Geomagnetic Events and Relative Paleointensity Records -
Clues to High-Resolution Paleomagnetic Chronostratigraphies
of Late Quaternary Marine Sediments?
U. Bleil* and T. von Dobeneck
Fachbereich Geowissenschaften, Universitiit Bremen, Postfach 33 0440,
D-28334 Bremen, Germany
*corresponding author (e-mail):bleil@geomarin.uni-bremen.de
Abstract: Magnetochronostratigraphies of marine sediment series are generally determined by
correlating the polarity pattern derived from their natural remanent magnetization (NRM) to a geomagnetic polarity time scale (GPTS) inferred from dated marine magnetic anomaly lineations. With
regard to the Quaternary, this conventional method can only provide a poor resolution as even the
latest available GPTS comprises but a few reversals for this time interval. Numerous recent
paleomagnetic studies have revealed supplementary prominent NRM features in marine sedimentary
deposits, namely (I) recurrent abrupt changes in stable remanent directions documenting a succession of several geomagnetic events within the Brunhes Chron and (2) conspicuous variations in
NRM intensity normalized to the concentration of magnetic minerals (the so-called relative
paleointensity) which were attributed to pronounced fluctuations in Earth's paleofield strength.
Detailed records of both phenomena are presented here for late Quaternary sediments recovered on
the Ceara Rise in the western equatorial Atlantic. Based on an oxygen isotope age model, that was
further refined by orbital tuning and sub-Milankovitch correlations of continuous magnetic
susceptibility logs, the polarity and normalized intensity time series indicate repeated full reversals
of the Earth's magnetic field configuration during the last about 380 kyr associated with distinct
changes in relative paleointensity. The data sets are discussed as primary proxies to umavel the
geomagnetic field history and reviewed in their perspectives and deficiencies to develop a highresolution magnetostratigraphic framework for the late Quaternary. They also substantially contribute
to the basic understanding of NRM acquisition processes in marine sediments summarized in a
model outlining their temporal and spatial variability as function of sediment lithology.
Introduction
A precise age control of sediment sequences is
indispensable for almost all paleoceanographic studies. Using various proxies to reconstruct environmental conditions and changes ofthe geologic past
requests not only their accurate calibration, but also
reliable time frameworks. Paleomagnetic methods
have been established as a prime choice for this
purpose in Neogene, Paleogene and older strata.
Their application to Pleistocene deposits, for which
typically high-resolution dating schemes are mandatory, remains limited, however, as only a small
number of field reversals has been clearly documented so far. Specifically the Brunhes Chron,
spanning the last about 780 kyr, is generally
referred to as a period of uniform normal polarity
of the Earth's magnetic field. Even the most recent
geomagnetic polarity time scales (Cande and Kent
1992; 1995) list but a single short reversed interval, the 'Emperor Cryptochron' (504 to 493 ka).
On the other hand, repeated 'geomagnetic events'
have been reported for the late Quaternary, among
others, the 'Mono Lake', 'Laschamp', 'Norwegian-Greenland Sea', 'Fram Strait', 'Baffin Bay'
and 'Biwa I - III' events. Such anomalous field
directions, which extremely deviate from a regular normal dipole configuration, were determined
From FISCHER G, WEFER G (eds), 1999, Use of Proxies in Paleoceanography: Examples from the South Atlantic. Springer-Verlag
Berlin Heidelberg, pp 635-654
Clues to High-Resolution Paleomagnetic Chronostratigraphies
of Late Quaternary Marine Sediments?
U. Bleil* and T. von Dobeneck
Fachbereich Geowissenschaften, Universitiit Bremen, Postfach 33 0440,
D-28334 Bremen, Germany
*corresponding author (e-mail):bleil@geomarin.uni-bremen.de
Abstract: Magnetochronostratigraphies of marine sediment series are generally determined by
correlating the polarity pattern derived from their natural remanent magnetization (NRM) to a geomagnetic polarity time scale (GPTS) inferred from dated marine magnetic anomaly lineations. With
regard to the Quaternary, this conventional method can only provide a poor resolution as even the
latest available GPTS comprises but a few reversals for this time interval. Numerous recent
paleomagnetic studies have revealed supplementary prominent NRM features in marine sedimentary
deposits, namely (I) recurrent abrupt changes in stable remanent directions documenting a succession of several geomagnetic events within the Brunhes Chron and (2) conspicuous variations in
NRM intensity normalized to the concentration of magnetic minerals (the so-called relative
paleointensity) which were attributed to pronounced fluctuations in Earth's paleofield strength.
Detailed records of both phenomena are presented here for late Quaternary sediments recovered on
the Ceara Rise in the western equatorial Atlantic. Based on an oxygen isotope age model, that was
further refined by orbital tuning and sub-Milankovitch correlations of continuous magnetic
susceptibility logs, the polarity and normalized intensity time series indicate repeated full reversals
of the Earth's magnetic field configuration during the last about 380 kyr associated with distinct
changes in relative paleointensity. The data sets are discussed as primary proxies to umavel the
geomagnetic field history and reviewed in their perspectives and deficiencies to develop a highresolution magnetostratigraphic framework for the late Quaternary. They also substantially contribute
to the basic understanding of NRM acquisition processes in marine sediments summarized in a
model outlining their temporal and spatial variability as function of sediment lithology.
Introduction
A precise age control of sediment sequences is
indispensable for almost all paleoceanographic studies. Using various proxies to reconstruct environmental conditions and changes ofthe geologic past
requests not only their accurate calibration, but also
reliable time frameworks. Paleomagnetic methods
have been established as a prime choice for this
purpose in Neogene, Paleogene and older strata.
Their application to Pleistocene deposits, for which
typically high-resolution dating schemes are mandatory, remains limited, however, as only a small
number of field reversals has been clearly documented so far. Specifically the Brunhes Chron,
spanning the last about 780 kyr, is generally
referred to as a period of uniform normal polarity
of the Earth's magnetic field. Even the most recent
geomagnetic polarity time scales (Cande and Kent
1992; 1995) list but a single short reversed interval, the 'Emperor Cryptochron' (504 to 493 ka).
On the other hand, repeated 'geomagnetic events'
have been reported for the late Quaternary, among
others, the 'Mono Lake', 'Laschamp', 'Norwegian-Greenland Sea', 'Fram Strait', 'Baffin Bay'
and 'Biwa I - III' events. Such anomalous field
directions, which extremely deviate from a regular normal dipole configuration, were determined
From FISCHER G, WEFER G (eds), 1999, Use of Proxies in Paleoceanography: Examples from the South Atlantic. Springer-Verlag
Berlin Heidelberg, pp 635-654