The Eocene/Oligocene Transition - a cyclostratigraphic perspective
Zusammenfassung der Projektergebnisse
Prior to IODP Expedition 320/321 knowledge on late Eocene and Oligocene paleoceanography in the equatorial Pacific was only based on data from ODP Site 1218. The recovery of new, carbonate-rich sediments in combination with high quality magnetostratigraphy over a depth transect covering several Cenozoic key horizons during Exp. 320/321 provided the opportunity to tremendously improve our knowledge about paleoceanographic conditions during the middle to late Eocene and the Eocene/Oligocene transition (EOT). The main objective of our project was to investigate if orbital forcing through an influence on the carbon cycle is imprinted upon middle to late Eocene records in the equatorial Pacific. We aimed to evaluate how changes in the Carbonate Compensation Depth (CCD) and the Carbonate Accumulation Events (CAE) are related to global climate changes and if they are driven by orbital cycles. On our way to configure an accurate astronomical age model we started with defining a complete high-resolution time series correlating and integrating Leg 199 and Exp. 320 XRF core scanning data, physical property data, and stratigraphic data. Subsequently, we developed an integrated cyclostratigraphic framework based on the identification of the stable long eccentricity cycle in published and new high-resolution records encompassing bulk and benthic stable isotope, calibrated XRF core scanning, and magnetostratigraphic data from ODP Sites 171B-1052, 189-1172, 199-1218, and 207-1260 as well as IODP Sites 320-U1333, and -U1334 spanning magnetic polarity Chrons C12n to C20n. After these extremely time consuming but tremendously important steps we applied orbital tuning of the records to the La2011 orbital solution. The resulting new time scale not only revised and refined the existing orbitally tuned age model and the Geomagnetic Polarity Time Scale (GPTS) from 31 to 43 Ma but also exhibited that climate variability in this 12-million years long interval of the middle-to-late Eocene and early Oligocene is mainly influenced by Earth’s eccentricity cycle. In order to test whether the long-period carbonate cycles in the equatorial Pacific sediments are related to an orbital frequency from 31 to 43 Ma, we calibrated the obtained XRF intensity data for Sites 1218, 1219, 1220, U1331, U1332, U1333, and U1334 as part of the Cenozoic Equatorial Pacific Mega- Splice applying the NMS (Normalized Median-Scaled) data reduction of Lyle et al. (2012). After cross calibration with coulometric carbonate estimates across the EOT we obtained exceptionally high quality CaCO3 wt% records of more than 1200 meters of sediment cores over a depth transect in a very short amount of time. Based on these records we show that especial eccentricity cycles had a major impact on Earth’s climate dynamics in the middle to late Eocene. To our surprise the 2.4 myr modulation of eccentricity seems to trigger very shallow CCD events through an up to now unknown mechanism at 40, 38, and 35.3 Ma. In contrast to changes in the CCD the CAE in the equatorial Pacific seem to be related to the 1.2 myr minima in the modulation of the obliquity cycle. For the first time this suggests a close coupling of nutrient redistribution in the equatorial Pacific expressed in productivity changes and high latitude processes likely via ocean circulation. Closing the middle Eocene ‘cyclostratigraphic gap’ is a breakthrough in astronomical tuning. We achieved this ultimate goal of the project by establishing an integrated stratigraphic framework based on the identification of the stable long eccentricity cycle (405 kyr) across magnetic polarity chrons C20r and C21n (43 to 48 Ma) with new data from South Atlantic ODP Site 1263 (Leg 208) in a joined effort with S. Bohaty and J. Zachos. Our new data now connect the anchored with the floating cyclostratigraphic time scales and enable to develop a full astronomical time scale for the entire Cenozoic.
Projektbezogene Publikationen (Auswahl)
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(2012) A Cenozoic record of the equatorial Pacific carbonate compensation depth. Nature, 488. 609-614
Pälike, H, Lyle, MW, Nishi, H, Raffi, I, Ridgwell, A, Gamage, K, Klaus, A, Acton, GD, Anderson, L, Backman, J, Baldauf, JG, Beltran, C, Bohaty, SM, Bown, PR, Busch, WH, Channell, JET, Chun, COJ, Delaney, ML, Dewang, P, Dunkley Jones, T, Edgar, KM, Evans, HF, Fitch, P, Foster, GL, Gussone, N, Hasegawa, H, Hathorne, EC, Hayashi, H, Herrle, JO, Holbourn, AEL, Hovan, SA, Hyeong, K, Iijima, K, Ito, T, Kamikuri, SI, Kimoto, K, Kuroda, J, Leon-Rodriguez, L, Malinverno, A, Moore, TC, Murphy, B, Murphy, DP, Nakamur, H, Ogane, K, Ohneiser, C, Richter, C, Robinson, RS, Rohling, EJ, Romero, OE, Sawada, K, Scher, HD, Schneider, L, Sluijs, A, Takata, H, Tian, J, Tsujimoto, A, Wade, BS, Westerhold, T, Wilkens, RH, Williams, T, Wilson, PA, Yamamoto, Y, Yamamoto, S, Yamazaki, T and Zeebe, RE
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(2012) Data report: raw and normalized elemental data along the Site U1338 splice from X-ray fluorescence scanning. In: Pälike, H, Lyle, M, Nishi, H, Raffi, I, Gamage, K, Klaus, A and Expedition 320/321 Scientists (eds.) Proceedings of the Integrated Ocean Drilling Program, 320/321. Integrated Ocean Drilling Program Management International, Inc., Tokyo
Lyle, MW, Olivarez Lyle, A, Gorgas, TJ, Holbourn, AEL, Westerhold, T, Hathorne, EC, Kimoto, K and Yamamoto, S
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(2012) Revised composite depth scales and integration of IODP Sites U1331-U1334 and ODP Sites 1218-1220. In: Proceedings of the Integrated Ocean Drilling Program, 320/321. Integrated Ocean Drilling Program Management International, Inc., Tokyo
Westerhold, T, Röhl, U, Wilkens, R, Pälike, H, Lyle, M, Jones, TD, Bown, PR, Moore, T, Kamikuri, SI, Acton, GD, Ohneiser, C, Yamamoto, Y, Richter, C, Fitch, P, Scher, HD, Liebrand, D and Expedition 320/321 Scientists
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(2013) Middle Eocene to early Oligocene calcareous nannofossil biostratigraphy at IODP Site U1333 (equatorial Pacific). Micropaleontology, 59(1). 69-82
Toffanin, F, Agnini, C, Rio, D, Acton, GD and Westerhold, T
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2013. Orbital pacing of Eocene climate during the Middle Eocene Climate Optimum and the chron C19r event: Missing link found in the tropical western Atlantic. Geochemistry, Geophysics, Geosystems, 14(11). 4811-4825
Westerhold, T. and Röhl, U.
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2013. Orbitally tuned time scale and astronomical forcing in the middle Eocene to early Oligocene. Climate of the Past Discussion, 9, 6635-6682
Westerhold, T., Röhl, U., Pälike, H., Wilkens, R. H., Wilson, P. A., Acton, G. D.
