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| Titel |
Palynological constraints on timing and duration of Siberian Traps volcanic events |
| VerfasserIn |
Henk Visscher, Henrik Svensen, Cindy Looy, Kirsten Fristad, Alexander Polozov, Sverre Planke |
| Konferenz |
EGU General Assembly 2010
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 12 (2010) |
| Datensatznummer |
250041437
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| Zusammenfassung |
| Lacustrine sediments intercalated locally in the voluminous flood basalts and pyroclastic
rocks of the Siberian Traps igneous province are characterized by the presence of surprisingly
diverse assemblages of macroscopic and microscopic plant fossils. In addition, these
intertrappean sediments contain a wide variety of faunal remains, such as conchostracans,
ostracodes, gastropods and insects. Outside the area of presently exposed flood basalt,
plant fossils may also occur abundantly in the sedimentary infill of crater lakes
above vent structures in the southern part of the Tunguska Basin on the Siberian
Platform.
Because of a possible cause-effect relationship between Siberian Traps magmatism and
end-Permian mass-extinctions, vegetation that must have grown in the immediate vicinity of
the eruptive centres is one of the most obvious biota to be investigated for evidence of
terrestrial biosphere crisis. On the basis of literature information and new palynological data
from cored crater-lake sediments, in this presentation we briefly address the basic question to
what extent the Siberian plant fossil record confirms age-equivalence between biotic and
volcanic events.
At present, most published biostratigraphic interpretations of the floral and faunal records
refute any correspondence of end-Permian biotic turnover with the Siberian Traps. In effect,
the records are long since being used to advocate an exclusively Triassic age for the Siberian
volcanism, the main phase of flood basalt eruption taking place during late Early Triassic
(Olenekian) and early Middle Triassic (Anisian) times. However, re-evaluation of the
chronostratigraphic significance of plant megafossils and faunal remains has resulted in
alternative views, which suggest a Late Permian age for part or the whole of the volcanic
sequence exposed on the Siberian Platform.
Compositional characters of palynomorph assemblages indicate age-equivalence of the
flood basalts in the northern part of the Tunguska Basin and the crater-lake sediments
associated with phreatomagmatic volcanism towards the south. Our interpretation of the
palynological record corroborates a Late Permian age. Comparable assemblages are known
from Permian-Triassic boundary sections in North China, the Russian Platform, the Barents
Sea, Greenland and Canada. These records were previously regarded as earliest Triassic, but
are now known to predate the first appearance of the conodont Hindeodus parvus, which
formally defines the base of the Triassic. They are presently considered to represent the
latest Permian (late Changshingian). A latest Permian age for the main phase of
Siberian Traps magmatism confirms age concepts based on U-Pb and 40Ar-39Ar
geochronology.
Palynomorph assemblages from sedimentary interbeds of the predominantly pyroclastic
lower part of the Siberian Traps succession can be readily distinguished from those of the
flood basalts and crater lakes. Yet they are also Late Permian in age, and can be correlated
with similar assemblages from North China and the Russian Platform. It remains
questionable whether the volcanic deposits of the Tunguska Basin cross the Permian-Triassic
boundary. Triassic continuation of volcanic activity may be apparent in the West Siberian
Basin and on the Taymyr Peninsula, but palynological information from these areas needs
further verification.
It may be concluded that our palynological age-assessment of Siberian flood volcanism
and coeval phreatomagmatic activity in the Tunguska Basin would support a first-order
causal link between the most prominent phase of Siberian Traps magmatism and the
end-Permian biosphere crisis. Ongoing paleoecological analysis of the Siberian
floral records may contribute to an understanding of the precise nature of this link. |
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