Relative paleointensity from Oligocene-Miocene Equatorial Pacific and South Atlantic sediments

Author(s): Channell, J. E. T.; Lanci, Luca
Author Affiliation(s): Primary:
University of Florida, Gainesville, FL, United States
University of Urbino, Italy
Volume Title: AGU 2013 fall meeting
Source: American Geophysical Union Fall Meeting, Vol.2013; American Geophysical Union 2013 fall meeting, San Francisco, CA, Dec. 9-13, 2013. Publisher: American Geophysical Union, Washington, DC, United States
Note: In English
Summary: We compare three 9-Myr-long records of relative paleointensity (RPI) for the Late Oligocene to Early Miocene from the equatorial Pacific (IODP Site U1334 and ODP Site 1218) and South Atlantic (ODP Site 1090). The three records are compared with published RPI records for the same time interval from IODP Site U1333 (equatorial Pacific) and DSDP Site 522 (South Atlantic). Age models at all sites are constrained by magnetic polarity stratigraphy through correlation to a common geomagnetic polarity timescale. The RPI records do not contain significant power at specific (orbital) frequencies, and hence there is no significant coherency between RPI proxies and the normalizers used to construct the proxies, although ∼400 kyr eccentricity power is significant in some of the normalizers. There is no obvious control on RPI proxies from mean sedimentation rate within polarity chrons, magnetic grain size proxies or magnetic concentration parameters. The salient test is whether the equatorial Pacific records can be correlated one to another, and to the records from the South Atlantic. All records are dominated by RPI minima at polarity reversals, as expected, although the comparison within polarity chrons is compelling enough to conclude that the intensity of the Earth's axial dipole is being recorded. This is supported by the fit of RPI data after refined correlation of Sites U1334 and 1218 using core-scanning data, rather than polarity reversals alone. We do not see a consistent relationship between polarity-chron duration and mean RPI, and no consistent skewness ("sawtooth" pattern) for RPI within polarity chrons. Stacks of RPI records for 17.5 Ma to 26.5 Ma are similar whether 3, 4 or 5 RPI records are incorporated into the stack. Long-term changes in RPI on Myr timescales are apparent, attributed to core-mantle boundary heat-flow variations, and superimposed on a pacing that that resembles RPI records for the Quaternary where minima are associated with polarity reversals but also occur within polarity chrons at a pacing of roughly 50 kyr that is not periodic. The equatorial Pacific to South Atlantic correlations indicate that RPI can be used as a (global) stratigraphic tool in pre-Quaternary sediments with typical pelagic sedimentation rates of a few cm/kyr.
Year of Publication: 2013
Research Program: DSDP Deep Sea Drilling Project
IODP Integrated Ocean Drilling Program
IPOD International Phase of Ocean Drilling
ODP Ocean Drilling Program
Key Words: 12 Stratigraphy, Historical Geology and Paleoecology; Angola Basin; Atlantic Ocean; Cenozoic; DSDP Site 522; Deep Sea Drilling Project; East Pacific; Equatorial Pacific; Expedition 320; Expeditions 320/321; IODP Site U1333; IODP Site U1334; IPOD; Integrated Ocean Drilling Program; Leg 177; Leg 199; Leg 73; Magnetic intensity; Miocene; Neogene; North Pacific; Northeast Pacific; ODP Site 1090; ODP Site 1218; Ocean Drilling Program; Oligocene; Pacific Ocean; Paleogene; Paleomagnetism; South Atlantic; Tertiary
Coordinates: S425449 S425449 E0085359 E0085359
N085300 N085300 W1352200 W1352200
N080000 N080000 W1315824 W1315824
Record ID: 2015040866
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