Vahlenkamp, Maximilian and De Vleeschouwer, David and Batenburg, Sietske J. and Edgar, Kirsty M. and Hanson, Emma and Martinez, Mathieu and Pälike, Heiko and MacLeod, Kenneth G. and Li, Yong-Xiang and Richter, Carl and Bogus, Kara and Hobbs, Richard W. and Huber, Brian T. (2020) 'A lower to middle Eocene astrochronology for the Mentelle Basin (Australia) and its implications for the geologic time scale.', Earth and planetary science letters., 529 . p. 115865.
The geologic time scale for the Cenozoic Era has been notably improved over the last decades by virtue of integrated stratigraphy, combining high-resolution astrochronologies, biostratigraphy and magnetostratigraphy with high-precision radioisotopic dates. However, the middle Eocene remains a weak link. The so-called “Eocene time scale gap” reflects the scarcity of suitable study sections with clear astronomically-forced variations in carbonate content, primarily because large parts of the oceans were starved of carbonate during the Eocene greenhouse. International Ocean Discovery Program (IODP) Expedition 369 cored a carbonate-rich sedimentary sequence of Eocene age in the Mentelle Basin (Site U1514, offshore southwest Australia). The sequence consists of nannofossil chalk and exhibits rhythmic clay content variability. Here, we show that IODP Site U1514 allows for the extraction of an astronomical signal and the construction of an Eocene astrochronology, using 3-cm resolution X-Ray fluorescence (XRF) core scans. The XRF-derived ratio between calcium and iron content (Ca/Fe) tracks the lithologic variability and serves as the basis for our U1514 astrochronology. We present a 16 million-year-long (40-56 Ma) nearly continuous history of Eocene sedimentation with variations paced by eccentricity and obliquity. We supplement the high-resolution XRF data with low-resolution bulk carbon and oxygen isotopes, recording the long-term cooling trend from the Paleocene-Eocene Thermal Maximum (PETM – ca. 56 Ma) into the middle Eocene (ca. 40 Ma). Our early Eocene astrochronology corroborates existing chronologies based on deep-sea sites and Italian land sections. For the middle Eocene, the sedimentological record at U1514 provides a single-site geochemical backbone and thus offers a further step towards a fully integrated Cenozoic geologic time scale at orbital resolution.
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|Publisher Web site:||https://doi.org/10.1016/j.epsl.2019.115865|
|Publisher statement:||©2019 The Author(s).Published by Elsevier B.V. This is an open access article under the CCBY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).|
|Date accepted:||26 September 2019|
|Date deposited:||15 October 2019|
|Date of first online publication:||09 October 2019|
|Date first made open access:||15 October 2019|
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