The impact of the Miocene Carbonate Crash in the Atlantic and Pacific: Evidence from carbonate budgets and silt grain size studies
Zusammenfassung der Projektergebnisse
The crucial changes in the Equatorial Pacific associated with the CC‐events are manifested in the rise of the CCD starting at 10.5 Ma. Our results support, however, the Atlantic preservation patterns are improving more gradually from 9.6 Ma to 9 Ma (Rockall Plateau 982) and 10.2 Ma to 9 Ma (Ceara Rise), which can be interpreted as enhanced NCW formation. A similar trend was found in studies of oxygen and Neodymium isotopes as well. The sediments of Pacific Site 1237 reveal increasing dissolution from about 10.4 to 9.5 Ma in accordance with the development of overall Equatorial Pacific preservation patterns. However this development is not associated with a rapid decrease of carbonate accumulation. The lower carbonate contents here are caused by a combination of dilution with ashes and lowered carbonate accumulation due to decreases in carbonate productivity before the CC‐events and some dissolution. Thus we conclude that the carbonate accumulation in the Pacific and the Atlantic is at least partly caused by lowered productivity in an interval between 11.5 and 10.5Ma. Carbonate budgets are dominated by coarse nannofossils in the size range of 2‐10µm. Hence MAR of carbonate primarily may not be responding to preservation pattern but reflect variations in the nannolith production rates, in particular if the contribution of planktic foraminifers is rather low. Viewed on longer time scales the coarse nannofossil are replaced by fine nannofossil as shown for Site 927 with a decrease in average diameter of about 1.5µm between 4.2 and 3.2Ma. Possibly, the size variations reflect the ecologic competition of planktonic organisms in a changing environment. The question is, if these changes in mean size leads to consequences for the carbonate budget. The following hypotheses are based on the prerequisite that the amount of nannoliths per cell do not vary much. This prerequisite of constant nannolith number per cell is supported by studies of extinct placolith bearing coccospheres that show regardless of taxonomy a small number of coccoliths per coccosphere i. e. a mean of 12 and 18. Two main consequences of this observation could be: 1) If no significant change in the size of the coccoliths has been observed, nevertheless, because of more favorable ecologic conditions considerably more nannoliths may have been produced accounting for an increase in nannofossil carbonate budget. 2) In case of overall smaller nannolith sizes due to adaptational or evolutionary changes nannofossil carbonate accumulation may decrease significantly.
Projektbezogene Publikationen (Auswahl)
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IODP‐ICDP meeting Greifswald (2006): “The Miocene carbonate Crash: First results from carbonate budgets and silt grain size analysis (ODP Sites 927,928)”
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GV‐Meeting Potsdam (2007): ”The Miocene carbonate crash: First results from carbonate budgets and silt grain size analysis in the Atlantic (ODP Sites 927, 928) and Pacific (Site 1237)”
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IAS‐25th meeting Patras (2007): “The Miocene carbonate Crash: Results from carbonate budgets and silt grain size analysis in the Atlantic (ODP Sites 927, 928) and Pacific (Site 1237)”
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IAS‐26th meeting Bochum (2008): “Size evolution of Globigerinoides sacculifer in the Atlantic (Ceara Rise, Site 926) in the Middle to Late Miocene”; “Palaeoceanographic inferences from carbonate sedimentation in the Atlantic (Ceara Rise, Rockall Bank) and Pacific (Nazca Ridge) in the Middle to Late Miocene”
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IODP‐ICDP meeting Hannover (2008): “Middle to late Miocene (12‐9 MA) carbonate preservation and accumulation changes in the Atlantic (Céara Rise Sites) and Pacific (Site 1237)”
