Calcareous nannoplankton changes during the middle Eocene in the Agost section (Spain): evidence for hyperthermal events
Abstract
The transition from Lower Eocene to Middle Eocene (Ypresian/Lutetian) has been known as one of the four most important intervals where sharp climatic deteriorations took place during the Cenozoic (Miller et al., 1987; Miller, 1992). The Y/L transition, with its sudden upturn in δ18O values, represents the start of a phase of increasing oxygen isotopic ratios after the end of the Early Eocene Climatic Optimum (EECO) (Zachos et al., 2001) and is one of the key intervals for understanding the evolution and the response of the calcareous nannoplankton to the paleoclimatic variations of the Cenozoic. The causes which determined the end of the EECO and the details of the long transition towards the Middle Eocene Climatic Optimum (MECO) are still largely to be deciphered due to a scarcity of land-sections and oceanic sites containing continuous successions of Lutetian sediments. A detailed calcareous nannofossil study has been performed through the entire Lutetian up to the base of Bartonian of the Agost section (Betic Cordillera, SE Spain). This section has been proposed as a suitable candidate to locate the GSSP for the Ypresian / Lutetian (= Early/Middle Eocene) boundary by Larrasoaña et al. (2008). The integrated magnetobiochronology of this interval suggested a relatively high sedimentation rate and improved the biostratigraphic resolution. Variations of calcareous nannofossil assemblages characterize more than 8 million years of climatic variability suggesting alternating cool and warm episodes and/or recurrent changes affecting the water column conditions. A radical reorganization of the assemblages occurs during the Y/L transition and other important and transient modifications following one another have been observed during the Lutetian in the Agost section. Some warm/hyperthermal climate events, could be inferred on the basis of the outstanding richness of the assemblages, the transient increase in abundance of taxa known in the literature for their preference for warm/oligotrophic waters and on evidence for surface water acidification. Two probable hyperthermal events, both preceding the MECO has been suggested: one close to the appearance of Hantkenina spp. in Subzone CP13b and the other much earlier in CP12a Subzone at the closure of the EECO, just at the end of the Ypresian.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2010
- Bibcode:
- 2010AGUFMPP23B1745M
- Keywords:
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- 0473 BIOGEOSCIENCES / Paleoclimatology and paleoceanography;
- 4944 PALEOCEANOGRAPHY / Micropaleontology;
- 9606 INFORMATION RELATED TO GEOLOGIC TIME / Paleogene