Contributions of various types of damage to inactivation of T4 bacteriophage by protons

Mean doses for damage induced by 3.7-MeV protons in T3 phage were measured for the following effects: inactivation, killing, adsorption, DNA injection, capsid rupture with DNA release, and single- and double-strand DNA breaks. These effects have been related to phase survival in the same experiment because of the variability inherent in such measurements. The experiments were carried out in nutrient broth, phosphate buffer, and phosphate buffer plus histidine as suspension media. The following conclusions can be drawn: (i) DNA double-strand breakage is the dominant cause of inactivation in nutrient broth; (ii) scavengers protect the DNA inside the capsid to only a small degree; (iii) indirect actions affect functions associated with proteins; (iv) DNA release, as measured by capsid rupture, accounts for only a small percentage of the loss of viability; (v) essentially all DNA from adsorbed phage is injected even though a large proportion of the DNA contains double-strand breaks

Magnetostratigraphy and biostratigraphy of the Middle Triassic Margon section (Southern Apls, Italy)

A magnetostratigraphic study has been performed on the paleontologically well constrained pelagic Middle Triassic (Lower/Upper Ladinian boundary) section at Margon (Trento, Southern Alps, Italy). Rock magnetic investigations indicate the presence of both, high and low coercivity minerals. Specimens subjected to progressive thermal demagnetization procedures show that nearly all of them exhibit a low temperature magnetization component, parallel to the present-day field before bedding correction, and a high temperature one, characterized by either positive or negative and opposite polarity, considered as the characteristic Triassic magnetization. The comparison of the Margon magnetic polarity zonation with those of two coeval sections poses some problems when ammonoid- and conodont based stratigraphies have to be correlated. However, good correlation has been obtained for the recognized Middle Triassic ammonoid biozones in the Tethyan realm. Valuable data to the construction of a standard magnetostratigraphic and paleontological scale are contributed by the results from the Margon section.A magnetostratigraphic study has been performed on the paleontologically well constrained pelagic Middle Triassic (Lower/Upper Ladinian boundary) section at Margon (Trento, Southern Alps, Italy). Rock magnetic investigations indicate the presence of both, high and low coercivity minerals. Specimens subjected to progressive thermal demagnetization procedures show that nearly all of them exhibit a low temperature magnetization component, parallel to the present day field before bedding correction, and a high temperature one, characterized by either positive or negative and opposite polarity, considered as the characteristic Triassic magnetization. The comparison of the Margon magnetic polarity zonation with those of two coeval sections poses some problems when ammonoid- and conodontbased stratigraphies have to be correlated. However, good correlation has been obtained for the recognized Middle Triassic ammonoid biozones in the Tethyan realm. Valuable data to the construction of a standard magnetostratigraphic and paleontological scale are contributed by the results from the Margon section. © 2001 Elsevier Science B.V. All rights reserved

Magnetostratigraphy of Early–Middle Toarcian expanded sections from the Iberian Range (central Spain)

The magnetostratigraphy of the Lower–Middle Toarcian has been established in two well-dated stratigraphically expanded sections: the Sierra Palomera and the Ariño sections, located in the Iberian Range, in central-eastern Spain. Two magnetisation components could be isolated by thermal cleaning: a secondary syntectonic component of always normal polarity unblocking at intermediate temperatures up to 450 °C/475 °C (A component) and a high temperature unblocking component up to 575 °C (B component). The B component passes fold and reversal tests and is considered the characteristic remanent magnetisation of primary origin. The first Toarcian palaeomagnetic pole for Iberia has been obtained: Plat = 77.4°, Plon = 241.3°E (dm = 5.4° dp = 6.0°). Five pairs of normal and reversed polarity zones were calibrated to regional ammonite subzones. The pattern can be calibrated to other Toarcian magnetostratigraphic studies, but provides a more detailed biostratigraphic framework. A refined magnetic polarity time scale is proposed for the Lower–Middle Toarcian.Ministerio de Educación y CienciaDepto. de Geodinámica, Estratigrafía y PaleontologíaDepto. de Física de la Tierra y AstrofísicaFac. de Ciencias GeológicasFac. de Ciencias FísicasTRUEpu

The Global Boundary Stratotype Section and Point (GSSP) of the Toarcian-Aalenian Boundary (Lower-Middle Jurassic)

The Global Boundary Stratotype Section and Point (GSSP) for the Aalenian Stage, formally defined at the base of bed FZ107 in the Fuentelsaz section, Castilian Branch of the Iberian Range (Spain), has been ratified by the IUGS. Multidisciplinary biostratigraphical data, based on ammonites, brachiopods, ostracods, bivalves, foraminifera, calcareous nannofossils assemblages and palynomorphs, assure worldwide correlations; magnetostratigraphic data increase this correlation power. The position of the boundary coincides with the first occurrence of the ammonite assemblage characterized by Leioceras opalinum and Leioceras lineatum and corresponds with a normal polarity interval correlated with the up-to-date Jurassic magnetic polarity time scale (Gradstein and others, 1994; Ogg, 1995)