The Wide Field Spectrograph (WiFeS)

This paper describes the Wide Field Spectrograph (WiFeS) under construction at the Research School of Astronomy and Astrophysics (RSAA) of the Australian National University (ANU) for the ANU 2.3 m telescope at the Siding Spring Observatory. WiFeS is a powerful integral field, double-beam, concentric, image-slicing spectrograph designed to deliver excellent throughput, wavelength stability, spectrophotometric performance and superb image quality along with wide spectral coverage throughout the 320–950 nm wavelength region. It provides a 25×38 arcsec field with 0.5 arcsec sampling along each of twenty five 38×1 arcsec slitlets. The output format is optimized to match the 4096×4096 pixel CCD detectors in each of two cameras individually optimized for the blue and the red ends of the spectrum, respectively. A process of “interleaved nod-and-shuffle” will be applied to permit quantum noise-limited sky subtraction. Using VPH gratings, spectral resolutions of 3000 and 7000 are provided. The full spectral range is covered in a single exposure at R=3000, and in two exposures in the R=7000 mode. The use of transmissive coated optics, VPH gratings and optimized mirror coatings ensures a throughput (including telescope atmosphere and detector) >30% over a wide spectral range. The concentric image-slicer design ensures an excellent and uniform image quality across the full field. To maximize scientific return, the whole instrument is configured for remote observing, pipeline data reduction, and the accumulation of calibration image libraries.     

Holocene glacier and deep water dynamics,Adélie Land region,East Antarctica

This study presents a high-resolution multi-proxy investigation of sediment core MD03-2601 and documents major glacier oscillations and deep water activity during the Holocene in the Adélie Land region, East Antarctica. A comparison with surface ocean conditions reveals synchronous changes of glaciers, sea ice and deep water formation at Milankovitch and sub-Milankovitch time scales. We report (1) a deglaciation of the Adélie Land continental shelf from 11 to 8.5 cal ka BP, which occurred in two phases of effective glacier grounding-line retreat at 10.6 and 9 cal ka BP, associated with active deep water formation; (2) a rapid glacier and sea ice readvance centred around 7.7 cal ka BP; and (3) five rapid expansions of the glacier–sea ice systems, during the Mid to Late Holocene, associated to a long-term increase of deep water formation. At Milankovich time scales, we show that the precessionnal component of insolation at high and low latitudes explains the major trend of the glacier–sea ice–ocean system throughout the Holocene, in the Adélie Land region. In addition, the orbitally-forced seasonality seems to control the coastal deep water formation via the sea ice–ocean coupling, which could lead to opposite patterns between north and south high latitudes during the Mid to Late Holocene. At sub-Milankovitch time scales, there are eight events of glacier–sea ice retreat and expansion that occurred during atmospheric cooling events over East Antarctica. Comparisons of our results with other peri-Antarctic records and model simulations from high southern latitudes may suggest that our interpretation on glacier–sea ice–ocean interactions and their Holocene evolutions reflect a more global Antarctic Holocene pattern.     

Practical versus absolute salinity measurements: New advances in high performance seawater salinity sensors

Optical salinity sensors described here measure directly the seawater refractive index and thus enable a measurement of the seawater density and composition variation. We detail the measurement dependence to environmental parameters (in particular temperature and pressure) compared to conductivity sensors, and demonstrate that it may be advantageous to directly measure refractive index rather than electrical conductivity and so obtain a more direct route to density and absolute salinity.     

Zircon texture and chemical composition as a guide to magmatic processes and mixing in a granitic environment and coeval volcanic system

