Paleointensity record from Pleistocene sediments (1.4-0 Ma) off the California Margin

Citation
Y. Guyodo et al., Paleointensity record from Pleistocene sediments (1.4-0 Ma) off the California Margin, J GEO R-SOL, 104(B10), 1999, pp. 22953-22964
Citations number
49
Categorie Soggetti
Earth Sciences
Journal title
JOURNAL OF GEOPHYSICAL RESEARCH-SOLID EARTH
ISSN journal
21699313 → ACNP
Volume
104
Issue
B10
Year of publication
1999
Pages
22953 - 22964
Database
ISI
SICI code
0148-0227(19991010)104:B10<22953:PRFPS(>2.0.ZU;2-L
Abstract
High resolution magnetic measurements of 45 m of sediment from the Delgada Fan area at Ocean Drilling Program Site 1021 (39 degrees 5'N/127 degrees 46 'W) were performed in order to extract a reliable signal of relative paleoi ntensity. A detailed chronology was established by correlation of the magne tic susceptibility variations to the insolation curve for the past 1.4 Myr covered by the record. The remanence carrier is pseudo-single-domain-sized magnetite that varies in concentration by a factor <3. Stepwise alternating field demagnetization isolated a very stable natural remanent magnetizatio n (NRM) which showed the succession of the Cobb and Jaramillo Subchrons and directional changes associated with the Punaruu event (1.105 Ma). Two tech niques have been used to extract the signal of relative paleointensity. A s ignificant climatic component remained present in the curve obtained from t he slopes of the NRM versus the anhysteretic remanent magnetization (ARM). In contrast the NRM and the susceptibility (k(lf)) both being driven by orb ital forcing, normalization by susceptibility is not contaminated by climat ically driven changes and is thus taken as our best estimate of relative pa leointensity. Comparison with other high-resolution records and compilation s reinforces the actual geomagnetic origin of the variations displayed by t he NRM/k signal. Overall, this record confirms the succession of distinct h ighs and lows which are concomitant with full field reversals and short-ter m geomagnetic events present during the Matuyama Cion. The presence of larg e oscillations of the field with no periodicity confirms that the geomagnet ic field (at least his dipolar part) is highly unstable and may have remain ed in this mode for a long period of time.