Lithological heterogeneity in a back-barrier sand island: Implications for modelling hydrogeological frameworks     

Jonathan Hodgkinson  Malcolm E. Cox  Stephen McLoughlin  Gary J. Huftile 《Sedimentary Geology》2008,203(1-2):64-86

Sediment mineralogy, quartz-grain surface-textures, grain-size analysis, bore-hole logging and ground penetrating radar are combined to develop a three dimensional stratigraphic model of a back-barrier sand island in southeast Queensland, Australia. The island consists of an unconsolidated sedimentary pile above an erosional bounding surface at the top of the underlying bedrock. The stratigraphy is complex, recording the shift in depositional environments from fluvio-deltaic to strandplain, via estuarine stages of evolution. The back-barrier island deposits are correlated with the stratigraphy of the adjacent coastal plain to the west and the barrier island to the east. Extrapolation of optically stimulated luminescence dates obtained from the barrier island combined with direct dating of the back-barrier island sediments is used to constrain the depositional age and chronology of the back-barrier island stratigraphy. The modern depositional environment evolved from a chenier plain into a barrier island system by the flooding of an interdune swale and development of a shore-parallel back-barrier tidal lagoon. The lithological heterogeneity of the back-barrier island succession was controlled by the presence of a bedrock incised palaeovalley and changes in relative sea-level.Sedimentary facies associations constrain the spatial distribution of hydraulic properties controlled by lithological heterogeneity. Post-depositional alteration horizons are integrated with the facies model to account for the effects of weathering and diagenesis on hydraulic behaviour. The derived hydrostratigraphy describes a vertically stacked, dual aquifer, island groundwater system consisting of a semi-confined palaeovalley aquifer overlain by an unconfined strand-plain aquifer.Hydrostratigraphic analysis based on sedimentary facies associations, integrated with post-depositional alteration characteristics reveals great complexity of groundwater systems within small island settings. The facies modelling approach employed in this study more accurately estimates the distribution of lithological heterogeneity and the associated variations in hydraulic properties in the sedimentary pile.  相似文献   

Cretaceous foraminifera from the Turonian succession at Beer, southeastern Devon, England     

Malcolm B. Hart   《Cretaceous Research》2008,29(5-6):1035

During Winter 2000/2001 a major cliff fall occurred at the back of the bay in Beer, southeastern Devon. In the subsequent remedial works the cliff was cleared of loose material prior to stabilisation works. This process provided a suite of samples from previously inaccessible parts of the cliff succession. By adding these samples to earlier suites of samples collected over the last 30 years it has been possible to improve our knowledge of the foraminifera of Turonian age in southwestern England.The planktic foraminifera are, perhaps, the most significant component of the assemblages as many of the taxa recorded in Devon are of southern aspect and are relatively rare in others parts of the U.K. The planktic zonation recognised in this section is, therefore, almost identical with that recorded in Tethyan areas and a precise correlation can be generated. There are relatively large numbers of important taxa such as Helvetoglobotruncana helvetica, Dicarinella imbricata, Marginotruncana sigali, M. pseudolinneiana, M. coronata and M. schneegansi. The benthic foraminifera, by comparison, are relatively rare and are represented by a low diversity assemblage. This is typical of northwestern European chalk successions of Turonian age and is coincident with the highest sea levels of the Cretaceous. In the middle to late Turonian there is a dramatic shallowing event that is recorded world-wide at this level. The assemblage changes towards the top of the accessible succession at Beer record this significant, world-wide event.  相似文献   

A magnetotelluric study of the Alpine Fault, New Zealand   总被引：1，自引：0，他引：1  

Malcolm Ingham  & Colin Brown 《Geophysical Journal International》1998,135(2):542-552

Magnetotelluric soundings have been made at seven locations on a 4  km profile crossing the Alpine Fault in the South Island of New Zealand. The 'distortion' techniques of Groom & Bailey (1989 ) and Lilley (1998a , b ) have been used to derive regional apparent resistivity and phase curves that correspond to electromagnetic induction in orientations parallel and perpendicular to the fault. 2-D inversion of the regional responses reveals that a narrow (<1  km wide) conductive zone is associated with the Alpine Fault. This conductor is most probably related to the heating of deep circulating meteoric water in a region in which enhanced temperatures occur at shallow depth due to the tectonic uplift of the Southern Alps.  相似文献   

Statistical and hydrochemical methods to compare basalt- and basement rock-hosted groundwaters: Atherton Tablelands,north-eastern Australia   总被引：1，自引：0，他引：1  

