The British Tertiary igneous province: palaeomagnetism of the dyke swarm along the Sleat coast of Skye

Summary. A palaeomagnetic investigation has been made of a swarm of more than 400 dykes along the south coast of Skye, Scotland, by the Sound of Sleat.
Seven red lamprophyre dykes have palaeomagnetic directions inconsistent with Tertiary age, and not inconsistent with their previously held Caledonian age. The remaining 409 dykes have palaeomagnetic directions that are consistent with a Lower Tertiary age. We present evidence suggesting that the Tertiary dykes might have been emplaced during a short time, over which the geomagnetic polarity occupied as few as three polarity intervals (NRN or RNR).
Certain 'intermediate' directions of magnetization have also been found, and are presented here.     

The Beach Crowding Index: A Tool for Assessing Social Carrying Capacity of Vulnerable Beaches

The aim of this article is to introduce the Beach Crowding Index (BCI), a procedure to assess the social carrying capacity of vulnerable beaches. The study uses the people at one time (PAOT) approach and data gathered weekly throughout the bathing season regarding the number of beachgoers in 100 m² cells of the beach to assess how many beachgoers it can comfortably hold. The procedure is based on fieldwork, interviews with beachgoers, and geographic information system (GIS) analysis and has been tested on four beaches in protected areas on the Spanish Mediterranean coast. On a scale from 0 to 4, minimum scores throughout the bathing season are 0.7 and maximum 3.7, although results showed wide variation between the beaches, the section of the beach, and the time of day. This study suggests that determining the location of beachgoers and collecting a long-term series of data is fundamental to assessing social carrying capacity and that the BCI procedure can be used for a large number of applications.     

Palaeomagnetism of the teschenitic rocks (Lower Cretaceous) in the Outer Western Carpathians of Poland: constraints for tectonic rotations in the Silesian unit

Results of palaeomagnetic investigations of the Lower Cretaceous teschenitic rocks in the Silesian unit of the Outer Western Carpathians in Poland bring evidence for pre-folding magnetization of these rocks. The mixed-polarity component reveals inclinations, between 56° and 69°, which might be either of Cretaceous or Tertiary age. Apparently positive results of fold and contact tests in some localities and presence of pyrhotite in the contact aureole suggest that magnetization is primary, although a Neogene or earlier remagnetization cannot be totally excluded since inclination-only test between localities gives 'syn-folding' results. Higher palaeoinclinations (66°–69°) correlate with a younger variety of teschenitic rocks dated for 122–120 Ma, while lower inclinations (56°–60°) with an older variety (138–133 Ma). This would support relatively high palaeolatitudes for the southern margin of the Eurasian plate in the late part of the Early Cretaceous and relatively quick northward drift of the plate in this epoch, together with the Silesian basin at its southern margin. Declinations are similar to the Cretaceous–Tertiary palaeodeclinations of stable Europe in the eastern part of the studied area but rotated ca. 14°–70° counter-clockwise in the western part. This indicates, together with older results from Czech and Slovakian sectors of the Silesian unit, a change in the rotation pattern from counter-clockwise to clockwise at the meridian of 19°E. The rotations took place before the final collision of the Outer Carpathians nappe stack with the European foreland.     

Arsenic anomalies in shallow Venetian Plain (Northeast Italy) groundwater

A pilot area within the Venetian Plain was selected to assess the arsenic (As) contamination of groundwater. The area represents a typical residential, industrial and agricultural organization representative of most western countries, and is also devoid of lithologies with high or anomalous As content. Hydrogeological and chemical data have been collected, the latter spatialized by a geostatistical approach. The unconfined aquifer reservoir varies from a predominantly gravel composition in the north to a sandy and silt–clay composition further south, including peat layers. The hydrochemical features of the waters are rather homogeneous, featuring low mineral content and a Ca-bicarbonate signature. In contrast, the redox state is highly variable; oxidizing conditions are predominant in the northern and coarse parts of the aquifer, whereas reducing potentials prevail in the southern and silt–clay parts. Several well waters contain arsenic in excess of drinkable limits (=10 ppb), and most of these wells are located in the southern area. A large portion of the studied area has a high probability of containing non-potable water (up to 150 ppb As). Remarkably, As “hot spots” (As > 300 ppb, up to 431 ppb) were identified at the transition from gravel to silt–clay sediments. No industrial or agricultural source of As has been found.     

