First high dynamic range and high resolution images of the sky obtained with a diffractive Fresnel array telescope

This paper presents high contrast images of sky sources, obtained from the ground with a novel optical concept: Fresnel arrays. We demonstrate the efficiency of a small 20?cm prototype Fresnel array for making images with high brightness ratios, achieving contrasts up to 4 × 10⁵ on sky sources such as Mars and its satellites, and the Sirius?A?CB couple. These validation results are promising for future applications in space, for example the 4 m array we have proposed to ESA in the frame of the ??Call for a Medium-size mission opportunity for a launch in 2022??. Fresnel imagers are the subject of a topical issue of Experimental Astronomy published in 2011, but only preliminary results were presented at the time. Making images of astronomical bodies requires an optical component to focus light. This component is usually a mirror or a lens, the quality of which is critical for sharp and high contrast images. However, reflection on a mirror and refraction through a lens are not the only ways to focus light: an alternative is provided by diffraction through binary masks (opaque foils with multiple precisely etched sub-apertures). Our Fresnel arrays are such diffractive focusers, they offer weight, price and size advantages over traditional optics in space-based astronomical instruments. This novel approach requires only void apertures of special shapes in an opaque material to form sharp images, thus avoiding the wavefront distortion, diffusion and spectral absorption associated with traditional optical media. In our setup, lenses and/or mirrors are involved only downstream (at small sizes) for focal instrumentation and chromatic correction. Fresnel arrays produce high contrast images, the resolution of which reaches the theoretical limit of diffraction. Unlike mirrors, they do not require high precision polishing or positioning, and can be used in a large domain of wavelengths from far IR to far UV, enabling the study of many science cases in astrophysics from exoplanet surfaces and atmospheres to galaxy evolution.     

Depth of faulting and ancient heat flows in the Kuiper region of Mercury from lobate scarp topography

Mercurian lobate scarps are interpreted to be the surface expressions of thrust faults formed by planetary cooling and contraction, which deformed the crust down to the brittle–ductile transition (BDT) depth at the time of faulting. In this work we have used a forward modeling procedure in order to analyze the relation between scarp topography and fault geometries and depths associated with a group of prominent lobate scarps (Santa Maria Rupes and two unnamed scarps) located in the Kuiper region of Mercury for which Earth-based radar altimetry is available. Also a backthrust associated with one of the lobate scarps has been included in this study. We have obtained best fits for depths of faulting between 30 and 39 km; the results are consistent with the previous results for other lobate scarps on Mercury.The so-derived fault depths have been used to calculate surface heat flows for the time of faulting, taking into account crustal heat sources and a heterogeneous surface temperature due to the variable insolation pattern. Deduced surface heat flows are between 19 and 39 mW m^?2 for the Kuiper region, and between 22 and 43 mW m^?2 for Discovery Rupes. Both BDT depths and heat flows are consistent with the predictions of thermal history models for the range of time relevant for scarp formation.     

A~200 ka pollen record from Okinawa Trough:Paleoenvironment reconstruction of glacial-interglacial cycles

Pollen analysis was carried out on the Core MD982194 of 29.78 m retrieved from the Middle Okinawa Trough which was dated as old as~200 ka BP.The results revealed that pollen assemblages mainly presented an alternation of coniferous and herb pollen.The coniferous saccate pollen,principally Pinus and Tsuga,predominated in most parts of the core,especially highlighted in the interstadial stages including MIS 1,3,5 and MIS7,whereas the herb pollen significantly increased in the glacial periods.Thus the pollen flora and their percentages showed the sensitive changes under the influence of ice volume during the glacial and interglacial periods.Our record from this core has first documented that the percentage of Cyperaceae was extremely high in the glacial stages with a notable increase in Artemisia,Gramineae,Asteraceae,Chenopodiaceae,and freshwater algae,which can be used as a proxy for sea-level change at the study site because of their close negative correlation of the orbital-scale changes in sea level.The distance between the continental coastline and the Okinawa Trough has deeply shortened due to the sea-level drop in the LGM.As a result,the sediment materials from Yangtze River were extensively deposited on the flat,exposed continental shelf owing to the rapid decline of river flow speed,leading to that pollen grains from Okinawa Trough are derived mainly from the flat coastal vegetation of exposed continental shelf at glacial stages.Changes of pollen assemblage were consistent with the variation of temperature and humidity,which showed that the percentage of arboreal pollen was highly augmented at MIS 7,5 and MIS 1,corresponding to the strengthening of the East Asian summer monsoon and increasing of rainfall.Moreover,the peak of Pinus percentage in MIS 5.3,5.1 and MIS 3.3 may be closely linked by orbital and sub-orbital cycles of solar radiation and monsoonal variability.The present study of core MD981294 implied lower temperature and precipitation during the lowest sea-level stage(LGM),and more visibly testified that the vegetation of the flat plain on the exposed continental shelf was dominated by intrazonal communities such as halophyte grasslands and freshwater wetlands instead of zonal steppe or semi-arid desert.All above evidence demonstrated that the fundamental changes of pollen assemblage and their origins in Okinawa Trough since~200 ka BP were affected by combine factors including the coastline position and climate fluctuation.Moreover,the substantial shortening of distance between shoreline and the Okinawa Trough driven by orbital insolation cycles was clearly indicated by the pollen spectra,whereas the source-area climate signal of the pollen record was largely weakened.     

