GOCE: precise orbit determination for the entire mission

The Gravity field and steady-state Ocean Circulation Explorer (GOCE) was the first Earth explorer core mission of the European Space Agency. It was launched on March 17, 2009 into a Sun-synchronous dusk-dawn orbit and re-entered into the Earth’s atmosphere on November 11, 2013. The satellite altitude was between 255 and 225 km for the measurement phases. The European GOCE Gravity consortium is responsible for the Level 1b to Level 2 data processing in the frame of the GOCE High-level processing facility (HPF). The Precise Science Orbit (PSO) is one Level 2 product, which was produced under the responsibility of the Astronomical Institute of the University of Bern within the HPF. This PSO product has been continuously delivered during the entire mission. Regular checks guaranteed a high consistency and quality of the orbits. A correlation between solar activity, GPS data availability and quality of the orbits was found. The accuracy of the kinematic orbit primarily suffers from this. Improvements in modeling the range corrections at the retro-reflector array for the SLR measurements were made and implemented in the independent SLR validation for the GOCE PSO products. The satellite laser ranging (SLR) validation finally states an orbit accuracy of 2.42 cm for the kinematic and 1.84 cm for the reduced-dynamic orbits over the entire mission. The common-mode accelerations from the GOCE gradiometer were not used for the official PSO product, but in addition to the operational HPF work a study was performed to investigate to which extent common-mode accelerations improve the reduced-dynamic orbit determination results. The accelerometer data may be used to derive realistic constraints for the empirical accelerations estimated for the reduced-dynamic orbit determination, which already improves the orbit quality. On top of that the accelerometer data may further improve the orbit quality if realistic constraints and state-of-the-art background models such as gravity field and ocean tide models are used for the reduced-dynamic orbit determination.     

A ~565 Ma old glaciation in the Ediacaran of peri-Gondwanan West Africa

International Journal of Earth Sciences - In the Cadomian orogen of the NE Bohemian Massif and of SW Iberia, a post-Gaskiers glacial event dated at c. 565 Ma has been detected. Such...     

Untersuchungen zur Abgrenzung der ArtenPhormidium uncinatum undPhormidium autumnale

Zusammenfassung Vergleichende Untersuchungen der Morphologie, der Gr?ssenverh?ltnisse, des Pigmentgehaltes und des Lichtreaktionsverhaltens führen zu dem Schluss, dass es sich beiPhormidium autumnale undPhormidium uncinatum um zwei verschiedene, durchaus unterscheidbare Arten handelt. Die Zusammenfassung zu einer Sammelart wird daher abgelehnt.

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Summary Investigations on the morphology, the dimensions, the pigment contents and the light reaction behaviour strongly indicate thatPhormidium uncinatum andPhormidium autumnale are distinctly different species. We therefore object to the unification of the two into one species.

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Résumé Il résulte des recherches comparant les morphologies, les dimensions, les contenus de pigment et les photoréactions desPhormidium autumnale etPhormidium uncinatum que ces derniers appartiennent à deux espèces différentes bien à distinguer. Nous refusons par conséquent un regroupement des deux Phormidia dans une espèce.

     

Fluid evolution,wallrock alteration,and ore mineralization associated with the Rodalquilar epithermal gold-deposit in southeast Spain

At Rodalquilar gold mineralization is found in Late Tertiary volcanic rocks of the Sierra del Cabo de Gata and is related to a caldera collapse. Radial and concentric faults were preferred sites for gold deposition. Hydrothermal activity produced a specific alteration zoning around gold-bearing vein structures, grading from an innermost advanced argillic via an argillic into a more regionally developed propylitic zone. Advanced argillic alteration with silica, pyrophyllite, alunite, and kaolinite extends down to several hundred m indicating a hypogene origin. High-grade gold mineralization in vein structures is confined to the near-surface part of the advanced argillic alteration. Fine-grained gold is associated with hematite, jarosite, limonite, or silica. At a depth of about 120 m, the oxidic ore assemblage grades into sulfide mineralization with pyrite and minor chalcopyrite, covellite, bornite, enargite, and tennantite. Two types of fluids from different sources were involved in the hydrothermal system. Overpressured and hypersaline fluids of presumably magmatic origin initiated the hydrothermal system. Subsequent hydrothermal processes were characterized by the influx of low-salinity solutions of probable marine origin and by interactions between both fluids. Deep-reaching, advanced argillic alteration formed from high-salinity fluids with 20–30 equiv. wt% NaCl at about 225°C. Near-surface gold precipitation and silification are related to fluids with temperatures of about 175°C and 3–4 equiv. wt% NaCl. Gold was transported as Au(HS) ₂ ^– , and precipitation resulted from boiling with a concomitant decrease in temperature, pressure, and pH and an increase in fO₂. All features of the Rodalquilar gold deposit reveal a close relationship to acid-sulfate-type epithermal gold mineralization.     

