Dating of glauconite from the Ngalia Basin,Northern Territory,Australia∗

Rb‐Sr and K‐Ar measurements have been made on five glauconite samples from the near basal Treuer Member of the Vaughan Springs Quartzite of the Ngalia Basin, Northern Territory, Australia. Comparison of results between and within the two groups of data demonstrates that variable losses of radiogenic strontium and argon have occurred, but allows a minimum age of 1280 m.y. to be calculated for the member. Sedimentation began in the Ngalia Basin shortly before the time of deposition of this member.

Regional correlations suggest that this minimum age applies to the adjacent Amadeus Basin as well.

Measurements were also made on glauconite from a single sample of the Lower Palaeozoic Djagamara Formation which is in the same sequence. It yields a mid‐Ordovician K‐Ar age which generally agrees with the broad range of post‐Lower Cambrian to pre‐Carboniferous age determined from fossil evidence in bounding formations. A low Rb/Sr ratio prevented calculation of a Rb‐Sr age, but the combination of K‐Ar age and Rb‐Sr measurements allowed an accurate initial ⁸⁷Sr/⁸⁶Sr ratio of .739 to be determined. This is much greater than ocean water values, and it appears that such information on young samples and/or those of low Rb/Sr ratio could help define the source material for glauconite formation.     

贺兰山北段牛头沟金矿区围岩的原岩恢复、时代及其地质意义

牛头沟金矿区位于华北陆块鄂尔多斯地块西缘贺兰山北段之基底杂岩带,赋矿地层为一套古元古界宗别立群第二亚群(Pt1Z2)中-深程度变质岩系,主要岩石类型是黑云斜长片麻岩和变粒岩。岩石地球化学特征分析及原岩恢复说明,蚀变岩型金矿体的围岩由正、副变质岩类共同组成,其中变粒岩的原岩为沉积碎屑岩,黑云斜长片麻岩的原岩为花岗闪长质侵入岩。离子探针锆石U-Pb定年表明,表壳岩的形成时代小于2120Ma,花岗闪长岩锆石U-Pb年龄为1950±8.9Ma,辉绿岩脉的侵入与花岗闪长岩属同期。综合研究表明,矿区变质岩的原岩形成时代不是前人认为的晚太古代,而是古元古代。同时应将属于正变质岩类黑云斜长片麻岩(原岩为花岗闪长岩)从宗别立群(Pt1Z)地层中分离出来,作为侵入岩单元考虑。     

Road construction over voids caused by active gypsum dissolution, with an example from Ripon, North Yorkshire, England

Sudden subsidence problems, caused by gypsum karst developed in the Permian sequence of Northern England, have caused difficult conditions for road construction. This paper presents the design strategy, mathematical modelling and parameters used to construct roads to cope with such difficult ground conditions. Because it is impossible to locate all the subsidence features along a route, the road design has to cope with potential future problems. This is achieved by using reinforcement-comprising layers of tensile membrane material within the earth embankment. This will prevent dangerous catastrophic collapse and maintain serviceability, but will allow sagging to show where major problems exist. The modelling showed that for the situation at Ripon, two layers of tensile membrane material within the earth embankment fulfilled the design brief for the road.     

Preliminary diagnoses of three new amphipod species from wellington harbour (note)

Preliminary diagnoses are given of Urothoe wellingtonensis n.sp. (Family Haustoriidae), Paraphoxus spinibasus n.sp., and P. chelatus n.sp. (Family Phoxocephalidae).     

Spatial localization of closeness and betweenness measures: a self-contradictory but useful form of network analysis

Closeness and betweenness are forms of spatial network analysis grounded in a long-standing tradition of measuring accessibility and flow potential. More recently, these measures have been enhanced by the concept of spatial localization, producing effective models for the prediction of pedestrian and vehicle driver behaviour.

A contradiction arises where the distance metric used to define locality does not match the distance metric used to define shortest paths for closeness and betweenness. A typical case is the use of angular shortest paths within a Euclidean buffer as a pedestrian flow model. Such a model assumes that people make a mode choice based on distance, but a route choice based on least angular change – even when this results in an excessively long ‘problem route’, which conflicts with their criterion for mode choice.

This study examines the prevalence of problem routes and the magnitude of their effect on some pedestrian and vehicle models. We show that while in a weighted analysis, pathological cases could invalidate an entire model, in the models presented the effect of this contradiction is minor. We do this by comparing model predictions to real flow data, using four strategies for handling problem routes: ignore, discard, reroute and strict locality. Strict locality is justified on the grounds of bounded rationality. We find all strategies to give broadly similar results, although the reroute and strict strategies give marginally better simulation accuracy. We also present a discussion of the characteristics of each strategy, and findings on computational efficiency.

