Limnological studies on a shallow reservoir in western Venezuela (Tulé Reservoir)

Limnological features of Tulé Reservoir, a large and shallow reservoir in western Venezuela were studied from May 1992 to December 1993. This reservoir is polymictic, with a low water transparency. Levels of nitrogen were high and phytoplankton productivity was low. The phytoplankton productivity values may be explained by the low concentrations of orthophosphate during the larger part of the sampling period and the frequent mixing and resuspension of sediments. Heterotrophic bacteria were between 1651.67 and 4365.00 Colony-forming Units/ml. Species composition of the crustacean zooplankton community was similar to other neotropical eutrophic reservoirs.     

Structure, mineralogy, and Pb isotopic composition of the As-Au-Ag deposit Rotgülden, Eastern Alps (Austria): significance for formation of epigenetic ore deposits within metamorphic domes

The abandoned As–Au–Ag mining district Rotgülden is located within the eastern Tauern window of the Eastern Alps and was reinvestigated in order to evaluate ore deposition during Alpine/late orogenic tectonic processes. Four major ore types have been recognized: (1) quartz-sulfide veins within Variscan basement rocks; (2) deformed metamorphic massive ores within fold hinge zones (“saddle reefs”) of Permian to Mesozoic cover sequences; (3) ores in tension gashes of the cover sequence; and (4) irregular replacement ore bodies in marbles of the cover sequence. Ore deposition was intimately related to late orogenic exhumation by stretching of footwall sequences within the Tauern metamorphic core complex during late Oligocene and Neogene. Hydrothermal systems developed and metals from apparently distinct sources were deposited under decreasing temperature conditions. Lead is distinctly radiogenic and resembles the lead in Au-quartz veins of the Mesozoic cover sequence of the Hohe Tauern. Received: 24 January 1996 / Accepted: 24 July 1997     

Evolution and geodynamic significance of the tertiary orogenic volcanism in Northeastern Greece

The Tertiary volcanism of Eastern Macedonia and Western Thrace (Greece) developed in association with the sedimentary basin which formed, from Eocene to Oligocene, along the southern margin of the Rhodope Massif.The volcanic products, ranging in composition from basaltic andesites to rhyolites, show an overall calc-alkaline orogenic affinity, while chemical characteristics identify different groups of rocks, probably reflecting minor differences among parent magmas. The observed evolution within any group of rocks is compatible with fractional crystallization processes acting on relatively shallow magma bodies.The Sr isotopic composition of rhyolitic member shows an initial⁸⁷Sr/⁸⁶Sr ratio comparable with that of basaltic andesites, reinforcing the hypothesis of a crystal/liquid line of descent.Geochemical and petrographic evidence, on the whole, suggests that the investigated orogenic association developed on an active continental margin characterized by a relatively thick crust, acting as a density filter for the basic magmas and facilitating their storage and fractionation within the crust itself. Minor contamination by interaction with host materials may also have occurred.Stratigraphic and K/Ar geochronological data indicate that the volcanic activity started in Upper Eocene and reached its maximum development in Upper Oligocene. From Lower Miocene, the volcanism shifted southward in the Central Aegean area and in part of Western Anatolia, coming to an end by Middle Miocene.The southward migration of the volcanic front has been interpreted as a consequence of the increase in the dipping of the Benioff zone, due to the decrease of penetrative strength after the main phase of continental collision.     

Gated communities, commodification and aestheticization: The case of the Lisbon metropolitan area

This paper focuses on the commodification processes and the aestheticization practices that shape gated communities and on the way these are connected to their segregational dimension, which is illustrated through the case of the Lisbon Metropolitan Area (LMA). First, I discuss the (increasing) aestheticization of commodities, emphasising some of the more problematic theoretical issues it involves. Following this discussion I present and analyse the ‘Lisbon case’. I provide a brief overview of gated communities in the LMA and then present and analyse the results obtained through a content analysis of LMA gated community advertisements and observation of their site semantics as conveyed through general built form, including physical location, planning, architecture, landscaping, and toponymy. I relate these findings to the LMA gated community market characteristics and to the broader prevailing socio-spatial context regarding their emergence.     

Structural evolution of the Pleistocene Cimini trachytic volcanic complex (Central Italy)

Structural, geomorphological, geophysical and volcanological data have been processed for the implementation of a dedicated GIS through which the structural evolution of the Pleistocene trachytic Cimini volcano (central Italy) has been reconstructed. The evolution of the Cimini complex includes three main close-in time phases: (1) intrusion of a shallow laccolith, rising along NW and NE trending faults and stagnating at the contact between the Mesozoic-Cenozoic and the Pliocene-Pleistocene sedimentary units constituting the bedrock of the volcano; (2) emplacement of lava domes along radial and tangential fractures formed by the swelling induced by the laccolith growth; (3) ignimbrite eruptions and final effusion of olivine-latitic lavas. Domes are both of Pelean and low lava dome type and their morphology was controlled by the location on the inclined surface of the swelled area. Some domes show to have uplifted upper Pliocene thermally metamorphosed clay sediments, suggesting a cryptodome-like growth. Comparison of the top of the Mesozoic-Cenozoic units with the top of the upper Pliocene-Pleistocene sedimentary complex, suggests that the laccolith emplaced in a graben of the Mesozoic-Cenozoic sedimentary complex filled by the Pliocene–Pleistocene sediments uplifted by the shallow intrusion. Stress patterns acting on the Cimini area have been deduced analysing the drainage network and the morphotectonic lineaments. Rose diagrams show a large dispersion of the lineaments reflecting the local presence of radial and tangential fractures. The most frequent extensional NW and NE trending lineaments have regional significance and controlled the magma uprise leading to the laccolith emplacement.     

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...     

Assessment of future trends on groundwater quality in a nitrate vulnerable zone (Esposende–Vila do Conde sector,NW Portugal): towards a combined conceptual and mass transport modelling

Hydrogeology Journal - Nitrate contamination of groundwater is an important public health issue worldwide. For environmental and public health reasons, water should not contain more than...