Stratabound ore deposits related to synsedimentary tectonics: South-West Sardinia (Italy) and Sierra de Aracena (Spain); a comparison

Deposition of stratabound Zn-Pb-Ba ores in the Lower Cambrian carbonates in South-west Sardinia show a distinct relation with the prominent tensional tectonics in the area. A part of the mineral deposits are syngenetic (sedimentary-exhalative), other massive sulfides and/or barite are early diagenetic. Other occurrences (MVT) are from early to late-diagenetic. They are mostly confined to matrix- and cementbreccias which might be dependent on the Cambrian tectonics. The Precambrian-Lower Cambrian (?) carbonates occupying the core of the Aracena anticline, at the boundary between the provinces of Huelva and Badajoz (South-west Spain), are also an important metallotect for Zn-Pb-Ag-Ba mineralization. The ores at Aracena are stratabound (to stratiform) (Sedex) and occur as disseminations or layers in a volcano-sedimentary sequence with carbonate intercalations. Both the carbonate intervals and the ores show evidence of synsedimentary tectonics, like slumpings, slump breccias and neptunian dykes. Their deposition most likely occurred in a subtidal environment controlled by faults. Apparently, in South-west Sardinia and in the Sierra de Aracena, both sedimentary evolution and ore deposition were strictly related, and conditioned by several pulses of tensional tectonics.     

From outcrop and petrographic studies to basin-scale fluid flow modelling: The use of the Albanian natural laboratory for carbonate reservoir characterisation

The Albanian fold-and-thrust belt and the Peri-Adriatic Depression are well documented by means of seismic reflection profiles, GPS reference points, potential data, wells and outcrops. The continuous Oligocene to Plio-Quaternary sedimentary records help to constrain both the burial history of Mesozoic carbonate reservoirs, the timing of their deformation, and the coupled fluid flow and diagenetic scenarios.Since the mid-90s, the Albanian foothills were used as a natural laboratory to develop a new integrated methodology and work flow for the study of sub-thrust reservoir evolution, and to validate on real case studies the use of basin modelling tools as well as the application of new analytical methods for the study petroleum systems in tectonically complex areas.The integration of the interactions between petrographic and microtectonic studies, kinematic, thermal and fluid flow basin modelling, is described in detail. The fracturing of the reservoir intervals has a pre-folding origin in the Albanides and relates to the regional flexuring in the foreland. The first recorded cement has a meteoric origin, implying downward migration and the development of an earlier forebulge in the Ionian Basin. This fluid, which precipitates at a maximum depth of 1.5 km, is highly enriched in strontium, attesting for important fluid–rock interaction with the Triassic evaporites, located in diapirs. From this stage, the horizontal tectonic compression increases and the majority of the fluid migrated under high pressure, characterised by brecciated and crack-seal vein. The tectonic burial increased due to the overthrusting, that is pointed out by the increase of the precipitation temperature of the cements. Afterwards, up- or downward migration of SO₄²⁻, Ba²⁺ and Mg²⁺-rich fluids, which migrated probably along the décollement level, allows a precipitation in thermal disequilibrium. This period corresponds to the onset of the thrusting in the Ionian Zone. The last stage characterised the uplift of the Berati belt, developing a selective karstification due likely to the circulation of meteoric fluid.The main results of the fluid flow modelling show that the Upper Cretaceous–Paleocene carbonate reservoirs in the Ionian zone have been charged from the Tortonian onward, and that meteoric fluid migration should have intensely biodegraded the hydrocarbon in place. Concerning the migration paths, it has been demonstrated that the thrusts act principally as flow barriers in Albania, mainly due the occurrence of evaporites (non-permeable), except in the foreland, where they do not occur.     

