Geology and the Allied liberation of Normandy: highlights to help mark the 75th anniversary of D‐Day, 6 June 1944     

Edward P. F. Rose 《Geology Today》2019,35(3):107-114

During the Second World War, the Allied invasion of the French coast of Normandy on D‐Day, 6 June 1944, was the greatest amphibious assault in world history. An article in Geology Today (v.11, for 1995, pp.58–63) marked the 50th anniversary of the end of the war in Europe, on 8 May 1945, by describing how British military geologists had participated in planning for D‐Day and in the NW Europe campaign that followed it. The work of these geologists provides a classic case history, revealing that ‘military geology’ has many potential applications. Geological factors influenced site selection for temporary airfields, predictions of trafficability for the Normandy beaches, the development of potable water supplies, and quarrying for road metal—and more besides. This new article helps to mark the 75th anniversary of D‐Day by further details of how geologists and geology contributed to Allied victory.  相似文献   

On the possibility of earth-type habitable planets around 47 UMa     

Manfred Cuntz  Werner von Bloh  Siegfried Franck 《Icarus》2003,162(1):214-221

We investigate whether Earth-type habitable planets can in principle exist in the planetary system of 47 UMa. The system of 47 UMa consists of two Jupiter-size planets beyond the outer edge of the stellar habitable zone, and thus resembles our own Solar System most closely compared to all exosolar planetary systems discovered so far. Our study of habitability deliberately follows an Earth-based view according to the concept of Franck and colleagues, which assumes the long-term possibility of photosynthetic biomass production under geodynamic conditions. Consequently, a broad variety of climatological, biogeochemical, and geodynamical processes involved in the generation of photosynthesis-driven life conditions is taken into account. The stellar luminosity and the age of the star/planet system are of fundamental importance for planetary habitability. Our study considers different types of planetary continental growth models and takes into account a careful assessment of the stellar parameters. In the event of successful formation and orbital stability, two subjects of intense research, we find that Earth-type habitable planets around 47 UMa are in principle possible! The likelihood of those planets is increased if assumed that 47 UMa is relatively young (?6 Gyr) and has a relatively small stellar luminosity as permitted by the observational range of those parameters.  相似文献   

THE BLOOMINGTON (LL6) CHONDRITE AND ITS SHOCK MELT GLASSES     

Robert T. Dodd  Edward J. Olsen  Roy S. Clarke 《Meteoritics & planetary science》1985,20(3):575-581

The Bloomington meteorite, a 67.8 gram veined, brecciated chondrite, fell during the summer of 1938 in Bloomington, Illinois. Its olivine, orthopyroxene and metal compositions (fo₆₉, en₇₄ and Fe₅₂ Ni₄₈ respectively) and its texture identify it as a brecciated LL6 chondrite of shock facies d. Shock melt glasses occur in Bloomington as sparse melt pockets and veins in clasts and as isolated masses in the black, clast-rich matrix. The vein glasses chemically resemble bulk LL-group chondrites and thus appear to reflect total melting of the host meteorite. The melt pocket and matrix glasses, like those described previously in L-group chondrites, have more varied compositions and are typically enriched in normative plagioclase. All glasses that we analyzed in Bloomington have FeO/MgO and Na/Al ratios similar to those of LL-group chondrites, indicating that melting of this meteorite involved neither a significant change in the oxidation state of iron nor loss of sodium to a vapor phase. Bloomington is a monomict breccia whose components formed in place as a result of a single episode of shock and attendant melting.  相似文献   

Orbit computation for transneptunian objects     

Jenni Virtanen  Gonzalo Tancredi  Edward Bowell 《Icarus》2003,161(2):419-430

Using statistical orbital ranging, we systematically study the orbit computation problem for transneptunian objects (TNOs). We have automated orbit computation for large numbers of objects, and, more importantly, we are able to obtain orbits even for the most sparsely observed objects (observational arcs of a few days). For such objects, the resulting orbit distributions include a large number of high-eccentricity orbits, in which TNOs can be perturbed by close encounters with Neptune. The stability of bodies on the computed orbits has therefore been ascertained by performing a study of close encounters with the major planets. We classify TNO orbit distributions statistically, and we study the evolution of their ephemeris uncertainties. We find that the orbital element distributions for the most numerous single-apparition TNOs do not support the existence of a postulated sharp edge to the belt beyond 50 AU. The technique of statistical ranging provides ephemeris predictions more generally than previously possible also for poorly observed TNOs.  相似文献   

