Lead isotope abundance studies on mineral occurrences in the British Isles and their geological significance

1962 ◽  
Vol 254 (1042) ◽  
pp. 295-360 ◽  
Keyword(s):  
Great Britain ◽  
Excellent Agreement ◽  
Large Scale ◽  
Lead Isotope ◽  
Sedimentary Rocks ◽  
British Isles ◽  
Geological Time ◽  
North West ◽  
Basement Rocks ◽  
Metamorphic Basement

Lead isotope abundances are reported for ninety-eight galena specimens from Great Britain and Ireland. The analyses were made with a solid-source mass spectrometer. Comparison analyses show excellent agreement with results from other laboratories using solid-source techniques, but differences of 1 to 5% may occur for individual abundances when comparison is made with laboratories utilizing the lead tetramethyl vapour technique. The model chosen for calculation of ages from the isotopic composition is that of Holmes and Houtermans, using the published values of Patterson for the isotopic comparison of primeval lead in iron meteorites and modern lead in ocean sediments. This model permits calculation of the parameters uranium-238/lead-204 and thorium-232/uranium-238 in the source of the ores, which may exhibit small regional differences. The Holmes-Houtermans model ages of three suites of galenas from south-west England, northern England and southern Norway give excellent agreement with published values of the absolute ages of genetically associated igneous rocks. Other models used for interpreting lead isotope abundances do not generally give such satisfactory agreement. The significance of the isotope data from Great Britain and Ireland is discussed regionally in terms of the age of mineralization as well as the possible correlation and origin of different deposits. Of the ninety-eight leads investigated, eighty-six are assumed to be normal and to obey the conditions of the Holmes-Houtermans model. The remaining twelve are B -type leads, as defined by Houtermans, i.e. the model ages are demonstrably older than the true age of mineralization. The main criteria for recognizing normal leads are, first, the close regional grouping of isotope abundances and, secondly, that the model age does not exceed the age of the enclosing sedimentary rocks on the basis of the most recently published geological time-scales of the fossiliferous strata. Detailed consideration of normal leads suggests the existence of six periods of mineralization in the British Isles, ranging in age from Lower Palaeozoic to Upper Mesozoic. The two most important and clearly defined groups are associated with the Caledonian and Hercynian orogenies, respectively. There is, as yet, no isotopic evidence for Tertiary mineralization in the British Isles. A discussion of the causes of normal lead isotope abundances indicates that the latter could be the result of large-scale crustal homogenization processes in continental geosynclinal-orogenic belts. However, there is not enough critical evidence to identify definitely the source of normal lead ores with either crust or mantle. B -type leads probably arise by comparatively localized remobilization and regeneration of lead from metamorphic basement complexes with high lead/uranium ratios, or low radiogenic lead content. The source of such leads frequently appears to be somewhat heterogeneous and ore solutions may not have the opportunity for extensive mixing before the site of deposition is reached. However, B -type leads in some cases give an approximation to the true age of the basement rocks from which they are derived. Processes of this type probably account for the 5-type leads in the north-west and central highlands of Scotland and in County Galway, western Ireland, where the occurrences are situated in metamorphic basement rocks. No cases have been definitely recognized within the British Isles in which lead has a negative, or anomalously young, model age ( J -type leads). The results presented in this paper do not support the view of Russell and co-workers that most vein-type deposits which have traversed sedimentary rocks exhibit J -type anomalies—a consequence of their suggestion that B -type leads, as defined by Houtermans, should be regarded as normal leads.

scholarly journals ITALIAN GEOLOGY AND CLIMATE CHANGE IN THE DEEP PAST

2020 ◽  
Author(s):  
Hugh C. Jenkyns
Keyword(s):  
Climate Change ◽  
Large Scale ◽  
World Wide ◽  
Sedimentary Rocks ◽  
Volcanic Eruptions ◽  
Black Shales ◽  
Geological Time ◽  
Anoxic Events ◽  
River Valleys ◽  
Water Character

