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| Titel |
Can eustatic charts go beyond first-order? Insights from the Permo-Triassic |
| VerfasserIn |
Benjamin Guillaume, Julien Monteux, Stéphane Pochat, Laurent Husson, Gael Choblet |
| Konferenz |
EGU General Assembly 2016
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 18 (2016) |
| Datensatznummer |
250129256
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| Publikation (Nr.) |
 EGU/EGU2016-9339.pdf |
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| Zusammenfassung |
| To the first order, eustatic charts are in accord with our understanding of the geodynamic
processes that control sea level. By extrapolation, second-order features are also
thought to obey to the same rules, and are thus often taken for granted. But this
assumption may be jeopardized by a close examination of a characteristic example.
The Permo-Triassic period is characteristic for both its purported eustatic signal
and its geodynamic and climatic setting are well defined and contrasted. Both the
fragmentation of the Pangean supercontinent and the late Paleozoic melting of
ice sheets argue for a rise of the eustatic sea level (ESL) whereas eustatic charts
show the opposite. Here we review the possible mechanisms that could explain the
apparent sea level low, and find that some of them do lower the ESL while others
instead only modify the referential, either uplifting continents or tilting the margins
where the control points are located. In the first category, we find that (i) dynamic
deflections of the Earth surface above subduction zones and their location with respect to
continents primarily control absolute sea level while the Pangean supercontinent forms
and breaks up, (ii) endorheism that ubiquitously developed at the time of Pangean
aggregation also contributed to lowering the ESL by storing water out of the oceanic
reservoir. In the second category, we show that (i) the thermal uplift associated to
supercontinental insulation and (ii) the dynamic uplift associated with the emplacement
of a superplume both give rates of change in the range of long-term changes of
ESL. We also show that (iii) the dynamic tilting of continental margins not only
produces apparent sea level changes, but also modifies the absolute sea level, which in
turn may end up in the paradoxical situation wherein fingerprints of ESL drop are
found in the geological record whereas ESL is actually rising. We conclude that the
establishment of second to third order absolute sea level changes may stay for a while a
chimera. |
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