Constraining the age of Lateglacial and early Holocene pollen zones and tephra horizons in southern Sweden with Bayesian probability methods

The sediment sequence from Hasseldala port in southeastern Sweden provides a unique Lateglacial/early Holocene record that contains five different tephra layers. Three of these have been geochemically identified as the Borrobol Tephra, the Hasseldalen Tephra and the 10-ka Askja Tephra. Twenty-eight high-resolution C-14 measurements have been obtained and three different age models based on Bayesian statistics are employed to provide age estimates for the five different tephra layers. The chrono- and pollen stratigraphic framework supports the stratigraphic position of the Borrobol Tephra as found in Sweden at the very end of the Older Dryas pollen zone and provides the first age estimates for the Askja and Hasseldalen tephras. Our results, however, highlight the limitations that arise in attempting to establish a robust, chronologically independent lacustrine sequence that can be correlated in great detail to ice core or marine records. Radiocarbon samples are prone to error and sedimentation rates in lake basins may vary considerably due to a number of factors. Any type of valid and 'realistic' age model, therefore, has to take these limitations into account and needs to include this information in its prior assumptions. As a result, the age ranges for the specific horizons at Hasseldala port are large and calendar year estimates differ according to the assumptions of the age-model. Not only do these results provide a cautionary note for overdependence on one age-model for the derivation of age estimates for specific horizons, but they also demonstrate that precise correlations to other palaeoarchives to detect leads or lags is problematic. Given the uncertainties associated with establishing age-depth models for sedimentary sequences spanning the Lateglacial period, however, this exercise employing Bayesian probability methods represents the best possible approach and provides the most statistically significant age estimates for the pollen zone boundaries and tephra horizons. Copyright (C) 2006 John Wiley & Sons, Ltd.

Torn between two horizons. Perceptions of Buenos Aires riverfront

If you stand on the edge of a river you are likely to see the otherside. From a narrow stream in the countryside to broad urban bodies of water, one of the conditions of rivers in Europe is the relative  narrowness and ease to cross. Other rivers, such as Rio de la Plata are very far from this condition,  with a width of 48 km at the merging of delta del Paraná and 219 km where it meets the sea. This 
condition had a great significance in the way Buenos Aires was perceived and the way it developed 
historically. A boundless flat land confronted with a boundless flat river is a very particular condition 
that invites each person to frame their own view. The riverfront is therefore the fringe and horizon 
of the city. As a horizon it is the link with others, with the outside, with faraway lands, and for some 
even the reminder of home. These areas, in their harbor condition, are the fringe of the city; they 
are working areas, contested spaces, open for speculation and social conflict. 
In this paper I intend to explore a series of different perceptions of the river from the land and the 
land from the river as the riverfront evolved from a fortified defense system through to the 
combination of a commercial harbor, airport and populated public spaces. For this purpose I will 
investigate the writings of travelers, urban designers and policy makers who were instrumental in 
the transformation of the riverfront. 

Do spectral gamma ray data really reflect humid-arid palaeoclimates? A test from the Palaeogene Interbasaltic weathered horizons at the Giant’s Causeway, N.Ireland

Since 1999, the rapid, inexpensive and non-destructive use of Th/K and Th/U ratios from spectral gamma ray measurements have been used as a proxy for changes in palaeo-hinterland weathering. This model is tested here by analysis of in situ palaeoweathering horizons where clay mineral contents are well-known. A residual palaeoweathered horizon of Palaeogene laterite (developed on basalt) has been logged at 14 locations across N. Ireland using spectral gamma ray detectors. The results are compared to published elemental and mineralogical data. While the model of K and U loss during the early stages of weathering to smectite and kaolinite is supported, the formation (during progressively more advanced weathering) of gibbsite and iron oxides has reversed the predicted pattern and caused U and Th retention in the weathering profile. The severity (duration, humidity) of weathering and palaeoweathering may be estimated using Th/K ratios as a proxy. The use of Th/U ratios is more problematic should detrital gibbsite (or similar clays) or iron oxides be detected. Mineralogical analysis is needed in order to evaluate the hosts for K, U and Th: nonetheless, the spectral gamma ray machine offers a real-time, inexpensive and effective tool for the preliminary or conjunctive assessment of degrees of weathering or palaeoweathering.

Emerging horizons for tick-borne pathogens: from the ‘one pathogen–one disease’ vision to the pathobiome paradigm

Ticks as vectors of several notorious zoonotic pathogens, represent an important and increasing threat for human, animal health in Europe. Recent application of new technology revealed the complexity of the tick microbiome that might impact upon its vectorial capacity. Appreciation of these complex systems is expanding our vision of tick-borne pathogens leading us to evolve a more integrated view that embraces the “pathobiome” representing the pathogenic agent integrated within its abiotic and biotic environments. In this review, we will explore how this new vision will revolutionize our understanding of tick-borne diseases. We will discuss the implications in terms of research approach for the future in order to efficiently prevent and control the threat posed by ticks.

Les Horizons (Paris. 1912)

Périodicité : Mensuel

Les Horizons / dir. Marcel Millet

1912/06 (A1,N3).

Les Horizons / dir. Marcel Millet

1913/06 (A2,N10).

Les Horizons / dir. Marcel Millet

1912/02 (A1,N1).

Les Horizons / dir. Marcel Millet

1913/03 (A2,N8).

Les Horizons / dir. Marcel Millet

1912-1913.

Les Horizons / dir. Marcel Millet

1912/10 (A1,N4).