An ion-association model for estimating acidity constants (at 25°C and 1 ATM total pressure) in electrolyte mixtures related to seawater (ionic strength < 1 mol kg⁻¹ H₂O)     

A.G. Dickson  M. Whitfield 《Marine Chemistry》1981,10(4):315-333

The ion-association model of Garrels and Thompson (1962) has been extended in order to incorporate the major acid—base systems present in seawater. The data for the activity coefficients of the various species considered have been presented as a function of ionic strength, thus making it possible to apply the model to solutions with ionic strengths in the range 0–1 mol kg^?1 H₂O. The model therefore allows the prediction of a variety of equilibrium thermodynamic data for natural waters.The model was used to estimate the stoichiometric acidity constants of the major weak acids present in seawater; the conditions simulated correspond to actual measurements made in seawater media at a variety of ionic strengths (salinities). The estimates obtained are generally in good agreement with the experimental results (all within 10% and usually within 5%), thus confirming the usefulness of this model.  相似文献   

Sea‐cliff retreat and shore platform widening: steady‐state equilibrium?     

Mark E. Dickson  Hiroki Ogawa  Paul S. Kench  Andrew Hutchinson 《地球表面变化过程与地形》2013,38(9):1046-1048

We challenge the notion of steady‐state equilibrium in the context of progressive cliff retreat on micro‐tidal coasts. Ocean waves break at or close to the abrupt seaward edge of near‐horizontal shore platforms and then rapidly lose height due to turbulence and friction. Conceptual models assume that wave height decays exponentially with distance from the platform edge, and that the platform edge does not erode under stable sea‐level. These assumptions combine to a steady‐state view of Holocene cliff retreat. We argue that this model is not generally applicable. Recent data show that: (1) exponential decay in wave height is not the most appropriate conceptual model of wave decay; (2) by solely considering wave energy at gravity wave frequencies the steady‐state model neglects a possible formative role for infragravity waves. Here we draw attention to possible mechanisms through which infragravity waves may drive cliff retreat over much greater distances (and longer timescales) than imaginable under the established conceptual model. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

Origin and significance of the Toolebuc gamma‐ray anomaly in parts of the Eromanga Basin     

A. R. Ramsden  B. L. Dickson  R. L. Meakins 《Australian Journal of Earth Sciences》2013,60(3-4):285-296

The Toolebuc Formation, which is a potentially important source of oil shale in the Eromanga Basin of NW Qld, exhibits a marked gamma‐ray response that has long beeen used as a stratigraphic marker. At Julia Creek, a large area of the Formation contains low‐grade oil shale that is accessible to mining. Detailed investigation, by gamma‐ray spectrometry and neutron activation analysis, of drill core samples from this deposit and from the type section of the Toolebuc Formation at Boulia (BMR Boulia 3A stratigraphic drill hole) show that the Toolebuc gamma‐ray anomaly in the northern Eromanga Basin is due to the presence of uranium. Analyses for organic carbon and phosphorus show that the uranium is associated primarily with organic matter in the oil shales and with phosphatic skeletal fish debris in the accompanying coquinites.

Drill core samples from Tibooburra, N.S.W. were also analysed (BMR Urisino‐1 stratigraphic drill hole) to investigate whether the gamma‐ray anomalies observed in the Bulloo Embayment on the southern margin of the Eromanga Basin (possibly correlative with the Toolebuc Formation) might also be indicative of oil shale. The results show that the much weaker anomaly at this locality is due principally to potassium and reflects the presence of an argillaceous siltstone within glauconitic sandstones.  相似文献   

Structural and Lithological Controls on the Northern Margin of the Tibetan Plateau     

Rowan VERNON  Dickson CUNNINGHAM  ZHANG Jin  Richard ENGLAND 《《地质学报》英文版》2013,87(Z1):64-65

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Comparison of humus and till as prospecting material in areas of thick overburden and multiple ice-flow events: An example from northeastern New Brunswick     

Bruce. E. Broster  Marni L. Dickson  Michael A. Parkhill 《Journal of Geochemical Exploration》2009,103(2-3):115-132

Thirty-nine elements in humus and till matrix were compared at 109 sites overlying Ag–As–Cu–Mo–Pb–Zn mineralized occurrences in northeastern New Brunswick to assess humus for anomaly identification. Humus element concentrations were not consistently correlative with maximum or minimum concentrations found in the underlying till or bedrock. The humus demonstrated significantly higher mean elemental concentrations than the till for six specific elements: 9 times greater for Mn, 6 times greater for Cd, 5 times greater for Ag and Pb, 3 times greater for Hg, and double the concentration of Zn. Spatial dispersal patterns for these elements were much larger for humus content than that exhibited by the till matrix analysis, but did not delineate a point source. For elements in till, the highest concentrations were commonly found directly overlying the underlying mineralized bedrock source or within one km down-glacier of the source.The complexity of the humus geochemical patterns is attributed to the effects of post-glacial biogenic, down-slope hydrodynamic and solifluction modification of dispersed mineralization in the underlying till, and the greater capacity of humus to adsorb cations and form complexes with some elements, relative to the till matrix. Humus sampling in areas of glaciated terrain is considered to be mostly valuable for reconnaissance exploration as elements can be spatially dispersed over a much larger area than that found in the till or underlying bedrock.  相似文献   

