Complex internal architecture of a debris‐flow deposit revealed using ground‐penetrating radar,Cass, New Zealand

Previous research on debris‐flow deposit structure typically reports little to no visually discernible stratigraphy. The preliminary findings presented here provide evidence for more complex internal deposit architecture with inverse grading and subunits thought to reflect individual flow surges. Ground‐penetrating radar surveys, geospatial data and field observations are used to describe 10 subunits traceable over the 14 lateral radargrams imaging the lower 38 m of the deposit. Additional subunits are depicted further upslope in a longitudinal transect. As well as demonstrating the need for continued investigation of deposit architecture using non‐traditional techniques, these results may help improve future interpretations of post‐event deposits.     

Populus nigra L. establishment and fluvial landform construction: biogeomorphic dynamics within a channelized river

Populations of the riparian pioneer species Populus nigra L. which establish on alluvial bars within river channels modulate sediment dynamics and fluvial landforms. Dense cohorts of P. nigra have colonized gravel point bars along the channelized River Garonne, France, during the last 20 years and have enhanced the vertical, lateral and longitudinal development of the bars. For this period, the geomorphic characteristics of two wooded point bars on this laterally stable river are closely linked to the spatial distribution and intensity of establishment and resistance of different cohorts of P. nigra. Furthermore, P. nigra colonization dynamics were controlled by engineer effects of this same species. This relationship is illustrated by a significant correlation between key geomorphic and biological variables measured in situ and characterized with a set of four aerial photographs taken between 2000 and 2010. The development of wooded point bars, which are discrete biogeomorphic units, over the studied period, appear to result from a specific biogeomorphic positive feedback of matter aggregation and vegetation establishment related to sediment trapping and stabilization by pioneer engineer plants. We propose a conceptual model of biogeomorphic unit construction for channelized, lateral stable rivers. We consider the resultant biogeomorphic units as functional from an ecological point of view because P. nigra enhances at the cohort scale (i) its own inherent capacity to resist hydrogeomorphic disturbances, and (ii) its resilience capacity as a result of successful colonization, especially downstream of mature poplar stands. Copyright © 2016 John Wiley & Sons, Ltd.     

Sand blows as a potential tool for magnitude estimation of pre-instrumental earthquakes

A worldwide database of liquefaction-induced sand blows has been compiled to generate empirical relationships between earthquake parameters and sand blow geometries. Curves resulting from these empirical relationships can be used afterwards for the study of historic and pre-historic earthquakes that formed sand blows. This database only incorporates instrumental earthquakes inducing sand blows, characterised in terms of magnitude (Mw), hypocentral location and focal mechanism solution. Two relationships are herein presented. The first curve, minimum likelihood of liquefaction occurrence (magnitude/epicentral distance), displays a logarithmic behaviour, as others already proposed. The second curve of sand-blow diameter vs epicentral distance is the first proposal of this kind, whose shape follows a negative power-law. Magnitude estimations of (pre-)historic earthquakes then may be attempted through these empirical relationships. Resulting magnitudes derived from these curves should be mostly considered as underestimated. The curves will reflect actual magnitudes only if, correspondingly, the farthest and largest blow has ever been reported during the after-earthquake survey. Following the same principle, a magnitude estimation resulting from the measuring of a sand blow can only be considered as minimal because it is almost impossible to ascertain that the measured feature is the biggest one produced by the earthquake under evaluation. Finally, these results call for thorough surveys of induced effects after every future moderate-to-large earthquake, as any empirical relationship simply improves by incorporating new data.     

Mars and its magnetic field— Some new aspects

This paper is the continuation of an earlier one on planetary evolution of Earth and Mars (Franck and Orgzall, 1987). Here models for the history of the Martian magnetic field are presented. It is concluded, that Mars once had a substantial magnetic field that was switched off approximately 1 billion years ago on the one hand due to missing gravitational energy supply— the core reached its eutectic composition earlier— and on the other hand due to dynamic inhibitions.     

Luminescence spectroscopy and microscopy applied to study gem materials: a case study of C centre containing diamonds

The methods of luminescence spectroscopy and microscopy are widely used for the analysis of gem materials. This paper gives an overview of the most important applications of the analysis of laser and UV excited luminescence by spectroscopy and visually by microscopy with emphasis on diamond, and specifically natural type Ib diamond, little studied so far. Luminescence based techniques are paramount to the gemmological analysis of diamond, in order to determine whether it is natural, treated or synthetic. The great sensitivity of luminescence helps detect some emitting centres that are undetectable by any other analytical method. Hence, especially for diamond, luminescence is an enabling technology, as illustrated by its pioneering use of imagery for the separation of natural and synthetic diamond, and of spectroscopy for the detection of High Pressure–High Temperature treatment. For all other gemstones the applications are at the moment less numerous, but nevertheless they remain highly important. They provide quickly information on the identification of a gem material, and its treatment. Besides the study of broad band emissions caused by various colour centres, the typical PL-causing trace elements (amongst others) are chromium, manganese, uranium and rare earth elements. In pearls the study of broad band luminescence can be useful, and particularly the study of pink to red porphyrin luminescence in pearls from certain species such as Pinctada and Pteria and others can help identify the pearl-producing mollusc, or if a pearl has been dyed or not. Type Ib diamonds are representative of the importance and complexity of the analysis of luminescence by microscopy and spectroscopy. They show a wide range of sometimes very complex emissions that result in luminescence colours from green to yellow to orange or red. These emissions show generally very inhomogeneous distribution. They are caused by a range of defects, however only a few of them are well characterized.     

