The ‚loess’︁ section at Borden,Kent, SE England

A 5.3m profile originally described as loess with a buried interglacial soil is reinterpreted from petrographic evidence and thermoluminescence dating as a Holocene colluvial accretionary soil. Mineralogical analyses of coarse silt (16–63 μm) fractions suggest that most of the silty colluvium was derived from weathered Thanet Beds upslope, though some loess was incorporated during the final depositional phase. Thin sections show that clay illuviation occurred penecontem-poraneously with deposition of colluvium. Thermoluminescence properties suggest partial optical bleaching of the grains during rapid deposition, which is consistent with a Holocene colluvial origin.     

Observing the reconnection region in a transequatorial loop system

A vertical current sheet is a crucial element in many flare/coronal mass ejection (CME) models. For the first time, Liu et al. reported a vertical current sheet directly imaged during the flare rising phase with the EUV Imaging Telescope (EIT) onboard the Solar and Heliospheric Observatory (SOHO). As a follow-up study, here we present the comprehensive analysis and detailed physical interpretation of the observation. The current sheet formed due to the gradual rise of a transequatorial loop system. As the l...     

Genetic improvement of New Zealand aquaculture species: programmes,progress and prospects

Aquaculture, like terrestrial farming, cannot achieve economic and sustainable production without high performing genetic stocks tailored to the conditions under which they are grown. It is essential, therefore, that aquaculture investment includes genetics and biotechnology to adapt marine livestock to the novel conditions of intensive aquaculture and to the demanding markets into which they are sold. The return on investment in well-structured breeding programmes can be very high, and significant performance and economic gains have been demonstrated in multiple species. Many factors must be considered in designing a genetic improvement programme, including the reproductive biology of the species and the identification of realistic and commercially relevant breeding goals based on the resources and facilities available. This paper reviews the options available to aquaculturists and provides examples of how these are being applied to six aquaculture species in New Zealand: king salmon, hāpuku, kingfish, Greenshell^TM mussels, Pacific oysters and pāua (abalone).     

A comparative study of the Rare Earth Element (REE) distributions within the Lower Cretaceous dolomites and limestones of Central Tunisia

REE distribution, strontium content and oxygen isotopic composition have been studied in the Lower Cretaceous dolomites and their interbedded and/or parental limestones of Central Tunisia. Dolomites, as indicated by previous sedimentologic, geochemical and isotopic study, are different in origin. Environments of dolomite formation include: evaporitic sabkha, deep phreatic, karst and lacustrine. With the exception of the sabkha environment, dolomitizing fluids presumably have been essentially meteoric. The comparison between REE distributions in dolomites and limestones clearly suggests that the general shapes of the REE patterns are preserved during dolomitization. Nevertheless, the total REE amounts are somewhat lowered in dolomites comparatively to parental limestones. Moreover, within the dolomites, the total REE contents are positively correlated to the Sr and δ¹⁸O contents; thus indicating that the decrease in REE, Sr, and δ¹⁸O contents is related to a decrease in the salinity of dolomitizing fluids. In addition, dolomites associated with emergence surfaces (karst) are the most impoverished in REE. Furthermore, they are relatively enriched in light REE, indicating a more or less important fractionation with the REE distributions. This enrichment has been related to the influence of the inorganic complexes which favours the greatest solubility of the heavy REE in basic solution with respect to the lightest members of the REE group.     

On the role of diapirism in the, segregation, ascent and final emplacement of granitoid magmas

Only bodies of magma with a high crystal content and partially molten (crustal) country rocks can ascend as diapirs; once such an envelope is pierced, the diapiric ascent of the pluton is arrested by the high viscosity of a solid aureole. Deformation by shortening of the carapace of these bodies may lead to the expulsion of a magma with a relatively low crystal content, which may then continue ascent via fractures and dykes.

The details of the mechanisms of granitoid magma segregation are still unknown, but it appears that many magmas hegin their ascent through the crust as mushes with at least 50% melt, and that such magmas are rheologically able to ascend through a thickness of crust. This ascent mechanism explains the dearth of structures attributable to the ascent of granitoids, in contrast to the abundance of structures that developed during their final emplacement.

When a magma becomes too crystalline (melt < 25%) to continue its ascent via dykes, it is immobilised. At approximately this stage, a hydrous magma may become saturated with water and release fluids into the aureole, making it particularly susceptible to deformation. Magma that continues to arrive at this level is also immobilised, and the pluton grows as a ballooning diapir. These characteristically deform themselves and their aureoles by bulk shortening.

