THEORETICAL ANALYSIS OF AN IMPERVIOUS,HEATED-CYLINDER ‘GROUNDWATER VELOCIMETER’

An isothermally heated, impervious cylinder, which is placed normal to the path of flowing groundwater, is theoretically evaluated for its potential to serve as a kind of ‘groundwater velocimeter’. The essential task is to determine whether the variation in heat output along the cylinder perimeter is sufficiently large to permit measurement for typical groundwater velocities. Using finite elements, the governing equations of advective thermal transport in saturated porous media are solved to obtain the variation in heat output along the circumference of the heated cylinder. An annular region of different hydraulic conductivity is assumed to separate the cylinder from the surrounding formation. The creation of such a region during placement of a cylinder is inevitable. A parametric study led to the following conclusions: (1) A smaller cylinder radius is preferable since the time to achieve a particular degree of asymmetry in heat output is then greatly reduced. (2) An annular region of lower hydraulic conductivity, relative to formation, reduces output asymmetry by no more than 25%, but if hydraulic conductivity is increased, output asymmetry can increase several times. (3) For annular regions having a higher hydraulic conductivity than the surrounding formation, annular thickness is not important. (4) The least groundwater speed which may be accurately measured by such a device will depend heavily upon instrumentation but is tentatively placed at about 5⋅0×10⁻⁵ cm/s. Theoretical results are approximately confirmed by preliminary experiments with a prototype device which has been constructed so as to directly measure the expected variation in thermal output. Partial construction details are provided.     

Infiltration of Aqueous Fluid and High Fluid: Rock Ratios During Greenschist Facies Metamorphism: A Discussion

Ferry's (1984) analysis of the biotite isograd in pelitic schistsof the Waterville Formation (south-central Maine, U.S.A.) ledto the conclusion that metamorphism had been caused by infiltrationof 1–2 rock volumes of aqueous fluid. We find that thisimportant observation is extremely sensitive to the assumedtemperature of metamorphism and to corresponding uncertaintiesin the thermodynamic data and solution assumptions. Uncertaintiesin the experimental calibrations of the geothermometers areon the order of ? 30?C. In addition, an analysis of the effectsof minor substituents on calcite-dolomite and garnet-biotitegeothermometers indicates that Ferry's (1980) temperatures areabout 40?C too low in the garnet zone. Correcting the phaseequilibria to higher temperatures by this latter amount lowersfluid:rock ratios by an order of magnitude to about 0?1:1. Sincesmall uncertainties have such great effects it is clearly importantto perform careful uncertainty analyses before using Ferry'sapproach to draw wide-ranging conclusions about fluid-rock interactions.Given a 40?C upward revision of temperature it is not necessaryto invoke pervasive infiltration of aqueous fluid as the majoragent of metamorphism. With these low fluid:rock ratios thewater source could reasonably be a thin sequence of underlyingmetapelites and/or the granitic intrusives which accompaniedthe Acadian orogeny.     

Population Dynamics and Settlement Systems

The paper uses five broad classes of settlement in the Waikato as a base for exploring age and gender specific changes to population distributions. The trends are assessed over the period 1981 to 1991, an era of significant change to the economic and social fabric of the region. Links between this change and the inferred patterns of movement are suggested. Notable patterns include migration deficits in the youthful and elderly age classes in sparsely settled rural areas, and more substantial numbers of elderly in other non metropolitan settlements than expected. The policy implications of these distributions are considered in the concluding section of the paper.     

Major and Trace Element Variations in the Tertiary Lavas of Eastern Iceland and their Significance with respect to the Iceland Geochemical Anomaly

Major and trace element analyses of 130 lavas, including rareearth elements (REE) for 90 of them, are used to investigategeochemical variation in this lava series. The lavas are dividedinto six compositional groups, ranging from high magnesia basaltto rhyolite, on the basis of Fe/Mg ratio and the phenocrystphase assemblage. The high magnesia basalts range from tholeiiticto transitional and show a correlation between silica saturationand light REE enrichment. This chemical variation cannot beexplained in terms of open or closed system crystal fractionationinvolving the observed phenocryst phases, but is probably theresult of a two (or more) stage mantle process. When the observedvertical chemical zonation and subsequent erosion of the lavapile are taken into account, it is apparent that a range ofbasaltic compositions has been available for eruption throughoutthe history of the lava pile. The evolved (low Mg) lavas belong to a spectrum of closed systemcrystal fractionation trends derived from each of the high magnesiabasalts. However, silicic and intermediate lavas are all derivedfrom the more light REE enriched basalts. The crystal fractionationmodel is quantified using a least squares mixing computer programfor the major elements and the Rayleigh equation for the REE.The importance of minor phases (i.e. iron-titanium oxides andapatite) in controlling both major and trace element behaviourin the residual liquid during crystal fractionation is established.The large calculated bulk solid/liquid distribution coefficientsfor most of the analysed trace elements, at certain compositionalintervals in the series, suggest that few, if any, of the elementscan be considered as totally incompatible. In detail the chemicalvariation in the silicic and intermediate lavas cannot be producedby the partial melting of a basaltic source. Hybrid intermediatelavas can be distinguished chemically from differentiates becausethey lie on linear trends between basalt and rhyolite for mostelements. Intermediate differentiates are only formed in a narrowcrystallization interval which, together with their need tobe superheated in order to reach the surface, probably explainsthe paucity of these compositions in the lava pile.     

