Volcanogenic mineralization related to the Snowdon Volcanic Group (Ordovician), Gwynedd, North Wales
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The Ordovician (Caradoc) volcanic rocks of NE Snowdonia constitute two major groups, the Llewelyn Volcanic Group and the Snowdon Volcanic Group, which accumulated predominantly in shallow-water marine conditions. The younger Snowdon Volcanic Group comprised a bimodal, basalt-rhyolite suite and included a major caldera-forming eruption of acidic ash-flow tuffs superseded by both Surtseyan and Strombolian basaltic volcanism. Rhyolite domes were intruded into the volcanic sequence in the vicinity of the caldera. The Snowdon Cu-Pb-Zn vein mineralization comprises five paragenetic mineral assemblages. The veins cut rocks deposited within and over the caldera and it is proposed that the dominant controls of mineralization were volcanogenic. Circulation in hydrothermal cells, involving both juvenile fluids and seawater, deposited the minerals at a late stage in the evolution of the caldera.Ultramafic rock
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This outlines the Ordovician system in Asia and comprises the following chapterrs.I. Introductory note.II. The Ordovician formations from Siberia to the Himalaya.III. The Ordovician formations in Eastern and Southeastern Asia.IV. The Ordovician formations from the Taymir peninsula to the Ural mountains through Northland and Novaya Zemlya.V. The Ordovician Biota of Asia.VI. The major classification of the Ordovician system.Figures 1 and 2 show respectively the distribution of the system in the continent and the variation of its thickness in Eastern Asia.
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ABSTRACT Ordovician chitinozoans recovered from a grayish black shale are described for the first time for subsurface North-Central Florida. The bottom-most sample of the Sun Oil Company, Earl Odom No. 1 well, Suwannee County, Fla. was bracketed as Late Arenigian to Early Caradocian. The Ordovician is immediately overlain by Silurian sediments. A new chitinozoan species is described.
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Abstract The Ordovician was a key period in the biological and geological history of the Earth. ‘A Global Synthesis of the Ordovician System’ is presented in two volumes of The Geological Society, Special Publications series. The first volume (SP532) covers general aspects of the Ordovician and also includes the syntheses of the Ordovician successions of Europe. To provide a comprehensive global overview, this second volume (SP533) represents a journey through the Ordovician System around the world. Reviews of the Ordovician of North America include syntheses of Alaska, Greenland, Canada, the USA and Mexico, whereas the South American Ordovician is summarized in a specific chapter related to Argentina and neighbouring countries. The Ordovician System of Africa is presented in chapters covering the north and the south of the continent where significant Ordovician successions occur. Australia and New Zealand, as well as Antarctica, are visited in separate chapters. Asia provides the most complex Ordovician successions that are reviewed in chapters covering Turkey and the Levant region, the Middle East, Central Asia, Kazakhstan, India, SE Asia, China, Korea, and Japan. Our journey covers a great number of locations but, with many successions still to be fully described, our knowledge of the Ordovician of the world remains incomplete.
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Eight species of silicified strophomenid brachiopods from Ordovician rocks of Kentucky are described in this report. Seven species are strophomenaceans, including six from the Middle Ordovician and one, Leptaena kentuckiana n. sp., from the Upper Ordovician. Pionomena recens Neuman from the Middle Ordovician is referred to the Davidsoniacea. Three of these species also occur in the Middle Ordovician of the northern Mississippi Valley region. Rafinesquina is abundant at many localities throughout the Middle Ordovician section of Kentucky. Other silicified strophomenaceans are rare and have been recovered only from the lower part of the Middle Ordovician section of the area. Oepikinia minnesotensis has a high degree of polymorphism of outline shape, profile, and ornament. Some Middle Ordovician species heretofore placed in Strophomena are reassigned to Tetraphalerella. Furcitella and Holtedahlina are differentiated only by the presence of a prominent fold in adult valves of Holtedaklina because a bifid dorsal medial ridge occurs in species of both genera and because the transmuscle ridges of both genera are similar. The possession by Pionomena recens of a perideltidium, dentifers, dorsal medial node, and impunctate shell indicates relationship of this genus to the Davidsoniacea.
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The Ordovician is one of the longest and geologically most active periods in Phanerozoic history. The unique Ordovician biodiversifications established modern marine ecosystems, whereas the first plants originated on land. The two volumes cover all key topics on Ordovician research and provide a review of Ordovician successions across the globe.
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The Ordovician is one of the longest and geologically most active periods in Phanerozoic history. The unique Ordovician biodiversifications established modern marine ecosystems, whereas the first plants originated on land. The two volumes cover all key topics on Ordovician research and provide a review of Ordovician successions across the globe.
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