Insight into the development of a carbonate platform through a multi-disciplinary approach: a case study from the Upper Devonian slope deposits of Mount Freikofel (Carnic Alps,Austria/Italy)

The development and behavior of million year-scaled depositional sequences recorded within Palaeozoic carbonate platform has remained poorly examined. Therefore, the understanding of palaeoenvironmental changes that occur in geological past is still limited. We herein undertake a multi-disciplinary approach (sedimentology, conodont biostratigraphy, magnetic susceptibility (MS), and geochemistry) of a long-term succession in the Carnic Alps, which offers new insights into the peculiar evolution of one of the best example of Palaeozoic carbonate platform in Europe. The Freikofel section, located in the central part of the Carnic Alps, represents an outstanding succession in a fore-reef setting, extending from the Latest Givetian (indet. falsiovalis conodont zones) to the Early Famennian (Lower crepida conodont zone). Sedimentological analysis allowed to propose a sedimentary model dominated by distal slope and fore-reef-slope deposits. The most distal setting is characterized by an autochthonous pelagic sedimentation showing local occurrence of thin-bedded turbiditic deposits. In the fore-reef slope, in a more proximal setting, there is an accumulation of various autochthonous and allochthonous fine- to coarse-grained sediments originated from the interplay of gravity-flow currents derived from the shallow-water and deepwater area. The temporal evolution of microfacies in the Freikofel section evolves in two main steps corresponding to the Freikofel (Unit 1) and the Pal (Unit 2) limestones. Distal slope to fore-reef lithologies and associate changes are from base to top of the section: (U1) thick bedded litho- and bioclastic breccia beds with local fining upward sequence and fine-grained mudstone intercalations corresponding, in the fore-reef setting, to the dismantlement of the Eifelian–Frasnian carbonate platform during the Early to Late Frasnian time (falsiovalis to rhenana superzones) with one of the causes being the Late Givetian major rift pulse; (U2) occurrence of thin-bedded red nodular and cephalopod-bearing limestones with local lithoclastic grainstone intercalations corresponding to a significant deepening of the area and the progressive withdrawal of sedimentary influxes toward the basin, in relation with Late Frasnian sea-level rise. MS and geochemical analyses were also performed along the Freikofel section and demonstrate the inherent parallel link existing between variation in MS values and proxy for terrestrial input. Interpretation of MS in terms of palaeoenvironmental processes reflects that even though distality remains the major parameter influencing MS values, carbonate production and water agitation also play an important role.     

Localised strain in fissured clays: the combined effect of fissure orientation and confining pressure

Acta Geotechnica - This paper reports the main results of an experimental study on the mechanics of intensely fissured natural clays, extending our previous studies on scaly clay from Santa Croce...     

K/Rb-, Ca/Sr- und K/Ti-Verhältnisse in basaltoiden Gesteinen der Ostalpen und benachbarter Gebiete

Zusammenfassung Es wurden 69 basaltische Gesteine aus dem ostalpinen und westkarpatischen Orogen sowie aus dem pannonischen Zwischengebirge röntgenfluoreszenzspektrometrisch auf K, Ca, Rb, Sr und Ti analysiert. Eine Auswertung der Korrelationsdiagramme K/Rb, Ca/Sr und K/Ti ergibt für verwandte Gesteine definierte Konzentrationsfelder. Die Alkaliolivinbasalte zeichnen sich, soweit sie nicht durch sekundäre Prozesse Veränderungen erfahren haben, durch relativ enge Konzentrationsfelder aus. Als Mittelwerte wurden für 30 Proben von Alkaliolivinbasalten (<2% K) von 12 verschiedenen Vorkommen erhalten: 1,39% K, 6,58% Ca, 1,57% Ti, 48 ppm Rb und 1015 ppm Sr.Die Basalte des Orogenrandes erscheinen weniger alkalisch. Im Orogenbereich kann eine stärkere Kontamination mit sialischem Material möglich sein. Basalte des Orogenbereiches und des pannonischen Zwischengebirges weisen anscheinend mit zunehmender Sialmächtigkeit eine stärkere Tendenz zur Alkalisierung auf.

