Dating of Neoproterozoic and Cambrian orogenies in Tasmania*

A coherent set of timing constraints is produced for Tasmania's Proterozoic and Cambrian geology when only mineral ages are considered and whole‐rock ages excluded. The oldest recognised event is the formation of sedimentary deposits which contain detrital zircons that indirectly indicate a depositional age younger than 1180 Ma. Partial melts of these sedimentary rocks were incorporated in Neoproterozoic, Devonian and probably Cambrian felsic magmas. Neoproterozoic granite on King Island has an age of 760 ± 12 Ma and is part of a high‐level intrusive episode that accompanied the Wickham Orogeny, an event with regionally varied strain that is represented in northwestern Tasmania by a low‐angle unconformity, by altered granitoid with a magmatic age of 777 ± 7 Ma, and by the thick turbidite pile of the Burnie and Oonah Formations with its syndepositional intrusions of Cooee Dolerite. The late Neoproterozoic was relatively quiet tectonically but by early in the Middle Cambrian a crustal collision which marked the early phase of the Tyennan Orogeny brought about high‐level emplacement of ultramafic‐bearing allochthons and deep‐seated metamorphism of quartzose sedimentary and basaltic rocks. The ultramafic allochthons carried tonalite that had crystallised only shortly before at 510 ± 6 Ma, while the deep‐seated metamorphism produced eclogite at 502 ± 8 Ma. By middle Middle Cambrian times the metamorphic rocks had been uplifted and they experienced repeated uplift during the period of Mt Read volcanism and onward to the close of the Tyennan Orogeny in the Early Ordovician, an overall period of some 20 million years from the early Middle Cambrian. Regionally varied strain was again a feature during the Tyennan Orogeny, with the Smithton area in northwestern Tasmania and King Island occupying relatively undeformed cratonic positions.     

Secondary uranium mineralization in southern Finland and its relationship to recent glacial events

Uranium series dating has been carried out on secondary uranyl silicate minerals formed during sub-glacial and post-glacial weathering of Proterozoic uraninite ores in south west Finland. The samples were obtained from two sites adjacent to the Salpauselkä III ice marginal formation and cover a range of depths, from the surface to more than 60 m. Measured ages fall into three distinct groups, 70–100 ka, 28–36 ka and < 2500 yr. The youngest set is associated with surface exposures and the crystals display clear evidence of re-working. The most likely trigger for uranium release at depths below the surface weathering zone is intrusion of oxidising glacial melt water. The latter is often characterised by very high discharge rates along channels, which close once the overpressure generated at the ice margin is released. There is excellent correspondence between the two Finnish sites and published data for similar deposits over a large area of southern and central Sweden. None of the seventy samples analysed gave a U–Th age between 40 and 70 ka; a second hiatus is apparent at 20 ka, coinciding with the Last Glacial Maximum. Thus, the process responsible for uranyl silicate formation was halted for significant periods, owing to a change in geochemical conditions or the hydrogeological regime. These data support the presence of interstadial conditions during the Early and Middle Weichselian since in the absence of major climatic perturbations the uranium phases at depth are stable. When viewed in conjunction with proxy data from mammoth remains it would appear that the region was ice-free prior to the Last Glacial Maximum.     

Assessing Tower Flux Footprint Climatology and Scaling Between Remotely Sensed and Eddy Covariance Measurements

We describe pragmatic and reliable methods to examine the influence of patch-scale heterogeneities on the uncertainty in long-term eddy-covariance (EC) carbon flux data and to scale between the carbon flux estimates derived from land surface optical remote sensing and directly derived from EC flux measurements on the basis of the assessment of footprint climatology. Three different aged Douglas-fir stands with EC flux towers located on Vancouver Island and part of the Fluxnet Canada Research Network were selected. Monthly, annual and interannual footprint climatologies, unweighted or weighted by carbon fluxes, were produced by a simple model based on an analytical solution of the Eulerian advection-diffusion equation. The dimensions and orientation of the flux footprint depended on the height of the measurement, surface roughness length, wind speed and direction, and atmospheric stability. The weighted footprint climatology varied with the different carbon flux components and was asymmetrically distributed around the tower, and its size and spatial structure significantly varied monthly, seasonally and inter-annually. Gross primary productivity (GPP) maps at 10-m resolution were produced using a tower-mounted multi-angular spectroradiometer, combined with the canopy structural information derived from airborne laser scanning (Lidar) data. The horizontal arrays of footprint climatology were superimposed on the 10-m-resolution GPP maps. Monthly and annual uncertainties in EC flux caused by variations in footprint climatology of the 59-year-old Douglas-fir stand were estimated to be approximately 15–20% based on a comparison of GPP estimates derived from EC and remote sensing measurements, and on sensor location bias analysis. The footprint-variation-induced uncertainty in long-term EC flux measurements was mainly dependent on the site spatial heterogeneity. The bias in carbon flux estimates using spatially-explicit ecological models or tower-based remote sensing at finer scales can be estimated by comparing the footprint-weighted and EC-derived flux estimates. This bias is useful for model parameter optimizing. The optimization of parameters in remote-sensing algorithms or ecosystem models using satellite data will, in turn, increase the accuracy in the upscaled regional carbon flux estimation.     

