Precise U-Pb age constraints for end-Triassic mass extinction, its correlation to volcanism and Hettangian post-extinction recovery

New precise zircon U-Pb ages are proposed for the Triassic-Jurassic (Rhetian-Hettangian) and the Hettangian-Sinemurian boundaries, The ages were obtained by ID-TIMS dating of single chemical-abraded zircons from volcanic ash layers within the Pucara Group, Aramachay Formation in the Utcubamba valley, northern Peru. Ash layers situated between last and first occurrences of boundary-defining ammonites yielded Pb-206/U-238 ages of 201.58 +/- 0.17/0.28 Ma (95% c.l., uncertainties without/with decay constant errors, respectively) for the Triassic-Jurassic and of 199.53 +/- 0.19/0.29 Ma for the Hettangian-Sinemurian boundaries. The former is established on a tuff located 1 m above the last local occurrence of the topmost Triassic genus Choristoceras, and 5 m below the Hettangian genus Psiloceras. The latter sample was obtained from a tuff collected within the Badouxia canadensis beds. Our new ages document total duration of the Hettagian of no more than c. 2 m.y., which has fundamental implications for the interpretation and significance of the ammonite recovery after the topmost Triassic extinction. The U-Pb age is about 0.8 +/- 0.5% older than Ar-40-Ar-39 dates determined on flood basalts of the Central Atlantic Magmatic Province (CAMP). Given the widely accepted hypothesis that inaccuracies in the K-40 decay constants or physical constants create a similar bias between the two dating methods, our new U-Pb zircon age determination for the T/J boundary corroborates the hypothesis that the CAMP was emplaced at the same time and may be responsible for a major climatic turnover and mass extinction. The zircon Pb-206/U-238 age for the T/J boundary is marginally older than the North Mountain Basalt (Newark Supergroup, Nova Scotia, Canada), which has been dated at 201.27 +/- 0.06 Ma [Schoene et al., 2006. Geochim. Cosmochim. Acta 70, 426-445]. It will be important to look for older eruptions of the CAMP and date them precisely by U-Pb techniques while addressing all sources of systematic uncertainty to further test the hypothesis of volcanic induced climate change leading to extinction. Such high-precision, high-accuracy data will be instrumental for constraining the contemporaneity of geological events at a 100 kyr level. (C) 2007 Elsevier B.V. All rights reserved.

Edge excitations and topological order in rotating Bose gas

The edge excitations and related topological orders of correlated states of a fast rotating Bose gas are studied. Using exact diagonalization of small systems, we compute the energies and number of edge excitations, as well as the boson occupancy near the edge for various states. The chiral Luttinger-liquid theory of Wen is found to be a good description of the edges of the bosonic Laughlin and other states identified as members of the principal Jain sequence for bosons. However, we find that in a harmonic trap the edge of the state identified as the Moore-Read (Pfaffian) state shows a number of anomalies. An experimental way of detecting these correlated states is also discussed.

Detrital zircon and micropalaeontological ages as new constraints for the lowermost tectonic unit (Talea Ori unit) of Crete, Greece

The Talea Ori unit is the lowermost known tectonic unit of Crete and the most external part of the Hellenides. Its stratigraphy ranges from Late Carboniferous to Oligocene and outcrops of the lower part are only known in the Talea Ori mountains (central Crete). In this area, a black sandstone at the base of the Galinos Beds, thought to be the oldest formation, contains zircons which were dated using the single grain evaporation method. The majority of these grains yielded Late Carboniferous ages (Variscan), while a small group yielded Early Proterozoic ages. The age distribution of these zircons suggests that, at the Carboniferous-Permian boundary, not much of the older North Gondwanan basement was exposed and that a river system carried detrital material from the Variscan belt towards the forming Neotethyan rift. Additionally, higher up in the stratigraphy benthic foraminifers (miliolids) were found in clasts from a conglomerate which was so far thought to be of Early Triassic age [Epting, M., Kudrass, H.-R., Leppig, U., Schaffer, A., 1972. Geologie der Talea Ori/Kreta. N. Jb. Geol. Palaont. Abh. 141, 259-285.]. These miliolids belong to the species Hoyenella inconstans [Michalik, J., Jendrejakova, O., Borza, K., 1979. Some new foraminifera species of the Fatra-Formation (Uppermost Triassic) in the West Carpathians. Geol. Carpath. 30 (1), 61-91.], thus attributing a Late Triassic (Carnian-Norian?) maximal age to this conglomerate. The carbonate platform from which the miliolids-bearing clasts come is not known. The presence to the north of a continuous hemipelagic record from the Carboniferous to the Triassic (Phyllite-Quartzite and Tripali units), attributed to the Palaeotethys realm, allows the Talea Ori unit and its lateral equivalents (the Ionian zone) to be assigned to the westward continuation of the Cimmerian block and therefore to the northern margin of the East Mediterranean Neotethys ocean. (c) 2006 Elsevier B.V. All rights reserved.

Hamiltonian and Lagrangian constraints of the bosonic string

We study the Hamiltonian and Lagrangian constraints of the Polyakov string. The gauge fixing at the Hamiltonian and Lagrangian level is also studied.

Constraints on additional Z' gauge bosons from a precise measurement of the Z mass

We analyze the constraints on the mass and mixing of a superstring-inspired E6 Z' neutral gauge boson that follow from the recent precise Z mass measurements and show that they depend very sensitively on the assumed value of the W mass and also, to a lesser extent, on the top-quark mass.

