Clumped isotope thermometry on fossil corals from the early Eocene Otway Basin, Australia

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https://meetingorganizer.copernicus.org/EGU2019/EGU2019-18193.pdf
Author(s): Müller, Inigo Andreas; Waajen, Irene; Wallis, David; Nijhof, Rein; Frieling, Joost; Bijl, Peter K.; Ziegler, Martin
Author Affiliation(s): Primary:
Utrecht University, Department of Earth Sciences, Utrecht, Netherlands
Volume Title: European Geosciences Union general assembly 2019
Source: Geophysical Research Abstracts, Vol.21; European Geosciences Union general assembly 2019, Vienna, Austria, April 7-12, 2019. Publisher: Copernicus GmbH on behalf of the European Geosciences Union (EGU), Katlenburg-Lindau, Germany. ISSN: 1029-7006
Note: In English. 4 refs.
Summary: The Early Eocene is extensively studied due to its extremely warm climate and high atmospheric pCO2 conditions (e.g. Bijl et al., 2009; Evans et al., 2018); and in spite of the differing paleogeography is often seen as potential analog for future climate projections. Existing studies show significantly warmer sea surface temperatures at high latitudes and in general a more flatter meridional temperature gradient than modern times (e.g. Evans et al., 2018). However, most of these high latitude temperature estimates are derived solely of the TEX86 proxy where complications with the different calibrations bring in a certain uncertainty. In this study we show with carbonate clumped isotope ( 47) thermometry an alternative proxy to add further temperature estimates and insights to Early Eocene high latitude climate reconstructions. We collected fossil corals and gastropods from shallow marine beds of the Dilwyn formation that formed during the Early Eocene climatic optimum (54.5 Ma) in the Otway basin, at a paleolatitude of 60 °S. The application of 47 thermometry on fossil corals is challenging due to the high content of organics within the aragonitic skeleton, potential disequilibrium effects during skeleton formation, aragonite specific acid fractionation during isotope analysis and importantly, a potential diagenetic overprint on the primary aragonitic skeleton. In order to select well preserved corals we performed an extended screening of the material using a combination of multiple geochemical techniques (XRD, EBSD and XRF), before analyzing the finely powdered fossils for their 47. Our 47 temperature estimates on the fossil corals show approximately 10 °C colder waters than nearby sea surface temperature records based on TEX86 (Bijl et al., 2013; Pross et al., 2012) whereas T estimates from a gastropod shell align well with the TEX86 data. We discuss the observed offset between the different reconstructions taking into account different formation depths and local circulation of a relatively cold intermediate water mass in the Otway basin, matching bottom water temperature estimates from the nearby, but deeper Pacific site U1172 based on oxygen isotope thermometry of benthic foraminifera (Bijl et al., 2013). References: Bijl P.K., Schouten S., Sluijs A., Reichart G.J., Zachos J.C. and Brinkhuis H. (2009) Early Paleogene temperature evolution of the southwest Pacific Ocean. Nature 461, 776-779. Bijl P.K., Bendle J.A.P., Bohaty S.M., Pross J., Schouten S., Tauxe L., Stickley C.E., McKay R.M., Röhl U., Olney M., Sluijs A., Escutia C., Brinkhuis H. and Expedition 318 Scientists (2013) Eocene cooling linked to early flow across the Tasmanian Gateway. PNAS 110, 9645-9650. Evans D., Sagoo N., Renema W., Cotton L.J., Muller W., Todd J.A., Saraswati P.K., Stassen P., Ziegler M., Pearson P.N., Valdes P.J. and Affek H.P. (2018) Eocene greenhouse climate revealed by coupled clumped isotope-Mg/Ca thermometry. PNAS 115, 1174-1179. Pross J., Contreras L., Bijl P.K., Greenwood D.R., Bohaty S.M., Schouten S., Bendle J.A., Rohl U., Tauxe L., Raine J.I., Huck C.E., van de Flierdt T., Jamieson S.S.R., Stickley C.E., van de Schootbrugge B., Escutia C., Brinkhuis H. and Integrated Ocean Drilling Program Expedition 318 Scientists (2012) Persistent near-tropical warmth on the Antarctic continent during the early Eocene epoch. Nature 488, 73-77. [Copyright Author(s) 2019. CC Attribution 4.0 License: https://creativecommons.org/licenses/by/4.0/legalcode]
Year of Publication: 2019
Research Program: ODP Ocean Drilling Program
Key Words: 12 Stratigraphy, Historical Geology and Paleoecology; Anthozoa; Australasia; Australia; Carbonate clumped isotope thermometry; Cenozoic; Cnidaria; Cores; Dilwyn Formation; Eocene; Gastropoda; Geologic thermometry; Indian Ocean; Leg 189; Lower Eocene; Marine sediments; Mollusca; ODP Site 1172; Ocean Drilling Program; Otway Basin; Pacific Ocean; Paleoclimatology; Paleogene; Sedimentary rocks; Sediments; South Pacific; Southwest Pacific; Tasman Sea; Tertiary; West Pacific
Coordinates: S435800 S435700 E1495600 E1495500
Record ID: 2019050542
Copyright Information: GeoRef, Copyright 2019 American Geosciences Institute. Reference includes data from European Geosciences Union, Munich, Germany