We conclude that it is prudent in any computation of localized closeness and betweenness to consider the impact of problem routes; however, they do not necessarily invalidate these forms of analysis, which remain useful.     

An inexpensive sampler for obtaining bulk sediment cores

A large-volume core sampler for sediment—muck substrates is described. The sampler can acquire a discrete sediment core of 10 cm in diameter and up to 1.5 m long. Such samplers are needed to collect the volume necessary for analysis of sediments for contaminants, bulk density, or radioactive dating. The sampler consists of a 1- to 2-m length of PVC pipe mounted below a threaded metal pipe air exhaust—intake assembly. This assembly is quick-connected to standard threaded lengths (300 cm) of water pipe (2 cm diam) or electrical conduit so that bottom sediments in water depths of up to 10 m can be sampled. The core sampler is hand-operated and pushed into bottom sediments from a boat. It does not have to be triggered remotely because of the one-way modified check valve in the air exhaust—intake assembly. After the sampler is extracted from the sediment, the extension handle can be quickly removed for ease of sampler handling, and the core can be extruded from the PVC tube by air pressure.Contribution of the National Sedimentation Laboratory, Agricultural Research Service, U.S. Department of Agriculture, Oxford, Mississippi 38655, U.S.A.     

Rare earth element abundances in rocks and minerals from the Fiskenaesset Complex,West Greenland

Rare earth element (REE) abundances determined by activation analysis in rocks, plagioclase and mafic separates from the Fiskenaesset Complex are presented together with data on major and trace elements in the minerals. The REE data for the rocks and plagioclases are distinct from those of many other anorthositic complexes and the abundances are some of the lowest recorded for plagioclase from terrestrial anorthosites. The bulk and trace element compositions of the Fiskenaesset plagioclases show a number of similarities to those of lunar plagioclases. The plagioclases show a positive Eu anomaly of about 10 and a depletion in the heavy REE relative to the light ones. The mafic separates are enriched in the heavy REE relative to the light ones, and show no Eu anomaly except in one sample with a positive anomaly not attributable to plagioclase contamination. It is estimated, from experimental partition coefficient data, that the REE pattern in the magma at an early stage of fractionation was La (17×) to Lu (0.7× chondrites) with a possible positive Eu anomaly. This highly fractionated REE pattern may be attributed to partial melting of a garnet-bearing source.     

Genetic diversity and metal tolerance of two marine species: a comparison between populations from contaminated and reference sites

Long-term contamination of the marine environment surrounding a lead smelter offered a unique opportunity to examine how pollutants might have acted to alter genetic characteristics of populations of organisms in the receiving system. This study used random amplified polymorphic DNA analysis to compare the genetic diversity of populations of the prawn, Leander intermedius, and the isopod, Platynympha longicaudata from the smelter discharge site with reference populations. The genetic diversity of the prawn population from the smelter discharge site (Port Pirie) was lower than that found in one reference population, and not significantly different from the other two reference populations. Genetic diversity of the Port Pirie population of isopods was found to be significantly lower than that of all reference populations. Prawns and isopods were also exposed to metal mixtures in the laboratory in a similar ratio to that found in seston near the smelter effluent discharge site. Both pre-exposed and reference populations of prawns tolerated elevated levels of metals and exhibited no significant difference in response. This contrasted with the isopods, with the pre-exposed isopod population showing greater tolerance to elevated metal levels compared with the reference population. These results highlight the need to include a number of reference populations for comparative purposes in genetic diversity studies, and the need to assess the influence of pollution on the genetic diversity of more than one species if genetic diversity analyses are to be used to gauge remediation success.     

SEDIMENT RETENTION AND WATER QUALITY ENHANCEMENT IN DISTURBED WATERSHEDS

lPRoBLEMSTATEMENTANDOVERVIEWQualitywateriswithoutdoubtalimitingsubstance,notonlyforhumansbutforalllife.Yet,ashumanpopulation,activity,andpollutioncontinuetoincrease,naturalsourcesofreadilyuseablewateraredecliningatanalarmingfate.Humanscurrentlydiveftorregulatemorethanhalfofgloballyavailablefreshwaterrunofffortheirownpurposes(Posteletal.,l996),includingtheuseoflargedamsordiversionsonriversandthewidespreadcreationofotherartificialcatchments.Additionally,groundwatersourcesarebecomingin…