Using Rock Magnetic Proxy Records for Orbital Tuning and Extended
Time Series Analyses into the Super- and Sub-Milankovitch Bands
T. von Dobeneck* and F. Schmieder
Fachbereich Geowissenschaften, Universitiit Bremen, Postfach 33 0440,
D-28334 Bremen, Germany
* corresponding author (e-mail):dobeneck@geomarin.uni-bremen.de
Abstract: High-resolution rock magnetic proxy records of marine sediments, in particular magnetic
susceptibility logs, delineate variations of sediment lithology and mirror climatic and oceanographic
changes of different duration. Most commonly, Milankovitch cyclicity resulting from orbital forcing
of carbonate dissolution and terrigenous sedimentation prevails. Extracted by bandpass filtering,
these signal components can serve for multiple core correlation, cyclostratigraphic analyses and
orbital tuning. Phase relations between astronomical obliquity and precession cycles and their
equivalents in rock magnetic records depend on regional sedimentological settings. Two case studies
are developed to demonstrate specific aims, strategies, strengths and restrictions of rock magnetic
time series analyses and their extension into the super- and sub-Milankovitch bands. In the first
example, twelve Pleistocene susceptibility records spanning the oligotrophic subtropical South
Atlantic (SUSAS stack) were successfully tuned to obliquity and precession despite their low
average sedimentation rates < 1 cmlkyr. Multiple bandpass filtering and evolutionary spectral analysis
reveal two major base line shifts at around 0.95 and 0.6 Ma and various superstructures (e.g., amplitude
modulations) of orbital proxy response. Compared to analogous analyses of an adapted astronomical
target curve, converse residue patterns in the 41 kyr and 100 kyr bands indicate that Pleistocene ice
age cycles were mainly triggered by obliquity before 1.25 Ma and from 1.05 to 0.7 Ma, while eccentricity
modulation of precession predominated between 1.25 and 1.05 Ma and during the last 0.6 Ma. In the
second example, eight susceptibility records from the western equatorial Atlantic Ceara Rise (CEARIS
stack) were tuned to a lagged precession index signal. Subsequently, a high resolution core correlation
scheme was established on basis of their coherent high-frequency « 15 kyr) signal patterns. Basic
harmonics and interrnodulation frequencies of obliquity, and, predominately, precession resulting
from nonlinear proxy response were detected by sub-Milankovitch spectral and bispectral analyses.
Twin susceptibility peaks corresponding to a tropical double precession cycle appear even in the
unfiltered records. Millennial signal variations « 7 kyr) seem to coincide with Bond- and DansgaardOeschger cycles.
Introduction
Many marine rock magnetic records exhibit Milankovitch cyclicities - sometimes in striking agreement
with 8180, 8 l3 C or %CaC0 3 profiles. This phenomenon is generally explained by climatic impact
on the fluxes of magnetically enriched terrigenous
and 'non-magnetic' biogenic sedimentary components. They are increasingly employed as a data
base for high-resolution core correlation, orbital age
modelling and paleoceanographic time series analysis of marine sediments. Unlike ice-shield mediated
climate proxies, magnetic records sustain their
periodicity deep into pre-Quaternary times (Park
et al. 1993; Hilgen et al. 1995; Shackleton and
Crowhurst 1997). Paleoclimatic signatures of rnagnetic susceptibility and various remanence parameters have been described and stratigraphically exploited in paleoceanographic studies from all major oceans (e.g., Radhakrishnamurty et al. 1968;
Kent 1982; Robinson 1986; B10emendal et al. 1988;
deMenocal et al. 1991; Bickert et al. 1997).
From FISCHER G, WEFER G (eds), 1999, Use of Proxies in Paleoceanography: Examplesfrom the South Atlantic. Springer-Verlag
Berlin Heidelberg, pp 601-633
Time Series Analyses into the Super- and Sub-Milankovitch Bands
T. von Dobeneck* and F. Schmieder
Fachbereich Geowissenschaften, Universitiit Bremen, Postfach 33 0440,
D-28334 Bremen, Germany
* corresponding author (e-mail):dobeneck@geomarin.uni-bremen.de
Abstract: High-resolution rock magnetic proxy records of marine sediments, in particular magnetic
susceptibility logs, delineate variations of sediment lithology and mirror climatic and oceanographic
changes of different duration. Most commonly, Milankovitch cyclicity resulting from orbital forcing
of carbonate dissolution and terrigenous sedimentation prevails. Extracted by bandpass filtering,
these signal components can serve for multiple core correlation, cyclostratigraphic analyses and
orbital tuning. Phase relations between astronomical obliquity and precession cycles and their
equivalents in rock magnetic records depend on regional sedimentological settings. Two case studies
are developed to demonstrate specific aims, strategies, strengths and restrictions of rock magnetic
time series analyses and their extension into the super- and sub-Milankovitch bands. In the first
example, twelve Pleistocene susceptibility records spanning the oligotrophic subtropical South
Atlantic (SUSAS stack) were successfully tuned to obliquity and precession despite their low
average sedimentation rates < 1 cmlkyr. Multiple bandpass filtering and evolutionary spectral analysis
reveal two major base line shifts at around 0.95 and 0.6 Ma and various superstructures (e.g., amplitude
modulations) of orbital proxy response. Compared to analogous analyses of an adapted astronomical
target curve, converse residue patterns in the 41 kyr and 100 kyr bands indicate that Pleistocene ice
age cycles were mainly triggered by obliquity before 1.25 Ma and from 1.05 to 0.7 Ma, while eccentricity
modulation of precession predominated between 1.25 and 1.05 Ma and during the last 0.6 Ma. In the
second example, eight susceptibility records from the western equatorial Atlantic Ceara Rise (CEARIS
stack) were tuned to a lagged precession index signal. Subsequently, a high resolution core correlation
scheme was established on basis of their coherent high-frequency « 15 kyr) signal patterns. Basic
harmonics and interrnodulation frequencies of obliquity, and, predominately, precession resulting
from nonlinear proxy response were detected by sub-Milankovitch spectral and bispectral analyses.
Twin susceptibility peaks corresponding to a tropical double precession cycle appear even in the
unfiltered records. Millennial signal variations « 7 kyr) seem to coincide with Bond- and DansgaardOeschger cycles.
Introduction
Many marine rock magnetic records exhibit Milankovitch cyclicities - sometimes in striking agreement
with 8180, 8 l3 C or %CaC0 3 profiles. This phenomenon is generally explained by climatic impact
on the fluxes of magnetically enriched terrigenous
and 'non-magnetic' biogenic sedimentary components. They are increasingly employed as a data
base for high-resolution core correlation, orbital age
modelling and paleoceanographic time series analysis of marine sediments. Unlike ice-shield mediated
climate proxies, magnetic records sustain their
periodicity deep into pre-Quaternary times (Park
et al. 1993; Hilgen et al. 1995; Shackleton and
Crowhurst 1997). Paleoclimatic signatures of rnagnetic susceptibility and various remanence parameters have been described and stratigraphically exploited in paleoceanographic studies from all major oceans (e.g., Radhakrishnamurty et al. 1968;
Kent 1982; Robinson 1986; B10emendal et al. 1988;
deMenocal et al. 1991; Bickert et al. 1997).
From FISCHER G, WEFER G (eds), 1999, Use of Proxies in Paleoceanography: Examplesfrom the South Atlantic. Springer-Verlag
Berlin Heidelberg, pp 601-633