塔里木盆地下古生界碳酸盐岩热液岩溶的特征及地质模型   总被引：14，自引：1，他引：13  

潘文庆  刘永福  Dickson J A D  沈安江  韩杰  叶瑛  高宏亮  关平  张丽娟  郑兴平 《沉积学报》2009,27(5):983-994

随着塔中地区下古生界碳酸盐岩油气勘探地持续深入,分别在野外露头,塔中地区相关探井奥陶系储层中发现有萤石、闪锌矿、天青石、重晶石、硬石膏、焦沥青及热液石英等一系列热液矿物及其组合,越来越多的地质资料表明热液岩溶储层可能是塔里木盆地下古生界碳酸盐岩油气勘探中被忽视的一个重要储层类型。〖JP2〗通过总结近6年大量的针对野外露头热液岩溶现象地实地观察测量,以及通过对塔中82井区—24井区奥陶系储层发育段大量的岩石薄片观察、矿物能谱测定、地层水锶同位素测试,断裂性质的分析,深入研究热液溶蚀流体的活动特点以及对形成优质储层的控制作用,最终建立了热液岩溶储层的地质模型。研究表明,热液矿物主要沿断裂伴生的构造溶蚀缝和溶蚀孔洞发育,断裂是热液运移的主要通道,是形成优质储层的重要控制因素。塔中地区沿海西期走滑断裂附近的奥陶系灰岩将广泛发育热液溶蚀改造形成的储层,为塔中西部上奥陶统沿走滑断裂向内带拓展油气勘探打下了基础。  相似文献   

Coastal systems – By Simon K. Haslett     

Mark Dickson 《New Zealand geographer》2010,66(1):94-94

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Recognition of aeolian soils of the Blayney district, NSW: implications for mineral exploration     

Bruce L. Dickson  Keith M. Scott 《Journal of Geochemical Exploration》1998,63(3):237-251

Aeolian soils in the Blayney district are characterised by having approximately 80% of their mass finer than 63 μm, Ti/Zr ratios of approximately 12, radioelement contents of 0.7% K, 2 ppm eU and 11 ppm eTh and a position high in the landscape. Their Ti/Zr ratio and abundant quartz content distinguishes them from soils derived from Tertiary basalts, which share some of the other characteristics. Many soils in the district have a partial aeolian contribution, which can be recognised by a Ti/Zr ratio that differs from that of the underlying rock. Abundance of an aeolian contribution suggests that airborne radiometric surveys should be very carefully interpreted. Ground studies suggest that high Th content in soils contrasted with low Th in adjacent rocks can be indicative of an aeolian contribution in soils. A substantial amount of fine material in a soil can also significantly dilute geochemical signatures if −63 μm (<80 mesh) samples are used for soil surveys during exploration.  相似文献   

Tanzanian rainfall responses to El Niño and positive Indian Ocean Dipole events during 1951–2015          下载免费PDF全文

Dickson Mbigi  Ziniu Xiao 《大气和海洋科学快报》2021,14(6):41-47

The relative impacts of Indian and Pacific Ocean processes on Tanzanian rainfall was evaluated using composite and correlation analyses. It was found that the seasonal responses of rainfall to positive Indian Ocean Dipole (pIOD) and El Niño events are substantial from September–October–November (SON) to December–January–February (DJF), whereas the Indian Ocean Dipole (IOD) exerts more control than El Niño–Southern Oscillation (ENSO) in both seasons. The associated relationship with the sea surface temperature (SST) and large-scale atmospheric circulations revealed distinct features. For the pure pIOD years, there is above-normal rainfall over the entire country. A strong rainfall condition is evident over the Lake Victoria basin and coastal and northeastern highland parts of the country during SON, while areas of the central and southern highlands exhibit substantial rains during DJF. For the pure El-Niño events, Tanzania has suffered from insignificant, weak, and non-coherent rainfall conditions during SON. However, a contrasting insignificant rainfall signature is found between the northern and southern parts of the country during the subsequent DJF season. For the co-occurrence of pIOD and El Niño, significant, excessive rainfall conditions are restricted to over the northern coast and northeastern areas of the country during SON, consistent with the rainfall pattern for pIOD. A weak, positive rainfall condition is observed over the entire country in the following season of DJF. Generally, in terms of Tanzanian rainfall, the IOD/ENSO variability and the associated impacts can be explained by the anomalous SST and circulation anomalies.  相似文献   

Concentration products: Their definition, use and validity as stability constants     

A. G. Dickson  M. Whitfield  D. R. Turner 《Marine Chemistry》1981,10(6):559-565

In this note the authors reiterate the assumptions involved in defining concentration products so that they can be used as valid stability constants. It is noted that, if measurements made in simple ionic media are used to prepare a speciation model of a solution such as seawater, there are separate areas of responsibility involved. It is the duty of the original investigator to report his data in as straightforward and unambiguous a manner as possible. The authors suggest that this can best be achieved by reporting concentration quotients (β) which take no explicit account of interactions with the constituents of the medium, except where this is necessary to preserve the validity of β as a stability constant. The onus then lies with the users of this data to correct it in a manner consistent with the speciation model that they intend to apply. We illustrate this with data measured in sodium perchlorate media which are subsequently used for a speciation model of seawater.  相似文献