Geochemistry of an Island-Arc Plutonic Suite: the Uasilau-Yau Yau Intrusive Complex, New Britain, P.N.G

In the Uasilau-Yau Yau intrusive complex of central New Britain,Papua New Guinea, there is a compositional continuum in intrusiverock-types from gabbro to granodiorite and K-Ar mineral agesof the most mafic and most felsic components are not significantlydifferent (29?0.6 Ma versus 28.3?0.5 Ma, respectively). Tonaliteporphyry, the progenitor of porphyry copper mineralization inthe complex, represents a significantly younger intrusive eventat 24 Ma. Relatively calcic (An_95—50) plagioclase coresand salite to augite composition clinopyroxene are texturallyearly phases in the intrusive rocks. The main mafic mineral,calcic amphibole, generally has corroded clinopyroxene coresand may, like biotite, K-feldspar and quartz, generally be alate-stage, not a primary liquidus phase. Petrographic featuresindicate that the mafic minerals in the plutonic rocks crystallizedfrom melt, rather than being restite phases. The intrusive rocks cover an extensive silica range (45–75wt. per cent), do not exhibit simple straight-line variationon Harker diagrams for many elements (e.g. TiO₂, FeO, P₂O₅ andSr), and most are relatively depleted in incompatible traceelements (Rb, Zr, and REE). Major and trace element modellingsupports derivation of the complex by shallow level fractionalcrystallization dominated by removal of the phases calcic plagioclase,clinopyroxene, and magnetite from a parental magma closely resemblingrecent basaltic rocks in New Britain. The fact that the plutonicrocks are almost chemically indistinguishable from late Cainozoiccalc-alkaline volcanic rocks of New Britain supports fractionalcrystallization as a viable mechanism for generating these island-arcvolcanic rocks and indicates an analogous origin for the initialmagma. Granites, such as those of the Uasilau-Yau Yau intrusive complex,which are probably generated by partial melting of subductedoceanic crust or the overlying mantle, may be termed mantleor M-type granites. Documentation of the characteristics ofM-type versus normal I-type granites may enable the recognitionof M-type plutonic rocks in older, possibly more deeply erodedgeologic terrains. This would, by analogy to their volcanicequivalents, be very helpful in tectonic interpretations. Also,such plutonic rocks have known potential for Cu-Au mineralization.     

TESTING LAKE SEDIMENT AND DENDROGEOMORPHIC PROXIES FOR LITTLE ICE AGE ENVIRONMENTAL CHANGE IN THE UPPER FRASER RIVER AREA,BRITISH COLUMBIA,CANADA

This study assesses Little Ice Age (LIA) lake sediment morphological and geochemical records and moraine chronologies in the upper Fraser River watershed, British Columbia, Canada, to resolve differences in paleoenvironmental interpretation and to clarify sediment production and sediment delivery processes within alpine geomorphic systems. Moose Lake (13.9 km²), situated at 1032 m a.s.l., contains a partially varved record indicating variable rates of accumulation during the last millennium that, in general, coincide with previously documented LIA glacial advances in the region and locally. Dendrochronological assessment of forefield surfaces in the headwaters of the catchment (Reef Icefield) shows that periods of moraine construction occurred just prior to ad 1770, ad 1839 and ad 1883, and some time before ad 1570. Taken collectively, increases in varve thickness within eight Moose Lake sediment cores coincide with documented glacier advances over the twelfth through fourteenth centuries, the eighteenth century, and nineteenth through twentieth centuries. Glacial activity during the sixteenth century is also indicated. While varve thickness variations in proximal and distal sediments clearly reflect glacial activity upstream of Moose Lake, the intermediate varve record is relatively insensitive to these decadal and longer‐term catchment processes. Variations in Ca and related elements derived from glaciated carbonate terrain within the Moose River sub‐catchment (including Reef Icefield) indicate gradually increasing delivery from these sources from the twelfth through twentieth centuries even where the varve thickness record is unresponsive. Elevated carbonate concentrations confirm glacial activity c. ad 1200, ad 1500, ad 1750, and ad 1900.     

Using palaeoenvironmental DNA to reconstruct past environments: progress and prospects

Palaeoenvironmental DNA (PalEnDNA) is defined as ancient DNA (aDNA) originating from disseminated genetic material within palaeoenvironmental samples. Sources of PalEnDNA include marine and lake sediments, peat, loess, till, ice, permafrost, palaeosols, coprolites, preserved gut contents, dental calculus, tephras, and soils as well as deposits in caves/rockshelters and at archaeological sites. PalEnDNA analysis provides a relatively new tool for Quaternary and archaeological sciences and its applications have included palaeoenvironmental and palaeodietary reconstructions, testing hypotheses regarding megafaunal extinctions, human–environment interactions, taxonomic studies, and studies of DNA damage. Because PalEnDNA samples comprise markedly different materials, and represent wide‐ranging depositional and taphonomic contexts, various issues must be addressed to achieve robust, reproducible findings. Such issues include climatic and temporal limitations, the biological origin and state (free versus bound) of PalEnDNA, stratigraphic reliability, sterile sampling, ability to distinguish modern from aDNA signals, DNA damage and PCR amplification, DNA extraction methods, and taxonomic resolution. In this review, we provide a non‐specialist introduction to the use of PalEnDNA for Quaternary and archaeological researchers, assess attributes and limitations of this palaeoenvironmental tool, and discuss future prospects of using PalEnDNA to reconstruct past environments.