Refining the early and middle Eocene geomagnetic polarity time scale; new results from ODP Leg 208 (Walvis Ridge)

Author(s): Westerhold, Thomas; Roehl, Ursula; Frederichs, Thomas; Bohaty, Steven M.; Florindo, Fabio; Zachos, James C.; Raffi, Isabella; Agnini, Claudia
Author Affiliation(s): Primary:
University of Bremen, Department of Geosciences, Bremen, Germany
University of Southampton, United Kingdom
National Institute of Geophysics and Volcanology, Italy
University of California at Santa Cruz, United States
University of Chieti-Pescara, Italy
University of Padua, Italy
Volume Title: AGU 2015 fall meeting
Source: American Geophysical Union Fall Meeting, Vol.2015; American Geophysical Union 2015 fall meeting, San Francisco, CA, Dec. 14-18, 2015. Publisher: American Geophysical Union, Washington, DC, United States
Note: In English
Summary: Astronomical calibration of the Geomagnetic Polarity Time Scale (GPTS) for the Eocene (34-56 Ma) has advanced tremendously in recent years. Combining a cyclostratigraphic approach based on the recognition of the stable 405-kyr eccentricity cycle of Earth's orbit with high-resolution bio- and magnetostratigraphy from deep-sea sedimentary records (ODP Legs 171B, 189 and 207; IODP Exp. 320/321) resulted in a new calibration of the middle-to-late Eocene GPTS spanning Chrons C12r to C19n (30.9-41.3 Ma). A fully astronomically calibrated GPTS for the Eocene was established recently by integrating cyclo-bio-magnetostratigraphy from ODP Sites 702 and 1263 records spanning the middle Eocene with Site 1258 records covering the early Eocene. Comparison of this deep sea-derived GPTS with GTS2012 and GPTS calibration points from terrestrial successions show overall consistent results, but there are still major offsets for the duration of Chrons C20r, C22r and C23n.2n. Because of the relatively large uncertainty of the calibration point, a radioisotopic dated ash layer in DSDP 516F, at C21n.75 (46.24±0.5 Ma) the duration of C20r in GPTS2012 (2.292 myr) is uncertain. Offsets in durations of C22r and C23n.2n between GPTS2012 and the new astronomical GPTS (∼400-kyr longer C22r; ∼400-kyr shorter C23n.2n) could be due to uncertainties in the interpretation of Site 1258 magnetostratigraphic data. Here we present new results toward establishing a more accurate and complete bio-, magneto- and chemostratigraphy for South Atlantic Leg 208 sites encompassing magnetochrons C13 to C24 (33 to 56 Ma). Our study aims to integrate paleomagnetic records from multiple drilled sites with physical property data, stable isotope data and XRF core scanning data to construct an astronomically calibrated framework for refining GPTS age estimates. This effort will complete the Early-to-Middle Eocene GPTS and allow evaluation of the relative position of calcareous nannofossil events to magnetostratigraphy.
Year of Publication: 2015
Research Program: IODP Integrated Ocean Drilling Program
ODP Ocean Drilling Program
Key Words: 12 Stratigraphy, Historical Geology and Paleoecology; Atlantic Ocean; Blake Nose; Blake Plateau; Cenozoic; Demerara Rise; East Pacific; Eocene; Equatorial Atlantic; Expeditions 320/321; Integrated Ocean Drilling Program; Leg 171B; Leg 189; Leg 207; Leg 208; Middle Eocene; North Atlantic; North Pacific; Northeast Pacific; Northwest Atlantic; Ocean Drilling Program; Pacific Ocean; Paleogene; Paleomagnetism; South Atlantic; Tertiary; Walvis Ridge; West Atlantic
Coordinates: S290000 S270000 E0030000 E0013000
Record ID: 2016109241
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