The Neogene and Lower Pleistocene crags of Upper Normandy: Biostratigraphic revision and paleogeographic implications

The biostratigraphic revision of the benthic foraminifera present in the coastal Cenozoic quartzose and shelly sands (crags) at Fécamp and Valmont (Seine-Maritime) reveals Early Pliocene (Fécamp) and Early Pleistocene (Valmont) ages. The Tortonian-Messinian thanatocœnosis contained in the Fécamp Crag shows the presence of a former bryozoan-rich platform on the floor of the Channel that was reworked during the Lower Pliocene transgression. Tortonian-Messinian and Lower Pliocene deposits have been found in Belgium, England, Brittany, and at Fécamp, but are absent in Cotentin (North-West Normandy), which was uplifted at this period. The Lower Pleistocene tidal sands and crags described in Cotentin, Upper Normandy and the southern North Sea Basin indicate a marine passage between the Channel and the North Sea.     

Introduction

Manisa Fault is a geomorphologically distinct normal dip-slip fault, which oversees the southern edge of the Manisa Graben that is a continuum of the Gediz Graben towards the west. This study aims to determine the neotectonic activity of the Manisa Fault and the most recent time of the change in its stress condition through age-dating data obtained by using ²³⁰Th/²³⁴U dating methodology applied on the calcite coating that develops over hanging-wall of the Manisa Fault and the calcite veins that occur as fracture fillings. The age of the calcite precipitations associated with the Manisa Fault was determined to be between 307?±?203 and 444?±?101?ka by using the ²³⁰Th/²³⁴U dating method. Evaluation of the carbonate precipitations on the Manisa Fault along with the age data and the kinematic indicators ascertained that the Manisa Fault switched to a dip-slip normal faulting character from Middle Pleistocene onwards and that the region was under the effect of a NE–SW directional extensional regime. In addition, the opening rate was attempted to be determined using the roll-over anticline structure that advanced depending upon the movement of the fault on the upper horizontal strata of colluviums, which developed in association with the Manisa Fault. Along with the evaluation of the rise in the horizontal stratification in colluvium and the obtained age data, opening rate of the Manisa Fault was determined as 0.01?mm?y^?1.     

Les filons sédimentaires jurassiques de Longobucco-Caloveto (Calabre,Italie); application à l’étude des paléostructures d’une marge téthysienne

Résumé

La région de Longobucco-Caloveto, dans le Nord du massif de la Sila, en Calabre, montre de très nombreux filons sédimentaires jurassiques qui traversent des schistes cambro-ordovicien ou des granites hercyniens. Ces filons se répartissent en deux groupes. Les plus anciens, d’âge carixien, sont associés à des failles normales qui ont permis la formation d’un demi-graben rempli par des sédiments du Domérien. Les plus récents, d’âge compris entre le Lias supérieur et le Malm, marquent la fracturation de hauts-fonds qui se sont effondrés au Dogger. Ces filons enregistrent ainsi la formation du segment de la marge de la Téthys auquel correspondent les séries de Longobucco-Caloveto. L’étude des relations entre les filons sédimentaires et la fracturation permet de montrer, dans une région pourtant fortement tectonisée au Tertiaire, que différentes failles sont d’âge jurassique : certaines d’entre-elles sont recoupées par des filons et donc antérieures à ceux-ci; d’autres systèmes de filons sont parallèles à des systèmes de failles et donc postérieurs à ces derniers ou contemporains. Us filons sédimentaires apparaissent ainsi comme un moyen intéressant, bien qu’encore peu utilisé, de caractén-sation des dispositifs paléotectoniques.     