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K/Rb-, Ca/Sr- and K/Ti-tatios in basaltic rocks of the Eastern Alps and neighbouring regions

Summary Using x-ray fluorescence spectrometry 69 samples of basaltic rocks from the Eastern Alps, the Western Carpathian Mountains, the Hungarian Plain, and the Bakony Mountains were analysed for the elements K, Ca, Ti, Rb and Sr. The correlation diagrams show defined concentration fields for similiar rock types. Alkaliolivine basalts, which are not influenced by secondary processes, are characterized by small concentration fields. The average values of 30 samples of alkali olivine basalts (<2% K), taken from 12 volcanoes, are: 1.39% K, 6.58% Ca, 1,57% Ti, 48 ppm Rb and 1015 ppm Sr.Some basalts of the orogene border seem to be less alkalic. A higher contamination with sialic material may be possible in the region of the orogene. Basalts from the region of the orogene and from the Hungarian Plain show a strong tendency towards the formation of alkali rich rock types. A relation to the thickness of the sial seems to be probable.

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Mit 4 Abbildungen     

Ra/Ra and Ra/Ba ratios in the Western Mediterranean Sea: Barite formation and transport in the water column

²²⁶Ra, ²²⁸Ra and Ba distributions as well as ²²⁸Ra/²²⁶Ra and ²²⁶Ra/Ba ratios were measured in seawater, suspended and sinking particles at the DYFAMED station in the Western Mediterranean Sea at different seasons of year 2003 in order to track the build-up and fate of barite through time. The study of the ²²⁸Ra_ex/²²⁶Ra_ex ratios (Ra_ex = Ra activities corrected for the lithogenic Ra) of suspended particles suggests that Ba_ex (Ba_ex = Ba concentrations corrected for the lithogenic Ba, mostly barite) formation takes place not only in the upper 500 m of the water column but also deeper (i.e. throughout the mesopelagic layer). Temporal changes in the ²²⁸Ra_ex/²²⁶Ra_ex ratios of sinking particles collected at 1000 m depth likely reflect changes in the relative proportion of barite originating from the upper water column (with a high ²²⁸Ra/²²⁶Ra ratio) and formed in the mesopelagic layer (with a low ²²⁸Ra/²²⁶Ra ratio). ²²⁸Ra_ex/²²⁶Ra_ex ratios measured in sinking particles collected in the 1000 m-trap in April and May suggest that barite predominantly formed in the upper water column during that period, while barite found outside the phytoplankton bloom period (February and June) appears to form deeper in the water column. Combining ratios of both the suspended and sinking particles provides information on aggregation/disaggregation processes. High ²²⁶Ra_ex/Ba_ex ratios were also found in suspended particles collected in the upper 500 m of the water column. Because celestite is expected to be enriched in Ra [Bernstein R. E., Byrne R. H. and Schijf J. (1998) Acantharians: a missing link in the oceanic biogeochemistry of barium. Deep-Sea Res. II45, 491-505], acantharian skeletons may contribute to these high ratios in shallow waters. The formation of both acantharian skeletons and barite enriched in ²²⁶Ra may thus contribute to the decrease in the dissolved ²²⁶Ra activity and ²²⁶Ra/Ba ratios of surface waters observed between February and June 2003 at the DYFAMED station.     

The effects of vegetative ash on infiltration capacity, sediment transport, and the generation of progressively bulked debris flows

Through the alteration of the physical characteristics of a landscape, such as the destruction of vegetation and the formation of a hydrophobic layer, a fire can dramatically amplify erosion rates. On the basis of field observations, it has been proposed that the deposition of a layer of ash on the ground surface can enhance the erosion of mountainous terrain by surface runoff and might even be a necessary condition for the generation of progressively bulked debris flows. In this study, a flume was constructed to investigate the role of ash in increasing both the volume and the transport capacity of runoff. The experiments demonstrated that the presence of ash on the soil surface reduces the ability of flowing water to infiltrate; this effect is even greater when the ash has been pre-wetted. In addition, the ability of ash slurries to infiltrate decreases with increasing ash concentration. The results also indicate that the transport capacity of runoff is enhanced by the incorporation of ash into the flow because of the increased fluid density. However, the addition of ash reduces the boundary Reynolds number such that, at high ash concentrations and with fine-grained sediment, sediment transport declines as the flow becomes hydraulically smooth. The experimental results were also used to evaluate the ability of steep flow fronts, a common characteristic of debris flows and flash floods, to increase sediment transport rates. Finally, it is proposed that ash slurries may evolve into progressively bulked debris flows through a positive feedback between fluid density, transport capacity, and erosivity.     

