7.9 CycIo- and Event Stratigraphy
Basin, offCalifomia (Schaafand Thurow 1997; Cannariato
et al. 1999). The 11 year sun spot cyc1es found in varved marine salt deposits and lake sediments (Richter-Bemburg
1960; Glenn and Kelts 1991) represent a strict periodicity.
To find these short-period signals in sediments, an unusually
high sedimentation rate and very good stratigraphic resolution are necessary. In the context ofthis volume this topic is
not discussed further.
Parasequences of the Milankovitch type occur periodically, but the duration of these periods may change
with time (e.g. from approximately 100 to 40 ka or
from 40 to 20 ka). The sedimentological expression of
these cycles can be significantly modified when the
orbital signals are superimposed on third order cycles
(Fig. 7.35, also cf. Fig. 7.44). In this connection it is
important to note that the maximum rate of sea-Ievel
fall is much greater for higher frequency oscillations
than for lower ones (cf. Fig. 7.6c). High-frequency
eustatic variations therefore have a greater potential for
causing erosion and distinct sequence boundaries. This
holds true even for times of long-term sea-Ievel rise,
which normally cannot produce submarine unconformities. If the basin tends to be filled up with sediment all the time, superimposed short sea-Ievel oscillations frequently lead to subaerial erosion (cf. Fig.
7 .6b). Shallow-marine carbonates, in particular, which
undergo early cementation and lithification, have been
found to record and preserve high-frequency eustatic
variations (Sect. 7.9.4). The erosion potential ofminor
oscillations is restricted, however, to shallow-water
environments.
7.8.6 Summary (Hierarchy and Causes of
Cycles)
- First order continental encroachment or flooding cycles (megacycles) resulted from plate
tectonic motions. They led, in combination
with enhanced or subdued volcanic activity, to
a greenhouse or icehouse state of the earth.
- Second order transgressive-regressive cycles
(periods of 3-50 Ma) originated mainly from
regional tectonism and also caused the emergence and flooding of wide regions along continental margins.
- The origin of the common sequence cycles
(third order, 0.5-3 Ma) is not clear.
- Higher order (high-frequency) cycles are
mainly controlled by astronomie al forcing
(Milankovitch frequency band) which can be
magnified by feedback mechanisrns of the
Earth leading to climate change and, in certain
times, to pronounced glacio-eustasy.
- High-order cycles are commonly superimposed
onto cycles of lower order and thus create complex variations in sea level and climate.
359
7.9 Cyclo- and Event Stratigraphy
7.9.1 Introduction
Cyclostratigraphy deals with minor, relatively shortperiod (high-frequency) sedimentary cycles (mainly
Milankovitch cycles) and has recently become a field
of great interest because of its linkage with climate
change and its potential to complement and refine
chronostratigraphy and stratigraphie correlation. In
particular in the Quatemary and Neogene, cyclostratigraphy based on the astronomie al time scale and
tested by the oxygen isotope record of pelagic to
hemipelagic marine sediments is being widely used by
marine sedimentologists and oceanographers.
Their aim is to investigate the evolution ofthe ice age and its
impact on the circulation systems of the oceans, the production ofbiogenic sediment, and the distribution ofterrigenous
material in the oceans (e.g. Shackleton et al. 1990;
Tiedemann et al. 1994; Berger 1997; Berger et al. 1996).
Cyc10stratigraphy is also a tool in the study of older sediments (e.g. House and Gale 1995), but in these cases it is
often difficult to use its potential for refining biostratigraphic
or chronostratigraphic dating (see Sect. 7.9.5). Examples of
cyc10stratigraphy in lake sediments have been mentioned in
Section 7.7.1.
Event stratigraphy refers to the study of sedimentological events which are either depositional or nondepositional (e.g. Einseie 1998). Depositiona1 events,
such as mass flows and turbidity currents, are generally more or 1ess instantaneous, whereas nondepositional events (erosion, omission) may span significant time intervals. Both cyclostratigraphy and
event stratigraphy are useful in the study of larger sequences (see Sect. 7.9.8).
7.9.2 The Astronomical Time Scale
(Milankovitch Cycles)
Climatic change is induced by variations in the orbital
parameters ofthe Earth (Milankovitch theory). These
are the eccentricity, E, of the Earth's orbit around the
Sun, the deviation, tilt or obliquity, 0, of the Earth's
axis of rotation from a vertical axis on the orbital
plane, and the precession, P, expressing a certain relationship between obliquity and eccentricity. These parameters have the following periods (Fig. 7.37a):
E-lOO ka and -400 (more accurately E1=106, and
E2=410 ka); 0=41 ka, and P-21 (19-23) ka. The orbital signals are superimposed on each other (Fig.
7.37b) with the result that the intensities ofthe individual signals change with time and latitude of the region
studied.
