A scanning electron microscope study of surface textures of quartz grains from glacial environments     

W. BRIAN WHALLEY  DAVID H. KRINSLEY 《Sedimentology》1974,21(1):87-105

Surface textures of quartz sand grains from several glacial environments at the Feegletscher, Switzerland examined by means of scanning electron microscopy are described. The difference between supraglacial and subglacial material is very slight. At the moment the interpretation of these textures must be done with care until the full statistical relation to environments can be ascertained. This does not necessarily invalidate earlier investigations although it does mean that glacial and extraglacial environments in the vicinity of glaciers are apparently not distinguishable. Examination of surface precipitation features suggests a sequence of events which can be used to help discriminate between different ages of deposits in an area. A similarity between some of the surface debris from moraine samples and those seen in loess and quickclay deposits is also suggested.  相似文献   

THE PRESENT STATUS OF ZIRCON: A REPLY     

BRIAN MARSHALL 《Sedimentology》1968,10(3):214-216

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A local ensemble Kalman filter for atmospheric data assimilation   总被引：6，自引：0，他引：6  

EDWARD OTT  BRIAN R. HUNT  ISTVAN SZUNYOGH  ALEKSEY V. ZIMIN  ERIC J. KOSTELICH  MATTEO CORAZZA  EUGENIA KALNAY  D. J. PATIL  JAMES A. YORKE 《地球，A辑:动力气象学与海洋学》2004,56(5):415-428

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Regional river flow,water quality,aquatic ecological impacts and recovery from drought     

BRIAN S. CARUSO 《水文科学杂志》2013,58(5):677-699

Abstract

During severe drought and low flows in the Otago Region of the South Island of New Zealand, increased bacterial contamination of rivers occurred in agricultural/pastoral catchments due to greater stock use of waterways and the lack of dilution and flushing flows. Concentrations and loadings of nitrogen and phosphorus generally decreased due to the lack of rainfall, runoff and transport from diffuse sources. Other analytes, including dissolved solids and pH, did not change to any considerable degree and were quite spatially variable. Although the health of benthic macroinvertebrate communities can decrease with a lower diversity and fewer sensitive taxa, effects were not significant in most rivers. Algal blooms occurred in some locations, particularly in lowland agricultural catchments with low water velocities and little shade. The prolonged lack of flushing flows can be a significant problem. Fish kills occurred where they became stranded and isolated from the main flow and where there was a lack of deeper pool refuges. Temperatures in excess of 25°C can also result in isolated fish kills, but the duration of these high temperatures appears to be the most critical factor. Adverse effects from drought can be widespread and severe in some locations, but appear to be relatively short-lived with recovery occurring rapidly with increasing flows at most locations. This indicates a degree of resilience of rivers to drought and low flows with long-term impacts that are not severe.  相似文献   

Aspects of the large-scale tropical atmospheric circulation     

BRIAN HOSKINS  RICHARD NEALE  MARK RODWELL  GUI-YING YANG 《地球，A辑:动力气象学与海洋学》1999,51(1):33-44

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Late Pleistocene morainal bank facies at Greystones, eastern Ireland: an example of sedimentation during ice marginal re-equilibration in an isostatically depressed basin     

A. MARSHALL MCCABE  COLM O'COFAIGH† 《Sedimentology》1995,42(4):647-663

A late Pleistocene morainal bank is sited in a depocentre to the lee of a major rock ridge, near Greystones, in the western Irish Sea Basin. During deglaciation the ridge provided a pinning point during tidewater wastage northwards. Sedimentation patterns and palaeocurrent data show morainal bank growth by discharge from a single basal efflux located to the east or south-east of the ridge during ice marginal re-equilibration. The four lithofacies associations which are recognized from the western part of the formerly more extensive apron are related largely to variable jet and plume sedimentation. At the base of the 1.6 km long exposure, Lithofacies association 1 (massive mud, muddy diamict and laminated mud) was deposited from turbid plumes, variable ice rafting and traction current activity. Lenticular units of gravels within this mud bank record high energy pulses and sediment fluxes from the efflux jet. Lithofacies association 2 (sands, laminated muds and muddy diamict) is discontinuous and occurs within basins along a marked erosion surface cut in Lithofacies association 1. It is associated with a decrease in jet strength, traction currents and suspension sedimentation. Lithofacies association 3 is a tabular body of interbedded diamicts and gravels which is present along the entire section. It documents the decay phase of re-equilibration as the ice margin disintegrated catastrophically and released large volumes of heterogeneous sediment which was resedimented by quasicontinuous mass flow. Lithofacies association 4 consists of stratified and massive gravels within distributary channels cut into underlying facies and represents the last phase of meltwater activity. Sediment geometries, particularly sedimentary contrasts representing erosion surfaces at a variety of scales and abrupt textural contrasts are attributed to jet switching. Lithofacies association 1 (60%) and Lithofacies association 3 (30%) are the dominant facies. In favourable topographic settings this stratigraphic couplet is a signature for re-equilibrated ice margins in isostatically depressed basins dominated by tidewater fronts, rapid ice flux and high relative sea level. Morainal banks document rapid environmental change and in the Irish Sea Basin they form part of a deglacial event stratigraphy related to unstable tidewater margins and high relative sea level. Deglaciation was therefore controlled primarily by high relative sea level rather than climatic forcing. Facies variations should therefore not be used for stratigraphic correlations in place of direct stratigraphy. This type of situation may be more common than hitherto realized in Late Pleistocene, mid-latitude shelves where most of the preserved stratigraphy is characterized by complex, interbedded sequences formed when isostatic depression exceeded sea-level fall.  相似文献   

