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| Titel |
The Valanginian positive carbon-isotope event; a coupled organic and bulk carbonate δ13C record from the western North Atlantic |
| VerfasserIn |
Kate Littler, Stuart Robinson, Paul Bown |
| 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 |
250037476
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| Zusammenfassung |
| The Valanginian positive carbon-isotope excursion (~135–138 Ma; also known as the
“Weissert OAE”) represents a major perturbation to the Early Cretaceous carbon cycle. This
apparently global event has previously been documented in marine isotope records from the
Tethyan region, the North Atlantic, Pacific and in a terrestrial isotope record from the Crimea.
A bulk carbonate carbon-isotope (δ13Ccarb) excursion of ~+1.5 per mil, is seen in many of
these records, often accompanied by a corresponding excursion of ~+4 per mil in the bulk
organic-matter (δ13Corg) record. Although the positive excursion is apparent in both
δ13Ccarb and δ13Corg records, a lack of synchronicity between the two materials during both
the onset of the excursion and the subsequent recovery period has been suggested. To date,
this has been difficult to verify due to the low-resolution nature of existing δ13Corg
records.
Lithologically separated, coupled δ13Corg and δ13Ccarb records from marine cores at two
North Atlantic sites (DSDP Sites 534 and 603) were analysed. As previously documented, the
excursion is clearly visible in the inorganic carbon-isotope record at these sites, but is now
also evident in the bulk organic-matter record. A minor lag was observed between δ13Corg
and δ13Ccarb during the onset of the excursion, with both materials attaining peak positive
values during the same interval within magnetochron M11. A longer duration lag
exists between recovery of the δ13Ccarb values to pre-excursion values, in the Early
Hauterivian, and the recovery of the δ13Corg record, which does not occur until the mid
Hauterivian. Such an offset raises questions regarding carbon cycling, as both records
may be expected to reflect the δ13C of seawater. However a change in the type and
provenance of the organic matter preserved in these sediments with time, which would
influence the bulk δ13Corg record, cannot be discounted. A lithological control on
stable-isotope ratios is also identified in both δ13Ccarb and δ13Corg records at these
sites, which may help to explain much of the “noise” often seen in such records. |
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