Spatiotemporal analysis of the atmospheric and surface urban heat islands of the Metropolitan Area of Toluca,Mexico

The dynamic of consolidation of urban areas in Latin America has allowed that almost 80% of the population concentrates in cities; this has produced changes in land covers and modified regional climate, propitiating the appearance of urban heat islands. The Metropolitan Area of Toluca, State of Mexico, Mexico, holds the fifth national place in population size and experiences this process, because of this, the objective is to analyze and compare the spatiotemporal characteristics of the atmospheric urban heat island obtained from data gathered from 12 urban and rural weather stations with the surface urban heat island obtained from the digital processing of four Landsat 8 images. Results show the year-round presence of night-time atmospheric urban heat islands, which reach a peak in autumn (up to 6 °C). Daytime atmospheric urban heat islands occur in summer and autumn with a maximum intensity of 4 °C. For their part, surface urban heat islands occur in spring, summer and autumn and reach maximums of 19 °C in intensity. A strong correlation was found between wetness and surface temperature (coefficient of determination, 0.8) in spring and winter. Soil wetness directly impacts the formation of weak urban heat islands in dry season, and intense ones in wet season, while the green areas and the winds affect the spatial distribution of the same.     

A three-step floating catchment area method for analyzing spatial access to health services

Gravity-based spatial access models have been widely used to estimate spatial access to healthcare services in an attempt to capture the interaction of various factors. However, these models are inadequate in informing health resource allocation work due to their inappropriate assumption of healthcare demand. For the purpose of effective healthcare resource planning, this article proposes a three-step floating catchment area (3SFCA) method to minimize the healthcare-demand overestimation problem. Specifically, a spatial impedance-based competition scheme is incorporated into the enhanced two-step floating catchment area (E2SFCA) method to account for a reasonable model of healthcare supply and demand. A case study of spatial access to primary care physicians along the Austin–San Antonio corridor area in central Texas showed that the proposed method effectively minimizes the overestimation of healthcare demand and reflects a more balanced geographic pattern of spatial access than E2SFCA. In addition, by using an adjusted spatial access index, the 3SFCA method indicates strong potential for identifying health professional shortage areas. The study concludes that 3SFCA is a promising method to provide health professionals and decision makers with useful healthcare accessibility information.     

Cloud formation along mountain ridges on Titan

Cassini radar passes have shown a number of mountain ranges on Titan. Radar data covering approximately one quarter of Titan's surface places mountains in primarily equatorial regions with the mean height of about 900 m. The flow of air over topographic features can both trigger and enhance cloud formation. Orographically induced clouds near terrestrial mountain ranges include shallow wave clouds produced from upslope flow as well as precipitating stratus and cumulus type clouds; mountains can provide the perturbations needed to trigger convective clouds. The Titan regional atmospheric modeling system (TRAMS) has been used to explore a number of convective cloud properties and is now used to report on clouds formed when a mountain peak is placed within the model domain. Using a range of heights and surface winds compatible with Cassini/Huygens data, constraints can be placed on the scenarios in which clouds can be expected to form. Given sufficiently humid conditions (at least 50% humidity), convection is triggered. For drier environments similar to the Huygens landing site, short-lived, optically thin clouds form from air rising upslope. Precipitation is also seen in the cases of the convective clouds, which could have implications for the eroded appearance of Titan's mountains.     

Dynamics,sediment transport,and morphology in a tide-dominated embayment

Western Port, Victoria, Australia is a tide-dominated embayment with an unusual and complex shape. Bottom currents and circulation and their effects on sediment processes were examined using instrumented tripods to measure currents, tides and wave activity, and to estimate sediment transport at nine locations in the bay. Overall bottom water movement patterns were determined by use of seabed drifters. The characteristics of the bay reflect a small catchment and low freshwater and sediment input. A complex system of channels is flanked by extensive intertidal areas. Tidal range varies up to more than 3 m, generating bottom currents up to 70cm s^?1. Flow directions generally conform to channel alignments but major deviations are important. Net circulation in the bay is clockwise around the large central island. The ratio of tidal range to half-tidal period (ΔH/ΔT) when compared with measured currents gave a method of prediction of the annual frequency distribution of maximum bottom current velocities. Determination of threshold current velocities enabled prediction of annual frequency of bedload movement (generally 50–100 per cent of tide cycles). Bedload mass transport for all observed tide cycles was calculated, and estimates of annual mass transport capacity (between 10² and 10⁶ g cm^?1 a^?1( were obtained from a relationship between predicted tidal conditions and mass transport. Seabed drifters delineated the major bottom water movements in the bay and adjacent Bass Strait, and also detailed circulation patterns. This linked the data from the tripod stations, in particular patterns of ebb- and flood-dominance. A coherent picture of the processes operating in Western Port is presented by integrating these studies with corroborative studies of sediment distribution and morphology, hydrochemistry, and mathematical modelling. Some morphological characteristics related to tide-dominance are discussed.