Mesozoic sedimentary rocks, of both deep- and shallow-water character, are present throughout Italy and well exposed in mountains and river valleys. Detailed studies of these sections by Italian geologists, beginning in the nineteenth century and continuing to this day, have produced a high-resolution biostratigraphy that allows identification of increments of geological time of less than a million years. Early work relied largely on ammonites to define biostratigraphy but was applicable primarily to sediments of Jurassic age. Study of deep-marine pelagic limestones and shales of Cretaceous age were subsequently, in the twentieth century, investigated using planktonic microfossils, the size of a sand grain, and even smaller nannofossils of micron scale. Pioneering work on magnetostratigraphy and cyclostratigraphy, undertaken primarily on Cretaceous sediments cropping out in Marche-Umbria, added further refinement to the measuring of small intervals of time in rock. With this stratigraphic background, distinct lithological and chemical signals, discovered first in Italian sequences, could be recognized world-wide and proven to be of global significance. In particular, the involvement of carbon isotopes has underscored the utility of chemostratigraphy, not only as a further aid to correlation, but also as a testimonial to major environmental change. Most significant in this context are the Cretaceous oceanic anoxic events, whose sedimentary record was first documented from Italy. These events were characterized by the development of organic-rich black shales deposited in waters largely lacking in oxygen during times of extraordinarily high temperatures known as hyperthermals. Hyperthermals, likely driven by supply of carbon dioxide from large-scale volcanic eruptions, illustrate the environmental impact on a planet affected by extreme global warming.

Sulphide remobilization in Archean volcano-sedimentary rocks and its significance in Proterozoic silver vein genesis, Cobalt, Ontario

1990 ◽  
Vol 27 (9) ◽  
pp. 1170-1181 ◽  
Author(s):  
Mark C. Smyk ◽  
David H. Watkinson
Keyword(s):  
Base Metal ◽  
Large Scale ◽  
Sedimentary Rocks ◽  
Hydrothermal Fluids ◽  
Fracture Zones ◽  
Sulphide Mineralization ◽  
Metal Sulphide ◽  
Basement Rocks ◽  
Sedimentary Succession ◽  
Archean Basement

The Archean volcano-sedimentary succession at Cobalt, Ontario, consists mainly of submarine andesitic flows and turbiditic interflow sedimentary rocks. Steeply dipping faults and large-scale, tight to isoclinar folds have developed in these basement rocks. The faults commonly host silver-vein-bearing structures that extend upward into overlying Proterozoic units. Synvolcanic and synsedimentary base metal sulphide deposits are ubiquitous in the Archean rocks. Epigenetic sulphide mineralization consists of remobilized and replacement sulphides and minor sulpharsenides. Epigenetic sulphides occur in permeable rocks and in fault and fracture zones, commonly in juxtaposition with silver veins.The coincidence of silver veins and structures containing remobilized sulphides suggests that sulphide remobilization from Archean basement rocks into Proterozoic vein-bearing structures predated or accompanied vein development. Sulphide remobilization may have also facilitated the mobilization (leaching) of metals from basement sulphides into the vein-forming hydrothermal fluids.

THE BASAL SEDIMENTARY ROCKS IN SOMERSET ISLAND, N.W.T.

1966 ◽  
Vol 3 (5) ◽  
pp. 697-711 ◽  
Author(s):  
M. F. Tuke ◽  
D. L. Dineley ◽  
B. R. Rust
Keyword(s):  
Marine Environment ◽  
Coastal Lagoons ◽  
Sedimentary Rocks ◽  
Trace Fossils ◽  
Middle Cambrian ◽  
Shallow Marine ◽  
Sedimentary Structures ◽  
Basement Rocks ◽  
Metamorphic Basement ◽  
Somerset Island

In northwest Somerset Island quartz sandstones of the Aston formation and dolostones of the overlying Hunting formation rest unconformably on metamorphic basement rocks. Except for stromatolites and trace fossils the formations are unfossiliferous, and their age has been interpreted as Proterozoic by previous authors.The Aston sandstones pass conformably upward into the Hunting dolostones, which are conformably overlain by Ordovician strata. A similar succession with Middle Cambrian trilobites at the base occurs on Boothia Peninsula. It is therefore suggested that the Aston and Hunting formations comprise a Palaeozoic succession continuous with the fossiliferous Ordovician rocks. This hypothesis does not appear to be incompatible with regional interpretations of Proterozoic–Palaeozoic relationships.The sedimentary structures and petrology of the Aston sandstones suggest that they were derived from the basement rocks and deposited in a shallow marine environment. Sedimentary structures and stromatolites in the Hunting dolostones show that they were laid down in coastal lagoons and tidal flats.

scholarly journals The emergence and spread of finch trichomonosis in the British Isles

2012 ◽  
Vol 367 (1604) ◽  
pp. 2852-2863 ◽  
Author(s):  
Becki Lawson ◽  
Robert A. Robinson ◽  
Katie M. Colvile ◽  
Kirsi M. Peck ◽  
Julian Chantrey ◽  
...  
Keyword(s):  
Great Britain ◽  
Disease Surveillance ◽  
Large Scale ◽  
First Year ◽  
Flock Size ◽  
British Isles ◽  
Trichomonas Gallinae ◽  
Protozoal Parasite ◽  
Seasonal Epidemic ◽  
Rate Of Decline