Simulated carbon and nitrogen flows of the planktonic food web during an upwelling relaxation period in St Helena Bay (southern Benguela ecosystem)

A vertically resolved ecosystem model is developed to simulate the dynamics of the pelagic food web in St Helena Bay during a representative period of relaxation after an upwelling event. The proposed model aims at coupling three biogeochemical cycles (carbon, nitrogen and silicon), using several recently developed concepts of the stoichiometric approach. A consequence of this approach is that important qualitative aspects are introduced, such as indicators of phytoplankton physiological state or variable food C:N ratios. For instance, the sedimentation and exudation rates for phytoplankton vary according to physiological state. An attempt is made to parameterize and simulate the diel cycles for vertical migration and feeding rhythms of large zooplankton, two important mesoscale processes that are thought to influence the overall dynamics of the huge phytoplankton blooms in the region.Observations of the Anchor Station Experiment 1987 (ASE’87) are used to assess the quality of the model. There is overall agreement between observations and the corresponding simulated results. The timing, the magnitude, and the vertical structure of the phytoplankton bloom are well reproduced. The balances for carbon and nitrogen flows and stocks compare well to the numerous estimates found from the literature for the southern Benguela region.On the basis of the model results, the origin of the new nutrients, the fate of the carbon fixed by phytoplankton, and the importance of the microheterotrophic pathways are discussed. It is concluded that sediments of the St Helena Bay and surrounding areas may play a crucial role in increasing the level of phytoplankton production. The results also suggest that exudation is the main process by which the carbon fixed by phytoplankton would have been lost, and that microheterotrophic pathways would have been intense during the experiment.     

A new view of martian evolution

Conventional evolutionary models for Mars adopt a dry mantle solidus. Taking into account the condensation conditions in the preplanetary nebula in the accretion zone of Mars, it can be concluded that large amounts of water or hydrated silicates have condensed in those regions. Therefore, water influences significantly the melting behaviour and the viscosity of the silicatic material. A model for the calculation of the thermal history of a planet is constructed. On this basis, and use of water — saturated solidus — it is possible to derive that the core is not liquid, as given in models employing a dry mantle solidus, but solid to a large extent, which prevents the operation of a large-scale dynamo and explains in that way the lack of a magnetic field. With these assumptions one can construct a possible evolutionary scheme that covers early crust differentiation, a hot thermal past and the missing magnetic field at present.     

In situ investigations of allanite hydrothermal alteration: examples from calc-alkaline and anorogenic granites of Corsica (southeast France)

Allanite is, with monazite, the main repository for light rare earth elements (REE) in the continental crust and can be used in U-Th-Pb geochronology. This mineral has been shown to be prone to alteration. The geochemical exchanges occurring between allanite and hydrothermal fluids were explored using backscattered scanning electron microscopy, electron microprobe, and laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS). The alteration mechanisms found show the restricted role of metamictization and correspond to the allanite to epidote transformation or to the leaching of the allanite A-crystallographic sites. Hence, the REE are mostly removed from this phase during fluid-mineral interactions, although a heavy rare earth-rich fluid may imprint its geochemical signature on the allanite altered zones. It appears that even if this REE holder presents evidence of alteration, the bulk mineral and whole-rock REE and Sm-Nd isotope signatures were not significantly affected in the cases studied. Alteration results mostly in the input of common lead, thus restricting the usefulness of allanite for U-Th-Pb dating when alteration occurs. Finally, the alteration mechanisms found here confirm the much more limited flexibility of silicates crystalline lattice as compared to phosphates.     

A spectral comparison of (379) Huenna and its satellite

We present near-infrared spectral measurements of Themis family Asteroid (379) Huenna (D ∼ 98 km) and its 6 km satellite using SpeX on the NASA IRTF. The companion was farther than 1.5″ from the primary at the time of observations and was approximately 5 magnitudes dimmer. We describe a method for separating and extracting the signal of a companion asteroid when the signal is not entirely resolved from the primary. The spectrum of (379) Huenna has a broad, shallow feature near 1 μm and a low slope, characteristic of C-type asteroids. The secondary’s spectrum is consistent with the taxonomic classification of C-complex or X-complex. The quality of the data was not sufficient to identify any subtle feature in the secondary’s spectrum.