On the use of anhysteretic remanent magnetization in paleointensity determination     

Monika E. Bailey  David J. Dunlop 《Physics of the Earth and Planetary Interiors》1977,13(4):360-362

The relative intensities of anhysteretic remanent magnetization (RAM) and thermoramanent magnetization (TRM) are strongly dependent on grain size, blocking temperature and applied field, and are poorly predicted by existing theories. Analog techniques that substitute ARM for TRM probably yield adequate relative paleointensities in suites of mineralogically similar rocks, but they yield uncertain estimates of absolute paleointensity.  相似文献   

Sedimentary evidence for an archaean shallow-water volcanic-sedimentary facies,Eastern Pilbara Block,Western Australia     

M.E. Barley  J.S.R. Dunlop  J.E. Glover  D.I. Groves 《Earth and Planetary Science Letters》1979,43(1):74-84

Sedimentological studies of the dominantly volcanic, ca. 3.5 b.y. Warrawoona Group, eastern Pilbara Block, Western Australia, indicate widespread shallow-water deposition. Many cherty metasediments within the ultramafic-mafic sequence represent silicified carbonate mud, sand, breccia and conglomerate, and show cross-lamination, ripple marks, scour-and-fill structures, and evidence of reworking. At North Pole, some cherty metasediments appear to be silicified and baritized gypsiferous evaporites, and contain microfossils. Felsic volcaniclastic rocks include pyroclastic deposits, cross-laminated tuffaceous metasediments and conglomerate. Subaerial volcanism apparently increased as deposition proceeded.The depositional basin was large, volcanically active and apparently shallow with subdued marginal relief. Felsic volcanoes formed topographic highs within the basin from which sheets of volcanically derived sediments interfingered with ultramafic-mafic volcanics. The Onverwacht Group of the Barberton Mountain Land, South Africa, is of similar age to the Warrawoona Group and probably represents a similar environment, but other greenstone belts may have formed in contrasting basins, possibly under differing tectonic regimes.  相似文献   

Dissolution rates of metals in Fe oxides: implications for sampling ferruginous materials with significant relict Fe oxides     

J. Xie  A. C. Dunlop 《Journal of Geochemical Exploration》1998,61(1-3)

A study of the pattern of dissolution of synthetic and natural Fe oxides in 6 M HCl indicates that the rate of element release from synthetic Fe oxides is strongly influenced by mineralogy and the level of element incorporation. Synthetic maghemite (γ-Fe₂O₃) samples are subject to much more rapid dissolution than goethite (FeOOH) and hematite (α-Fe₂O₃). In samples dominated by hematite and maghemite, Cu, Zn and particularly Pb, in comparison to Fe, are preferentially released during the early stages of dissolution. Similar patterns are apparent from the dissolution of hematite- and maghemite-dominated samples derived from natural gossan. Comparison of XRD scans with data from the dissolution of natural gossan samples transformed by incremental heating to hematite- and maghemite-dominated assemblages suggests that the degree of crystallinity may also be a significant factor in the release of elements incorporated in the Fe oxides. Ferruginous materials made up of varying proportions of goethite, hematite, maghemite, kaolinite and quartz are important sampling materials in a range of regolith environments. These are products of complex chemical and mechanical mobilization over long periods of geological time. If the patterns of Fe oxide dissolution in 6 M HCl and the release of incorporated metals reflect stability in such weathering regimes, knowledge of the retention characteristics of incorporated metals in different Fe oxide phases, as indicated by this study, will be useful in the planning and interpretation of geochemical surveys in such regions.  相似文献   

Hydrocarbons of the hypersaline basins of Shark Bay,Western Australia     

R.W. Dunlop  P.R. Jefferies 《Organic Geochemistry》1985,8(5):313-320

Shark Bay is an 8000 sq. km shallow marine embayment on the western coast of Western Australia. The waters exhibit a well established salinity gradient from oceanic to hypersaline. The chemical assemblage of sediment hydrocarbons along the salinity gradient may be classified into two distinct chemogeographic types. Firstly, oceanic sediments contain n-alkanes and a suite of highly branched and branched/cyclic C₂₅ alkenes. Hypersaline sediments are characterised by a high relative abundance of a C₂₅H₅₀ alkene together with an analogous C₂₀H₄₀ alkene and its parent C₂₀H₄₂ alkene (2,6,10-trimethyl-7-(3-methylbutyl)-dodecane). A pair of alkanes C₂₁H₄₂ and C₂₂H₄₄ increase in concentration and relative abundance with depth. The hydrocarbons of the hypersaline basins are found in only trace amounts in oceanic sediments. These chemical signals are overlain by further input indicative of the immediate biotic community.  相似文献   

