Measurement of water particle velocities in waves     

Brendan P. Mcnamee  Bruce B. Sharp  Leonard K. Stevens 《Applied Ocean Research》1983,5(1):49-53

Water surface profiles and horizontal and vertical water particle velocity components have been measured to investigate the properties of intermediate depth waves generated in the laboratory. The data has been compared with linear wave theory. It was found that linear theory predicted the attenuation of velocity field with depth successfully and that it overestimates both components of velocity slightly.  相似文献   

A Cordilleran model for the evolution of Avalonia   总被引：2，自引：0，他引：2  

R. Damian Nance  J. Brendan Murphy  J. Duncan Keppie 《Tectonophysics》2002,352(1-2)

Striking similarities between the late Mesoproterozoic–Early Paleozoic record of Avalonia and the Late Paleozoic–Cenozoic history of western North America suggest that the North American Cordillera provides a modern analogue for the evolution of Avalonia and other peri-Gondwanan terranes during the late Precambrian. Thus: (1) The evolution of primitive Avalonian arcs (proto-Avalonia) at 1.2–1.0 Ga coincides with the amalgamation of Rodinia, just as the evolution of primitive Cordilleran arcs in Panthalassa coincided with the Late Paleozoic amalgamation of Pangea. (2) The development of mature oceanic arcs at 750–650 Ma (early Avalonian magmatism), their accretion to Gondwana at ca. 650 Ma, and continental margin arc development at 635–570 Ma (main Avalonian magmatism) followed the breakup of Rodinia at ca. 755 Ma in the same way that the accretion of mature Cordilleran arcs to western North America and the development of the main phase of Cordilleran arc magmatism followed the Early Mesozoic breakup of Pangea. (3) In the absence of evidence for continental collision, the diachronous termination of subduction and its transition to an intracontinental wrench regime at 590–540 Ma is interpreted to record ridge–trench collision in the same way that North America's collision with the East Pacific Rise in the Oligocene led to the diachronous initiation of a transform margin. (4) The separation of Avalonia from Gondwana in the Early Ordovician resembles that brought about in Baja California by the Pliocene propagation of the East Pacific Rise into the continental margin. (5) The Late Ordovician–Early Silurian sinistral accretion of Avalonia to eastern Laurentia emulates the Cenozoic dispersal of Cordilleran terranes and may mimic the paths of future terranes transferred to the Pacific plate.This close similarity in tectonothermal histories suggests that a geodynamic coupling like that linking the evolution of the Cordillera with the assembly and breakup of Pangea, may have existed between Avalonia and the late Precambrian supercontinent Rodinia. Hence, the North American Cordillera is considered to provide an actualistic model for the evolution of Avalonia and other peri-Gondwanan terranes, the histories of which afford a proxy record of supercontinent assembly and breakup in the late Precambrian.  相似文献   

Robin Marian Law     

Brendan Gleeson 《New Zealand geographer》2003,59(1):5-6

  相似文献   

The geological sources of Hg contamination in Kejimkujik National Park,Nova Scotia,Canada: a GIS approach   总被引：1，自引：0，他引：1  

Krista D. Page  Brendan J. Murphy 《Environmental Geology》2003,43(8):882-891

Recent studies have shown that mercury (Hg) levels in many fish from remote lakes exceed the recommended guidelines for human consumption. Most of these studies conclude that the source of contamination lies in the atmosphere. Kejimkujik National Park (KNP), Nova Scotia, Canada, is considered to be a pristine ecosystem in which fish and loon Hg levels are anomalously high. Studies in the park have shown that atmospheric Hg concentrations may not be high enough to account for the Hg levels in the biota, indicating that the park may be an unusual system in terms of Hg distribution and migration. In an attempt to summarise and synthesise the numerous Hg data sets which have been produced in the park over the last 5-10 years, a geographic information systems (GIS) approach was used to create a common database using the watersheds in the park as the common parameter. By using a GIS database, new relationships and correlations are established and the spatial distribution of Hg levels is more readily evaluated and quantified. The results indicate that geological sources of Hg, arising from biotite-rich granite rocks, may play a larger role in the contamination of the park than previously thought.  相似文献   

The geology of kimberlite pipes of the Ekati property, Northwest Territories, Canada     