This study documents the chemical and textural responses of zircon in the Elba igneous complex, with particular reference to the 7- to 7.8-Ma-old Monte Capanne pluton in relation to its coeval volcanic counterpart (Capraia), using BSE imaging and quantitative electron microprobe analyses. The Monte Capanne pluton displays multiple field and geochemical evidence for magma mixing. The samples we have investigated (including monzogranitic, mafic enclave and dyke samples) display similar zircon textures and are associated with an extremely large range of trace and minor element (Hf, Y, HREE, Th, U) compositions, which contrast with relatively simple textures and zoning patterns in zircons from a Capraia dacite. We have used a relatively simple textural classification (patchy zoning, homogenous cores, oscillatory zoning and unzoned zircon) as the basis for discussing the chemical composition and chemical variation within zircons from the Monte Capanne pluton. Based on these data and other works (Dini et al. 2004 in Lithos 78:101–118, 2004) , it is inferred that mixing between metaluminous and peraluminous melts occurred early in the evolution of the Monte Capanne magma chamber. In particular, mixing was responsible for the development of the patchy-zoning texture in the zircon cores, which was associated with reactions between other accessory phases (including monazite, apatite, allanite), which we infer to have significantly affected the Th distribution in zircon. Zircons from the MC pluton displaying “homogeneous cores” have chemical affinities with zircons in the coeval Capraia volcanic system, consistent with the participation of a Capraia-like mantle end-member during mixing. Further zircon growth in the MC pluton produced the oscillatory zoning texture, which records both long-term (crystal fractionation) and transient (recharge with both silicic and mafic magmas) events in a hybrid magma chamber. It is inferred that Hf and the Th/U ratio cannot be used alone to infer magmatic processes due to their dependency on temperature, nor are they a diagnostic feature of xenocrystic grains. This study shows that zircon chemistry coupled with detailed textural analysis can provide a powerful tool to elucidate the complex evolution of a magma system.     

The impact and rotational light curves of Comet 9P/Tempel 1

UVES and HIRES high-resolution spectra of Comet 9P/Tempel 1 are used to investigate the impact and rotational light curves of various species with a view toward building a simple model of the distribution and activity of the sources. The emission by OH, NH, CN, C₃, CH, C₂, NH₂, and OI, are analyzed, as well as the light scattered by the dust. It is found that a simple model reproduces fairly well the impact light curves of all species combining the production of the observed molecules and the expansion of the material throughout the slit. The impact light curves are consistent with velocities of 400-600 m/s. Their modeling requires a three-step dissociation sequence “Grand-Parent → Parent → Daughter” to produce the observed molecules. The rotational light curve for each species is explained in terms of a single model with three sources. The dust component can however not easily be explained that way.     

Holocene fire regime changes from multiple-site sedimentary charcoal analyses in the Lourdes basin (Pyrenees,France)

One lake and three peat bogs from the Lourdes glacial basin (France) were used for macrocharcoal analyses and fire frequency reconstruction over the entire Holocene (11700 years). The chronology was based upon thirty-three 14C AMS dates. Comparison of the distribution of both CHarcoal Accumulation Rate (CHAR) and fire return intervals showed that charcoal accumulation significantly differs between the lake and the peat bogs, but that frequency calculation overcomes the disparity between these site types. A composite frequency was built from the four individual records to assess regional versus local variability and fire regime controls by comparisons with regional fire activity, Holocene climatic oscillations and vegetation history. The millennial variability can be depicted as follows: relatively high frequency between 8000 and 5000 cal a BP (up to 5 fires/500 yrs), relatively low frequency between 5000 and 3000 cal a BP (down to 0 fires/500 yrs), and an increase between 3000 and 500 cal a BP (up to 4 fires/500 yrs). From 8000 to 5000 cal a BP, fire frequency displays strong synchrony between sites and appears to be mostly driven by increased summer temperature characterizing the Holocene Thermal Maximum (HTM). On the contrary, during the last 3000 years fire frequency was heterogeneous between sites and most probably human-driven. However, higher frequency at the millennial scale during the mid-Holocene strongly suggests that the perception of human-driven fire regime depends on the strength of natural controls.     

