An astrochronology for the lower to middle Eocene of the Mentelle Basin (Australia) and its implications for the geologic time scale

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Author(s): Vahlenkamp, Maximilian; De Vleeschouwer, David; Batenburg, Sietske; Edgar, Kirsty M.; Hanson, Emma; Martinez, Mathieu; Palike, Heiko; MacLeod, Kenneth G.; Li, Yong-Xiang; Richter, Carl; Bogus, Kara; Hobbs, Richard W.; Huber, Brian T.
International Ocean Discovery Program, Expedition 369 Scientists
Author Affiliation(s): Primary:
University of Bremen, MARUM-Center for Marine and Environmental Sciences, Bremen, Germany
University of Oxford, United Kingdom
University of Birmingham, United Kingdom
Université de Rennes, France
University of Missouri, United States
Nanjing University, China
University of Louisiana at Lafayette, United States
Texas A&M University, United States
University of Durham, United Kingdom
National Museum of Natural History, United States
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
Summary: The geologic time scale for the Cenozoic Era significantly improved over the last decades by virtue of advances in radioisotopic dating and the integration of these dates with astrochronologic and cyclostratigraphic results. However, to date the middle Eocene, remains a weak link. This so-called "Eocene astronomical time scale gap" reflects a lack of suitable study sections with clear astronomically forced variations in carbonate content, primarily due to large parts of the Eocene ocean being starved of carbonate. During International Ocean Discovery Program (IODP) Expedition 369, a carbonate-rich sedimentary sequence of Eocene age was recovered at Site U1514 in the Mentelle Basin (southwest Australia). The sequence consists of nannofossil chalk and exhibits a rhythmic character in its clay content. Hence, IODP Site U1514 provides an excellent opportunity to extract an astronomical signal and to construct an Eocene astrochronology. Here, we use X-Ray fluorescence (XRF) core scanning at 3 cm resolution to quantify the clay content variability. The XRF-derived ratio between calcium and iron content (Ca/Fe) precisely tracks the lithologic variability and serves as the basis for the U1514 cyclostratigraphic framework. Our astrochronology reveals a 16 million-year-long (40-56 Ma) nearly continuous history of Eocene sedimentation with variations paced by astronomical climate forcing. 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) to the Middle Eocene Climatic Optimum (MECO). The well-expressed lithological alternations between clay-rich and clay-poor intervals reflect the combined imprints of obliquity and eccentricity. Our early Eocene astrochronology confirms existing chronologies based on deep-sea sites and Italian land sections. For the middle Eocene, the exceptional match of the tuned record at U1514 with astronomical solutions allows us to confirm astrochronologies previously suggested for the equatorial and South Atlantic (Site 702, 1260 and 1263) and to provide an important step towards a fully astronomically calibrated Cenozoic geologic time scale. [Copyright Author(s) 2019. CC Attribution 4.0 License:]
Year of Publication: 2019
Research Program: IODP Integrated Ocean Drilling Program
IODP2 International Ocean Discovery Program
Key Words: 12 Stratigraphy, Historical Geology and Paleoecology; Biostratigraphy; Carbonate rocks; Cenozoic; Chalk; Chemostratigraphy; Climate forcing; Cores; Cyclostratigraphy; Eocene; Expedition 369; IODP Site U1514; Indian Ocean; International Ocean Discovery Program; Lithostratigraphy; Marine sediments; Mentelle Basin; Microfossils; Nannofossils; Orbital forcing; Paleoclimatology; Paleogene; Sedimentary rocks; Sediments; Spectra; Tertiary; X-ray fluorescence spectra
Coordinates: S330714 S330714 E1130529 E1130529
Record ID: 2019050537
Copyright Information: GeoRef, Copyright 2019 American Geosciences Institute. Reference includes data from European Geosciences Union, Munich, Germany