Tectonic evolution of the Montagne Noire (french Massif Central): a model of extensional gneiss dome

Abstract

The tertonic interpretation of the Montagne Noire Gneiss Dome (southern French II Massif (Central) has been controversial for a long time. Several models have been proposed : diapirie uplift, wreneching and diapirism, compressive anticline, and metamorphie core complex. Evidence for extensional tectonics in the French Varisean Belt favours the latter interpretation. Strain and metamorphism patterns in the eastern part of the Montagne Noire result from two successive extensional deformations during Late Carboniferous to Permian times. The occurrence of a major detachment zone along the northern edge of the Montagne Noire Gneiss Dome as well the presence of sedimentary) basias to the north point to the asymmetry) of the Stephanian-Permian extensional system. We propose a new model of gneiss dome involving isostatie uprising and consecutive tectonic denudation of the duetile lower crust. This process results in asymmetrical extensional systems characterized by roll-under folding of the footwall and development of basins in the hangingwall as in the Montagne Noire. The model is finally discussed in comparison to previous interpretations.     

Stretching lineation and transport direction in the Ibero-Armorican arc during the siluro-devonian collision

Abstract

Large structures, lineations, foliations and sense of shear criteria are examined on the scale of the whole Ibero-Armorican Arc. Four sections (Galicia, Brittany-Vendée, Limousin and Eastern Massif Central) exemplify the major thrust sheets observed around the Arc. Stretching lineations are contemporaneous with the siluro-devonian metamorphism and are either transverse, oblique or parallel to the collision zone. A kinematic analysis shows that these lineations have resulted from a dominanüy transverse shear deformation which was followed by, or combined with, a longitudinal shear direction. On the scale of the entire Arc, this variation in the shear direction is interpreted as resulting from an early head on thrusting relative movement evolving to large scale movements parallel to the plate boundaries. Experiments with sand-silicone models support a model which generates the Arc by interaction between a transform sinistral direction, and a converning zone at a high angle to the transform direction.     

Seasonal variability of cohesive sediment aggregation in the Bach Dang–Cam Estuary, Haiphong (Vietnam)

In the Bach Dang–Cam Estuary, northern Vietnam, mechanisms governing cohesive sediment aggregation were investigated in situ in 2008–2009. As part of the Red River delta, this estuary exhibits a marked contrast in hydrological conditions between the monsoon and dry seasons. The impact on flocculation processes was assessed by means of surveys of water discharge, suspended particulate matter concentration and floc size distributions (FSDs) conducted during a tidal cycle at three selected sites along the estuary. A method was developed for calculating the relative volume concentration for the modes of various size classes from FSDs provided by the LISST 100X (Sequoia Scientific Inc.). It was found that all FSDs comprised four modes identified as particles/flocculi, fine and coarse microflocs, and macroflocs. Under the influence of the instantaneous turbulent kinetic energy, their proportions varied but without significant modification of their median diameters. In particular, when the turbulence level corresponded to a Kolmogorov microscale of less than ∼235 μm, a major breakup of flocs resulted in the formation of particles/flocculi and fine microflocs. Fluctuations in turbulence level were governed by seasonal variations in freshwater discharge and by the tidal cycle. During the wet season, strong freshwater input induced a high turbulent energy level that tended to generate sediment transfer from the coarser size classes (macroflocs, coarse microflocs) to finer ones (particles/flocculi and fine microflocs), and to promote a transport of sediment seawards. During the dry season, the influence of tides predominated. The turbulent energy level was then only episodically sufficiently high to generate transfer of sediment between floc size classes. At low turbulent energy, modifications in the proportions of floc size classes were due to differential settling. Tidal pumping produced a net upstream transport of sediment. Associated with the settling of sediment trapped in a near-bed layer at low turbulent energy, this causes the silting up of the waterways leading to the harbour of Haiphong.