Tom Nowicki  Barbara Crawford  Darren Dyck  Jon Carlson  Ross McElroy  Peter Oshust  Herb Helmstaedt 《Lithos》2004,76(1-4):1-27

This paper reviews key characteristics of kimberlites on the Ekati property, NWT, Canada. To date 150 kimberlites have been discovered on the property, five of which are mined for diamonds. The kimberlites intrude Archean basement of the central Slave craton. Numerous Proterozoic diabase dykes intrude the area. The Precambrian rocks are overlain by Quaternary glacial sediments. No Phanerozoic rocks are present. However, mudstone xenoliths and disaggregated sediment within the kimberlites indicate that late-Cretaceous and Tertiary cover (likely <200 m) was present at the time of emplacement. The Ekati kimberlites range in age from 45 to 75 Ma. They are mostly small pipe-like bodies (surface area mostly <3 ha but up to 20 ha) that typically extend to projected depths of 400–600 m below current surface. Pipe morphologies are strongly controlled by joints and faults. The kimberlites consist primarily of variably bedded volcaniclastic kimberlite (VK). This is dominated by juvenile constituents (olivine and lesser kimberlitic ash) and variable amounts of exotic sediment (primarily mud), with minor amounts of xenolithic wall-rock material (generally <5%). Kimberlite types include: mud-rich resedimented VK (mRVK); olivine-rich VK (oVK); sedimentary kimberlite; primary VK (PVK); tuffisitic kimberlite (TK) and magmatic kimberlite (MK). The presence and arrangement of these rock types varies widely. The majority of bodies are dominated by oVK and mRVK, but PVK is prominent in the lower portions of certain kimberlites. TK is rare. MK occurs primarily as precursor dykes but, in a few cases, forms pipe-filling intrusions. The internal geology of the kimberlites ranges from simple single-phase pipes (RVK or MK), to complex bodies with multiple, distinct units of VK. The latter include pipes infilled with steep, irregular VK blocks/wedges and at least one case in which the pipe is occupied by well-defined sub-horizontal VK phases, including a unique, 100-m-thick graded sequence. The whole-rock compositions of VK samples suggest significant loss of kimberlitic fines during eruption followed by variable dilution by surface sediment and concurrent incorporation of kimberlitic ash. Diamond distribution within the kimberlites reflects the amount and nature of mantle material sampled by individual kimberlite phases, but is modified considerably by eruption and depositional processes. The characteristics of the Ekati kimberlites are consistent with a two-stage emplacement process: (1) explosive eruption/s causing vent clearing followed by formation of a significant tephra rim/cone of highly fragmented, olivine-enriched juvenile material with varying amounts of kimberlitic ash and surface sediments (predominantly mud); and (2) infilling of the vent by direct deposition from the eruption column and/or resedimentation of crater rim materials. The presence of less fragmented, juvenile-rich PVK in the lower portions of certain pipes and the intrusion of large volumes of MK to shallow levels in some bodies suggest emplacement of relatively volatile-depleted, less explosive kimberlite in the later stages of pipe formation and/or filling. Explosive devolatilisation of CO₂-rich kimberlite magma is interpreted to have been the dominant eruption mechanism, but phreatomagmatism is thought to have played a role and, in certain cases, may have been dominant.  相似文献   

Effective resource estimates for primary diamond deposits from the EKATI Diamond Mine™, Canada     

D.R. Dyck  P.A. Oshust  J.A. Carlson  T.E. Nowicki  M.P. Mullins 《Lithos》2004,76(1-4):317-335

Primary economic diamond deposit modelling has rarely been documented in the public domain. This paper presents information collected from significantly diamondiferous kimberlite pipes located near Lac de Gras in the Arctic region of Canada's Northwest Territories. The resource estimation process is widely accepted as a cyclical iteration of data collection and evaluation processes. A resource database is typically assembled from a large inventory of exploration data. These data must be methodically quality checked before accepting the information for interpretive analysis. The foundation of a mineral resource model is based on clear understanding of the geology model along with subsidiary grade, volume, and density models. Defining these models is an iterative process of statistical analyses and interpretation. As a deposit progresses along a path towards development, reducing risk to acceptable levels is critical for identifying and realizing its maximum value.  相似文献   

