Counting fission tracks in mica external detectors

The different ways in which minerals and external detectors respond to chemical etching are outlined. While it is prossible that the distribution of angles of inclination of fission tracks in some materials can be determined from the measurement of the aspect ratios of the etch pits this cannot be done using mica detectors. A method of measuring the distribution of angles of inclination in mica detectors based on the frequency distribution of areas of fission track entry holes is proposed. The results of two experiments are presented, and a means of correcting the number of tracks lost during etching is described.     

The role of the chemical environment in frictional deformation: Stress corrosion cracking and comminution

The roles of chemically assisted crack and fracture propagation and chemically assisted comminution in frictional deformation are evaluated in this study. Double cantilever beam (DCB) crack propagation data are presented which show that the role of pH in chemically assisted fracture, and to a lesser extent the role of ionic concentration are important in stress corrosion cracking. Data on very slow crack growth and the stress corrosion limit are also presented. These data suggest that stress corrosion cracking may play an important role in compound earthquakes and in asperity breakdown in faults. The comminution literature is also reviewed in order to assess the role of chemically assisted comminution in frictional deformation. It appears that chemically assisted comminution may be important at low and high ionic strength because it may reduce the effective viscosity and the shear strength of fault gouge. At intermediate ionic concentration the role of pH, as an agent which enhances crack and fracture propagation, appears to be more important in reducing the coefficient of sliding friction.     

A lithospheric seismic profile along the axis of the Alps, 1975

Summary From 8 to 20 September 1975 refraction seismic measurements were carried out in close European cooperation on a long range profile along the strike of the Alps between France and Hungary. The execution and first results of the Alpine Longitudinal Profile 1975 are presented in this paper, which is the first of a series. 20 shots from 9 different shotpoints were recorded by 193 mobile stations along a main line of a length of 850 km as well as on a number of fans and additional shorter profiles. The recordings were subsequently digitized and a number of computer generated record sections are presented to illustrate the quality of the data. First results are given in the form of a simple crustal cross section along the main profile and of two velocity depth functions, which indicate a substantial difference in type between the westernmost part and the eastern part of the profile.G. Angenheister, J. Ansorge, K. Aric, D. Bamford, R. Cassinis, H. Gebrande, I. Guerra, R. Gutdeutsch, W. Kaminski, R. King, H. Miller, C. Morelli, St. Mueller, R. Nicolich, G. perrier, K. Posgay, C. Prodehl, S. Scarascia, E. Schmedes, P. Steinhauser, F. Thouvenot.     

Alpha emitters in a coral from Bikini lagoon: A testimony to nuclear blasts in the Western Pacific

In the years between 1946 and 1958, Bikini Atoll was the site of a series of nuclear device tests which led to the contamination of the calcium-carbonate tests of organisms, including those of corals. Alpha emitters and other radio-nuclides concentrated in these tests. The purpose of our study was to determine where in these test-alpha-emitters concentrated.Petrography of ultra thin sections, in conjunction with solid state alpha-track detectors, shows that it is possible to assign the alpha activity to different parts of the fabric within a coral. The application of this technique to a coral,Favites virens, from the lagoon of Bikini Atoll showed that the theca, septa and dissepiments of the coral skeleton contain very low concentrations of alpha emitters. By contrast, high concentration of alpha emitters occur in damaged parts of the coral. Some of these damaged areas contain cryptocrystalline calcium carbonate, different organisms (algae and/or bryozoan-like tests) and skeletal debris. High concentrations of alpha emitters are associated with the cryptocrystalline calcium carbonate (up to 3000 pCi/g), the skeletal debris (up to 550 pCi/g), bryozoan-like material, and algae (up to 700 pCi/g).

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Measurement of marine radionuclide distribution using a towed sea-bed spectrometer

The application of in situ gamma-ray spectrometry to the measurement of radionuclide concentration in sea water and sea-bed sediment is discussed with special reference to a towed sea-bed gamma-ray spectrometer survey of radio-effluent distribution in the Irish Sea. The sensitivity and accuracy of the method are established by comparing the spectrometer measurements with laboratory analyses of sediment samples. Contour maps produced from the spectrometer profiles are matched with the distribution of bottom sediment types and conclusions are drawn concerning the modes of transport and deposition of ¹³⁷Cs in the Irish Sea.     

