Report on the 4th International Meeting of the IUGS Lower Cretaceous Ammonite Working Group, the “Kilian Group” (Dijon, France, 30th August 2010)

The 4th Kilian Group meeting (Dijon, France, 30th August 2010) focused on the Aptian and Albian Stages. For the Aptian, a two-fold division of the stage was adopted for the Mediterranean area with a boundary between the Dufrenoyia furcata and Epicheloniceras martini Zones. The main changes to the zonal scheme concern the Lower Aptian with: the introduction of a Deshayesites luppovi Subzone in the upper part of the Deshayesites oglanlensis Zone; the replacement of Deshayesites weissi by Deshayesites forbesi as new index-species of the second interval zone; the introduction of a Roloboceras hambrovi Subzone in the upper part of the D. forbesi Zone; and the subdivision of the D. furcata Zone into the D. furcata and Dufrenoyia dufrenoyi Subzones. For the Albian, the upper part of the Douvilleiceras mammillatum Zone (Lower Albian) is now characterized by a Lyelliceras pseudolyelli Subzone. The main amendments concern the Upper Albian. The base of this substage is defined by the base of the Dipoloceras cristatum Zone. Above it, the Upper Albian zonal scheme comprises in stratigraphic order the Mortoniceras pricei, Mortoniceras inflatum, Mortoniceras fallax, Mortoniceras rostratum, Mortoniceras perinflatum and Arrhaphoceras briacensis Zones.     

Neoproterozoic to Lower Palaeozoic successions of the Tandilia System in Argentina: implication for the palaeotectonic framework of southwest Gondwana

The Cryogenian to Uppermost Ediacaran successions of the Tandilia System (Sierras Bayas Group and Cerro Negro Formation) in central-eastern Argentina is exceptional because of its unmetamorphosed and nearly undeformed character, its sediment provenance trend and the absence of any identified glacial deposit and the deposition of warm water carbonates. We decipher a dramatic change in the basin evolution from small-scale depositional areas during the Neoproterozoic to a larger basin related to an active continental margin throughout the Uppermost Ediacaran. The base of the succession is represented by immature detritus of alkaline composition (Villa Mónica Formation), but towards the top of this formation, the material is sorted and reworked, nonetheless still reflecting in its detritus the local rocks. The clastic deposition is interrupted by diagenetic overprinted dolomites. The unconformable overlying quartz-arenitic Ediacaran Cerro Largo Formation reworked the Cryogenian Villa Mónica Formation and contains mainly felsic granitic and metamorphic basement material of slightly wider variety, while the dominant alkaline geochemical signature in rocks of the Villa Mónica Formation disappears. Based on diagenetic, petrographic and sedimentological data, we can interpret the unconformity representing a longer time of erosion. The Cerro Largo Formation shows a transition to mudstones and the heterolithic facies of the Olavarría Formation. The top of the Sierras Bayas Group is represented by limestones (Loma Negra Formation), which are discordantly overlain by the Uppermost Ediacaran Cerro Negro Formation. The latter displays detrital material derived from a continental arc, mafic and felsic sources. Several arc-related geochemical proxies (Th/Sc?<?0.8; Zr/Sc?<?10; La/Sc?<?2; Ti/Zr?>?20) are recorded in the sediment detritus, as are syn-depositional pyroclastites. The absence of volcanic material in the underlying rocks allows proposing that the Cerro Negro Formation is related to an active continental margin fringing Gondwana (??Terra Australis Orogen??) as a retro-arc or retro-arc foreland basin.     

Ecosystem-based marine spatial management: Review of concepts, policies, tools, and critical issues

Conventional sectoral management and piecemeal governance are considered less and less appropriate in pursuit of sustainable development. Ecosystem based marine spatial management (EB-MSM) is an approach that recognizes the full array of interactions within an ecosystem, including human uses, rather than considering single issues, species, or ecosystem services in isolation. Marine spatial planning and ocean zoning are emerging concepts that can support EB-MSM. EB-MSM is driven by high-level goals that managers aim to achieve through the implementation of measures. High-level goals and objectives need to be translated into more operational objectives before specific targets, limits and measures can be elaborated.Monitoring, evaluation and adaptation are necessary to ensure that marine management measures are both effective and efficient. Solid monitoring frameworks are the foundation of adaptive management, as they provide the necessary information to evaluate performance and the effectiveness of management actions. Marine protected areas (MPAs) - possibly set up in networks - constitute a key component in EB-MSM policies and practises and have been applied as a cornerstone in conservation of marine biodiversity, management of fish populations, development of coastal tourism, etc. Moreover, MPA experiences have provided methods and concepts (such as zoning) to a wider EB-MSM context. The assignment of values to biophysical features of the marine environment allows the direct assessment of related management choices and may assist EB-MSM.A range of monetary valuation techniques have been proposed to reduce attributes of goods and services to a single metric. However, in the marine environment such an approach is often over simplistic, and thus less reductive techniques may be necessary. Rather than producing a single metric, the results of non-monetary assessments guide policy allowing weight to be given as necessary to potential areas of conflict and consensus.Strategies to take into account climate change effects and geohazard risks in EB-MSM have been applied or proposed worldwide. EB-MSM regimes must be alert to such risks and flexible to account for changes.     

