Metamorphic evolution of aluminous granulites from Labwor Hills,Uganda     

Michael Sandiford  Fiona B. Neall  Roger Powell 《Contributions to Mineralogy and Petrology》1987,95(2):217-225

Sapphirine-cordierite-quartz and spinel-cordierite-quartz form relic assemblages of probable Archaean age in Fe-rich aluminous metapelites from Labwor Hills, Uganda, and reflect an unusually high temperature metamorphism (1,000° C) at pressures in the vicinity of 7–9 kbars and a(O₂) near the magnetite-hematite buffer. Subsequent reaction textures include the replacement of spinel and cordierite by sillimanite and hypersthene and formation of sapphirine-hypersthene-K-feldspar-quartz symplectites which are interpreted as pseudomorphs after osumilite. A petrogenetic grid appropriate to these assemblages suggests these reaction textures may be due to cooling at constant or increasing pressure and constant a(O₂), or decreasing a(O₂) at constant temperature and pressure. The former interpretation is supported by the coexistence of ilmenohematite and magnetite during the development of the reaction textures, and by the comparatively low Al₂O₃-contents of secondary hypersthene. This pressure-temperature path implies that: (1) metamorphism occurred at deep levels within normal thickness crust, probably less than 40–45 km thick, due to an extreme thermal perturbation induced either by emplacement of mantle-derived magmas or by thinning of the subcontinental lithosphere in an extensional tectonic regime, (2) the excavation and surface exposure of the granulites is due to a subsequent, postgranulite facies metamorphism, crustal thickening most probably involving their incorporation into an allochthonous upper crustal thrust sheet during the formation of the Mozambique foldbelt.  相似文献   

Application of the Mussel Watch concept in studies of the distribution of hydrocarbons in the coastal zone of the Ebro Delta     

Robert W Risebrough  Brock W De Lappe  Wayman Walker  Bernd R.T Simoneit  Joan Grimalt  Joan Albaiges  Jose Antonio Garcia Regueiro  Antoni Ballester Inolla  Manuel Mariño Fernandez 《Marine pollution bulletin》1983,14(5):181-187

The Mussel Watch concept was applied in a study of man-induced chemical changes in the Ebro Delta on the Catalonian coast to obtain a preliminary assessment of the distribution of synthetic organic compounds, petroleum and biogenic hydrocarbons in the local coastal zone. Mussels, oysters and clams were selected as the indicator organisms. Levels of petroleum accumulated by mussels were generally high, in the order of 100–800 μg^?1 dry weight, equivalent to those in mussels in the most polluted harbours and bays of California. The relative distributions of the steranes and pentacyclic triterpanes in the mussels were significantly different from those found in petroleum from a local field, indicating that local petroleum was not contributing to the present contamination. The composition of biogenic compounds was variable, probably reflecting differences in the composition of local plankton communities, PCB levels were high in relation to current levels in mussels from US sites, reflecting continuing PCB use in Spain. The Delta appears to be a point source of a number of organochlorine compounds, including HCB, the DDT compounds, endrin and γ-chlordane. Levels of the DDT compound o,p′-DDD, a pharmacologically active substance, were unexpectedly high; identification was confirmed by GS/MS. Many unidentified peaks were present on EC chromatograms, indicating a more complex pattern of contamination than might be suggested by printed summaries of data.  相似文献   

Distribution of hydrocarbons in the oyster,Pinctada margaratifera,along the coast of Kuwait     

Victor C Anderlini  Layla Al-Harmi  Brock W De Lappe  Robert W Risebrough  Wayman Walker  Bernd R.T Simoneit  Amos S Newton 《Marine pollution bulletin》1981,12(2):57-62

Concentrations of total hydrocarbons within the boiling point range of the alkanes n-C₁₄ and n-C₃₂ were determined in oysters, Pinctada margaratifera, from coastal waters of Kuwait. Levels of petroleum-derived hydrocarbons were highest in an area adjacent to the major oil loading facilities. Whether the use of dispersants to treat minor spills increases levels of incorporation of petroleum compounds into the food webs could not be concluded from the data of this study. Levels of total petroleum-type hydrocarbons in the oysters at this site were equivalent to those in mussels, Mytilus sp., from harbours, bays and urban coastal areas of California. The Kuwaiti oysters lacked a C₂₈ pentacyclic triterpane that was present in extracts of mussels from southern California that had been recently exposed to a minor spill or to a natural seepage. Levels of DDE and PCB were comparable to those in relatively unpolluted areas of North America.  相似文献   

