The Dorn gold deposit in northern Victoria Land,Antarctica: Structure,hydrothermal alteration,and implications for the Gondwana Pacific margin

The Dorn gold deposit in northern Victoria Land, Antarctica is a fault related gold-only deposit and it represents the first described occurrence of gold mineralization in Paleozoic terranes of the Antarctic continent. The deposit is hosted in lower greenschist facies Middle Cambrian metavolcanic and metasedimentary rocks of the Bowers terrane. Gold-bearing veins are located in a brittle–ductile reverse high-strain zone, which was produced by transpressional deformation that overprints the structures of the Cambrian–Ordovician Ross Orogeny. The vein system is surrounded by a hydrothermal alteration zone that is as much as 300-m-wide, where the host rocks are partially to completely transformed into Fe–Mg carbonate-rich rocks with different degrees of replacement of the original mineralogy and texture.The type of host rock, the temperature estimates for mineralization from 290–320 °C, the quartz dominant vein system with sulfides and Fe-rich carbonates, and the controlling structures linked to a convergent margin tectonic setting together suggest that this mineralized vein system can be classified as an orogenic gold deposit. Close analogies are found with deposits of the Stawell zone in western Victoria, which is consistent with the correlation between units and hydrothermal events in northern Victoria Land and southeastern Australia.     

Criteria for recognition of localization and timing of multiple events of hydrothermal alteration in sandstones illustrated by petrographic,fluid inclusion,and isotopic analysis of the Tera Group,Northern Spain

Stratigraphic relations, detailed petrography, microthermometry of fluid inclusions, and fine-scale isotopic analysis of diagenetic phases indicate a complex thermal history in Tithonian fluvial sandstones and lacustrine limestones of the Tera Group (North Spain). Two different thermal events have been recognized and characterized, which are likely associated with hydrothermal events that affected the Cameros Basin during the mid-Cretaceous and the Eocene. Multiple stages of quartz cementation were identified using scanning electron microscope cathodoluminescence on sandstones and fracture fills. Primary fluid inclusions reveal homogenization temperatures (Th) from 195 to 350°C in the quartz cements of extensional fracture fillings. The high variability of Th data in each particular fluid inclusion assemblage is related to natural reequilibration of the fluid inclusions, probably due to Cretaceous hydrothermal metamorphism. Some secondary fluid inclusion assemblages show very consistent data (Th = 281–305°C) and are considered not to have reequilibrated. They are likely related to an Eocene hydrothermal event or to a retrograde stage of the Cretaceous hydrothermalism. This approach shows how multiple thermal events can be discriminated. A very steep thermal gradient of 97–214°C/km can be deduced from δ¹⁸O values of ferroan calcites (δ¹⁸O −14.2/−11.8‰ V-PDB) that postdate quartz cements in fracture fillings. Furthermore, illite crystallinity data (anchizone–epizone boundary) are out of equilibrium with high fluid inclusion Th. These observations are consistent with heat-flux related to short-lived events of hydrothermal alteration focused by permeability contrasts, rather than to regional heat-flux associated with dynamo-thermal metamorphism. These results illustrate how thermal data from fracture systems can yield thermal histories markedly different from host-rock values, a finding indicative of hydrothermal fluid flow.     

Multimodal ensemble Kalman filtering using Gaussian mixture models

In this paper we present an extension of the ensemble Kalman filter (EnKF) specifically designed for multimodal systems. EnKF data assimilation scheme is less accurate when it is used to approximate systems with multimodal distribution such as reservoir facies models. The algorithm is based on the assumption that both prior and posterior distribution can be approximated by Gaussian mixture and it is validated by the introduction of the concept of finite ensemble representation. The effectiveness of the approach is shown with two applications. The first example is based on Lorenz model. In the second example, the proposed methodology combined with a localization technique is used to update a 2D reservoir facies models. Both applications give evidence of an improved performance of the proposed method respect to the EnKF.     

Glaciers and rock glaciers’ distribution at 28° SL,Dry Andes of Argentina,and some considerations about their hydrological significance

The area studied includes a little-known portion on the Dry Andes of the San Juan Frontal Cordillera, Argentina, where the hydrological significance of glaciers and rock glaciers was earlier never studied. The surveyed sector includes Cerro El Potro (5,870 m ASL) and nearby mountain chains (28°S). The predominant landforms in these areas were shaped in a periglacial environment superimposed on an earlier glacial landscape. These regions comprise abundant rock glaciers, a noteworthy rock glacier zone in the world, of which little is known in South America. This work employs geomorphological mapping to analyze the distribution of active rock glaciers in relation to altitude, aspect and slope using optical remote sensing techniques with GIS. Statistical estimation techniques were used based on a Digital Elevation Model (DEM) and aerial photos and Spot images interpretation. The specific density of rock glaciers’ estimation in the surveyed area (Argentine border) is 1.56% with corresponds to 38 rock glaciers with an area of 5.86 km² and 0.12 km³ of water equivalent. Furthermore, the analytical results show that elevations >4,270 m ASL, a southeast-facing aspect, and slope between 2° and 40° favor the existence of rock glaciers, Finally, a comparison with glacier water equivalent, which covers an area of ~16 km² and 0.9 km³ of water equivalent, shows that glaciers are the main stores of water at 28°S (Cerro El Potro Glacier). However, the importance of rock glaciers as water reserves in this portion of Argentina should not be underestimated.     

