602
von Dobeneck and Schmieder
The article on marine 'Environmental Magnetism' by Frederichs etaI. (this volume) outlines the
physical and sedimentological principles of rock
magnetic climate proxies. Lithological changes in
sediment series can be traced by a range of specific rock magnetic parameters which indicate concentrations ofpara-, ferri- and antiferromagnetic
minerals, discriminate among remanence-carrying
minerals (various iron oxides, oxyhydroxides and
sulfides), estimate average ferrimagnetic grain
sizes, or quantify additional magnetic properties such
as coercivity or anisotropy.
There is no universal rationale for the linkage
of climate and sedimentary magnetic mineral inventories, but detailed rock magnetic studies usually
provide the means to identify prevailing orbital forcing mechanisms within a regional context. Pronounced climate dependence has been observed for
eolian dust load, ice-rafted debris, ocean current
transport and sea-level related shelf erosion - all
important sources or pathways of magnetic mineral
deposition. The likewise cyclic accumulation of
calcareous and siliceous microfossils plays a complementary and often dominant role in generating
magnetic signals by modulating the concentration
of the magnetic mineral fraction. Magnetic signal
patterns can be obscured by too stable or too complex sedimentation conditions, discontinuous deposition (bottom current erosion, debris flows), intercalated high- or low-magnetic (tephra, fossil) layers, and, most severely, by reductive diagenesis of
primary ferrimagnetic minerals in sub- or anoxic
marine environments (Tarduno 1994; Tarduno and
Wilkison 1996; Frederichs et aI., this volume).
Isothermal magnetic parameters are determined
by measuring the magnetic moment of artificially
magnetized, but otherwise untreated bulk sediment
samples. They represent averaged volume properties, are precise and well reproducible. Because of
the ubiquity of magnetic iron minerals in nature and
the availability of highly sensitive magnetometers,
virtually every lithology can be investigated and
characterized by magnetic parameter sets. The
attainable speed and spatial resolution of whole-core
measurements convinced a growing number of
marine geoscientists to integrate rock magnetic
methods, especially magnetic susceptibility logging,
into their methodical repertory.
This paper intends to explain and illustrate standard and advanced concepts of Quaternary cyclostratigraphy with emphasis on marine rock magnetic records. The three main sections are concerned with
- stepwise refinement of multiple core correlation
schemes, phase analysis, and orbital tuning,
- evolutionary spectral analysis of Milankovitch and
super-Milankovitch signal variations covering longperiodic (> 100 kyr) amplitude modulations and
transitions of basic climate cycles
- higher-order spectral analysis of sub-Milankovitch
signal components related to climate variations of
shortduration« 18 kyr}.
As necessary restriction and tribute to the most
popular rock magnetic parameter in paleoceanography, our case studies will exclusively focus on
magnetic susceptibility records.
Experimental Methods
Traditional single sample measurements in rock
magnetism are increasingly replaced by faster nondestructive techniques. High-resolution whole-core
or half-core logging of magnetic susceptibility K
(Robinson 1990) is now a routine procedure in
marine sediment studies. The lateral sensor characteristics ofthe widely used 'Bartington' susceptometer have half-widths of 50 to 25 mm for loop
sensors of various diameters and of 12 to 4 mm for
different spot sensors. These values also represent
conservative minimum estimates for the attainable
spatial resolution.
Modem pass-through SQUID magnetometers
equipped with additional magnetization coils measure isothermal and anhysteretic remanent magnetization at resolutions ranging from 80 mm for whole
core logging down to 30 mm for 'U -channel' (axial
subcore) measurements (Weeks et al. 1993). A
10 mm resolution for surface remanence measurements is obtained by a newly developed high-Tc
SQUID 'Rock Magnetic Micro-Scanner' (von
Dobeneck et aI. 1996).
Spatial resolutions down to 1 mm at the expense of a laborious single sample preparation are
achieved by measuring magnetic hysteresis loops.