Rotational excitation of protonated hydrogen cyanide (HCNH+) by He atom at low temperature

We report on ab initio coupled-cluster calculations of the interaction potential energy surface for the HCNH⁺–He complex. The aug-cc-pVTZ Gaussian basis, to which is added a set of bond functions placed at mid-distance between HCNH⁺ center of mass and He atom is used. The HCNH⁺ bonds length are set to their values at the equilibrium geometry, i.e., r _e [HC]=1.0780 Å, r _e [CN]=1.1339 Å and r _e [NH]=1.0126 Å. The interaction energy presents a global minimum located $266.9~\mathrm{cm^{-1}}$ below the HCNH⁺–He dissociation limit. Using the interaction potential obtained, we have computed rotational excitation cross sections in the close-coupling approach and downward rate coefficients at low temperature (T≤120 K). It is expected that the data worked out in this study may be beneficial for further astrophysical investigations as well as laboratory experiments.     

The Kuroshio Extension and its recirculation gyres

This paper reports on the strength and structure of the Kuroshio Extension and its recirculation gyres. In the time average, quasi-permanent recirculation gyres are found to the north and south of the Kuroshio Extension jet. The characteristics of these recirculations gyres are determined from the combined observations from the Kuroshio Extension System Study (KESS) field program (June 2004–June 2006) and include current meters, pressure and current recording inverted echo sounders, and subsurface floats. The position and strength of the recirculation gyres simulated by a high-resolution numerical model are found to be consistent with the observations. The circulation pattern that is revealed is of a complex system of multiple recirculation gyres that are embedded in the crests and troughs of the quasi-permanent meanders of the Kuroshio Extension. At the location of the KESS array, the Kuroshio Extension jet and its recirculation gyres transport of about 114 Sv. This represents a 2.7-fold increase in the transport of the current compared to the Kuroshio's transport at Cape Ashizuri before it separates from the coast and flows eastward into the open ocean. This enhancement in the current's transport comes from the development of the flanking recirculation gyres. Estimates from an array of inverted echo sounders and a high-resolution ocean general circulation model are of similar magnitude.     

Observational searches for chromospheric G-mode oscillations from CaII H-line observations

We have used a high spatial and temporal resolution of long time sequence of spectra in CaII H-line obtained at the Vacuum Tower Telescope (VTT) of the Sacramento Peak Observatory on a quiet region at the center of the solar disk over a large number of bright points and network elements to search for atmospheric (chromospheric) g-mode oscillations. An important parameter of the H-line profile, intensity at H_2v(Ih_2V), has been derived from a large number of line profiles. We derived the light curves of all the bright points and network elements. The light curves represent the main pulse with large intensity amplitude and followed by several follower pulses with lower intensity amplitudes. The light curves of these bright points would give an impression that one can as well draw curves towards and away from the highest peak (main pulse) showing an exponential growth and decay of the amplitudes. An exponential decaying function has been fitted for all the light curves of the bright points to determine the damping time of the modes that are more or less the same, and one value of the coefficient of exponent can represent reasonably well the decay for all the cases. The FFT analysis of temporal variation of both the bright points and the network elements indicates around 10-min periodicity. We speculate that this longer period of oscillation may be related to chromospheric g-mode oscillations.     

Radar observations of asteroid 25143 Itokawa (1998 SF36)

Abstract— We observed 25143 Itokawa, the target of Japan's Hayabusa (MUSES‐C) sample‐return mission, during its 2001 close approach at Arecibo on twelve dates during March 18‐April 9 and at Goldstone on nine dates during March 20‐April 2. We obtained delay‐Doppler images with range resolutions of 100 ns (15 m) at Arecibo and 125 ns (19 m) at Goldstone. Itokawa's average circular polarization ratio at 13 cm, 0.26 ± 0.04, is comparable to that of Eros, so its cm‐to‐m surface roughness probably is comparable to that on Eros. Itokawa's radar reflectivity and polarization properties indicate a near‐surface bulk density within 20% of 2.5 g cm^?3. We present a preliminary estimate of Itokawa's shape, reconstructed from images with rather limited rotation‐phase coverage, using the method of Hudson (1993) and assuming the lightcurve‐derived spin period (12.132 hr) and pole direction (ecliptic long., lat. = 355°, ?84°) of Kaasalainen et al. (2003). The model can be described as a slightly asymmetrical, slightly flattened ellipsoid with extents along its principal axes of 548 times 312 times 276 m ± 10%. Itokawa's topography is very subdued compared to that of other asteroids for which spacecraft images or radar reconstructions are available. Similarly, gravitational slopes on our Itokawa model average only 9° and everywhere are less than 27°. The radar‐refined orbit allows accurate identification of Itokawa's close planetary approaches through 2170. If radar ranging planned for Itokawa's 2004 apparition succeeds, then tracking of Hayabusa during its 2005 rendezvous should reveal Yarkovsky perturbation of the asteroid's orbit.     

