| Title: | Investigations of enhanced organic matter burial during the Cenomanian/Turonian boundary event and the related positive carbon-isotope excursion: implications of the OAE 2 for the global carbon cycle? |
| Author: | Astrid Forster |
| Date Submitted: | 04/29/2002 |
| Address: | P.O. Box 59
Department of Biogeochemistry and Toxicology
Den Burg
Texel
The Netherlands
1790 AB
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| Phone: | +31/222/367 580 |
| Email: | forster@nioz.nl |
| Co-Authors: | Kuypers, M., Max Planck Inst. Mar. Microbiol.; Bombardiere, L., Univ. of Newcastle; Farrimond, P., Univ. of Newcastle; Jenkyns, H., Univ. of Oxford; Tsikos, H., Univ. of Oxford; Sinninghe Damsté, J., Royal Netherl. Inst. Sea Res. |
| Affiliation: | Royal Netherlands Institute for Sea Research (NIOZ) |
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| Abstract URL: | http://cis.whoi.edu/science/GG/ccod/viewAbstracts.cfm?RefNumber=19725516 |
| Author Homepage: | http://www.geology.de/forster |
| Author Project webpage: | http://www.icbm.de/ctnet |
| Keywords: | Cretaceous Gubbio Tarfaya Eastbourne Oceanic Anoxic Event OAE biomarker organic carbon burial carbon isotopes; carbon cycle; Cenomanian/Turonian boundary event; |
| Abstract: | The Cenomanian/Turonian (C/T) boundary event is the most prominent of the Cretaceous oceanic anoxic events (OAEs), characterized by a strong faunal crisis and a globally observed positive carbon-isotope excursion expressed in both carbonate and organic matter. To investigate the causes and consequences of this enhanced organic carbon burial event, the European C/T-net has chosen the C/T-OAE (OAE2) for a multidisciplinary research project focusing on C/T-sections in SE-England (Eastbourne), Morocco (Tarfaya Basin) and in Italy (Gubbio). The mid-Cretaceous period was characterized by the coincidence of intensified volcanism and oceanic crust production, a peak sea-level highstand and high paleotemperatures. Assuming that the increase in the atmospheric CO2 concentration as the result of volcanic outgassing was the main cause for the Cretaceous "Greenhouse" climate, could the sequestration of organic carbon in the course of the OAE2 have provided a feed-back mechanism in the global carbon cycle to compensate for this? Corroborating evidence is provided by investigations of the carbon-isotope excursion from C/T-boundary sections offshore NW-Africa within the Proto-North Atlantic Ocean, based on  measurements on specific compounds derived from terrestrial leaves and marine phytoplankton.
Target sites for biomarker related investigations by the C/T-net are black shale-bearing sections in Morocco (Tarfaya), the South Atlantic (DSDP site 530) and Italy (Gubbio), where a core was drilled and sampled in high resolution by the entire network. The C/T-boundary interval is represented by the Livello Bonarelli, a one meter-thick regionally traceable band of carbonate-free black shales. Samples were selected for biomarker analysis and biomarker specific measurements with isotope ratio monitoring-GC-MS. Investigations of free biomarkers confirm that the black shales are still immature and the organic matter is mainly of marine, phytoplanktonic origin. Isorenieratane, a molecular fossil specific for certain green sulfur bacteria and indicative for photic zone anoxia, was not found. This is in contrast to C/T-sites consisting mainly of black shales from the southern Proto-North Atlantic (i.e.: DSDP sites 367 & 144 or Tarfaya Basin), where sulfur-bound isorenieratane is abundantly present before and during the OAE2. Preliminary results indicate that the excursion measured for specific phytoplanktonic biomarkers at Gubbio is surprisingly small compared to the isotopic excursion (up to 6  ) in the southern Proto-North Atlantic. The observed difference may be caused by a larger increase in overall primary productivity in the southern part of the Proto-North Atlantic compared to the Gubbio region during the C/T-OAE. This could imply that the Gubbio site mainly records the effect of enhanced organic carbon burial during the OAE2 on the global carbon reservoir stripped of additional local effects.
This work is supported by the European Community's Improving Human Potential Program under contract HPRN-CT-1999-00055, C/T-NET. |
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