Paleoecological evidence of major declines in total organic carbon concentrations since the nineteenth century in four nemoboreal lakes

A decade of widespread increases in surface water concentrations of total organic carbon (TOC) in some regions has raised questions about longer term patterns in this important constituent of water chemistry. This study uses near-infrared spectroscopy (NIRS) to infer lake water TOC far beyond the decade or two of observational data generally available. An expanded calibration dataset of 140 lakes across Sweden covering a TOC gradient from 0.7 to 24.7 mg L⁻¹ was used to establish a relationship between the NIRS signal from surface sediments (0–0.5 cm) and the TOC concentration of the water mass. Internal cross-validation of the model resulted in an R ² of 0.72 with a root mean squared error of calibration (RMSECV) of 2.6 mg L⁻¹. The TOC concentrations reconstructed from surface sediments in four Swedish lakes were typically within the range of concentrations observed in the monitoring data during the period represented by each sediment layer. TOC reconstructions from the full sediment cores of four lakes indicated that TOC concentrations were approximately twice as high a century ago.     

Improving Baltic Sea wave forecasts using modelled surface currents

Ocean Dynamics - Currents in the Baltic Sea are generally weak, but during strong winds they can grow high enough to affect the surface wave propagation and evolution. To evaluate the significance...     

Apparent diameters of 172 B5V-A5V stars of the Catalogue of Geneva Observatory

The spectrophotometric method for computing the apparent stellar diameters, proposed by Chalonge and Divan (1950) and modified by Fracassini and Pasinetti (1967) has been applied to 172 B5V-A5V stars (single and belonging to galactic clusters) of the Catalogue of Geneva Observatory (Rufener, 1971). In the straight line diagrams log vsm, drawn for the stars of the same spectral type, it is possible to identify some peculiar stars (with peculiarities in the diameter or monochromatic brightness). The agreement with the values of the apparent diameters of Leo, Ori, Lyr and CMa, obtained by Hanbury Brownet al. (1967), is very good. The comparison with the diagramss _v vs (B-V)₀,R vs (B-V)₀ deduced by Wesselink (1969), seems satisfactory. The comparison with the results obtained by other authors and the great number of stars which will be observed in the photometric system in seven colors of Geneva, demonstrate the wide possibilities of this spectrophotometric method for determining the apparent stellar diameters.

---

Sommario Il metodo spettrofotometrico di Chalonge e Divan (1950) per il calcolo dei diametri stellari apparenti, modificato da Fracassini e Pasinetti (1967), è stato applicato a 172 stelle B5V-A5V (isolate e in ammassi galattici) del Catalogo dell'Osservatorio di Ginevra (Rufener, 1971). Costruiti i diagrammi lineari log -m _v per i vari gruppi di stelle dello stesso tipo spettrale, è possibile identificare alcune stelle peculiari con diametri e brillanze monochromatiche anomale. Il confronto con i diametti apparenti di Leo, Ori, Lyr e CMa determinati da Hanbury Brownet al. (1967) mostra un accordo molto buono. Il confronto con le relazionis _v -(B-V)₀eR-(B-V) ₀ ottenute da Wesselink (1969) appare soddisfacente. Il confronto con i risultati ottenuti da altri autori e il grande numero di stelle che saranno osservate nel sistema fotometrico in sette colori di Ginevra, dimostrano le ampie possibilità di questo metodo spettrofotometrico per la determinazione dei diametri stellari apparenti.

---

---

Thesis for the degree on Applied Physics.     

Error determination in the photogrammetric assessment of shoreline changes

The evaluation of error or uncertainty in shoreline change studies is an issue of prime importance for providing an adequate framework for calculated rates of change and to allow the establishment of threshold values above which the rates would be significant. In this note, a practical, easy-to-use method is presented to estimate error involved in the calculation of shoreline changes on aerial photographs, including the three most used types of shoreline indicators: high water line, dune/cliff toe and cliff top. This approach takes into account the specific characteristics of each shoreline proxy, such as relief in the case of the cliff top or tidal oscillations in the case of the high water line. At the same time it includes the error components that are independent from the proxy, basically related to the technical aspects of the process such as photo scanning and georeferencing. A practical example of application of the method is provided for several types of data inputs, based on shoreline changes around the Bay of Cádiz (SW Spain).     

Mapping wildfire evacuation vulnerability in the western US: the limits of infrastructure

Residential development in fire-prone areas of the western United States is a growing concern. The steady addition of homes to this region places more people and property at risk each year. In many areas housing is increasing without commensurate improvements in the road network, particularly in regards to the number, capacity and arrangement of community exit roads. This results in steadily increasing minimum evacuation times, as each additional household contributes to potential evacuation travel-demand in a wildfire. The goal of this research is to perform a comprehensive geographic search of the western U.S. for communities in wildfire-prone areas that may represent difficult evacuations due to constrained egress. The problem is formulated as a spatial search for fire-prone communities with a high ratio of households-to-exits and solved using methods in spatial optimization and geographic information systems (GIS). The results reveal an initial inventory and ranking of the most difficult wildfire evacuations in the West. These communities share a unique vulnerability in that all residents may not be able to evacuate in scenarios with short warning time. For this reason they represent prime candidates for emergency planning, and monitoring their development is a growing need.     

The Runaway Weed: Costs and Failures of Phragmites australis Management in the USA

While public funding of invasive species management has increased substantially in the past decade, there have been few cross-institutional assessments of management programs. We assessed management of Phragmites australis, a problematic invader of coastal habitats, through a cross-institutional economic survey of 285 land managers from US public and private conservation organizations. We found that from 2005 to 2009, these organizations spent >$4.6 million per year on P. australis management, and that 94 % used herbicide to treat a total area of ～80,000 ha. Despite these high expenditures, few organizations accomplished their management objectives. There was no relationship between resources invested in management and management success, and those organizations that endorsed a particular objective were no more likely to achieve it. Our results question the efficacy of current P. australis management strategies and call for future monitoring of biological management outcomes.