Fission-track retention age of the Bondoc mesosiderite     

R.K. Bull  S.A. Durrani 《Earth and Planetary Science Letters》1980,49(2):181-187

Whitlockites have been extracted from the Bondoc mesosiderite and found to contain ～(0.7–2.7) × 10⁶ cm^?2 of spontaneous-fission tracks. Thermal-neutron irradiation of these crystals along with terrestrial apatite age standards, and measurement of the track densities so induced, lead to the determination of a whitlockite track-retention age of 2.68 (±0.30) Gyr for Bondoc, which is essentially independent of the initial (Pu/U) ratio.This young age is in qualitative, and, within the experimental uncertainties, in quantitative, agreement with the slow cooling rates determined for many mesosiderites [1,2] and specifically for Bondoc [6] from Ni distributions in the metal phase.  相似文献   

Chemical textures on quartz grains: An experimental approach using salts     

A. W. Magee  P. A. Bull  A. S. Goudie 《地球表面变化过程与地形》1988,13(8):665-676

Two groups of fresh crushed Brazilian quartz grains (0.4–0.6 mm) were placed in 10 ml of various saturated salt solutions (sodium sulphate, sodium chloride, magnesium sulphate, sodium carbonate, and sodium carbonate and soil). One group was placed in an environmental cabinet programmed to simulate summer diurnal temperature and relative humidity values recorded in Wheeler Valley, a dry valley in southern Victoria Land, Antarctica. The other group was allowed to remain at normal laboratory conditions. Quartz grains from both groups were removed at pre-selected intervals for examination using the scanning electron microscope. After 50 hours chemical surface textures were formed on the quartz grains in all but the sodium sulphate solution. At the 140 hour interval all the salt solutions used were producing chemical surface textures on the quartz grains. This paper demonstrates that chemical surface textures can be produced on quartz grain surfaces by saturated salt solutions in a short period of time and may prove to be representative of chemical surface textures produced in a saturated saline environment.  相似文献   

The design of precast concrete pavements on low bearing capacity subgrades     

R. F. Ackroyd  J. W. Bull 《Computers and Geotechnics》1985,1(4):279-291

By using the finite element method and combining it with Westergaard's analysis for concrete pavements, a new design method using 2 metre by 2 metre precast concrete pavement units is presented for heavy duty pavements on low bearing capacity subgrades. One design example is included.  相似文献   

Homeostatic representation for risk decision making: a novel multi-method simulation approach for evacuation under volcanic eruption     

Favereau  Marcel  Robledo  Luis F.  Bull  María T. 《Natural Hazards》2020,103(1):29-56

Natural Hazards - All decision-making processes are complex and include a high number of variables. Particularly, decisions related to disaster risk reduction despite having an inherent...  相似文献   

Tectonic controls on Miocene sedimentation in the Southern Taranaki Basin and implications for New Zealand plate boundary deformation     

Suzanne Bull  Andrew Nicol  Dominic Strogen  Karsten F. Kroeger  Hannu S. Seebeck 《Basin Research》2019,31(2):253-273

Miocene strata in the southern Taranaki Basin (STB), up to 3 km thick, provide a distal record of erosion associated with plate boundary deformation in New Zealand. 2D and 3D seismic reflection data tied to drillhole stratigraphy have been used to constrain four main phases of basin development. These are: (a) Early Miocene (22–19 Ma) subsidence, dominantly bathyal water depths and deposition of minor submarine fans along the eastern basin margin. (b) Middle Miocene (19–14 Ma) widespread submarine fan deposition on a bathyal basin floor in the central STB. (c) Rapid Middle–Late Miocene (14–7 Ma) progradation of the shelf break northwards across the STB. (d) Widespread uplift and erosion of the STB during the latest Miocene–Pliocene (7–4.5 Ma). Bathyal water depths and fan deposition in the Early Miocene were influenced by vertical motions on major reverse faults and regional subsidence produced by subduction of the Pacific plate beneath northern New Zealand. Subsequent submarine fan deposition and northward shelf‐break progradation reflect increasing input of terrigenous material, primarily eroded from an uplifting region to the south of the STB. Sedimentation patterns in the STB are consistent with the age and locations of conglomerates deposited in onshore West Coast basins, related to this uplift and erosion. Sediment transport in the West Coast region was mainly parallel to NNE trending active reverse faults, and in the STB was perpendicular to the NE‐SW orientated shelf break, especially from ca. 14–7 Ma, when sedimentation rates exceeded fault‐displacement rates. Increases in sedimentation rates in the STB coincide with regional increases in the rates of shortening that appear to reflect plate boundary‐wide events and have been attributed to, or correlated with, increases in the plate convergence rate. Miocene sedimentation patterns in the STB thus reflect both intra‐basinal deformation and tectonic signals from the wider developing New Zealand plate boundary.  相似文献   