Drainage sampling for uranium in the Torrington district, New South Wales, Australia   总被引：1，自引：0，他引：1  

A.K. Ishak  A.C. Dunlop 《Journal of Geochemical Exploration》1985,24(1):103-119

A brief orientation study has been conducted to evaluate the use of drainage geochemical sampling for U in the granitic and forested terrain of the Torrington district of northeastern New South Wales. Anomalous U levels are present in both stream sediments and waters draining a known W prospect containing accessory U. The U dispersion is affected by interrelated environmental factors such as catchment physiography and the organic content of the stream sediments. The influence of organic content on U level in stream sediments is most significant. Variation in sediment organic content is related to accumulation of vegetal organic debris and charcoal in stream channels by sheetwashing of sparsely covered forest floors particularly in catchments of high topographic relief. The U is apparently absorbed onto the organic material from ephemerally flowing stream waters. Temporal variations in U content of stream sediment are indicated which necessitate careful consideration in planning and interpreting the results of a survey in this environment.  相似文献   

Deep radio imaging of the SCUBA 8-mJy survey fields: submillimetre source identifications and redshift distribution     

R. J. Ivison  T. R. Greve  Ian Smail  J. S. Dunlop  N. D. Roche  S. E. Scott  M. J. Page  J. A. Stevens  O. Almaini  A. W. Blain  C. J. Willott  M. J. Fox  D. G. Gilbank  S. Serjeant  D. H. Hughes 《Monthly notices of the Royal Astronomical Society》2002,337(1):1-25

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The coercive force spectrum of magnetite at high temperatures: evidence for thermal activation below the blocking temperature     

David J. Dunlop  Mohammad-Mansour Bina 《Geophysical Journal International》1977,51(1):121-147

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Starburst galaxies and structure in the submillimetre background towards the Hubble Deep Field     

J. A. Peacock  M. Rowan-Robinson  A. W. Blain  J. S. Dunlop  A. Efstathiou  D. H. Hughes  T. Jenness  R. J. Ivison  A. Lawrence  M. S. Longair  R. G. Mann  S. J. Oliver  S. Serjeant 《Monthly notices of the Royal Astronomical Society》2000,318(2):535-546

We use an 850-μm SCUBA map of the Hubble Deep Field (HDF) to study the dust properties of optically-selected starburst galaxies at high redshift. The optical/infrared (IR) data in the HDF allow a photometric redshift to be estimated for each galaxy, together with an estimate of the visible star-formation rate. The 850-μm flux density of each source provides the complementary information: the amount of hidden, dust-enshrouded star formation activity. Although the 850-μm map does not allow detection of the majority of individual sources, we show that the galaxies with the highest UV star-formation rates are detected statistically, with a flux density of about S ₈₅₀=0.2 mJy for an apparent UV star-formation rate of 1  h ⁻² M_⊙ yr⁻¹. This level of submillimetre output indicates that the total star-forming activity is on average a factor of approximately 6 times larger than the rate inferred from the UV output of these galaxies. The general population of optical starbursts is then predicted to contribute at least 25 per cent of the 850-μm background. We carry out a power-spectrum analysis of the map, which yields some evidence for angular clustering of the background source population, but at a level lower than that seen in Lyman-break galaxies. Together with other lines of argument, particularly from the NICMOS HDF data, this suggests that the 850-μm background originates over an extremely wide range of redshifts – perhaps 1≲ z ≲6.  相似文献   

Two-dimensional modelling of optical Hubble Space Telescope and infrared tip–tilt images of quasar host galaxies     

R. J. McLure  J. S. Dunlop  M. J. Kukula 《Monthly notices of the Royal Astronomical Society》2000,318(3):693-702

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The topography of drumlins; assessing their long profile shape     

Matteo Spagnolo  Chris D. Clark  Anna L.C. Hughes  Paul Dunlop 《地球表面变化过程与地形》2011,36(6):790-804

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