Magmas that are able to ascend to shallow depths, largely by virtue of lower water contents and higher initial temperatures, tend to become finally accommodated by such brittle processes as stoping and cauldron subsidence. High level intrusions lend to be tabular, are also fed by dykes or conduits, and assemble in tabular batholiths.     

Malaria reinfestation on the Northern Border of Argentina

Until 1950 malaria was a major public health hazard in Argentina affecting a large number of people in the northern territory. In that year a Malaria Eradication Programme began and this initiated a dramatic fall in incidence especially in the north east in subsequent years.In 1970 there was an increase in the incidence in the north west of the country. Than, in 1989 malaria was diagnosed along the northeastern border. The earlier outbreak was associated with the growth of border traffic and increasing immigration. Ecological changes consequent upon the building of large dams in the Paraná basin have been blamed for the outbreak in 1989.The reinfestation of malaria of northern Argentina is analysed, from the point of view of the trends in incidence during the period 1937–89 and especially the increase after 1970. Control measures are also proposed.     

Detecting post-depositional sediment disturbance in sandy deposits using optical luminescence

Post-depositional mixing or exhumation is common in surficial sediments, yet may be unobservable from field evidence. However, any disturbance may have significant consquences in terms of establishing a reliable luminescence age determination. Optically stimulated luminescence (OSL) measurements, particularly measurements at the single grain level, can be used to gain an insight into both contemporary and past post-depositional processes.

This paper examines sites from Texas and Florida (USA) with independent chronological control to demonstrate the potential effects of varying degrees of bioturbation on OSL. Results show that contemporary soil forming processes clearly impact on the palaeodose (D_e) replicate distributions which are measured in order to derive an OSL age. Significant levels of scatter and apparently zero dose grains are observed in the upper-most sediments; declining with depth from the surface. D_e replicates from undisturbed and fully bleached sediments are unskewed, show low overdispersion (OD) and comparable single grain and single aliquot OSL ages. Bioturbated sediments, however, may show highly skewed multi-model D_e distributions with higher OD values, zero dose grains at depth, and significant diffences between single grain and single aliquot results. True burial ages may be derived from minimally bioturbated sediments through the application of statistical analysis such as finite mixture modelling to isolate D_e components. However, for significantly bioturbated sediments, the latter approach, even at the single grain level, produces inaccurate ages. In such cases we argue that additional evidence (both dating and contexual) may be required to identify with confidence the burial D_e population.     

Developing a protocol for selecting and dating sandy sites in East Central Texas: Preliminary results

Vast areas of East Central Texas are overlain by deep unconsolidated sands, previously assumed to have been formed by in situ weathering and pedoturbation of the bedrock. This hypothesis would imply that palaeoenvironmental and archaeological reconstructions are of limited value. However, recent research has hinted that some elements of the landscape may have undergone repeated phases of erosion and redeposition, suggesting firstly that a reliable record of past environmental conditions may be gleaned from these deposits, and secondly that optically stimulated luminescence (OSL) may provide the key to unlocking this record. This research examines the depositional history of sites shown to provide a reliable chronology. Dates from these sites show that aeolian deposition occurred in East Central Texas at a number of times during the Holocene and Late Glacial, whilst three episodes of gullying occurred between approximately 123,000 and 44,000 years ago. The concordance of some of these results indicates that some phases of deposition may be regional.     

Recent floods in Bangladesh: Possible causes and solutions

In recent years the frequency of abnormal floods in Bangladesh has increased substantially, causing serious damage to lives and property. The most crucial questions that need to be addressed are: what really causes the havoc-creating floods and is there any solution to the problem? The heavy monsoon downpour and synchronization of flood-peaks of the major rivers are generally considered to be the main causes of the floods. Some underlying factors also deserve serious consideration as possible contributors to the recent floods: change in the base level of the rivers due to local sea level rise and subsidence, inadequate sediment accumulation on flood plains, a possible increase in the watershed area due to seismic and neotectonic activities in the region, river bed aggradation due to siltation and damming of rivers, soil erosion due to unwise tilling practices, deforestation in the upstream region, and excessive development and population growth. Without regional cooperation among the co-riparian nations any major interbasin flood control activity is considered to be almost impossible. However, among other proposals in this paper, extensive annual dredging of the rivers, channels and creeks, and reoccupation of the abandoned channels in Bangladesh through re-excavations could still increase the water carrying capacity of the rivers. Land elevations could be increased if the dredged or excavated materials are dispersed on the flood plains, which would in turn reduce the severity of floods.