A numerical Round Robin on tunnels under seismic actions

Although the seismic behaviour of shallow circular tunnels in soft ground is generally safer than aboveground structures, some tunnels were recently damaged during earthquakes. In some cases, damage was associated with strong ground shaking and site amplification, which increased the stress level in the tunnel lining. Pseudo-static and simplified dynamic analyses enable to assess transient changes in internal forces during shaking. Nevertheless, experimental evidences of permanent changes in internal loads in the tunnel lining would suggest that a full dynamic analysis including plastic soil behaviour should be performed when modelling the dynamic interaction between the tunnel and the ground. While sophisticated numerical methods can be used to predict seismic internal forces on tunnel structures during earthquakes, the accuracy of their predictions should be validated against field measurements, but the latter are seldom available. A series of centrifuge tests were therefore carried out at the University of Cambridge (UK) on tunnel models in sand, in the framework of a research project funded by the Italian Civil Protection Department. A numerical Round Robin on Tunnel Tests was later promoted among some research groups to predict the observed behaviour by means of numerical modelling. In this paper, the main results of five selected numerical predictions are summarized and compared with the experimental results.     

Relevance of Pentane- and Hexane-Utilizing Bacterial Indicators for Finding Hydrocarbon Microseepage: A Study from Jamnagar Sub-basin, Saurashtra, Gujarat, India

Mesozoic sediments are source rocks for nearly half the world’s hydrocarbon reserves. Hence, there is great interest in the oil industry to know the trap and sub-trappean sediment thickness and their extent in the trap covered regions of Jamnagar study area. The microbial prospecting method is applied in the Jamnagar sub-basin, Gujarat for evaluating the prospects for hydrocarbon exploration by investigating the anomalous abundance of n-pentane- and n-hexane-oxidizing bacteria of this area. A total of 150 near-surface soil samples were collected in Jamnagar sub-basin, Gujarat for the evaluation of hydrocarbon resource potential of the basin. In this study, bacterial counts for n-pentane-utilizing bacteria range between 1.09 × 10² and 9.89 × 10⁵ cfu/g and n-hexane-utilizing bacteria range between 1.09 × 10² and 9.29 × 10⁵ cfu/g. The adsorbed hydrocarbon gases consisting of ethane plus hydrocarbons (ΣC₂₊) of 1–977 ppb and n-pentane (nC₅) of 1–23 ppb. The integrated geomicrobial and adsorbed soil gas studies showed the anomalous hydrocarbon zones nearby Khandera, Haripur, and Laloi areas which could probably aid to assess the true potential of the basin. Integrated geophysical studies have shown that Jamnagar sub-basin of Saurashtra has significant sediment thickness below the Deccan Traps and can be considered for future hydrocarbon exploration.     

Effects of grazing by Daphnia on algal carotenoids: Implications for paleolimnology

Reverse-phase thin layer chromatography was used to quantify algal carotenoid degradation resulting from grazing by Daphnia magna in suspensions of lyophilized Oscillatoria utermöhlii, O. limnetica, Anabaena flos-aquae and Synechococcus sp. Three samples were removed every 24 h from 0 h to 144 h and the carotenoid, carbon and nitrogen content of the remaining algal-fecal mixture was determined. Grazing by Daphnia reduced carotenoid concentrations by 30%–80% after 144 h, with myxoxanthophyll being the most labile pigment in experiments with filamentous cyanophytes. However, as a group, the carotenoids were more resistant to the combined effects of grazing by Daphnia and bacterial action than were particulate algal carbon (78% to 82% lost by 144 h) or nitrogen (86%–90%) during the period in which easily digestible material remained. The maximal extent of carotenoid enrichment relative to particulate carbon ranged from 150% to 300% of initial pigment concentrations but declined with repeated coprophagy. On the basis of these results and published pigment budgets, we conclude both that fecal transportation of pigments may be an important determinant of carotenoid accumulation rates and that carotenoid stratigraphies should record predator-mediated changes in zooplankton community structure, especially in oligotrophic conditions.     

Space-time interaction amongst clusters of mining induced seismicity

Elementary cluster analysis of induced seismicity in a South African gold mine has shown that there is a clear interaction amongst the clusters; and that the level of the interaction is a function of the distance. The clusering algorithm used is an adaptation of the single-link cluster analysis which considers both three-dimensional space and time. A high level of interaction between the clusters is demonstrated from the cross-correlation analysis of seismic activity rates and radiated energy. A distinct decrease in the value of correlation coefficients was detectable as distance increased. This was somewhat surprising, considering the simplicity of the technique used. Since no attempt is made to study the physical mechanisms of interaction, these results are very preliminary, but interesting from an observational point of view.