A postglacial coleopterous assemblage from Lockport Gulf,New York

The Lockport Gulf site near Lockport, New York, is a 1.9-m sequence of organic-rich marls having a basal date of approximately 10,920 yr B.P. Six bulk samples with a combined weight of 48 kg produced over 780 individual fossil insects representing five orders, as well as molluscs and abundant plant macrofossils. Coleoptera were represented by 24 families. Several major beetle groups (Carabidae, ground beetles; Hydrophilidae, water scavenger beetles; Elmidae, riffle beetles; Staphylinidae, rove beetles; and Scolytidae, bark beetles) indicate a riffle-and-pool stream, surrounded by marsh, with open riparian habitats and nearby trees. Two zones were recognized based on the Coleoptera assemblages. The Zone 1 fauna (ca. 10,920–9800 yr B.P.) was dominated by boreal forest taxa with abundant bark beetles indicating the presence of spruce trees. In Zone 2 (ca. 9700-9100 yr B.P.) the combination of species with a restricted modern distribution in the Great Lakes-St. Lawrence Forest region and pine and deciduous tree inhabitants suggests a change in vegetation by 9700 yr B.P. Thermal estimates from a faunal analysis indicate that the climatic conditions were stable across the spruce-pine transition, with the mean July temperature in the range of 16° to 18°C.     

Amino acid geochemistry of fossil bones from the Rancho La Brea asphalt deposit,California

Low aspartic acid d:l ratios and modern collagenlike concentration values indicate that amino acids in bones from the Rancho La Brea asphalt deposit, Los Angeles, California are better preserved than amino acids in bones of equivalent age that have not been preserved in asphalt. Amino acids were recovered from 10 Rancho La Brea bone samples which range in age from less than 200 to greater than 36,000 yr. The calibrated rates of aspartic acid racemization range from 2.1 to 5.0 × 10^?6yr^?1. Although this wide range of rate constants decreases the level of confidence for age estimates, use of the larger rate constant of 5.0 × 10^?6yr^?1 provides minimum age estimates which fit the known stratigraphic and chronologic records of the Rancho La Brea deposits.     

Fission track ages on apatite of Bergell rocks from Central Alps and Bergell boulders in Oligocene sediments

Previous radiometric dating studies indicated that the Bergell region, in contrast to other regions of the Central Alps, experienced an early, rapid uplift, but with decreasing rate. Furthermore, there is also a geological record of the early uplift history of the Bergell granite by the existence of boulders which were derived from this granite and which occur in the Late Oligocene sediments of the Po plain.In this work the uplift history of the Bergell is studied in more detail by fission track dating of additional apatites from the Bergell region. Secondly, by determining apatite fission track ages the granitic boulders of the Po plain can be re-assigned to their original vertical position within the Bergell intrusive before erosion removed them in Late Oligocene time. A rather conservative estimate replaces them 6 km above the present morphology of the Bergell massif. Thus, the thickness of the Bergell granite must have been at least 8 km.Generally, fission track studies on boulders may become an important tool to study the vertical extent of mountain chains during the geological past.     

Reaction rims between olivine and plagioclase in metaperidotites, Ötztal Alps,Austria

Crustal garnetiferous metaperidotites occurring in a large garnet-amphibolite complex of the pre-Alpine Austroalpine unit are interpreted as metamorphosed cumulates within a metagabbroic intrusive complex. The garnet-coronas are a result of anhydrous reactions between olivine and plagioclase induced by high pressure metamorphism which at the same time was also responsible for the observed conversion of the gabbroic rocks to eclogites and amphibolites.     

Das Problem des hypothetischen „Pazifischen Kontinentes“ gesehen von der chilenischen Pazifikküste

Zusammenfassung Die verbreitet in den Pazifik hinausweisenden Strukturlinien der prämesozoischen Orogene Chiles fordern die ehemalige Existenz sialischer Kruste jenseits der heutigen Küste an Stellen, wo derzeit nur dünne, simatische Kruste vorhanden ist. Fünf Möglichkeiten des Verschwindens dieser kontinentalen Kruste werden diskutiert. Aus der ruhigen Lagerung der känozoischen Sedimente vor der heutigen Küste wird geschlossen, daß der wesentliche Teil der Umwandlung von kontinentaler Kruste in ozeanische seit längerer Zeit beendet ist.

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From the structural trends of the pre-Mesozoic orogenes pointing toward the Pacific, the existence of a former sialic (continental) crust, then beyond the modern coast of Chile, may be inferred. This inference applies in places where at present only a thin simatic crust is encountered. Five modes of disappearance of this sialic (continental) crust are discussed. The rather undisturbed position of the Cenozoic sediments off the present coast indicates that the main transformation of continental crust in oceanic crust has stopped some time ago.

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Résumé Les directions structurales des anciens orogènes exigent l'existence d'une écorce sialique au-delà de la côte actuelle du Chili, à des endroits où il ne se trouve à present qu'une mince croûte simatique. Dans le present article cinq explications pour la disparition de cette écorce continentale sont discutées. La position peu disloquée des sediments cénozoiques, au-delà de la côte actuelle, montre que la partie essentielle de la transformation de la croûte continentale en une crôute océanique est terminée depuis longtemps.

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