(U‐Th)/He zircon dating of Chesapeake Bay distal impact ejecta from ODP site 1073     

M. B. Biren  J.‐A. Wartho  M. C. VAN Soest  K. V. Hodges  H. Cathey  B. P. Glass  C. Koeberl  J. W. Horton  W. Hale 《Meteoritics & planetary science》2019,54(8):1840-1852

Single crystal (U‐Th)/He dating has been undertaken on 21 detrital zircon grains extracted from a core sample from Ocean Drilling Project (ODP) site 1073, which is located ~390 km northeast of the center of the Chesapeake Bay impact structure. Optical and electron imaging in combination with energy dispersive X‐ray microanalysis (EDS) of zircon grains from this late Eocene sediment shows clear evidence of shock metamorphism in some zircon grains, which suggests that these shocked zircon crystals are distal ejecta from the formation of the ~40 km diameter Chesapeake Bay impact structure. (U‐Th/He) dates for zircon crystals from this sediment range from 33.49 ± 0.94 to 305.1 ± 8.6 Ma (2σ), implying crystal‐to‐crystal variability in the degree of impact‐related resetting of (U‐Th)/He systematics and a range of different possible sources. The two youngest zircon grains yield an inverse‐variance weighted mean (U‐Th)/He age of 33.99 ± 0.71 Ma (2σ uncertainties n = 2; mean square weighted deviation = 2.6; probability [P] = 11%), which is interpreted to be the (U‐Th)/He age of formation of the Chesapeake Bay impact structure. This age is in agreement with K/Ar, ⁴⁰Ar/³⁹Ar, and fission track dates for tektites from the North American strewn field, which have been interpreted as associated with the Chesapeake Bay impact event.  相似文献   

A shift towards wetter and windier conditions in southern Sweden around the prominent solar minimum 2750 cal a BP          下载免费PDF全文

ANETTE MELLSTRÖM  NATHALIE VAN DER PUTTEN  RAIMUND MUSCHELER  RIXT DE JONG  SVANTE BJÖRCK 《第四纪科学杂志》2015,30(3):235-244

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Reconstructing Quaternary Rhine–Meuse dynamics in the southern North Sea: architecture,seismo‐lithofacies associations and malacological biozonation     

K. F. RIJSDIJK  I. C. KROON  T. MEIJER  S. PASSCHIER  T. A. G. P. VAN DIJK  F. P. M. BUNNIK  A. C. JANSE 《第四纪科学杂志》2013,28(5):453-466

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KALMOD,a stochastic-deterministic model for simulating groundwater flow with Kalman filtering     

ZHOU YANGXIAO  F. C. VAN GEER 《水文科学杂志》2013,58(4):375-389

Abstract

This paper presents the program KALMOD which has been developed to enable the execution of the integration of the Kalman filtering and the numerical groundwater flow model MODFLOW on microcomputers. The program can be applied to quantify and reduce the uncertainty of the groundwater flow model, and to analyse and design groundwater monitoring networks. KALMOD consists of a preprocessor, a processor and a postprocessor. The preprocessor acts as an interface between the user and the processor. The processor manipulates the measurement processes and carries out the filtering tasks. The filtering algorithm is implemented so that it is relatively efficient with respect to computer memory and execution time. The postprocessor was designed to present the model results in graphics. The program is suitable for small scale problems and for educational purposes.  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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Infrared stimulated luminescence dating of an Eemian (MIS 5e) site in Denmark using K‐feldspar     

JAN‐PIETER BUYLAERT  SÉBASTIEN HUOT  ANDREW S. MURRAY  PETER VAN DEN HAUTE 《Boreas: An International Journal of Quaternary Research》2011,40(1):46-56

Buylaert, J.‐P., Huot, S., Murray, A.S. & Van den haute, P.: Infrared stimulated luminescence dating of an Eemian (MIS 5e) site in Denmark using K‐feldspar. Boreas, 10.1111/j.1502‐3885.2010.00156.x. ISSN 0300‐9483. Infrared stimulated luminescence (IRSL) dating of K‐feldspars may be an alternative to quartz optically stimulated luminescence (OSL) dating when the quartz OSL signal is too close to saturation or when the quartz luminescence characteristics are unsuitable. In this paper, Eemian (MIS 5e) coastal marine sands exposed in a cliff section on the coast of southern Jutland (Denmark) are used to test the accuracy and precision of IRSL dating using K‐feldspars. This material has been used previously to test quartz OSL dating ( Murray & Funder 2003 ): a small systematic underestimation of <10% compared to the expected age of ～130 ka was reported. In our study, a single‐aliquot regenerative‐dose (SAR) IRSL protocol is used to determine values of equivalent dose (D_e) and the corresponding fading rates (g values). A significant age underestimation (of up to ～35%) is observed; this is attributed to anomalous fading. Using a single site‐average fading rate of 3.66 ± 0.09%/decade to correct the IRSL ages for all samples provides good agreement between the average fading‐corrected K‐feldspar age (119 ± 6 ka) and the independent age control (132–125 ka). This is despite the reservations of Huntley & Lamothe (2001) that their fading correction method is not expected to work on samples older than ～20–50 ka. This fading‐corrected feldspar result is not significantly different from the overall revised quartz age (114 ± 7 ka) also presented here. We conclude that fading‐corrected IRSL ages measured using K‐feldspar may be both precise and accurate over a greater age range than might be otherwise expected.  相似文献   