Distinguishing base-surge deposits and volcaniclastic fluviatile sediments: an ancient example from the Lower Devonian Snowy River Volcanics, south-eastern Australia   总被引：2，自引：0，他引：2  

Stuart W. Bull  & Cas 《Sedimentology》2000,47(1):87-98

A 500‐m‐long road cutting in the Lower Devonian Snowy River Volcanics (SRV), eastern Victoria, Australia, exposes phreatomagmatic units and volcaniclastic sediments. Based on bed geometry, sorting and sedimentary structures, it was possible to distinguish base‐surge deposits from ephemeral fluvial deposits in this relatively well‐exposed ancient succession. Where the base‐surge deposits infill irregular topography, bed sets mantle the pre‐existing surface but thicken into topographic lows. In contrast, where the fluvial deposits infill topographic depressions, beds onlap laterally against channel walls. In addition, curvi‐planar slide surfaces within the base‐surge deposits generated by inter‐eruptive slumping indicate rapid emplacement as a constructional tuff rampart (? maar). The base‐surge deposits are always poorly sorted and commonly contain accretionary lapilli, reflecting their deposition from turbulent, low‐particle‐concentration, steam‐rich pyroclastic currents. In contrast, the fluvial deposits are relatively well‐sorted, reflecting hydraulic sorting and winnowing during tractional transport and deposition. There are significant differences in the types of sedimentary structures present. (1) Bedding in the base‐surge deposits is entirely tabular, and beds can be traced laterally to the limits of the outcrop. In contrast, the fluvial deposits have abundant internal scour surfaces that result in beds/bedding intervals lensing out laterally over intervals of the order of 5–10 m. (2) Cross‐beds with relatively high‐angle foresets are restricted to the fluvial deposits. (3) Laterally persistent tabular beds that contain abundant, densely packed accretionary lapilli are restricted to the base‐surge deposits. In summary, although base‐surge deposits and ephemeral fluvial deposits can appear superficially similar, it is possible to apply facies models carefully to distinguish between them, even in ancient successions.  相似文献   

A review of kinematic indicators from mass-transport complexes using 3D seismic data   总被引：2，自引：0，他引：2  

Suzanne Bull  Joe Cartwright  Mads Huuse 《Marine and Petroleum Geology》2009

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Lipid analysis of a ground sloth coprolite     

Fiona L. Gill  Matthew P. Crump  Remmert Schouten  Ian D. Bull 《Quaternary Research》2009,72(2):284-288

Coprolites can provide detailed information about the nutritional habits and digestive processes of the animals that produced them and may also yield information about the palaeoenvironment in which the animal existed. To test the utility of the lipid biomarker approach to coprolite analysis, lipids were extracted from a coprolite of the Pleistocene ground sloth Nothrotheriops shastensis. Gas chromatography/mass spectrometry results revealed a dominant spiroketal sapogenin component identified, using nuclear magnetic resonance spectroscopy, as epismilagenin. The dominance of epismilagenin is probably due to ingestion of Yucca spp. and Agave spp., which is consistent with previous studies on the diet of this species.  相似文献   

Measurement of the In Situ Compressional Wave Properties of Marine Sediments     

Robb  G.B.N. Best  A.I. Dix  J.K. White  P.R. Leighton  T.G. Bull  J.M. Harris  A. 《Oceanic Engineering, IEEE Journal of》2007,32(2):484-496

Geoacoustic inversion requires a generic knowledge of the frequency dependence of compressional wave properties in marine sediments, the nature of which is still under debate. The use of in situ probes to measure sediment acoustic properties introduces a number of experimental difficulties that must be overcome. To this end, a series of well-constrained in situ acoustic transmission experiments were undertaken on intertidal sediments using a purpose-built in situ device, the Sediment Probing Acoustic Detection Equipment (SPADE). Compressional wave speed and attenuation coefficient were measured from 16 to 100 kHz in medium to fine sands and coarse to medium silts. Spreading losses, which were adjusted for sediment type, were incorporated into the data processing, as were a thorough error analysis and an examination of the repeatability of both the acoustic wave emitted by the source and the coupling between probes and sediment. Over the experimental frequency range and source-to-receiver (S-R) separations of 0.99-8.1 m, resulting speeds are accurate to between 1.1% and 4.5% in sands and less than 1.9% in silts, while attenuation coefficients are accurate to between 1 and 7 dBm in both sands and silts. Preliminary results indicate no speed dispersion and an attenuation coefficient that is proportional to frequency.  相似文献   

The geo-morphology of the Mole Gap     

S.W. Wooldridge  A.J. Bull 《Proceedings of the Geologists' Association. Geologists' Association》1925,36(1):1-IN6

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