The melting relationships of a madupite from the Leucite Hills,Wyoming, to 30 Kb

The water-undersaturated melting relationships of a mafic, peralkaline, potassic madupite (with about 3% H₂O as shown by chemical analysis) from the Leucite Hills, Wyoming, have been studied at pressures up to 30 kb. At low pressures (<5 kb) leucite is the dominant liquidus phase, but it is replaced at higher pressures by clinopyroxene plus olivine (<5–7 kb), clinopyroxene (7–12.5 kb), clinopyroxene plus minor spinel (12.5–17.5 kb), and clinopyroxene alone (17.5–> 30 kb). At all pressures there is a reaction relationship with falling temperature between melt, olivine and probably clinopyroxene to yield phlogopite. Apatite is stable within the melting interval to pressures above 25 kb. Electron microprobe analyses demonstrate that the clinopyroxene is diopsidic, with low aluminium and titanium contents. Pressure has relatively little effect on the composition of the pyroxene. Phlogopite is also aluminium-poor and has only a moderate titanium content. The experimental results indicate that madupite is not the partial melting product of hydrous lherzolite or garnet lherzolite in the upper mantle and it seems improbable that it is derived by melting of mantle peridotite with a mixed H₂O-CO₂ volatile component. Madupite could, however, be the partial melting product of mica-pyroxenite or mica-olivine-pyroxenite in the upper mantle. It is pointed out that the chemistry of some potassium-rich volcanics may have been affected by volatile transfer and other such processes during eruption and that experimental studies of material affected in this way have little bearing upon the genesis of potassic magmas. Finally, the experimental results enable constraints to be placed upon the P-T conditions of the formation of richterite-bearing mica nodules found in kimberlites and associated rocks. Maximum conditions are 25 kb and 1,100 ° C.     

Bulk organic δC and C/N as indicators for sediment sources in the Pearl River delta and estuary,southern China

Preservation of organic matter in estuarine and coastal areas is an important process in the global carbon cycle. This paper presents bulk δ¹³C and C/N of organic matter from source to sink in the Pearl River catchment, delta and estuary, and discusses the applicability of δ¹³C and C/N as indicators for sources of organic matter in deltaic and estuarine sediments. In addition to the 91 surface sediment samples, other materials collected in this study cover the main sources of organic material to estuarine sediment. These are: terrestrial organic matter (TOM), including plants and soil samples from the catchment; estuarine and marine suspended particulate organic carbon (POC) from both summer and winter. Results show that the average δ¹³C of estuarine surface sediment increases from −25.0 ± 1.3‰ in the freshwater environment to −21.0 ± 0.2‰ in the marine environment, with C/N decreasing from 15.2 ± 3.3 to 6.8 ± 0.2. In the source areas, C₃ plants have lower δ¹³C than C₄ plants (−29.0 ± 1.8‰ and −13.1 ± 0.5‰ respectively). δ¹³C increases from −28.3 ± 0.8‰ in the forest soil to around −24.1‰ in both riverbank soil and mangrove soil due to increasing proportion of C₄ grasses. The δ¹³C_POC increases from −27.6 ± 0.8‰ in the freshwater areas to −22.4 ± 0.5‰ in the marine-brackish-water areas in winter, and ranges between −24.0‰ in freshwater areas and −25.4‰ in brackish-water areas in summer. Comparison of the δ¹³C and C/N between the sources and sink indicates a weakening TOM and freshwater POC input in the surface sedimentary organic matter seawards, and a strengthening contribution from the marine organic matter. Thus we suggest that bulk organic δ¹³C and C/N analysis can be used to indicate sources of sedimentary organic matter in estuarine environments. Organic carbon in surface sediments derived from anthropogenic sources such as human waste and organic pollutants from industrial and agricultural activities accounts for less than 10% of the total organic carbon (TOC). Although results also indicate elevated δ¹³C of sedimentary organic matter due to some agricultural products such as sugarcane, C₃ plants are still the dominant vegetation type in this area, and the bulk organic δ¹³C and C/N is still an effective indicator for sources of organic matter in estuarine sediments.     

Recent occurrence of Cylindrospermopsis raciborskii in Waikato lakes of New Zealand

Cylindrospermopsis raciborskii is a toxin‐producing species of cyanobacteria that in autumn 2003 was recorded for the first time in three shallow (max. depth ≤5 m) Waikato lakes and a hydro‐electric dam on the Waikato River, New Zealand. It formed water blooms at densities >100 000 cells/ml in Lakes Waahi and Whangape. Net rates of population growth >0.2 day_–1 were recorded for C. raciborskii in Lakes Ngaroto, Waahi, and Karapiro, based on comparisons of low numbers (detection of <10 cells/ml) from initial samples and its presence at bloom densities (>15 000 cells/ml) in the subsequent sample “x"‐"y” days later. C. raciborskii may be well adapted to rapid proliferation in the Waikato lakes, which are eutrophic to hypertrophic, with high light attenuation, and where nitrogen (N) fixation may provide it with a competitive advantage over non‐nitrogen fixing algae under N‐limited conditions.     

Studies on groundwater recharge characteristics at a reclaimed land site with an equatorial climate using time‐series and spectral analyses

Groundwater recharge studies are essential for investigating the feasibility of using the reclaimed lands in Singapore for subsurface storage and recovery of water. Through time‐series and spectral analyses, net recharge percentages and stress‐filtering characteristics at the reclaimed land were found to depend strongly on the stress transfer velocity, which was a combined function of rainfall pattern and vadose zone thickness. Based on stress transfer velocity, a theory was established to provide logical explanations for the rainfall–recharge relationship, the observed stress‐filtering characteristics and the recharge percentage characteristics at the unconfined sandy aquifer. Although the reclaimed land site has a lithollogically homogeneous soil profile, a non‐uniform recharge pattern was observed to be influenced pronouncedly by the uneven density distribution of bush grasses. Under a bare soil condition, significantly lower recharge percentages were observed for areas under the influence of offshore tides. The unconfined sandy aquifer appears to dampen out the wave propagation of offshore tides rapidly within a short distance from the tidal source, though it has a fairly straight shoreline and is created from highly compacted sand fills. Copyright © 2006 John Wiley & Sons, Ltd.     

Precambrian microfossils from the McArthur River lead-zinc-silver deposit northern territory,Australia

Structurally preserved insoluble organic cellular matter is intimately associated with Precambrian lead-zinc-silver ore in the McArthur River deposit, Australia. The ore is essentially a non-metamorphosed mineralized bituminous dolomitic shale of marine volcanic association and has some similarities with the Mt. Isa and Broken Hill deposits.