Establishing the role of pedogenesis in changing soil hydraulic properties

Chronosequences provide suitable sources for the study of changes in soil hydraulic behaviour as a result of long-term pedogenesis. For a podsol chronosequence in the Scottish Highlands, data are presented to indicate the changes that have occurred over 13000 years in the saturated hydraulic conductivity (K_sat) in each horizon. As the soil profile has evolved into a differentiated sequence of three horizons, the resulting hydrological changes can be both measured and quantified by relating K_sat to textural properties and bulk density. The results are significant for interpretation of changing runoff processes and slope stability.     

The significance of rainstorm variations to shallow translational hillslope failure

Landsliding in eastern Scotland results from high-magnitude rainstorms generated under either cyclonic or anticyclonic conditions, particularly during the summer. Data from Aviemore indicated that cyclonic storms produce higher rainfall totals than anticyclonic storms, as well as being of longer duration and lower intensity. The distribution of rain during individual storms also varies with the synoptic conditions under which the storms are produced. These different rainfall characteristics produce different geomorphic responses, which can be investigated in detail using physical based modelling. In this paper, a physically based coupled hydrology–stability model is used to assess the significance of these rainfall characteristics to soil moisture response and slope instability for mature podsols. The results provide evidence that rainstorms of different synoptic origin produce varying hydrological response, involving both the extent and the timing of moisture content change. This affects the depth and timing of slope failure, with anticyclonic storms promoting a large, rapid response in the factor of safety at shallow depths within the soil. Cyclonic storms produce a more gradual response, with the region of probable failure being deeper. Futhermore, each of these storm types is associated with different rainfall distributions, and this is also shown to have a significant effect on the timing and depth of slope instability.     

The petrology and origin of coals from the lower Carboniferous Mattson formation, southwestern district of Mackenzie, Canada

Petrographic analyses were carried out on thin coals and coaly sediments from the Lower Carboniferous Mattson Formation at Clausen Creek and Jackfish Gap-Yohin Ridge in the northern part of the Liard Basin, northern Canada. The composition and optical characteristics indicate that the coals are high-volatile bituminous B, predominantly sapropelic (canneloid) and accumulated subaquatically.The coals are dominantly composed of inertinite-rich and exinite-rich durities with subsidiary inertites and clarodurites; vitrite is minor and liptite is rare. The inertinite-rich microlithotypes are dominated by semifusinite, but micrinite, semimacrinite and ?resino-inertinites are abundant. Sporinite, comprising megaspores, crassispores, tenuispores and miospores, is the dominant liptinite maceral with subsidiary cutinite and minor alginite. Except for pyrite, mineral matter is minimal.Three populations of telocollinite are observed: a low-reflectance variety (I), commonly associated with micrinite (as vitrinertite), displays weak brown fluorescence and a reflectance some 0.4-0.5% lower than type II; type II is non-fluorescing telocollinite, with intermediate reflectance (0.67-0.74% R_om), it occurs as vitrite and is also associated with micrinite; and a higher-reflectance telocollinite (III), having no fluorescence or association with micrinite, has variable reflectance (0.74-0.8% R_om) implying higher oxidation or gelification levels.The abundance of semimacrinite, macrinite and ?resino-inertinites in inertites and durites (I) suggests that much of the peat accumulated subaquatically. Furthermore, fluorescing vitrinite and an abundance of micrinite (derived by oxidation or coalification of bituminite), suggest that the coal accumulated under anaerobic conditions. The predominance of semifusinite in humic laminae and micrinite in sapropelic layers suggests extensive surface or near-surface oxidation of the peat. Oxidised sporinites suggest that they were wind-borne.Depositional environment is interpreted as marginal marine, perhaps in shallow lakes in the middle to upper delta plain. Peat accumulations probably began subaquatically at the oxygen-hydrogen sulphide interface, but periodic subaerial exposure and natural oxidation gave rise to the high inertinite coals. Upper Mattson coals are interbedded with algal laminites and probably accumulated in a lagoonal setting.     

Pitchblende and galena ages in the Alligator Rivers region,Northern Territory,Australia

U-Pb and Pb isotopic studies have been made of pitchblendes and associated galenas from four major deposits in the Alligator Rivers region of the Northern Territory, Australia. These are compared with previously-published data on deposits in the South Alligator Valley and in the Westmoreland area on the Queensland border. In all, four different times of possible mineral formation have been detected (1880 ± m. y., 1700 ± m. y., 800–900 m. y., 400–500 m. y.) Some deposits reveal only one time, others two; no deposit shows evidence for all four. The associated galenas are in general highly radiogenic (206/204 ratios range from 2000 to 29, 000); some can be interpreted as reflecting development in two completely different generations of pitchblende. The clearest evidence for solid-state formation of galena from presently-existing pitchblende is to be found at Nabarlek, where the major time of pitchblende formation (920 m. y.) bears no relationship to any known Rb-Sr or K-Ar age.     