Plio-Quaternary extension in the Venezuelan Andes: Mapping from SAR JERS imagery

The geometry of extensional structures is described for the first time in the active setting of the Venezuelan Andes using remote sensing imagery. We favored the use of a mosaic of Synthetic Aperture Radar (SAR) scenes of the Japanese Earth Resources Satellite-1 (JERS-1) assisted by complementary remote sensing devices (Landsat TM, digital elevation models) and field observations to make a structural analysis at regional scale. Radar images are particularly efficient in the Venezuelan Andes where dense vegetation and frequent cloud covering earlier lent difficulties to remote sensing studies. We focused our analysis in the Valera–Rio Momboy and Bocono faults corner and in the Mucujun area. We show that, in an area where ongoing compression and strike–slip deformations occur, brittle extension can be detected independently from previous knowledge. Extensional structures correspond to elongated tilted blocks with dimension less than 10 km in width. Blocks are bounded by curved faults in plan view, the concavity being turned towards the axial part of the belt. The geometry and kinematics of such structures suggest that syn-orogenic extension started together with initiation of right-lateral strike–slip motion along the Bocono Fault in the Plio-Quaternary.     

Structural control of sinkholes and subsidence hazards along the Jordanian Dead Sea coast

For about four decades, the Dead Sea (DS) level and the surrounding water table has been dropping dramatically. At least from the eighties, the direct vicinity of the Lisan Peninsula (LP), Jordan, has been facing high rates of subsidence and sinkhole hazards. Between 2000 and 2002, the Arab Potash Company (APC) lost two salt evaporation ponds resulting in a loss of $70 million. In the fertile plain of Ghor al Haditha (GAH), three deep and wide bowl-shaped subsidence areas threaten human activities and infrastructures. Over the part of the Lisan Peninsula that emerged before the 1960s, relict fossil sinkholes occurred everywhere, whereas new collapses constantly appear in the southern area only. In this paper, we have integrated 15 years of field observations related to sinkholes and subsidence with interpretation of space borne radar interferometric outputs, aerial photographs and satellite images. This has helped to place hazardous areas in their geological context and to clarify them within the framework of the general tectonic setting of the area.     

Facies and paleogeographic importance of the pre-rift limestones from NE-Egypt/Sinai

The depositional environments of the Phanerozoic limestones of northeastern Egypt were reconstructed, based on microfacies and fossil content of the following limestonedominated sequences: Late Carboniferous, Late Anisian/ Ladinian (Carnian?), Bajocian/Kimmeridgian, Aptian/ Albian, Late Cenomaman/Early Turonian, Late Coniacian, Maastrichtian, Late Paleocene/Early Eocene. The African Craton in the south and the Tethyan sea in the north mainly controlled the sedimentation of most Phanerozoic strata; they increase in thickness towards the north, due to the gentle north/northwest dip of the Precambrian cratonal basement. Different subsiding areas enabled the filling of different depocenters since Jurassic times (with a maximum during the Cretaceous).The Early/Middle Cretaceous sediments were deposited along the broad North-African shelf system, with nearshore depositional environments, characterized by the interfingering of siliciclastics with marls and limestones; maximum thicknesses were encountered in several shallow depocenters. The Mid-Cretaceous platform was destroyed during Late Cretaceous times: Synsedimentary folding in the northern areas and vertical block fault movements further south (along rejuvenated pre-existing fault systems) are due to a N/NW-ward drift of the African Plate. Broad areas of North Africa were covered by chalks and marls in Senonian times, while phosphates and platform carbonates were locally deposited, due to synsedimentary structural unrest. The synsedimentary tectonic movements came to an end in Late Cretaceous times and were rejuvenated in Early Tertiary. The beginning Red Sea/Gulf of Suez rift influenced the sedimentation processes of the neighbouring Early Tertiary strata. Carbonates were mainly formed close to the uplifted areas, while the sedimentation of marls, clays and chalks prevailed in most other areas.

