUT  G. KONERT † 《Journal of Metamorphic Geology》1983,1(3):227-240

Abstract. Plagioclase porphyroblasts from silvergrey schists belonging to the Nevado Filabride Complex in the Sierra Alhamilla (Betic Zone, SE Spain) are interpreted as having been formed preand synkinematically with respect to the second phase of deformation. Different types of inclusion patterns represent 'snap-shots'(high growth-rate/strain-rate ratio features) of the formation of a diffentiated crenulation cleavage during this second phase of deformation, by the processes of kinking, crenulation and associated differentiation.
Regional considerations indicate an Alpine age for this tectono-metamorphic event, which can be explained by the'hot emplacement'of the higher Nevado Filabride units. The observed structural evolution is not consistent with a pre-Alpine polyphase deformation history.  相似文献   

From ¹⁴C/¹²C measurements towards radiocarbon dating of ice     

R. S. W. VAN DE WAL  J. J. VAN ROIJEN  D. RAYNAUD  K. VAN DER BORG  A. F. M. DE JONG  J. OERLEMANS  V. LIPENKOV  P. HUYBRECHTS 《Tellus. Series B, Chemical and physical meteorology》1994,46(2):94-102

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Trace elements and individual particle analysis of atmospheric aerosols from the Antarctic peninsula     

PAULO ARTAXO  MARTA L. C. RABELLO  WILLY MAENHAUT  RENÉ VAN GRIEKEN 《Tellus. Series B, Chemical and physical meteorology》1992,44(4):318-334

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Weichselian in Sweden before 15,000 B.P.     

JAN LUNDØLVIST 《Boreas: An International Journal of Quaternary Research》1981,10(4):395-402

A brief summary is given of the present state of knowledge about the Weichselian glaciations and interstadials in sweden. The following stages are discussed: (1) The first Weichselian glaciation (W1). This glaciation has not been identified. Probably only northern Sweden was ice-covered. (2) The Jämtland Interstadial , dated at > 50,000 B.P. and correlated with the Finnish Peräpohjola and the Danish Brörup Interstadials. - (3) The second Weichselian glaciation (W II). There are several uncertainteis concerning this glaciation. Sweden was probably ice-covered down to the latitude of Stockholm. – (4) A Middle Weichsedlian interstadial , or complex of interstadials. Some radiocarbon dates indicate, although very uncertain, that most of Sweden may have been free of ice some time rather well known. – Some main problems which have to be investigated are also identified.  相似文献   

Genesis of the Woodstock drumlin field, southern Ontario, Canada     

JAN A. PIOTROWSKI 《Boreas: An International Journal of Quaternary Research》1987,16(3):249-265

The Woodstock drumlin field was formed about 15,000 years ago during the Port Bruce Stadial of the Late Wisconsinan. It consists of three sections, each composed of texturally different till sheets (Tavistock A, B and C Tills) deposited during marginal oscillations of the Huron ice lobe advancing from the Lake Huron depression. A statistically significant relation between till texture and drumlin morphometry has been determined. Features composed of clayey-silt Tavistock A Till are smaller and more elongate than those built up of sandy-silt Tavistock C Till, which reflects a different susceptibility of the drumlin deposits to the moulding action of the glacier. Based on the field data it is suggested that the drumlinizing glacier was temperate all the way up to its margin and basal sliding occurred also at its outermost peripheries. In the drumlin region immediately behind end moraines the shear strength/shear stress ratio was around I and increased progressively in the upstream direction. In the proposed mechanism of drumlin formation the key factor is pore water dissipation (1) through the permeable substratum and (2) into dilatantly expanding granular deposits, both resulting in the necessary increase of the basal till strength.  相似文献   

Weichselian Convolution Phenomena and processes in fine sediments.     

JEF VANDENBERGHE  PETER VAN DEN BROEK 《Boreas: An International Journal of Quaternary Research》1982,11(4):299-315

In three excavations in the southern Netherlands and northern Belgium, the Weichselian convolutions in fine sand, silt and clay deposits were investigated, and an attempt was made towards a semi-quantitative approach to some sediment parameters. This, together with a detailed field survey, enabled interpretation of the deformations as forms of periglacial loadcasting. They originated from the time of permafrost degradation when large quantites of water were available. The amplitude of the involutions can be related to the depth of the permafrost table at that time. During the weichselian, two periods occurred in which this involution process could have been active  相似文献   

P–T–fluid evolution in the Mahalapye Complex, Limpopo high-grade terrane, eastern Botswana     

K. HISADA  L. L. PERCHUK  T. V. GERYA  D. D. VAN REENEN  B. K. PAYA 《Journal of Metamorphic Geology》2005,23(5):313-334

Metapelites, migmatites and granites from the c. 2 Ga Mahalapye Complex have been studied for determining the P–T–fluid influence on mineral assemblages and local equilibrium compositions in the rocks from the extreme southwestern part of the Central Zone of the Limpopo high‐grade terrane in Botswana. It was found that fluid infiltration played a leading role in the formation of the rocks. This conclusion is based on both well‐developed textures inferred to record metasomatic reactions, such as Bt ? And + Qtz + (K₂O) and Bt ± Qtz ? Sil + Kfs + Ms ± Pl, and zonation of Ms | Bt + Qtz | And + Qtz and Grt | Crd | Pl | Kfs + Qtz reflecting a perfect mobility (Korzhinskii terminology) of some chemical components. The conclusion is also supported by the results of a fluid inclusion study. CO₂ and H₂O ( = 0.6) are the major components of the fluid. The fluid has been trapped synchronously along the retrograde P–T path. The P–T path was derived using mineral thermobarometry and a combination of mineral thermometry and fluid inclusion density data. The Mahalapye Complex experienced low‐pressure granulite facies metamorphism with a retrograde evolution from 770 °C and 5.5 kbar to 560 °C and 2 kbar, presumably at c. 2 Ga.  相似文献   

Glacial history of western Norway 15,000–10,000 B.P.     

JAN MANGERUD  EILIV LARSEN  ODDVAR LONGVA  EIVIND SØNSTEGAARD 《Boreas: An International Journal of Quaternary Research》1979,8(2):179-187

The deglaciation patterns of the Bergen and Nordfjord-Sunnmøre areas in western Norway are described and correlated. In the Bergen area the coast was first deglaciated at 12,600 B.P., with a succeeding re-advance into the North Sea around 12,200 B.P. Later, during the Allerød, the inland ice retreated at least 50 km, but nearly reached the sea again during the Younger Dryas re-advance, ending at 10,000 B.P. Sunnmøre was ice-free during an interstadial 28,000–38,000 B.P. Later the inland ice reached the sea. The final deglaciation is poorly dated in Sunnmøre, while further south in Nordfjord, it started slightly before 12,300 B.P., followed by a major retreat. No large re-advance of the inland ice occurred during the Younger Dryas. However, in the Sunnmøre-Nordfjord area many local glaciers formed outside the inland ice during the Younger Dryas. Limnic sediments outside one such cirque glacier have been cored and dated, proving that the glacier did not exist at 12,300-11,000 B.P., and that it was formed and disappeared in the time interval 11,000–10,000 B.P. (Younger Dryas). The erosion rate of the cirque glacier was 0.9 mm/year.  相似文献