A Road Map for the Generation of a Near-Infrared Guide Star Catalog for Thirty Meter Telescope Observations

The near-infrared instruments in the upcoming Thirty Meter Telescope (TMT) will be assisted by a multi conjugate Adaptive Optics (AO) system. For the efficient operation of the AO system, during observations, a near-infrared guide star catalog which goes as faint as 22 mag in J_Vega band is essential and such a catalog does not exist. A methodology, based on stellar atmospheric models, to compute the expected near-infrared magnitudes of stellar sources from their optical magnitudes is developed. The method is applied and validated in JHKs bands for a magnitude range of J_Vega 16–22 mag. The methodology is also applied and validated using the reference catalog of PAN STARRS. We verified that the properties of the final PAN STARRS optical catalog will satisfy the requirements of TMT IRGSC and will be one of the potential sources for the generation of the final catalog. In a broader context, this methodology is applicable for the generation of a guide star catalog for any existing/upcoming near-infrared telescopes.     

Source and fractionation controls on subduction-related plutons and dike swarms in southern Patagonia (Torres del Paine area) and the low Nb/Ta of upper crustal igneous rocks

The subduction system in southern Patagonia provides direct evidence for the variability of the position of an active continental arc with respect to the subducting plate through time, but the consequences on the arc magmatic record are less well studied. Here we present a geochemical and geochronological study on small plutons and dykes from the upper crust of the southern Patagonian Andes at ~?51°S, which formed as a result of the subduction of the Nazca and Antarctic plates beneath the South American continent. In situ U–Pb geochronology on zircons and bulk rock geochemical data of plutonic and dyke rocks are used to constrain the magmatic evolution of the retro-arc over the last 30 Ma. We demonstrate that these combined U–Pb and geochemical data for magmatic rocks track the temporal and spatial migration of the active arc, and associated retro-arc magmatism. Our dataset indicates that the rear-arc area is characterized by small volumes of alkaline basaltic magmas at 29–30 Ma that are characterized by low La/Nb and Th/Nb ratios with negligible arc signatures. Subsequent progressive eastward migration of the active arc culminated with the emplacement of calc-alkaline plutons and dikes?~?17–16 Ma with elevated La/Nb and Th/Nb ratios and typical subduction signatures constraining the easternmost position of the southern Patagonian batholith at that time. Geochemical data on the post-16 Ma igneous rocks including the Torres del Paine laccolith indicate an evolution to transitional K-rich calc-alkaline magmatism at 12.5?±?0.2 Ma. We show that trace element ratios such as Nb/Ta and Dy/Yb systematically decrease with increasing SiO₂, for both the 17–16 Ma calc-alkaline and the 12–13 Ma K-rich transitional magmatism. In contrast, Th/Nb and La/Nb monitor the changes in the source composition of these magmas. We suggest that the transition from the common calc-alkaline to K-rich transitional magmatism involves a change in the source component, while the trace element ratios, such as Nb/Ta and Dy/Yb, of derivative higher silica content liquids are controlled by similar fractionating mineral assemblages. Analysis of a global compilation of Nb/Ta ratios of arc magmatic rocks and simple geochemical models indicate that amphibole and variable amounts of biotite exert a major control on the low Dy/Yb and Nb/Ta of derivative granitic liquids. Lastly, we suggest that the low Nb/Ta ratio of silica-rich magmas is a natural consequence of biotite fractionation and that alternative models such as amphibolite melting in subduction zones and diffusive fractionation are not required to explain the Nb/Ta ratio of the upper continental crust.     

Soil-gas radon anomalies in three study areas of Central-Northern Calabria (Southern Italy)

Soil-gas radon concentrations and exhalation rates have generally been observed to be anomalously high along active faults in many parts of the world. The soil-gas method is based on the principle that faults and fractures in rocks are highly permeable pathways along which gases can migrate upward from deep crust and mantle to soil cover, retaining their source signatures. The present study summarizes the influence of fault zones on anomalous radon concentrations in soil by integrated geophysical and geo-structural analyses in three study areas of Central-Northern Calabria (Southern Italy). Soil-gas radon surveys have been carried out by means of an alpha scintillation counting system, at 12,509 locations between 2002 and 2004. A geostatistical approach has been used to estimate the spatial distribution of soil radon concentrations. Relations among soil-gas distribution and geo-structural features have been evaluated by ordinary multi-Gaussian kriging. Highest soil radon concentrations (ca. 90 kBq m^?3) have been measured in the Rossanese sector. In the three study areas, no appreciable differences can be noticed among lithotypes, with the highest concentration values (ca. 89 kBq m^?3) measured in alluvial deposit and in clay. Measurements of soil-gas radon reveal anomalies clearly connected to the tectonic structures. Increased signals are linearly distributed along regional WNW–ESE trending shear zones, with main pathways of concentration also recognizable along the E–W fault system in the Rossanese sector, the N–S fault system in the Crati Graben and the Catanzaro Trough, and the NE–SW fault system in the Catanzaro Trough. The distribution of epicentres of historical earthquakes occurred between 1184 and 2001 confirms the recent activity of the same fault systems. Soil-gas radon concentrations generally increase, as expected, with decreasing distance to the faults.