The Brunhes-Matuyama polarity transition was studied in three deep-sea sediment cores obtained from the mid-northern and equatorial Pacific Ocean. Rates of sedimentation vary from 0.7 to 1.1 cm k a
-1
. The cores were sampled across the transition in 4 mm slices, and each level was further subdivided into three specimens. Inclinations above and below the transition interval are in close agreement with that of an axial dipole field. Estimates of transition duration based on directional change range from 4900 to 8500 years. The transition can be described by a longitudinally confined portion in each of the v.g.p. paths, but is complicated by broad loops in all three records. While fine-scale sampling reveals considerable detail, the notable increase in within-level dispersion observed in the transition and the apparent differences in v.g.p. paths in nearby cores from the same region indicate that factors other than the geomagnetic field may contribute to these transition records.
Quaternary deposits in six sediment cores from the Scotia Sea, Antarctica,
were examined for the presence of volcanic ash layers. The cores were recovered
from water depths of 3369-4025 m. Altogether, 23 ash layers were found, 18 of
which have been investigated by electron-probe microanalysis. Deception Island is
identified as the source of all the ash layers analyzed. The upper ash layer in
each core can be correlated across all six cores, over a distance of -100 km, on
the basis of its unusual bimodal composition, major oxide geochemistry and
stratigraphie position. Two other ash layers can also be correlated between
several of the cores.
Abstract14C dates obtained by accelerator mass spectrometry (AMS) on monospecific foraminiferal samples from two deep-sea sediment cores raised in the Indian sector of the Southern Ocean have been corrected for the difference in 14C composition between atmosphere and sea surface by using a reconstruction of the latitudinal 14C gradient which existed in the Southern Ocean prior to 1962. The corrected AMS-14C data show a reduced sedimentation rate in core MD 84-527 between 25,000 and 10,000 yr BP. For core MD 84-551 the available data suggest that the sedimentation rate was higher during the Holocene than during the glacial period. These changes in sedimentation rates may be attributed to an increased opal dissolution during the last glacial maximum.
Brunhes-Matuyama polarity transition in three deep-sea sediment cores