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.