Controls on englacial sediment deposition during the November 1996 jökulhlaup,Skeiđarárjökull,Iceland     

Matthew J. Roberts  Andrew J. Russell  Fiona S. Tweed   skar Knudsen 《地球表面变化过程与地形》2001,26(9):935-952

This paper presents sedimentary evidence for rapid englacial debris entrainment during jökulhlaups. Previous studies of jökulhlaup sedimentology have focused predominantly on proglacial impact, rather than depositional processes within glaciers. However, observations of supraglacial floodwater outbursts suggest that englacial sediment emplacement is possible during jökulhlaups. The November 1996 jökulhlaup from Skei?arárjökull, Iceland presented one of the first opportunities to examine englacial flood deposits in relation to former supraglacial outlets. Using observations from Skei?arárjökull, this paper identifies and explains controls on the deposition of englacial flood sediments and presents a qualitative model for englacial jökulhlaup deposition. Englacial jökulhlaup deposits were contained within complex networks of upglacier‐dipping fractures. Simultaneous englacial deposition of fines and boulder‐sized sediment demonstrates that englacial fracture discharge had a high transport capacity. Fracture geometry was an important control on the architecture of englacial jökulhlaup deposits. The occurrence of pervasively frozen flood deposits within Skei?arárjökull is attributed to freeze‐on by glaciohydraulic supercooling. Floodwater, flowing subglacially or through upglacier‐dipping fractures, would have supercooled as it was raised to the surface faster than its pressure‐melting point could increase as glaciostatic pressure decreased. Evidence for floodwater contact with the glacier bed is supported by the ubiquitous occurrence of sheared diamict rip‐ups and intra‐clasts of basal ice within jökulhlaup fractures, deposited englacially some 200–350 m above the bed of Skei?arárjökull. Evidence for fluidal supercooled sediment accretion is apparent within stratified sands, deposited englacially at exceptionally high angles of rest in the absence of post‐depositional disturbance. Such primary sediment structures cannot be explained unless sediment is progressively accreted to opposing fracture walls. Ice retreat from areas of former supraglacial outbursts revealed distinct ridges characterized by localized upwellings of sediment‐rich floodwater. These deposits are an important addition to current models of englacial sedimentation and demonstrate the potential for post‐jökulhlaup landform development. Copyright © 2001 John Wiley & Sons, Ltd.  相似文献   

Book reviews     

Margaret Brock  David Rich  P.B. Mitchell  Roger Epps 《The Australian geographer》1995,26(1):97-100

WETLANDS: a threatened landscape (Institute of British Geographers Special Publication Series No.25) edited by M. Williams. 17 × 24 cm, x + 419 pp. Blackwell, Oxford 1993 (first published 1990) (ISBN 0 631 19199 2) $65.00 (soft).

GUIDE TO MAPS IN SOUTH AUSTRALIAN PARLIAMENTARY PAPERS 1852–1971 (Historical Geography Monograph No.7) edited by J. McQuilton. 21 × 29 cm, 178 pp. Australian Reference Publications, Melbourne 1994 (ISBN 0 9587876 4 6).

THE EMERGENCE OF BIOREGIONALISM IN THE MURRAY‐DARLING BASIN by J.M. Powell. 21 × 30 cm, 105 pp. Murray‐Darling Basin Commission, Canberra 1993. (ISBN 1 875209 212) $20.00 (soft).  相似文献   

Remote sensing of particle backscattering in Chesapeake Bay: A 6-year SeaWiFS retrospective view   总被引：1，自引：0，他引：1  

David G. Zawada  Chuanmin Hu  Tonya Clayton  Zhiqiang Chen  John C. Brock  Frank E. Muller-Karger 《Estuarine, Coastal and Shelf Science》2007,73(3-4):792-806