Braidplain deposition of the Upper Triassic Molteno Formation in the main Karoo (Gondwana) Basin, South Africa   总被引：1，自引：0，他引：1  

BRIAN R. TURNER 《Sedimentology》1983,30(1):77-89

ABSTRACT The Upper Triassic (Carnian?) Molteno Formation in the main Karoo (Gondwana) Basin, South Africa forms a northerly thinning, intracratonic clastic wedge comprising sandstones, shales and coals occurring within thick (up to 140 m) laterally persistent fining-upward sequences. These sequences were deposited by braided streams draining an alluvial plain which may have been built on to the distal slopes of alluvial fan complexes of glacial outwash type. Geometric relations between sequences indicate three phases of tectonic activity. The lowermost fining-upward sequence in the south accumulated against a rising mountain front; cessation of movement and an eastward shift in the main locus of tectonism and sedimentation was followed by renewed uplift and basinwide progradation of the second fining-upward sequence adjacent to a fault-block granite terrain located close to the present south-east coastline of South Africa. This is believed to be the granite at the eastern end of the Falkland Island Plateau, an interpretation consistent with its position on most continental reconstructions and the fracture zone marking its northern scarp face. Faulting is attributed to the first phase of extension prior to continental breakup. The sourceward recession and lack of gross fining-upward trends shown by the uppermost fining-upward sequences is accounted for by limited back-faulting of the still active basin margin. Cessation of activity and further basin margin recession occurred with deposition of the overlying floodplain deposits (Elliot Formation) which were distal equivalents of the braided alluvial plain.  相似文献   

The imperial vision of Halford Mackinder     

BRIAN W BLOUET 《The Geographical journal》2004,170(4):322-329

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PLACING KANGWANE IN THE NEW SOUTH AFRICA*     

BRIAN H. KING 《Geographical review》2006,96(1):79-96

ABSTRACT. The South African homelands were central to the apartheid ideology of racial segregation and separate development and as a result became the location for large segments of the African population. Apartheid‐era theorizations of the homelands tended to emphasize their importance to the state, with less attention directed to the divergent and unique social formations that often existed within them. Recent geographical research has been intent on evaluating the spatial imprint of these geographies for resident populations, as well as the varied class, gendered, and institutional formations that accompanied the democratic transition. Using a case study from the former KaNgwane homeland, this article examines the diverse ways in which rural households access environmental and economic resources to produce livelihoods. It is argued that a focus on community variation is needed to interrogate the differential encounters of these places with the local politics and development processes that are emerging in the new South Africa.  相似文献   

Palaeochannel reconstructions from point bar deposits: a three-dimensional perspective     

BRIAN J. WILLIS 《Sedimentology》1989,36(5):757-766

Quantitative determination of palaeochannel geometry and hydraulics from point bar deposits requires an understanding of the interaction between channel-bend migration, temporal and spatial variation of point bar geometry and facies, and outcrop orientation. This interaction is modelled with the aid of a computer program which predicts three-dimensional (3-D) geometry and grain size variation of point bars. Synthetic deposits are produced for the cases of down-valley bend migration and/or increase in channel-bend sinuosity. Two-dimensional (2-D) cross-sections in varying orientations across these simulated deposits display lateral-accretion bedset surface geometry, and variation in mean bedset grain size and local palaeocurrent orientation. Most cross-sections show point bar deposits thickening away from the meander-belt axis due to a lateral progression from thinner bend-exit deposits to thicker bend-apex deposits (caused by down-valley channel translation), and/or due to a progression from thinner low sinuosity deposits to thicker high sinuosity deposits caused by channel bend expansion. In association with this lateral thickening, bedset surfaces become steeper and more convex upwards while the variation in mean grain size up bedsets commonly increases. Down-valley point bar translation allows preservation only of deposits formed downstream of the band apex, and produces characteristic fining upwards sequences. Marked lateral and vertical variations in palaeocurrent directions due to varying channel orientation relative to a given cross-section are also predicted. These results indicate a need in palaeochannel reconstructions, for a more detailed examination of 3-D variations in bedset surface geometry, palaeocurrent orientation and grain size distribution within and between bedsets of laterally accreted sediment.  相似文献