Sökning: "Ordovician"

Visar resultat 11 - 15 av 40 avhandlingar innehållade ordet Ordovician.

  1. 11. The flux of extraterrestrial spinels to Earth associated with He-3 anomalies in Cenozoic and Ordovician sediments

    Författare :Samuele Boschi; Kärnfysik; []
    Nyckelord :NATURVETENSKAP; NATURAL SCIENCES; NATURVETENSKAP; NATURAL SCIENCES; Chromite; He-3 anomaly; Cenozoic; mid-Ordovician; asteroid breakup; ordinary chondrites; Popigai ejecta; iridium anomaly; Zircons; ice age;

    Sammanfattning : The main goal of this thesis is to reconstruct the flux of extraterrestrial matter to Earth in specific time intervals of our past in order to add an astronomical dimension to the understanding of Earth's history. To accomplish this, extraterrestrial chrome-spinel grains have been extracted and analysed. LÄS MER

  3. 12. Ordovician (Billingen and Volkhov stages) Brachiopod Faunas of the East Baltic

    Författare :Eva Egerquist; Lars Holmer; John S. Peel; Michael G. Bassett; Uppsala universitet; []
    Nyckelord :NATURVETENSKAP; NATURAL SCIENCES; Earth sciences; Early Middle Ordovician; Billingen Regional Stage; Volkhov Regional Stage; Diversity; Brachiopoda; Conodonta; Ostracoda; Estonia; Russia; Geovetenskap; Earth sciences; Geovetenskap;

    Sammanfattning : Lower-Middle Ordovician (Arenig) successions in the East Baltic have been investigated for more than one hundred and fifty years. Nevertheless detailed sampling still yields new species and better knowledge of the environment in which these organisms lived. LÄS MER

  4. 13. Conodont biostratigraphy, taxonomy and palaeoecology in the Darriwilian (Middle Ordovician) of Baltoscandia - with focus on meteorite and extraterrestrial chromite-rich strata

    Författare :Johanna Mellgren; Berggrundsgeologi; []
    Nyckelord :NATURVETENSKAP; NATURAL SCIENCES; Conodonts; biostratigraphy; taxonomy; palaeoecology; morphometrics; extraterrestrial chromite; meteorites; Darriwilian; Middle Ordovician; Baltoscandia;

    Sammanfattning : This thesis deals with conodont biostratigraphy and palaeoecology in the Darriwilian (Middle Ordovician) of Baltoscandia, with focus on limestone strata showing traces of the ~ 470 Ma L-chondrite parent body break-up. The evidence for this cosmic event includes abundant centimeter to decimeter-sized fossil meteorites and elevated levels of sediment-dispersed extraterrestrial L-type chromite found in a stratigraphical interval corresponding to the uppermost Lenodus antivariabilis, the L. LÄS MER

  5. 14. Silurian and Ordovician bentonites of Gotland (Sweden)

    Författare :Sven Snäll; Stockholms universitet; []
    Nyckelord :;

    Sammanfattning : .... LÄS MER

  7. 15. Late Ordovician Faunal Distribution and Ecospace Partitioning in Marine Impact Craters : The Aftermath of the Lockne and Tvären Events

    Författare :Åsa M Frisk; Lars Holmer; Jan Ove Ebbestad; Maurits Lindström; Alan Owen; Uppsala universitet; []
    Nyckelord :impact crater; Lockne; Tvären; ecospace; the Great Ordovician Biodiversification Event; NATURAL SCIENCES; NATURVETENSKAP;

    Sammanfattning : In the Middle to Late Ordovician a boost of marine biodiversity occurred which is regarded as the most rapid diversity in Earth’s history, and termed the Great Ordovician Biodiversification Event. This time is also unique in that at least four marine meteorite craters with a good record of post-impact sediments are preserved in Baltoscandia. LÄS MER