A conceptual framework for multi-regional climate change assessments for international market systems with long-term investments

A conceptual framework for climate change assessments of international market systems that involve long-term investments is proposed. The framework is a hybrid of dynamic and static modeling. Dynamic modeling is used for those system components for which temporally continuous modeling is possible, while fixed time slices are used for other system components where it can be assumed that underlying assumptions are held constant within the time slices but allowed to vary between slices. An important component of the framework is the assessment of the “metauncertainty” arising from the structural uncertainties of a linked sequence of climate, production, trade and decision-making models. The impetus for proposing the framework is the paucity of industry-wide assessments for market systems with multiple production regions and long-term capital investments that are vulnerable to climate variations and change, especially climate extremes. The proposed framework is pragmatic, eschewing the ideal for the tractable. Even so, numerous implementation challenges are expected, which are illustrated using an example industry. The conceptual framework is offered as a starting point for further discussions of strategies and approaches for climate change impact, vulnerability and adaptation assessments for international market systems.     

Effects of Roll Vortices on Turbulent Fluxes in the Hurricane Boundary Layer

Boundary-layer secondary circulations or ‘roll vortices’ can have a significant influence on the turbulent exchange of momentum, sensible heat and moisture throughout the hurricane boundary layer. In this study, analyses of data from a WP-3D aircraft of the National Oceanic and Atmospheric Administration (NOAA) are presented. As part of the Coupled Boundary Layer Air-Sea Transfer (CBLAST)-hurricane experiment sponsored through the Office of Naval Research and NOAA’s annual hurricane research program, flights were conducted to investigate energy exchange across the air–sea interface. We present the first in-situ aircraft-based observations of rolls in the hurricane boundary layer and investigate their influence on energy and momentum exchange. The rolls detected in Hurricane Isidore (year 2002) have a characteristic wavelength of about 900 m, in good agreement with analyses of data from a synthetic aperture radar image captured by the Canadian Space Agency’s RADARSAT satellite in the same storm. Our analyses of the airborne data suggest that roll vortices may be a significant factor modulating the air–sea momentum exchange.     

Sediment facies and pathways of sand transport about a large deep water headland,Cape Rodney,New Zealand

Cape Rodney is a large headland that protrudes 3–4 km into deep water in the Hauraki Gulf and separates the Mangawhai‐Pakiri and Omaha littoral cells. Detailed swath mapping of seabed sediments around Cape Rodney was carried out using by side‐scan sonar and ground‐truthed by SCUBA, grab sampling, and video. Despite the barrier imposed by the headland two pathways of sand transport around the headland, separated by the topographic high of Leigh Reef, have been identified. One lies close to the headland, where sand from the beach and nearshore of the Mangawhai‐Pakiri embayment is driven by waves and currents along a 500‐m‐wide pathway in c. 20–25 m depth around the headland to the vicinity of Leigh Harbour. The other lies in 50 m water‐depth seawards of Leigh Reef. Here fine sand, sourced from the nearshore of the Mangawhai‐Pakiri embayment and driven offshore from the tip of the headland, is transported back and forth by tidal currents in 50 m water depth on the floor of the Jellicoe Channel. The sand bodies along both these pathways are thin and so sand leakage from the Mangawhai‐Pakiri embayment is thought to be small. Transport at these depths is dependent on both tide and wave generated currents and episodic occurring during storm events. The sediment facies associated with little sand transport about a headland in deep water is one of thin and discontinuous and patchy sand cover between rocky areas and over coarser megarippled substrate. Ocean swell, tidally driven phase eddies that spin up on both sides of the headland, and bathymetry all play a role in shaping those facies.     

Studies in the application of recurrence relations to special perturbation methods

The integration by recurrent power series of certain differential equations occurring in celestial mechanics is shown to be very much more efficient and accurate than that produced by classical one step methods. It is shown that for any such system of differential equations the machine time taken to carry out an integration is a minimum for a certain choice of the number of terms taken in the recurrent power series. In the two-body orbits considered this number is about 15. For the same accuracy criterion the power series is faster than the Runge-Kutta method of the fourth order by a factor which varies between 6 and 15 depending on the eccentricity of the orbit.