Potassic primary melts of vulsini (Roman Province): evidence from mineralogy and melt inclusions

The origin and the relationships between the high potassic (HKS) and potassic (KS) suites of the Roman Comagmatic Province and the nature of their primary magmas have been intensively debated over the past 35 years. We have addressed these problems by a study of mineralogy (olivine Fo_92-87, Cr-spinel and diopside) and melt inclusions in olivine phenocrysts from a scoria sample of Montefiascone (Vulsini area). This rock is considered as one of the most primitive (MgO=13.5 wt%, NiO=340 ppm; Cr=1275 ppm) in the northern part of the Roman Comagmatic Province. The compositions of both the olivine and their melt inclusions are controlled by two main processes. In the case of the olivine Fo<90.5, fractional crystallization (olivine + diopside + minor spinel) was the principal mechanism of the magma evolution. The olivine (Fo_92-90.5) and the Cr-spinel (Cr#=100. Cr/(Cr+Al)=63-73) represent a near-primary liquidus assemblage and indicate the mantle origin of their parental magmas. The compositions of melt inclusions in these olivine phenocrysts correspond to those of poorly fractionated H₂O-rich ( 1 wt%) primary melts (MgO=8.4-9.7 wt%,FeO^total=6-7.5 wt%). They evidence a wide compositional range (in wt%: SiO₂=46.5-50, K₂O=5.3-2.8, P₂O₅=0.4-0.2, S=0.26-0.12; Cl=0.05-0.03, and CaO/Al₂O₃= 0.8-1.15), with negative correlations between SiO₂ and K₂O, Al₂O₃ and CaO, as well as positive correlations between K₂O, and P₂O₅, S, Cl, with nearly constant ratios between these elements. These results are discussed in terms of segregation of various mantle-derived melts. The high and constant Mg# [100.Mg/(Mg+Fe²⁺)] 73-75 of studied melts and their variable Si, K, P, Ca, Al, S contents could be explained by the melting of a refractory lithospheric mantle source, heterogeneously enriched in phlogopite and clinopyroxene (veined mantle source).     

The geometry of the joint pattern and its relation with fold structures in the Aywaille area (Ardennes,Belgium)

The geometry of the joint pattern in the Aywaille area (Ardennes, Belgium) is analysed with statistical methods. The orientations of intersecting joint-planes were recorded together with the bedding-plane. Four principal sets have been distinguished. These sets are related orthogonally to the bedding-plane and geometrically to the regional fold structure. All sets are considered to represent tensional structures, formed in a single period after the folding. The joint pattern is compared with a model given byPrice (1966). It is concluded that this model, describing the generation of joints in relation with folding, cannot explain completely the formation of the joint-sets under consideration here.

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Zusammenfassung Die Geometrie des Klutgefüges im Aywaille Gebiet (Ardennen, Belgien) wurde mit statistischen Methoden analysiert. Die Orientierungen sich schneidender Kluften und der Schichtflächen wurden erfaßt und vier Hauptkluftscharen unterschieden. Diese Scharen durchsetzen die Schichtflächen im rechten Winkel und in Symmetrie zur Faltenachse. Alle Klüfte werden als gleichzeitig nach der Faltung entstandene Zugklüfte gedeutet, Das Kluftgefüge wird mit einem vonPrice (1966) angegebenen Modell für das Entstehen von Klüften nach der Faltung verglichen. Es ergibt sich, daß dieses Modell nicht zur vollständigen Erklärung der betrachten Kluftscharen ausreicht.

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Résumé La géométrie du régime de fractures dans la région d'Aywaille (Ardennes, Belgique) est analysée par des méthodes statistiques. Les orientations des intersections des plans de fractures ont été enregistrées en inculant le plan de stratification. On a distingué quatre ensembles principaux. Ces ensembles sont reliés orthogonalement au plan de stratification et géométriquement au plissement régional. On considére que tous ces ensembles représentent des structures de traction, formées au cours d'une mème période postérieure au plissement. Ce type de fractures peut-être comparé au modèle donné par Price (1966). On peut en conclure que ce modèle, décrivant la formation des fractures associées au plissement, ne peut pas expliquer complètement le développement des ensembles de fractures étudiés ici.

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, 4 ( Aywaille, Ardenne, Belgium). . , . Price, (1966) . .