Katrina L. Locsey  Malcolm E. Cox 《Environmental Geology》2003,43(6):698-713

Multivariate analysis of physico-chemical and chemical data has enabled differentiation among groundwaters sourced from different lithological formations in the Atherton Tablelands region of north-eastern Australia. The main water resource is stored in basalt, although basement rocks such as granite and metamorphics also contain variable amounts of water. Groundwater in the basalt is mostly Mg-Ca-Na, HCO₃ type, with electrical conductivities less than 300 µS/cm and pH values from 6.5 to 8.5. Some of the other groundwater is quite similar, making the identification of hydrochemical facies difficult. Groundwater samples were grouped based on the results of a principal component factor analysis of the major dissolved constituents H₄SiO₄, Na⁺, Ca²⁺, Mg²⁺ and HCO₃^-, as well as pH and electrical conductivity. Based on this differentiation it was possible to identify the likely host rocks of groundwaters from unidentified lithological units, define the basalt thickness and provide a better understanding of the groundwater resource. Principal component factor analysis has also been useful in identifying the likely hydrochemical processes controlling the composition of these groundwaters, including the production of weak acids in the soil layers, silicate mineral weathering, ion-exchange reactions, evapotranspiration and the leaching of ions from organic matter. Supplementary material to this paper can be obtained by using the Springer LINK server located at http://dx.doi.org/10.1007/s00254-002-0667-z.  相似文献   

Summer field meeting, 31st July to 11th August, 1937. The dumfries district     

J. Pringle  D. Balsillie  Malcolm MacGregor  J.B. Simpson  R. Wallace  G.V. Wilson 《Proceedings of the Geologists' Association. Geologists' Association》1938,49(3):213-IN3

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Oil spill fishery impact assessment modeling: The fisheries recruitment problem     

Mark Reed  Malcolm L. Spaulding  Ernesto Lorda  Henry Walker  Saul B. Saila 《Estuarine, Coastal and Shelf Science》1984,19(6):591-610

A model to assess the impact of oil spill on fisheries, consisting of an oil spill fates model, a continental shelf hydrodynamics model, an ichthyoplankton transport and fates model, and a fish population model, has been applied to the Georges Bank-Gulf of Maine region to estimate the impact of oil spills on several important commercial fisheries. The model addresses direct impacts of oil on a fishery through hydrocarbon-induced egg and larval mortality. This early life stage mortality is estimated by dynamically mapping the spatial intersection of the surface and subsurface oil concentrations resulting from the spill with the developing eggs and larvae. Ichthyoplankton entering an area with hydrocarbon concentrations in excess of a specified threshold are assumed lost. Model output is given in terms of differential catch, comparing the non-impacted and the hydrocarbon impacted fisheries. Difficulties in establishing stock-recruit relationships, and the inability to predict first year survival even one year ahead make the quantification of absolute catch losses impossible. Output of the model system discussed here is therefore limited to relative rather than absolute catch losses.The paper is organized to demonstrate first the importance of the recruitment question to impact estimation, second that a modeling methodology is necessary to evaluate impacts given the magnitude of unexplained observed recruitment variability, and third a stochastic solution to the problem which places impact estimates in the context of a probability distribution. Lastly, the model system is applied to the problem of attaining better early life history mortality estimates, to ultimately improve impact estimation capabilities.  相似文献   

A model to describe gastric evacuation in cod (Gadus morhua L.) fed natural prey     

Santos  Jorge Dos; Jobling  Malcolm 《ICES Journal of Marine Science》1992,49(2):145-154

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Side-scan sonar mosaic of a sand Ridge field: southern Mid-Atlantic Bight     

Malcolm O. Green 《Geo-Marine Letters》1986,6(1):35-40

Side-scan sonar coverage of a 1.5 km by 1.5 km area of the inner shelf depicts the morphology of part of a submarine ridge field. The presence of megaripples indicates that ridge sediments are presently reworked by currents. Megaripples occur in the coarser sands of the north-facing ridge flanks. Distribution of megaripples and the ridge asymmetry support the hypothesis that sand ridges respond as large-scale bedforms to south-setting flows. Megaripple crests were observed to be aligned shore-parallel which indicates a pre-survey episode of shore-normal bedload transport.  相似文献   

Changes in ocean ventilation during the 21st Century in the CCSM3     

Frank O. Bryan  Gokhan Danabasoglu  Peter R. Gent  Keith Lindsay 《Ocean Modelling》2006,15(3-4):141

Changes in the ventilation rate of the global ocean during the 20th and 21st centuries, as indicated by changes in the distribution of ideal age, are examined in a series of integrations of the Community Climate System Model version 3. The global mean age changes little in the 20th Century relative to pre-industrial conditions, but increases in the 21st Century, by an amount that is independent of the range of climate forcings considered. The increase is primarily due to a decrease in the ventilation rate of Antarctic Bottom Water (AABW), and to a lesser degree, North Atlantic Deep Water (NADW). Changes in a regional volumetric census of age indicate that the changes in AABW are predominantly for waters that are already older than 100 years, so will likely have a moderate direct feedback on oceanic uptake of CO₂ and other tracers. On the other hand, the changes in NADW occur most strongly in waters that are a few decades old, so are more likely to have a feedback on the climate system. While the global mean age increases, the age does not increase everywhere in the ocean. Regions newly exposed to strong atmospheric forcing as sea ice retreats experience an increase in convection and decreasing age. Age also decreases over a large volume of the lower thermocline as the rate of upwelling of old deep water decreases with the weakening of the thermohaline circulation.  相似文献   

Test of a food consumption model for the Atlantic cod   总被引：3，自引：0，他引：3  

dos Santos  Jorge; Jobling  Malcolm 《ICES Journal of Marine Science》1995,52(2):209-219

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