Doublet craters on Venus     

Cheryl M Cook  William F Bottke Jr. 《Icarus》2003,165(1):90-100

Of the impact craters on Earth larger than 20 km in diameter, 10-15% (3 out of 28) are doublets, having been formed by the simultaneous impact of two well-separated projectiles. The most likely scenario for their formation is the impact of well-separated binary asteroids. If a population of binary asteroids is capable of striking the Earth, it should also be able to hit the other terrestrial planets as well. Venus is a promising planet to search for doublet craters because its surface is young, erosion is nearly nonexistent, and its crater population is significantly larger than the Earth's. After a detailed investigation of single craters separated by less than 150 km and “multiple” craters having diameters greater than 10 km, we found that the proportion of doublet craters on Venus is at most 2.2%, significantly smaller than Earth's, although several nearly incontrovertible doublets were recognized. We believe this apparent deficit relative to the Earth's doublet population is a consequence of atmospheric screening of small projectiles on Venus rather than a real difference in the population of impacting bodies. We also examined “splotches,” circular radar reflectance features in the Magellan data. Projectiles that are too small to form craters probably formed these features. After a careful study of these patterns, we believe that the proportion of doublet splotches on Venus (14%) is comparable to the proportion of doublet craters found on Earth (10-15%). Thus, given the uncertainties of interpretation and the statistics of small numbers, it appears that the doublet crater population on Venus is consistent with that of the Earth.  相似文献   

A simple model for lensing by black holes in galactic nuclei     

M. C. Werner  N. W. Evans 《Monthly notices of the Royal Astronomical Society》2006,368(3):1362-1368

The lensing properties of the Plummer model with a central point mass and external shear are derived, including the image multiplicities, critical curves and caustics. This provides a simple model for a flattened galaxy with a central supermassive black hole. For the Plummer model with black hole, the maximum number of images is four, provided the black hole mass is less than an upper bound which is calculated analytically. This introduces a method to constrain black hole masses by counting images, thus applicable at cosmological distance. With shear, the maximum number of images is six and we illustrate the occurrence of an astroid caustic and two metamorphoses.  相似文献   

Oxygen isotopic compositions and origins of calcium‐aluminum‐rich inclusions and chondrules     

Edward R. D. Scott  Alexander N. Krot 《Meteoritics & planetary science》2001,36(10):1307-1319

Abstract— Primary minerals in calcium‐aluminum‐rich inclusions (CAIs), Al‐rich and ferromagnesian chondrules in each chondrite group have δ¹⁸O values that typically range from ?50 to +5%0. Neglecting effects due to minor mass fractionations, the oxygen isotopic data for each chondrite group and for micrometeorites define lines on the three‐isotope plot with slopes of 1.01 ± 0.06 and intercepts of ?2 ± 1. This suggests that the same kind of nebular process produced the ¹⁶O variations among chondrules and CAIs in all groups. Chemical and isotopic properties of some CAIs and chondrules strongly suggest that they formed from solar nebula condensates. This is incompatible with the existing two‐component model for oxygen isotopes in which chondrules and CAIs were derived from heated and melted ¹⁶O‐rich presolar dust that exchanged oxygen with ¹⁶O‐poor nebular gas. Some FUN CAIs (inclusions with isotope anomalies due to fractionation and unknown nuclear effects) have chemical and isotopic compositions indicating they are evaporative residues of presolar material, which is incompatible with ¹⁶O fractionation during mass‐independent gas phase reactions in the solar nebula. There is only one plausible reason why solar nebula condensates and evaporative residues of presolar materials are both enriched in ¹⁶O. Condensation must have occurred in a nebular region where the oxygen was largely derived from evaporated ¹⁶O‐rich dust. A simple model suggests that dust was enriched (or gas was depleted) relative to cosmic proportions by factors of ～10 to >50 prior to condensation for most CAIs and factors of 1–5 for chondrule precursor material. We infer that dust‐gas fractionation prior to evaporation and condensation was more important in establishing the oxygen isotopic composition of CAIs and chondrules than any subsequent exchange with nebular gases. Dust‐gas fractionation may have occurred near the inner edge of the disk where nebular gases accreted into the protosun and Shu and colleagues suggest that CAIs formed.  相似文献   

The global Frasnian-Famennian »Kellwasser Event«   总被引：5，自引：0，他引：5  

Werner Buggisch 《International Journal of Earth Sciences》1991,80(1):49-72

During the UppermostP. gigas conodont zone (P. linguiformis zone) the stepwise Frasnian extinction culminates in the global transgressive-regressive Frasnian-Famennian »Kellwasser event«. Most pelagic organisms of the tropical marine environment are more or less affected by this mass extinction. During the early Upper Devonian extinction rates are clearly related to the deposition of black shales and the storage of a great amount of organic carbon in the (shelf) sediments. Contemporaneous positive excursions of the ¹³C recorded from pelagic limestones of Europe and Australia prove a worldwide change in the CO₂ content of the oceans surface water which is in balance with the atmosphere. If the climate is controlled by the CO₂ content of the atmosphere, a cyclic operation process might have developed with the succession: transgression — high organic production — deposition of organic carbon — lowering of CO₂ in the atmosphere — icehouse effect — polar glaciation — regression — erosion of organic carbon and re-supply of CO₂ to the ocean and atmosphere — greenhouse effect — deglaciation — transgression. During the change from a greenhouse to an icehouse effect an overturn of the anoxic oceans probably was one of the causes for the mass killing of low latitude marine organisms.

