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| Titel |
Integrative stratigraphy during extreme environmental changes and biotic recovery time: The Early Triassic in Indian Himalaya |
| VerfasserIn |
Sylvain Richoz, Leopold Krystyn, Thomas Algeo, Om Bhargava |
| Konferenz |
EGU General Assembly 2014
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 16 (2014) |
| Datensatznummer |
250089679
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| Publikation (Nr.) |
 EGU/EGU2014-3889.pdf |
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| Zusammenfassung |
| The understanding of extreme environmental changes as major extinction events,
perturbations of global biogeochemical cycles or rapid climate shifts is based on a precise
timing of the different events. But especially in such moving environments exact correlations
are difficult to establish what underlines the necessity of an integrated stratigraphy by using
all tools at disposition.
A Lower Triassic section at Mud in the Spiti Valley (Western Himalaya, India) is a
candidate section for the GSSP of the Induan-Olenekian Boundary (IOB). The succession
was deposited in a deep-shelf setting on the southern margin of the Neotethys Ocean. The
section contains abundant fossils allowing a very precise regional biostratigraphy and
displays no signs of sedimentary breaks. Analysis of pelagic faunas proves a significant,
two-step radiation phase in ammonoids and conodonts close to the Induan-Olenekian
boundary. These diversifications are coupled with a short-termed positive δ13Ccarb excursion
of global evidence. The Spiti δ13Ccarb excursion displays, however, different amplitude and
biostratigraphic position than in other relevant sections for this time interval. In this study, we
analyzed δ13Ccarb, δ13Corg, and δ15Norg as well as major, trace, and REE concentrations for
a 16-m-thick interval spanning the mid-Griesbachian to early Spathian substages, to
better constrains the chain of events. Prior to the first radiation step, high difference
gradient between the δ13Ccarb values of tempestite beds with shallow carbonate and
carbonate originated in deeper water is interpreted as a sign of a stratified water
column. This effect disappears with the onset of better oxygenated conditions at the
time of the ammonoid-conodont radiation, which correspond as well to δ13Ccarb,
δ13Corg and δ15Norg positive excursions. A decrease in Mo and U concentrations
occurring at the same point suggests a shift toward locally less reducing conditions. The
second step coincided with the change from terrigenous to almost pure carbonate
sedimentation. This new set of data demonstrates from on hand the rapidity of radiation of
the pelagic fauna in the aftermath of the Permian-Triassic extinction as soon as
environmental conditions were favourable again. On the other hand, it demonstrates that
bathymetry, for example, but also other local factors, could have had a significant impact
in the timing of these radiations and may hamper solid worldwide correlations. |
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