Pilbara galenas: Precise isotopic assay of the oldest Australian leads; model ages and growth-curve implications

Precise Pb isotopic data are reported for 19 galenas and 2 other minerals from the Archaean Pilbara District of Western Australia. Repeated measurements on the Broken Hill Standard Ore show good agreement with published calibrations from two other laboratories, and an overall 95 percent confidence level within ±0.05 percent per mass unit, whether fractionation correction is by the double-spike procedure or by use of a simple mass-dependent factor. Two stratiform deposits yield the most primitive ratios (²⁰⁶Pb/²⁰⁴Pb=11.89; ²⁰⁷Pb/²⁰⁴Pb=13.69; ²⁰⁸Pb/²⁰⁴Pb=31.79) and model ages in good agreement with the 3.45 Ga age on zircons from volcanics correlatable with the host-rocks. Other minor galena occurrences, with quartz-vein association, appear to be younger, with position along the growth curve surprisingly consistent with the age sequence predicted from field observation. The data also extend the time-range of previously-reported trends in apparent U/Pb of the conceptual Pb source, and reveal new features of the corresponding Th/U systematics: a generally-observable trend in the Archaean of Australia, Southern Africa and West Greenland is that the source Th/U seems significantly higher than is allowed for in any of the current Pb-growth models. In detail, the sample-sample variations in indicated source parameters are in many cases correlatable with the nature of the neighbouring rocks and emphasise that, whereas Pb isotope rations in the galenas of huge deposits may well serve as a convenient sampler of overall trends in the Earth's crust, subeconomic occurrences such as these may reveal valuable information about local variations in U-Th-Pb distribution.     

A re-assessment of the Upper Mississippi valley lead isotope data

Corrections for systematic bias, and a better regression method, are tested on the lead isotope data of Heyl, Delevaux, Zartman and Brock (1966). The new calculations suggest the time of mineralization in the Upper Mississippi zinc-lead district is more likely to lie in the range Mid Devonian (370 my) to Upper Pennsylvanian (280 my) on any reasonable assumption for the age of the basement. It is argued from the isotopic trends that the ore lead in this district was simply derived by radiogenic addition to lead originally derived from rocks of basement age, although the data do not exclude residence in the Lower Paleozoic sediments as an intermediate step. An isotopically different magmatic component is not required. Correlation with the geology suggests that genesis of the deposits probably was related to regional tectonic deformation in Middle to Late Paleozoic time.

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Zusammenfassung Korrekturen systematischer Fehler und eine bessere Regressionsmethode wurden anhand der Blei-Isotopendaten von Heyl, Delevaux, Zartman und Brock (1966) getestet. Diese neuen Berechnungen unter Annahme eines vernünftigen Alters des Grundgebirges zeigen, daß die Zeit der Mineralisation im Oberen Mississippi Zink-Blei Distrikt eher zwischen Mitteldevon (370 Millionen Jahre) und Oberkarbon (280 Millionen Jahre) zu setzen ist. Auf Grund der Verteilung der Isotopenverhältnisse wird auf eine einfache Formierung (durch Addition radioaktiver Zerfallsprodukte zum ursprünglichen Blei im Gestein mit demselben Alter wie das Grundgebirge) des Bleies im Bleierz geschlossen. Die Meßresultate schließen jedoch eine Ablagerung im Unterpaläozoikum als Übergangsstufe nicht aus. Magma mit andern Isotopenverhältnissen wird nicht angenommen. Vergleiche mit der Geologie deuten darauf hin, daß die Bildung der Ablagerungen im Zusammenhang mit tektonischen Deformationen im Mittleren bis Oberen Paläozoikum erfolgte.

     

Digital Photogrammetric Monitoring of River Bank Erosion

Detailed understanding of the processes which control river bank erosion requires high resolution information concerning temporal changes in bank morphology. This paper describes the successful use of digital photogrammetry to extract high resolution digital elevation models (DEMs) from terrestrial oblique stereopairs of rapidly eroding river banks, using the commercial software package Erdas Imagine. This software was developed for use with aerial photography and satellite imagery; problems relating to the use of oblique terrestrial images are discussed and solutions presented. Photography was acquired using semi-metric cameras, mounted on tripods and positioned about 15m from the eroding bank. Data for DEM point spacings of 20mm were obtained, with accuracies of approximately ±12mm in depth. Digital photogrammetry can permit faster analysis, provide better accuracies and involve less ground disturbance than conventional methods of monitoring river channel change. Most importantly, DEM generation is considered to be more useful than traditionally acquired points or profiles for landform monitoring strategies.     

Shellfish-associated enteric virus illness in the United States, 1934–1984

The regulation of shellfish and their growing waters is based on total and fecal coliform standards. Application of these standards has reduced the incidence of shellfish-borne bacterial illnesses in humans, but outbreaks of viral diseases, such as hepatitis A, Norwalk illness, and viral gastroenteritis, prevail. Hepatitis A virus contributed to 1,395 cases of shellfish-associated illness since 1961. An additional 6,049 cases of shellfish-associated gastroenteritis were reported over the past 50 years, 75% of which (4,609 cases) occurred since 1980. The alarming rate of disease outbreaks during the past 5 years may further increase as better reporting practices are initiated by health professionals and state and federal agencies. Actions necessary to reduce the incidence of shellfish-associated viral illness include development of methods for detecting viral pathogens in shellfish and harvest waters, correlation of levels of viral pathogens with potential viral and bacterial indicators, and acceleration of field monitoring and enforcement efforts.