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Zusammenfassung Während der OberstenP. gigas-Zone (=P. linguiformis-Zone) kulminiert das stufenweise Erlöschen der Frasne Organismen im globalen transgressiv-regressiven »Kellwasser-Ereignis«, das die Frasne-Famenne-Grenze markiert. Die meisten Organismengruppen der tropischen Meere werden mehr oder weniger von dem Massensterben betroffen. Während des tiefen Oberdevons sind die Aussterberaten offensichtlich mit der Ablagerung von Schwarzschiefern verknüpft, in denen eine große Menge organischen Kohlenstoffs auf den Schelfen fixiert wird. Gleichzeitige positive Exkursionen der ¹³C-Kurven, die in pelagischen Kalken aus Europa und Australien gemessen wurden, deuten auf eine weltweite Änderung der CO₂-Gehalte des ozeanischen Oberflächenwassers und der Atmosphäre hin.Sollte das Klima vom CO₂ in der Atmosphäre gesteuert werden, könnte sich folgender Autozyklus entwickelt haben: Transgression — hohe organische Produktion — Ablagerung von organischem Kohlenstoff — Erniedrigung des CO₂-Gehaltes in der Atmosphäre — Abkühlung — polare Vereisung-Regression — Erosion und Oxidation von organischem Kohlenstoff — Erhöhung des CO₂-Gehaltes in der Atmosphäre — Treibhauseffekt — Abschmelzen der polaren Vereisung — Transgression. Aufsteigende anoxische Wässer beim Übergang vom Treibhaus- zum »Kühlhauseffekt« dürften eine der Ursachen für das Massensterben tropischer mariner Organismen gewesen sein.

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Résumé Au cours de la partie supérieure de la zone de conodontes àP. gigas (= zone àP. linguiformis), l'extinction progressive des organismes frasniens a culminé au moment de l'événement de Kellwasser, marqué par une transgression-régression globale à la limite Frasnien-Famennien. La plupart des organismes pélagiques des milieux marins tropicaux ont été affectés à des degrés divers par cette extinction de masse. Pendant le début du Dévonien supérieur, les taux d'extinction sont clairement en relation avec le dépôt de boues noires et le stockage d'une grande quantité de matière organique dans les sédiments de shelf. Simultanément, des variations positives de ¹³C enregistrées dans des calcaires pélagiques d'Europe et d'Australie indiquent un changement modial de la teneur en CO₂ de l'eau de surface des océans et de l'atmosphère.Si on admet que le climat est régi par la teneur en CO₂ de l'atmosphère, le processus cyclique suivant a pu se développer: transgression — forte production organique — dépôt de carbone organique — baisse de la teneur en CO₂ de l'atmosphère — refroidissement — glaciation polaire — régression — érosion et oxydation du carbone organique — élévation de la teneur en CO₂ de l'atmosphère — effet de serre — fusion des glaces polaires — transgression. Lors du passage du stade de l'effet de serre à celui du refroidissement, une remontée des eaux anoxiques océaniques peut être à l'origine de l'extinction de masse des organismes marins tropicaux.

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Neutron techniques     

Glenn M. Frye Jr.  Philip P. Dunphy  Edward L. Chupp  Paul Evenson 《Solar physics》1988,118(1-2):321-346

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High resolution paleoenvironmental and chronological investigations of Norse landnám at Tasiusaq, Eastern Settlement, Greenland     

Kevin J. Edwards  J. Edward Schofield 《Quaternary Research》2008,69(1):1-15

High-resolution paleoenvironmental data from a peat profile with a small pollen source area are used to reconstruct the impacts of landnám on vegetation and soils at a Norse farm complex (∅2 at Tasiusaq) comprising two farms in the Eastern Settlement of Greenland. Analyses include the AMS ¹⁴C dating of plant macrofossil samples and the use of Bayesian radiocarbon calibration to construct improved age-depth models for Norse cultural horizons. The onset of a regional landnám may be indicated by the clearance of Betula pubescens woodland immediately prior to local settlement. The latter is dated to AD 950-1020 (2σ) and is characterised by possible burning of Betula glandulosa scrub to provide grassland pasture for domestic stock. Clearance and grazing resulted in accelerated levels of soil erosion at a westerly farm. This was followed by an easterly migration of settlement and agriculture. Site constraints prevent an assessment of the demise of the easterly farm, but pressures of overgrazing and land degradation may have been the major factors responsible for the abandonment of the earlier farm.  相似文献