Structural variations in derivatives of the bacteriochlorophylls of Chlorobiaceae: impact of stratigraphic resolution on depth profiles as revealed by methanolysis     

Michael A. Wilson  Dominic A. Hodgson  Brendan J. Keely   《Organic Geochemistry》2004,35(11-12):1299

Bacteriochlorophylls c and d, recovered from two sedimentary sequences, were converted to bacteriophaeophorbide methyl esters by methanolysis and analysed by atmospheric pressure chemical ionisation liquid chromatography-multistage mass spectrometry (APCI LC-MSⁿ). The distributions in both settings, a moderately consolidated sediment from Kirisjes Pond, Antarctica, and in a finely laminated microbial mat from Les Salines de la Trinitat, Spain, show significant variations within a narrow depth interval. The overall bacteriophaeophorbide c to d ratios in the two sediments are different, as are the ratios of particular C-3¹ diastereoisomers, indicating distinct differences between the bacterial communities that contributed to each sediment. Furthermore, a shift towards more extensive alkylation in homologues within each sediment is consistent either with changing environmental conditions in the depositional environments, or development-related changes in the structure of the bacterial community, leading to increased competition for light or nutrients.  相似文献   

Balancing trade‐off issues in land use change and the impact on streamflow and salinity management          下载免费PDF全文

Xiang Cheng  Kurt K. Benke  Craig Beverly  Brendan Christy  Anna Weeks  Kirsten Barlow  Mark Reid 《水文研究》2014,28(4):1641-1662

The south‐west region of the Goulburn–Broken catchment in the south‐eastern Murray–Darling Basin in Australia faces a range of natural resource challenges. A balanced strategy is required to achieve the contrasting objectives of remediation of land salinization and reducing salt export, while maintaining water supply security to satisfy human consumption and support ecosystems. This study linked the Catchment Analysis Tool (CAT), comprising a suite of farming system models, to the catchment‐scale CATNode hydrological model to investigate the effects of land use change and climate variation on catchment streamflow and salt export. The modelling explored and contrasted the impacts of a series of different revegetation and climate scenarios. The results indicated that targeted revegetation to only satisfy biodiversity outcomes within a catchment is unlikely to have much greater impact on streamflow and salt load in comparison with simple random plantings. Additionally, the results also indicated that revegetation to achieve salt export reduction can effectively reduce salt export while having a disproportionately smaller affect on streamflows. Furthermore, streamflow declines can be minimized by targeting revegetation activities without significantly altering salt export. The study also found that climate change scenarios will have an equal if not more significant impact on these issues over the next 70 years. Uncertainty in CATNode streamflow predictions was investigated because of the effect of parameter uncertainty. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

Perspectives on lithospheric evolution through tectonomagmatic processes: a volume in honour of Jaroslav Dostal—an introduction     

Shellnutt  J. Gregory  Murphy  J. Brendan  Greenough  John D.  Keppie  J. Duncan 《International Journal of Earth Sciences》2018,107(3):781-785

International Journal of Earth Sciences -  相似文献   

Effects of intraborehole flow on groundwater age distribution     

Brendan A. Zinn  Leonard F. Konikow 《Hydrogeology Journal》2007,15(4):633-643

Environmental tracers are used to estimate groundwater ages and travel times, but the strongly heterogeneous nature of many subsurface environments can cause mixing between waters of highly disparate ages, adding additional complexity to the age-estimation process. Mixing may be exacerbated by the presence of wells because long open intervals or long screens with openings at multiple depths can transport water and solutes rapidly over a large vertical distance. The effect of intraborehole flow on groundwater age was examined numerically using direct age transport simulation coupled with the Multi-Node Well Package of MODFLOW. Ages in a homogeneous, anisotropic aquifer reached a predevelopment steady state possessing strong depth dependence. A nonpumping multi-node well was then introduced in one of three locations within the system. In all three cases, vertical transport along the well resulted in substantial changes in age distributions within the system. After a pumping well was added near the nonpumping multi-node well, ages were further perturbed by a flow reversal in the nonpumping multi-node well. Results indicated that intraborehole flow can substantially alter groundwater ages, but the effects are highly dependent on local or regional flow conditions and may change with time.  相似文献