Traditional field techniques to monitor water quality in large estuaries, such as boat-based surveys and autonomous moored sensors, generally provide limited spatial coverage. Satellite imagery potentially can be used to address both of these limitations. Here, we show that satellite-based observations are useful for inferring total-suspended-solids (TSS) concentrations in estuarine areas. A spectra-matching optimization algorithm was used to estimate the particle backscattering coefficient at 400 nm, b_bp(400), in Chesapeake Bay from Sea-viewing Wide-Field-of-view Sensor (SeaWiFS) satellite imagery. These estimated values of b_bp(400) were compared to in situ measurements of TSS for the study period of September 1997–December 2003. Contemporaneous SeaWiFS b_bp(400) values and TSS concentrations were positively correlated (N = 340, r² = 0.4, P < 0.0005), and the satellite-derived b_bp(400) values served as a reasonable first-order approximation for synoptically mapping TSS. Overall, large-scale patterns of SeaWiFS b_bp(400) appeared to be consistent with expectations based on field observations and historical reports of TSS. Monthly averages indicated that SeaWiFS b_bp(400) was typically largest in winter (>0.049 m⁻¹, November–February) and smallest in summer (<0.031 m⁻¹, June–August), regardless of the amount of riverine discharge to the bay. The study period also included Hurricanes Floyd and Isabel, which caused large-scale turbidity events and changes in the water quality of the bay. These results demonstrate that this technique can provide frequent synoptic assessments of suspended solids concentrations in Chesapeake Bay and other coastal regions.  相似文献   

A synthesis of the early life history of the anglerfish, Lophius piscatorius (Linnaeus, 1758) in northern British waters   总被引：1，自引：0，他引：1  

Hislop  John R.G.; Gallego  Alejandro; Heath  Michael R.; Kennedy  Fiona M.; Reeves  Stuart A.; Wright  Peter J. 《ICES Journal of Marine Science》2001,58(1):70-86

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Hydrogen diffusivity and electrical anisotropy of a peridotite mantle     

Fiona Simpson  Andréa Tommasi 《Geophysical Journal International》2005,160(3):1092-1102

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The significance of the physical environment of the Macquarie Marshes     

Philippa M. Brock 《The Australian geographer》1998,29(1):71-90

This paper explores the significance of the Macquarie Marshes, in particular providing an overview of their physical attributes. Previous literature has generally been restricted to specific fields and much is unpublished ‘grey’ literature. This paper emphasises the importance of this internationally recognised wetland, both as a complete ecosystem, and for specific landscape, water‐quality filtering, vegetation and fauna attributes. It provides an extended summary of the area and of its 1997 status. By summarising previous research, it provides a base from which future research can be scoped.  相似文献   

An analysis of short-term albedo variations at Haut Glacier d'Arolla, Switzerland     

Ben W. Brock 《Geografiska Annaler: Series A, Physical Geography》2004,86(1):53-65

Abstract An analysis of ten‐minute albedo variations, recorded on Haut Glacier d'Arolla, Switzerland, over an 11 day period in the 1999 ablation season is presented. Most of the short‐term (<1 day) albedo variability is caused by variations in cloud cover, while solar zenith angle variations in the range 25° to 75° are of minor importance, probably due to the predominantly cloudy conditions during the measurement period. A new method to calculate albedo variation as a function of cloud cover is developed. Short‐term albedo variations are expressed by the ratio of the measured albedo to the daily albedo ‘minimum’, defined as the albedo under cloud‐free conditions when the solar zenith angle is <50°. Variations in cloud cover are quantified by the ratio of the measured incoming shortwave radiation flux to the theoretical direct‐beam shortwave radiation flux. The resulting relationships are successful, explaining 83% and 87–90% of short‐term albedo variation on snow and ice respectively, and may be incorporated into albedo parameterizations already used in numerical energy balance melt models, without the need for additional data. Simulations with a glacier energy balance model suggest that melt rates are overestimated by between 1 and 3 mm water equivalent per day if a correction is not made for the increase in albedo under cloudy conditions. Other causes of albedo variation are identified and evidence is found for the removal of fine debris from the glacier surface by intense rainfall, leading to an albedo increase. The implications for energy balance models and satellite‐derived albedo measurements are discussed.  相似文献