Nature and classification of microfossils of plant origin from Precambrian and lower Paleozoic
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A general consolidation of data relating to reports of Precambrian and lower Paleozoic spores of land plants and hystrichosphaers is presented. Emphasis is placed on the necessity of establishing clear and objective means of separating and classifying these organic remains. Their value lies in the theoretical interpretation of the origin of land plants as well as in the practical applications in stratigraphic correlations of the oldest sedimentary formations. -- F. M. Hueber.Recent compilation of data by the Kansas Geological Society's Basement Rocks Committee regarding the Precambrian in part of the Mid-Continent provides a framework in which to analyze further this rock complex. In Kansas alone, more than 2,100 wells are known to have penetrated the Precambrian, and approximately 50-60 tests a year are drilled into the basement. Studies are now in progress to attempt to determine detailed spatial relationships of these rocks and their intricate geologic history. By using only preliminary information, it is possible to differentiate general categories of rock types at the Precambrian surface, which in Kansas is buried beneath Paleozoic rocks at depths from 500 to 9,000 feet. Rocdk types recognized include granite, granodiorite, syenite, diabase, rhyolite, and metasediments; the interrelations of these are exceedingly complex. Sediments, chiefly alternating silicate-cemented sandstone and indurated shale, have been described from Missouri and may be abundant elsewhere. Outliers of schist capped by resistant quartzite form buried hills in central Kansas. Diabase and related types of mafic rocks are found; syenite may be in the form of intrusive plugs. Extrusive rocks are represented by the rhyolite and associated suites. Granite of various kinds is by far the most extensively recorded rock type in the Mid-Continent; granodiorite has very limited distribution. In many areas, the deeply weathered and perhaps even reworked pre-Reagan (or Lamotte) basement rock constitutes granite wash assumed here to be Precambrian. Geographic distribution of different rock types is suggestive of pre-Paleozoic structure. A wide band of metasediments through central Missouri, northeastern Kansas, northeastern Nebraska, and southeastern South Dakota forms a large arc convex southwest perhaps outlining the southwestern flank of the old Wisconsin Highlands. Present dip of the metasediments in west-central Missouri is known to be southwestward. Outside the belt of metasediments are igneous rocks and some metasediment outliers. Potassium-argon ages determined by J. L. Kulp on five samples from Barton, Rush, and Morris Counties, Kansas, yielded dates of 1,165 to 1,460 million years, comparable with ages elsewhere in the central United States. End_of_Article - Last_Page 272------------
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Thirty-four Rb-Sr isotope dilution analyses on muscovite books as well as four U-Pb zircon and monazite analyses demonstrate two distinct episodes of pegmatite emplacement in the Moines at 730 ± 20 m.y. and 450 ±10 m.y. (λ 87 Rb = 1.39 x 10 −11 y −1 ) . Confirmation of the Precambrian episode comes from a detailed Rb-Sr study on muscovite books from the Carn Gorm pegmatite in Central Ross-shire and from the concordance of Rb-Sr muscovite and U-Pb zircon ages from two pre-F2 pegmatites from the hornblende anorthite zone of Kennedy (1949) 11 km west of Glenfinnan in western Inverness-shire. Palaeozoic pegmatites were measured from Loch Monar in central Ross-shire and from occurences in the Moines east of the western tip of Loch Eilt in the Glenfinnan area. Near Glenfinnan Rb-Sr analyses on cross-cutting pegmatites yield an age of 445 ± 10 m.y. for a suite of post F3 lamprophyres. An older age limit for the F3 deformation is provided by a 450 ±10 m.y. monazite age from a post F2 to pre-F3 pegmatite. Both isotopic and geological evidence is presented for a post Arenig pre-450 ± 10 m.y. age for the second deformation in the Moines. Structural correlations in the Moines are briefly discussed as well as the evidence for two orogenic events corresponding in age to the episodes of pegmatite emplacement.
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A general consolidation of data relating to reports of Precambrian and lower Paleozoic spores of land plants and hystrichosphaers is presented. Emphasis is placed on the necessity of establishing clear and objective means of separating and classifying these organic remains. Their value lies in the theoretical interpretation of the origin of land plants as well as in the practical applications in stratigraphic correlations of the oldest sedimentary formations. -- F. M. Hueber.
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An occurrence of Lower Palaeozoic rocks within the Precambrian terrain near Sukkertoppen, West Greenland, was discovered in 1965 by Caj Kortman and Jens Gothenborg working under fil. mag. L. Keto for Kryolitselskabet Øresund AIS, Copenhagen. The material was kindly placed at the disposal of the writer for further study.
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Phyllite and quartzite, probably Precambrian, trend meridionally and dip steeply in the New River Gorge above the junction with the Salisbury River in southern Tasmania.Further upstream an association of silty dolomite and conglomerate is less deformed and may be younger.Siliceous conglomerate boulders occur in the New River below the gorge.Late Ordovician carbonates of the Gordon Group are exposed in the New River valley just above the junction with the Salisbury River and up the Salisbury to Vanishing Falls, above which a sheet of Jurassic dolerite seems to have been intruded along the unconformity between the Ordovician rocks and almost horizontal Late Palaeozoic sedimentary rocks of the Parmeener Supergroup.
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