The concept of the 'Alternating Gradient Force
Magnetometer' (AGFM) allows to determine high-
von Dobeneck and Schmieder
The article on marine 'Environmental Magnetism' by Frederichs etaI. (this volume) outlines the
physical and sedimentological principles of rock
magnetic climate proxies. Lithological changes in
sediment series can be traced by a range of specific rock magnetic parameters which indicate concentrations ofpara-, ferri- and antiferromagnetic
minerals, discriminate among remanence-carrying
minerals (various iron oxides, oxyhydroxides and
sulfides), estimate average ferrimagnetic grain
sizes, or quantify additional magnetic properties such
as coercivity or anisotropy.
There is no universal rationale for the linkage
of climate and sedimentary magnetic mineral inventories, but detailed rock magnetic studies usually
provide the means to identify prevailing orbital forcing mechanisms within a regional context. Pronounced climate dependence has been observed for
eolian dust load, ice-rafted debris, ocean current
transport and sea-level related shelf erosion - all
important sources or pathways of magnetic mineral
deposition. The likewise cyclic accumulation of
calcareous and siliceous microfossils plays a complementary and often dominant role in generating
magnetic signals by modulating the concentration
of the magnetic mineral fraction. Magnetic signal
patterns can be obscured by too stable or too complex sedimentation conditions, discontinuous deposition (bottom current erosion, debris flows), intercalated high- or low-magnetic (tephra, fossil) layers, and, most severely, by reductive diagenesis of
primary ferrimagnetic minerals in sub- or anoxic
marine environments (Tarduno 1994; Tarduno and
Wilkison 1996; Frederichs et aI., this volume).
Isothermal magnetic parameters are determined
by measuring the magnetic moment of artificially
magnetized, but otherwise untreated bulk sediment
samples. They represent averaged volume properties, are precise and well reproducible. Because of
the ubiquity of magnetic iron minerals in nature and
the availability of highly sensitive magnetometers,
virtually every lithology can be investigated and
characterized by magnetic parameter sets. The
attainable speed and spatial resolution of whole-core
measurements convinced a growing number of
marine geoscientists to integrate rock magnetic
methods, especially magnetic susceptibility logging,
into their methodical repertory.
This paper intends to explain and illustrate standard and advanced concepts of Quaternary cyclostratigraphy with emphasis on marine rock magnetic records. The three main sections are concerned with
- stepwise refinement of multiple core correlation
schemes, phase analysis, and orbital tuning,
- evolutionary spectral analysis of Milankovitch and
super-Milankovitch signal variations covering longperiodic (> 100 kyr) amplitude modulations and
transitions of basic climate cycles
- higher-order spectral analysis of sub-Milankovitch
signal components related to climate variations of
shortduration« 18 kyr}.
As necessary restriction and tribute to the most
popular rock magnetic parameter in paleoceanography, our case studies will exclusively focus on
magnetic susceptibility records.
Experimental Methods
Traditional single sample measurements in rock
magnetism are increasingly replaced by faster nondestructive techniques. High-resolution whole-core
or half-core logging of magnetic susceptibility K
(Robinson 1990) is now a routine procedure in
marine sediment studies. The lateral sensor characteristics ofthe widely used 'Bartington' susceptometer have half-widths of 50 to 25 mm for loop
sensors of various diameters and of 12 to 4 mm for
different spot sensors. These values also represent
conservative minimum estimates for the attainable
spatial resolution.
Modem pass-through SQUID magnetometers
equipped with additional magnetization coils measure isothermal and anhysteretic remanent magnetization at resolutions ranging from 80 mm for whole
core logging down to 30 mm for 'U -channel' (axial
subcore) measurements (Weeks et al. 1993). A
10 mm resolution for surface remanence measurements is obtained by a newly developed high-Tc
SQUID 'Rock Magnetic Micro-Scanner' (von
Dobeneck et aI. 1996).
Spatial resolutions down to 1 mm at the expense of a laborious single sample preparation are
achieved by measuring magnetic hysteresis loops.
The concept of the 'Alternating Gradient Force
Magnetometer' (AGFM) allows to determine high-