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Zusammenfassung Im Oberkarbon, Oberanis/Ladin (Carn?), Bajoc/Kimmeridge, Apt/Alb, Obercenoman/Unterturon, Oberconiac, Maastricht und Oberpaleozän/Untereozän treten kalkbetonte Abfolgen in Nordostägypten auf, deren Charakteristika mit Hilfe der Mikrofazies und des Fossilinhaltes beschrieben werden. Die Sedimentationsmuster der meisten phanerozoischen Ablagerungen können in einer stark vereinfachten Annäherung auf das Zusammenwirken festländischer Ablagerungsprozesse (Afrikanischer Kraton) im Süden und mariner Sedimentation (Tethys) weiter im Norden zurückgeführt werden. Die Sedimentmächtigkeiten nehmen generell nach Norden zu, was auf ein sanftes Einfallen des präkambrischen kristallinen Grundgebirges nach N/NW zurückzuführen ist. Daneben ist eine unterschiedlich starke Absenkung und Sedimentauffüllung verschiedener Depocenter seit dem Jura festzustellen.Die unter-/mittelkretazischen Sedimente wurden im Bereich des breiten, nordafrikanischen Schelfsystems abgelagert, das in verschiedene, überwiegend küstennahe Ablagerungsbereiche untergliedert werden kann; diese sind durch die Verzahnung von Siliziklastika mit Mergeln und Kalken gekennzeichnet und erreichen maximale Mächtigkeiten innerhalb der flachen Depocenter. Die mittelkretazische Plattform zerbrach in der Oberkreide: Synsedimentäre Faltung im Norden und Blockverwerfung weiter südlich (entlang reaktivierter alter Störungssysteme) werden auf die N/ NW Drift der Afrikanischen Platte zurückgeführt. Weite Gebiete Nordostafrikas wurden im Senon von ausgedehnten Kreide- und Mergelablagerungen bedeckt; die lokalen Vorkommen von Phosphaten und Plattformkarbonaten sind an synsedimentäre Strukturen gebunden. Im Alttertiär sind erneut synsedimentäre tektonische Bewegungen festzustellen (die auch im Zusammenhang mit dem beginnenden Rifting von Rotem Meer und Golf von Suez stehen). In der Umrandung herausgehobener Horstblöcke fand Karbonatsedimentation statt, während in den übrigen Gebieten Mergel, Tonsteine und Kreide (Chalks) abgelagert wurden.

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Résumé Les conditions de dépôt des calcaires phanérozoïques du nord-est de l'Egypte ont été reconstituées à partir des microfaciès et du contenu en fossiles des séries suivantes à dominante calcaire: Carbonifère supérieur, Amsien supérieur/Ladinien /(Carnien), Bajocien/Kimmeridgien, Aptien/Albien, Cénomanien supérieur/Turonien inférieur, Coniacien supérieur, Maestrichtien, Paléocène supérieur/ Eocène inférieur. La sédimentation de la plupart des couches phanérozoïques s'est organisée en fonction de la présence du craton africain au sud et de la Téthvs au nord; leur épaisseur augmente vers le nord, en relation avec la descente progressive vers le nord-nord-ouest de la surface du craton pré-cambrien. Des phénomènes de subsidence différentielle sont à l'origine de diverses aires d'accumulation importante à partir du Jurassique (avec un maximum au cours du Crétacé).Les sédiments d'âge crétacé inférieur et moyen se sont déposés le long du shelf nord-africain dans divers milieux littoraux, caractérisés par l'interdigitation de siliciclastites, de marnes et de calcaires, avec une puissance maximale dans les aires d'accumulation subsidentes. La plate-forme du Crétacé moyen a été détruite au cours du Crétacé supérieur: des plis syn-sédimentaires dans les parties septentrionales et des mouvements verticaux de »block faulting« plus au sud (le long du système de failles anciennes réactivées) traduisent la dérive vers le nord/nord ouest de la plaque africaine. Au Sénonien, de larges surfaces de l'Afrique du Nord ont été recouvertes de craies et de marnes, simultanément à des déôts locaux de phosphates et de carbonates de plate-forme, cette diversité traduisant l'instabilité structurale syn-sédimentaire. Les mouvements syn-sédimentaires ont pris fin au Crétacé supérieur puis ont été réactivés au début du Tertiaire. Le commencement de l'ouverture de la Mer Rouge et du Golfe de Suez a influencé la sédimentation du Tertiaire inférieur dans les régions voisines. Les carbonates se sont formés essentiellement dans les régions soulevées, tandis que le dépôt de marnes, argile et craies prévalait dans la plupart des autres endroits.

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