Finch trichomonosis, caused by the protozoal parasite Trichomonas gallinae , was first recognized as an emerging infectious disease of British passerines in 2005. The first year of seasonal epidemic mortality occurred in 2006 with significant declines of greenfinch Carduelis chloris and chaffinch Fringilla coelebs populations. Here, we demonstrate that large-scale mortality, principally of greenfinch, continued in subsequent years, 2007–2009, with a shifting geographical distribution across the British Isles over time. Consequent to the emergence of finch trichomonosis, the breeding greenfinch population in Great Britain has declined from ca 4.3 million to ca 2.8 million birds and the maximum mean number of greenfinches (a proxy for flock size) visiting gardens has declined by 50 per cent. The annual rate of decline of the breeding greenfinch population within England has exceeded 7 per cent since the initial epidemic. Although initially chaffinch populations were regionally diminished by the disease, this has not continued. Retrospective analyses of disease surveillance data showed a rapid, widespread emergence of finch trichomonosis across Great Britain in 2005 and we hypothesize that the disease emerged by T. gallinae jumping from columbiforms to passeriforms. Further investigation is required to determine the continuing impact of finch trichomonosis and to develop our understanding of how protozoal diseases jump host species.

Large-scale mapping of the catenas vegetation in Subarctic tundra

1995 ◽  
pp. 3-21
Author(s):  
S. S. Kholod
Keyword(s):  
Spatial Distribution ◽  
Vegetation Cover ◽  
Large Scale ◽  
Block Diagram ◽  
Abiotic Factors ◽  
Ecological Factors ◽  
Spatial Arrangement ◽  
Geological Time ◽  
Ecological Barriers ◽  
Functional Zones

One of the most difficult tasks in large-scale vegetation mapping is the clarification of mechanisms of the internal integration of vegetation cover territorial units. Traditional way of searching such mechanisms is the study of ecological factors controlling the space heterogeneity of vegetation cover. In essence, this is autecological analysis of vegetation. We propose another way of searching the mechanisms of territorial integration of vegetation. It is connected with intracoenotic interrelation, in particular, with the changing role of edificator synusium in a community along the altitudinal gradient. This way of searching is illustrated in the model-plot in subarctic tundra of Central Chukotka. Our further suggestion concerns the way of depicting these mechanisms on large-scale vegetation map. As a model object we chose the catena, that is the landscape formation including all geomorphjc positions of a slope, joint by the process of moving the material down the slope. The process of peneplanation of a mountain system for a long geological time favours to the levelling the lower (accumulative) parts of slopes. The colonization of these parts of the slope by the vegetation variants, corresponding to the lowest part of catena is the result of peneplanation. Vegetation of this part of catena makes a certain biogeocoenotic work which is the levelling of the small infralandscape limits and of the boundaries in vegetation cover. This process we name as the continualization on catena. In this process the variants of vegetation in the lower part of catena are being broken into separate synusiums. This is the process of decumbation of layers described by V. B. Sochava. Up to the slope the edificator power of the shrub synusiums sharply decreases. Moss and herb synusium have "to seek" the habitats similar to those under the shrub canopy. The competition between the synusium arises resulting in arrangement of a certain spatial assemblage of vegetation cover elements. In such assemblage the position of each element is determined by both biotic (interrelation with other coenotic elements) and abiotic (presence of appropriate habitats) factors. Taking into account the biogeocoenotic character of the process of continualization on catena we name such spatial assemblage an exolutionary-biogeocoenotic series. The space within each evolutionary-biogeocoenotic series is divided by ecological barriers into some functional zones. In each of the such zones the struggle between synusiums has its individual expression and direction. In the start zone of catena (extensive pediment) the interrelations of synusiums and layers control the mutual spatial arrangement of these elements at the largest extent. Here, as a rule, there predominate edificator synusiums of low and dwarfshrubs. In the first order limit zone (the bend of pediment to the above part of the slope) one-species herb and moss synusiums, oftenly substituting each other in similar habitats, get prevalence. In the zone of active colonization of slope (denudation slope) the coenotic factor has the least role in the spatial distribution of the vegetation cover elements. In particular, phytocoenotic interactions take place only within separate microcoenoses of herbs, mosses and lichens. In the zone of the attenuation of continualization process (the upper most parts of slope, crests) phytocoenotic interactions are almost absent and the spatial distribution of vegetation cover elements depends exclusively on the abiotic factors. The principal scheme of the distribution of vegetation cover elements and the disposition of functional zones on catena are shown on block-diagram (fig. 1).