     

The difficulties of dating mafic dykes: an Antarctic example

Archaen gneisses of the Vestfold Hills of East Antarctica are transected by several compositionally discrete suites of tholeiitic dykes. A representative of one of those suites, which has been dated in the present study, shows that not only Rb–Sr whole-rock isochrons, but also U–Pb zircon techniques (if not properly applied) can produce erroneous crystallisation ages. Two zircon populations were recovered from the mafic dyke itself, one of which is 2,483±9 Ma in age and clearly of xenocrystic origin. The other yields an age of 1,025±56 Ma, which is not ascribed to the magmatic crystallisation of the dyke, but rather to the time that it underwent metamorphic/metasomatic alteration as a response to high-grade tectonism in the adjacent mobile belt. It is presumed that the zircon in question formed by the breakdown of another mineral or minerals (possibly magmatic baddeleyite), due either to ingress of a siliceous fluid, or more probably by the release of silica from the breakdown of pyroxene to amphibole. A cogenetic 1–2 cm wide felsic vein, of late magmatic/early hydrothermal origin, also contains two zircon populations. Again, most of the grains therein, which are interpreted as of xenocrystic origin, grew at 2,483±9 Ma. However, a few euhedral zircons with very high U and Th contents grew at 1,248±4 Ma, which is taken to be the formation age of both the felsic vein and the enclosing mafic dyke.     

A contribution to the radiation climatology of Northern Europe

Theoretical and Applied Climatology - Global radiation data were assembled for twenty-three Northern European stations, in an area bounded approximately by latitudes 51° and 61° N, and...     

The distribution of solar radiation over the Earth's surface

Summary Records of total solar radiation measured on a horizontal surface (Q) on a monthly basis and of more than three years' duration are available for 88 stations. The stations are mainly concentrated in North America and Europe, and it is not possible to determine the global distribution of radiation directly from these records. Solar radiation and mean cloud amount (C) were therefore related by the quadratic regressionQ=Q _A (0.803–0.340C–0.458C ²), whereQ _A is the maximum possible radiation in the absence of an atmosphere (Angot's values) and the values ofC were obtained from the maps printed inShaw's Manual of Meteorology.Using the known distribution ofQ _A andC, values ofQ were calculated by use of the equation above for each 5° intersection of latitude and longitude over land, and for each 10° intersection over sea. Isopleths ofQ for each successive 50 gcal/cm² day are shown on the 12 monthly maps on which the distribution of radiation over the earth's surface is illustrated. Attention is drawn to certain features of these maps, in particular to the occurrence and movement of zones of high radiation, and a comparison is made of estimated and recorded radiation for twelve stations.

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Zusammenfassung Registrierungen der Monatswerte der Globalstrahlung auf Horizontalfläche (Q) über mindestens drei Jahre liegen für 88 Stationen vor; diese sind vorwiegend auf Nordamerika und Europa konzentriert, und es ist daher nicht möglich, auf Grund davon die gesamte Strahlungsverteilung über die Erde zu bestimmen. Es wird nun mit Hilfe der quadratischen RegressionsgleichungQ=Q _A (0.803–0.340C–0.458C ²) eine Beziehung zwischen GlobalstrahlungQ und mittlerer BewölkungC aufgestellt, woQ _A den Maximalwert der Globalstrahlung bei Fehlen einer Atmosphäre bedeutet und die Konstanten nachAngot und die Bewölkungsdaten nachShaw angenommen sind.Auf Grund der Verteilung vonQ _A undC wurden mit Hilfe der angegebenen Gleichung für jeden Bereich von je 5° Länge und Breite über Land von je 10° über Meer die Werte der Globalstrahlung berechnet. Isoplethen der Globalstrahlung für Stufen von je 20 gcal/cm² Tag sind in 12 Monatskarten wiedergegeben, auf denen die Strahlungsverteilung über die Erde dargestellt ist. Einige Resultate dieser Karten werden besprochen, im speziellen das Auftreten und die Verschiebung der Zonen hoher Strahlung; zudem wird für 12 Stationen eine Vergleichung zwischen der berechneten und der registrierten Strahlung durchgeführt.

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Résumé On possède des enregistrements de 88 stations pour les sommes mensuelles du rayonnement global sur une surface horizontale (Q) pour des périodes d'au moins 3 ans. Ces stations sont concentrées essentiellement en Amérique du Nord et en Europe ce qui ne permet pas d'en déduire la répartition du rayonnement global sur toute la terre. Pour cette raison l'auteur établit, au moyen de l'équation carrée de régressionQ=Q _A (0.803–0.340C–0.458C ²), une relation entre le rayonnement globalQ et la moyenne de la nébulositéC, oùQ _A représente la valeur maximale du rayonnement global sans atmosphère et où les constantes sont données selonAngot, la nébulosité selonShaw.A partir de la répartition deQ et deC et à l'aide de la formule précédente l'auteur a calculé les valeurs du rayonnement global pour des surfaces de 5° de latitude et de longitude sur terre et de 10° sur mer. Des isoplèthes représentent le rayonnement global par échelons de 50 gcal/cm² jour, sur 12 cartes mensuelles qui illustrent sa répartition sur toute la terre. L'auteur discute encore divers résultats de ces cartes, en particulier l'apparition et le déplacement des zones de fort rayonnement, et compare encore pour 12 stations les résultats obtenus par le calcul et par enregistrement.

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With 14 Figures