Higher order Lagrangian systems: Geometric structures, Dynamics, and Constraints

In order to study the connections between Lagrangian and Hamiltonian formalisms constructed from aperhaps singularhigher-order Lagrangian, some geometric structures are constructed. Intermediate spaces between those of Lagrangian and Hamiltonian formalisms, partial Ostrogradskiis transformations and unambiguous evolution operators connecting these spaces are intrinsically defined, and some of their properties studied. Equations of motion, constraints, and arbitrary functions of Lagrangian and Hamiltonian formalisms are thoroughly studied. In particular, all the Lagrangian constraints are obtained from the Hamiltonian ones. Once the gauge transformations are taken into account, the true number of degrees of freedom is obtained, both in the Lagrangian and Hamiltonian formalisms, and also in all the intermediate formalisms herein defined.

Northern agriculture : constraints and responses to global climate change

Selostus: Maatalous pohjoisilla äärialueilla: ilmastolliset rajoitukset ja ilmaston muutosten vaikutukset viljelyyn

Lifetime of an ocean island volcano feeder zone: constraints from U-Pb dating on coexisting zircon and baddeleyite, and 40Ar/39Ar age determinations, Fuerteventura, Canary Islands

High-precision isotope dilution - thermal ionization mass spectrometry (ID-TIMS) U-Pb zircon and baddeleyite ages from the PX1 vertically layered mafic intrusion Fuerteventura, Canary Islands, indicate initiation of magma crystallization at 22.10 +/- 0.07 Ma. The magmatic activity lasted a minimum of 0.52 Ma. Ar-40/Ar-39 amphibole dating yielded ages from 21.9 +/- 0.6 to 21.8 +/- 0.3, identical within errors to the U-Pb ages, despite the expected 1% theoretical bias between Ar-40/Ar-39 and U-Pb dates. This overlap could result from (i) rapid cooling of the intrusion (i. e., less than the 0.3 to 0.6 Ma 40Ar/39Ar age uncertainties) from closure temperatures (T-c) of zircon (699-988 degrees C) to amphibole (500-600 degrees C); (ii) lead loss affecting the youngest zircons; or (iii) excess argon shifting the plateau ages towards older values. The combination of the Ar-40/Ar-39 and U/Pb datasets implies that the maximum amount of time PX1 intrusion took to cool below amphibole T-c is 0.8 Ma, suggesting PX1 lifetime of 520 000 to 800 000 Ma. Age disparities among coexisting baddeleyite and zircon (22.10 +/- 0.07/0.08/0.15 Ma and 21.58 +/- 0.15/0.16/0.31 Ma) in a gabbro sample from the pluton margin suggest complex genetic relationships between phases. Baddeleyite is found preserved in plagioclase cores and crystallized early from low silica activity magma. Zircon crystallized later in a higher silica activity environment and is found in secondary scapolite and is found close to calcite veins, in secondary scapolite that recrystallised from plagioclase. close to calcite veins. Oxygen isotope delta O-18 values of altered plagioclase are high (+7.7), indicating interaction with fluids derived from host-rock carbonatites. The coexistence of baddeleyite and zircon is ascribed to interaction of the PX1 gabbro with CO2-rich carbonatite-derived fluids released during contact metamorphism.

Reproductive allocation and size constraints in the cladoceran Simocephalus vetulus (Müller)

Like many organisms, the cladoceran Simocephalus vetulus (Müller) continues to grow when reproducing, whereas the optimal strategy is to stop growing at maturity, and to invest all available production into reproduction thereafter. It has been proposed that a size constraint is responsible for the observed strategy (Perrin, Ruedi & Saiah, 1987), by preventing organisms from investing more than a given amount of energy into reproduction. This hypothesis is developed here and the two folowing prediction are derived: (1) the onset of reproduction should be independent of age and (2) the reproductive investement should be size-specific, thus independent of the productin rate. Both predictions are tested by rearing a clone of S.vetulus in a gradient of productivity. The results support the first prediction, but not the second one, so that the size-constraint hypothesis is disproved.

Topological magnetic irreversibility in superconducting Pb samples of various shapes

The magnetic-field dependence of the magnetization of cylinders, disks, and spheres of pure type-I superconducting lead was investigated by means of isothermal measurements of first magnetization curves and hysteresis cycles. Depending on the geometry of the sample and the direction and intensity of the applied magnetic field, the intermediate state exhibits different irreversible features that become particularly highlighted in minor hysteresis cycles. The irreversibility is noticeably observed in cylinders and disks only when the magnetic field is parallel to the axis of revolution and is very subtle in spheres. When the magnetic field decreases from the normal state, the irreversibility appears at a temperature-dependent value whose distance to the thermodynamic critical field depends on the sample geometry. The irreversible features in the disks are altered when they are submitted to an annealing process. These results agree well with very recent high-resolution magneto-optical experiments in similar materials that were interpreted in terms of transitions between different topological structures for the flux configuration in the intermediate state. A discussion of the relative role of geometrical barriers for flux entry and exit and pinning effects as responsible for the magnetic irreversibility is given.

Models that include supercoiling of topological domains reproduce several known features of interphase chromosomes.

Understanding the structure of interphase chromosomes is essential to elucidate regulatory mechanisms of gene expression. During recent years, high-throughput DNA sequencing expanded the power of chromosome conformation capture (3C) methods that provide information about reciprocal spatial proximity of chromosomal loci. Since 2012, it is known that entire chromatin in interphase chromosomes is organized into regions with strongly increased frequency of internal contacts. These regions, with the average size of ∼1 Mb, were named topological domains. More recent studies demonstrated presence of unconstrained supercoiling in interphase chromosomes. Using Brownian dynamics simulations, we show here that by including supercoiling into models of topological domains one can reproduce and thus provide possible explanations of several experimentally observed characteristics of interphase chromosomes, such as their complex contact maps.