Interpretation of Pb isotope compositions of galenas from the Midland Valley of Scotland and adjacent regions

1984 ◽  
Vol 75 (2) ◽  
pp. 85-96 ◽  
Author(s):  
John Parnell ◽  
Ian Swainbank
Keyword(s):  
Lower Devonian ◽  
Lead Isotope ◽  
Sedimentary Rocks ◽  
Isotope Ratios ◽  
Igneous Rocks ◽  
Pb Isotope ◽  
Lower Carboniferous ◽  
Granite Magma ◽  
Lower Palaeozoic ◽  
Caledonian Granite

ABSTRACTThe lead isotope compositions of 61 galenas from central and southern Scotland vary markedly between different regions. Most galenas from the southern Grampian Highlands yield isotope ratios (206Pb/204Pb 17·77 ± 0·25, 207Pb/204Pb 15·47 ± 0·05, 208Pb/204Pb 37·63 ± 0·26) less radiogenic than those from Midland Valley galenas (18·22 ± 0·12, 15·55 ± 0·05, 38·13 ± 0·14) whilst galena lead from the Southern Uplands (18·28 ± 0·12, 15·56 ± 0·03, 38·21 ± 0·18) is more radiogenic than that from the southern Midland Valley (18·12 ± 0·06, 15·52 ± 0·02, 38·06 ±0·10). The change in isotopie composition across the Highland Boundary fault reflects the presence or absence of Dalradian rocks which included a magmatic component of lead. Galenas from the Dalradian sequence in Islay, where igneous rocks are lacking, have a composition (18·14±0·04, 15·51±0·01, 37·90±0·02) more like Midland Valley galenas. In the Southern Uplands, galenas yield lead isotope ratios similar to those of feldspars from Caledonian granite (18·30 ± 0·14, 15·57 ± 0·04, 37·96 ± 0·15) analysed by Blaxland et al. (1979). The similar ratios reflect the incorporation of Lower Palaeozoic sedimentary rocks into the granite magma, rather than a granitic source for the mineralisation. The granites were then thermal-structural foci for later mineralising fluids which leached metals from the surrounding rocks. Within the Midland Valley, galenas hosted in Lower Devonian-Lower Carboniferous lavas are notably more radiogenic (18·31 ±0·12, 15·58 ± 0·06, 38·20 ± 0·16) than sediment-hosted galenas (18·14 ± 0·07, 15·52 ± 0·02, 38·08 ± 0·10). The Devonian lavas at least may have inherited lead from subducted (? Lower Palaeozoic) rock incorporated in the primary magma.

SPATIAL LAYOUT OF THE SOVIET UNION TIMBER PROCESSING COMPLEX: THE IDEA BEHIND THE FIRST FIVE-YEAR PLAN

2021 ◽  
Vol 7 (3) ◽  
pp. 131-154
Author(s):  
Ivan V. ZYKIN
Keyword(s):  
Soviet Union ◽  
Large Scale ◽  
Far East ◽  
Spatial Layout ◽  
Capital Investments ◽  
Wood Industry ◽  
North West ◽  
The North ◽  
The Soviet Union ◽  
Central Regions

During the years of Soviet power, principal changes took place in the country’s wood industry, including in spatial layout development. Having the large-scale crisis in the industry in the late 1980s — 2000s and the positive changes in its functioning in recent years and the development of an industry strategy, it becomes relevant to analyze the experience of planning the spatial layout of the wood industry during the period of Stalin’s modernization, particularly during the first five-year plan. The aim of the article is to analyze the reason behind spatial layout of the Soviet wood industry during the implementation of the first five-year plan. The study is based on the modernization concept. In our research we conducted mapping of the wood industry by region as well as of planned construction of the industry facilities. It was revealed that the discussion and development of an industrialization project by the Soviet Union party-state and planning agencies in the second half of the 1920s led to increased attention to the wood industry. The sector, which enterprises were concentrated mainly in the north-west, west and central regions of the country, was set the task of increasing the volume of harvesting, export of wood and production to meet the domestic needs and the export needs of wood resources and materials. Due to weak level of development of the wood industry, the scale of these tasks required restructuring of the branch, its inclusion to the centralized economic system, the direction of large capital investments to the development of new forest areas and the construction of enterprises. It was concluded that according to the first five-year plan, the priority principles for the spatial development of the wood industry were the approach of production to forests and seaports, intrasectoral and intersectoral combining. The framework of the industry was meant to strengthen and expand by including forests to the economic turnover and building new enterprises in the European North and the Urals, where the main capital investments were sent, as well as in the Vyatka region, Transcaucasia, Siberia and the Far East.

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