Early Cenozoic climate and tectonic evolution of the southwest Pacific Ocean
Palaeontology
Final Report Abstract
The results obtained during this project (and currently still undergoing) represent a considerable step forward in the knowledge of the paleogeographic history of the southwest Pacific area. In the last few years it became clear the pivotal role of the sedimentary record deposited on the continental crust of Zealandia in deciphering the history of the Tonga- Kermadec subduction zone, which started its activity in the Eocene. This major tectonic event may have had also severe consequences on the global climate trends, and it is thought to have caused the turnover from global warming to global cooling occurred at 52–50 Ma (early Eocene climatic optimum). This is because the shift of the Pacific plate from the eastward subduction beneath the continental crust of the American Cordillera to the west-Pacific subduction beneath oceanic crust (Izu-Bonin-Mariana and Tonga-Kermadec trenches) likely resulted in a dramatic decrease of the CO2 volcanic degassing. The results from the New Caledonian records developed under this project indicate that the northern Norfolk Ridge, as part of northern Zealandia, went through a major uplift and slopedevelopment between 46 and 45 Ma, manifested in the sediment as a shift from pelagic sedimentation to hematite-rich calciturbidite. We present the first precise age constraint of the Eocene convergence inception that shortly preceded the Tonga-Kermadec subduction initiation, and it is obtained by a rigorous integrate magneto-biostratigraphic approach. Our new age for the calciturbidite deposition is about 5 Myr younger than previously thought (~50 Ma). This datum represents a piece of the southwest Pacific history puzzle that connect perfectly with the geology of New Zealand, making the geological history of the whole northern Zealandia consistent. It is now clear that the westward shift of the Pacific plate motion caused coeval and dramatic changes in the sedimentation patterns of New Caledonia and New Zealand, which in turn give the possibility to date the motion change itself by means of magnetobiochronology. During this project we also integrate and refined the paleotemperature proxy dataset for the southwest Pacific, and this was facilitated by the robust chronology obtained within this and previous projects. Now there are the basis for exploring the connection between the large-scale tectonic event and global climate evolution. This developing idea is tightly connected with the rationale behind International Ocean Discovery Program (IDOP) Exp. 371 (Tasman frontier subduction initiation and Paleogene climate, 27 July–26 Sept. 2017), on which I sailed as onboard paleomagnetist and which recovered sediments are under scrutiny in my ongoing DFG-funded research project. Exp. 371 had a great impact on the international media (e.g., New York Times, Le Figaro, Vangardia, Sydney Morning Herald, etc.; known also as the Zealandia Expedition).
Publications
- 2018. Magneto-biostratigraphic constraints of the Eocene micrite– calciturbidite transition in New Caledonia: Tectonic implications. New Zealand Journal of Geology and Geophysics 61, 145–163
Dallanave, E., Agnini, C., Pascher, K.M., Maurizot, P., Bachtadse, V., Hollis, C.J., Dickens, G.R., Collot, J., Monesi, E.
(See online at https://doi.org/10.1080/00288306.2018.1443946) - Climatic and environmental changes across the Early Eocene Climatic Optimum at mid-Waipara River, Canterbury Basin, New Zealand. Earth Sciences Review
Crouch, E.M., Morgans, H.E.G., Shepherd, C.L., Naafs, B.D.A., Dallanave, E., Phillips, A., Hollis, C.J., Pancost, R.D.
(See online at https://doi.org/10.1016/j.earscirev.2019.102961)