The orbital signals produce small variations in insolation (usually recorded at 65° N latitude) and thus
changes in seasonality. The incoming signals are en-
Basin, offCalifomia (Schaafand Thurow 1997; Cannariato
et al. 1999). The 11 year sun spot cyc1es found in varved marine salt deposits and lake sediments (Richter-Bemburg
1960; Glenn and Kelts 1991) represent a strict periodicity.
To find these short-period signals in sediments, an unusually
high sedimentation rate and very good stratigraphic resolution are necessary. In the context ofthis volume this topic is
not discussed further.
Parasequences of the Milankovitch type occur periodically, but the duration of these periods may change
with time (e.g. from approximately 100 to 40 ka or
from 40 to 20 ka). The sedimentological expression of
these cycles can be significantly modified when the
orbital signals are superimposed on third order cycles
(Fig. 7.35, also cf. Fig. 7.44). In this connection it is
important to note that the maximum rate of sea-Ievel
fall is much greater for higher frequency oscillations
than for lower ones (cf. Fig. 7.6c). High-frequency
eustatic variations therefore have a greater potential for
causing erosion and distinct sequence boundaries. This
holds true even for times of long-term sea-Ievel rise,
which normally cannot produce submarine unconformities. If the basin tends to be filled up with sediment all the time, superimposed short sea-Ievel oscillations frequently lead to subaerial erosion (cf. Fig.
7 .6b). Shallow-marine carbonates, in particular, which
undergo early cementation and lithification, have been
found to record and preserve high-frequency eustatic
variations (Sect. 7.9.4). The erosion potential ofminor
oscillations is restricted, however, to shallow-water
environments.
7.8.6 Summary (Hierarchy and Causes of
Cycles)
- First order continental encroachment or flooding cycles (megacycles) resulted from plate
tectonic motions. They led, in combination
with enhanced or subdued volcanic activity, to
a greenhouse or icehouse state of the earth.
- Second order transgressive-regressive cycles
(periods of 3-50 Ma) originated mainly from
regional tectonism and also caused the emergence and flooding of wide regions along continental margins.
- The origin of the common sequence cycles
(third order, 0.5-3 Ma) is not clear.
- Higher order (high-frequency) cycles are
mainly controlled by astronomie al forcing
(Milankovitch frequency band) which can be
magnified by feedback mechanisrns of the
Earth leading to climate change and, in certain
times, to pronounced glacio-eustasy.
- High-order cycles are commonly superimposed
onto cycles of lower order and thus create complex variations in sea level and climate.
359
7.9 Cyclo- and Event Stratigraphy
7.9.1 Introduction
Cyclostratigraphy deals with minor, relatively shortperiod (high-frequency) sedimentary cycles (mainly
Milankovitch cycles) and has recently become a field
of great interest because of its linkage with climate
change and its potential to complement and refine
chronostratigraphy and stratigraphie correlation. In
particular in the Quatemary and Neogene, cyclostratigraphy based on the astronomie al time scale and
tested by the oxygen isotope record of pelagic to
hemipelagic marine sediments is being widely used by
marine sedimentologists and oceanographers.
Their aim is to investigate the evolution ofthe ice age and its
impact on the circulation systems of the oceans, the production ofbiogenic sediment, and the distribution ofterrigenous
material in the oceans (e.g. Shackleton et al. 1990;
Tiedemann et al. 1994; Berger 1997; Berger et al. 1996).
Cyc10stratigraphy is also a tool in the study of older sediments (e.g. House and Gale 1995), but in these cases it is
often difficult to use its potential for refining biostratigraphic
or chronostratigraphic dating (see Sect. 7.9.5). Examples of
cyc10stratigraphy in lake sediments have been mentioned in
Section 7.7.1.
Event stratigraphy refers to the study of sedimentological events which are either depositional or nondepositional (e.g. Einseie 1998). Depositiona1 events,
such as mass flows and turbidity currents, are generally more or 1ess instantaneous, whereas nondepositional events (erosion, omission) may span significant time intervals. Both cyclostratigraphy and
event stratigraphy are useful in the study of larger sequences (see Sect. 7.9.8).
7.9.2 The Astronomical Time Scale
(Milankovitch Cycles)
Climatic change is induced by variations in the orbital
parameters ofthe Earth (Milankovitch theory). These
are the eccentricity, E, of the Earth's orbit around the
Sun, the deviation, tilt or obliquity, 0, of the Earth's
axis of rotation from a vertical axis on the orbital
plane, and the precession, P, expressing a certain relationship between obliquity and eccentricity. These parameters have the following periods (Fig. 7.37a):
E-lOO ka and -400 (more accurately E1=106, and
E2=410 ka); 0=41 ka, and P-21 (19-23) ka. The orbital signals are superimposed on each other (Fig.
7.37b) with the result that the intensities ofthe individual signals change with time and latitude of the region
studied.
The orbital signals produce small variations in insolation (usually recorded at 65° N latitude) and thus
changes in seasonality. The incoming signals are en-