Palaeomagnetic study of IODP Sites U1331 and U1332 in the Equatorial Pacific; extending relative geomagnetic palaeointensity observations through the Oligocene and into the Eocene

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doi: 10.1093/gji/ggt412
Author(s): Yamamoto, Yuhji; Yamazaki, Toshitsugu; Acton, Gary D.; Richter, Carl; Guidry, Emily P.; Ohneiser, Christian
Author Affiliation(s): Primary:
Kochi University, Center for Advanced Marine Care Research, Kochi, Japan
Other:
Geological Survey of Japan, Japan
Sam Houston State University, United States
University of Louisiana, United States
University of Otego, New Zealand
Volume Title: Geophysical Journal International
Source: Geophysical Journal International, 196(2), p.694-711. Publisher: Oxford University Press on behalf of The Royal Astronomical Society, the Deutsche Geophysikalische Gesellschaft and the European Geophysical Society, International. ISSN: 0956-540X
Note: In English. Includes appendices. 42 refs.; illus., incl. 1 table, sketch map
Summary: Palaeomagnetic and rock magnetic measurements on sediment cores from Integrated Ocean Drilling Program (IODP) Sites U1331 and U1332 in the equatorial Pacific are used to examine changes in the relative palaeointensity (RPI) of the geomagnetic field during the Oligocene and Eocene. The main magnetic carrier of these sediments is interpreted to be partially oxidized magnetite, which varies in concentration by less than about a factor of six along the stratigraphic section. In some cases, these variations occur as abrupt changes or fluctuations. The largest change in lithology and rock magnetic properties occurs across the Eocene/Oligocene (E/O) boundary, with the radiolarian-rich late Eocene sediments having higher magnetic concentration than the nannofossil-rich early Oligocene sediments. RPI estimates computed from ratios of the natural remanent magnetization to anhysteretic remanent magnetization and isothermal remanent magnetization appear to be insignificantly influenced by the lithologic differences within either the Oligocene or Eocene but are significantly influenced by the differences between the Eocene and Oligocene sediments. We thus estimate the RPI separately for the Oligocene and Eocene intervals. For both sites, the RPI records always have minima at chron boundaries. The records also show large fluctuations between highs and lows even during stable polarity periods. These features are similar to what has been observed for RPI records spanning the past 3 Myr, suggesting persistent geomagnetic field behaviour since the Eocene. The two new records show consistent variation with the RPI reported from Site U1333, which is in the vicinity of Sites U1331 and U1332. The RPI variations during the Oligocene at Site U1332 are also generally consistent with those reported from the South Atlantic. One interesting feature is that the RPI is consistently high throughout most of Chron C12r (31.021-33.232 Ma). In addition, Cryptochron C18n.1n-1, which is characterized by common marked intensity lows in the RPI records, is observed at the age of 39.094-39.114 Ma for Site U1331 and 38.958-38.983 Ma for Site U1332.
Year of Publication: 2014
Research Program: IODP Integrated Ocean Drilling Program
Key Words: 03 Geochronology; 12 Stratigraphy, Historical Geology and Paleoecology; Cenozoic; Chronology; East Pacific; Eocene; Equatorial Pacific; Expedition 320; Expeditions 320/321; IODP Site U1331; IODP Site U1332; Integrated Ocean Drilling Program; Lithofacies; Magnetic properties; Magnetic susceptibility; North Pacific; Northeast Pacific; Oligocene; Pacific Ocean; Paleogene; Paleomagnetism; Relative age; Reversals; Secular variations; Stratigraphic boundary; Tertiary
Coordinates: N120405 N120405 W1420942 W1420942
N115443 N115443 W1410244 W1410244
Record ID: 2014039185
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