ON A FOSSIL FRESHWATER CRAYFISH FROM EASTERN MONGOLIA     

VICTOR VAN STRAELEN 《地质学报》1928,7(2):200-212

1.—Introduction. Father E. Licent, S. J., during one, of his travels in Eastern Mongolia, discovered, in the Lycoptera and Ephemeropsis shales, the remnants of three Decapod Crustaceans. They belong to a new species, which shall be designated as Astacus licenti, nov. sp., in honour of that indefatigable explorer, that is Father Licent.  相似文献   

REMARQUES SUR L'INTERPRETATION DES SONDAGES DE POLARISATION PROVOQUEE ESSAI DE THEORIE QUANTITATIVE *     

PHAM VAN NGOC  J. ROUSSEL  Et D. TOURNIER 《Geophysical Prospecting》1970,18(1):34-46

The transient phenomena associated with induced polarization are very complex and it is necessary to have both a proper understanding of the physical processes and a good supply of mathematical aids in order to make any advance in the quantitative interpretation of I.P. surveys. The analogy between the classical electrical sounding method and the induced polarization sounding method has led a number of workers to interpret the results of the latter like the results of the former. To clarify this idea, it seems very interesting to calculate a mathematical model in order to know the form of the anomaly that can be probably expected. The case of a thin horizontal polarizable layer, with the same uniform and isotropic conductibility as the homogeneous background, has been studied in this paper. The result of the calculation for the case of a single current electrode and a single potential electrode is given. From these data, the theoretical curve of IP sounding using the Wenner electrode array is computed. The master curve is compared with experimental curves obtained on scale models. A good correlation between these curves is noticed. In addition, it can be concluded that the mathematical model is proving the validity of the experiments on interpretation scale models.  相似文献   

DELINEATION OF SHALLOW SALT DOMES AND SURFACE FAULTS BY TEMPERATURE MEASUREMENTS AT A DEPTH OF APPROXIMATELY 2 METRES*     

J. PH. POLEY  J. VAN STEVENINCK 《Geophysical Prospecting》1970,18(Z1):666-700

The feasibility of using temperature measurements at a depth of about 2 m for locating and delineating salt domes and faults has been investigated both theoretically and in experimental field surveys. It is shown that measurable temperature anomalies in the soil are to be expected over shallow salt domes. In a field survey over a salt-dome area bordering the Groningen gas field, a large number of temperature measurements were made in small holes (2 m deep, 3 cm in diameter) within a relatively short time (some weeks). The results clearly indicate several temperature anomalies with differential temperatures of about 1°C. Comparison of our thermal contour map with interpretations of available seismic or gravity data, or with direct evidence from wells, showed an excellent correlation. Seismic data even support the shape of the thermal contours. Results in similar agreement with gravity or well data were obtained over salt ridges in a tropical area. Experiments showed that the technique worked as well in lakes and marshes as on dry land. In addition, some experimental evidence collected so far over shallow and surface faults is presented. In several cases, strong thermal anomalies coincided with known surface faults. A thermal model for a surface-fault zone is suggested which accounts satisfactorily for the observed thermal data. It suggests some diagnostic value for the fault's geometry. For shallow faults, however, lack of knowledge of subsurface detail prevented any unambiguous correlation with observed thermal anomalies. Accordingly any geological use of thermal analysis over shallow faults remains debatable. The field technique is simple, needs little correction and can, where useful, easily be included in routine gravity work to provide additional local information.  相似文献   

Subglacial bedforms and conditions associated with the 1991 surge of Skeiðarárjökull, Iceland     

RICHARD I. WALLER  THAIENNE A. G. P. VAN DIJK  ÓSKAR KNUDSEN 《Boreas: An International Journal of Quaternary Research》2008,37(2):179-194

Much previous research at surge-type glaciers has sought to identify features diagnostic of surge-type behaviour. However, in comparatively little work have subglacial landform–sediment characteristics been used to reconstruct changing basal processes and conditions during surge events. Subglacial bedforms described in this article are associated with the 1991 surge of Skeiðarárjökull, Iceland, and include a series of drumlins with superimposed flutes and basal crevasse-fill ridges. The drumlins were formed by the subglacial erosion of ice-contact fans. Sedimentary evidence indicates a shift from rigid-bed to soft-bed conditions during the surge. The presence of eroded but undeformed fan sediments suggests that they acted as a rigid bed when initially overridden. Subsequent deposition of a layer of deformation till resulted in a change to soft-bed conditions and the generation of flutes and subglacial crevasse-fill ridges. The lack of mixing between this till and the underlying stratified sediments indicates that subglacial sediment deformation was restricted to a thin layer and that its deposition resulted in a cessation of subglacial erosion. The drumlin is therefore a composite of both rigid-bed and soft-bed processes that illustrates changes in basal conditions and processes during the course of the event. The limited time frame in which the drumlin formed and the presence of kettleholes across its surface are distinctive features that may warrant further investigation in the search for features diagnostic of past surge events.  相似文献