7.9 CycIo- and Event Stratigraphy
traced back from the Present into the past 5 to 6 Ma (Lourens
et al. 1996).
During the past 600 to 800 ka, the 100 ka period was
dominant (Milankovitch chron) generating high-amplitude
sea-Ievel changes and rapid ice melting events ("terminations ", Berger 1997), but in the earlier Quatemary and Pliocene the 41 ka period (Laplace chron) mainly controlled the
climatic variation with high-frequency sea-Ievel changes of
lower amplitude (Fig. 7.37e; Tiedemann et al. 1994).
Changes in aridity of North Africa (Sahel zone), however,
record precession cycles (19-23 ka) in the early to middle
Pliocene.
In an excellent record of emerged late Pliocene shallowmarine cyclic sediments of New Zealand, the 41 ka period
also predominates over the 100 ka (Naish 1997). The cycles
or cyclothems consist of clastic material, are about 50 m in
thickness, and formed in a subduction-related, rapidly subsiding basin. They could be correlated with the benthic oxygen isotope curve and magnetic reversals. Shorter climatic
cycles are briefly mentioned in Sect. 7.8.5.
During the long history of the Earth, the periods of the
orbital parameters changed, particularly that ofthe obliquity,
which was shorter in the remote past than at present. For further details see, e. g., Berger et al. (1984), Berger and Loutre
(1991), Fischer (1991), Schwarzacher (1993), de Boer and
Smith (1994), Rouse (1995), Gale (1998).
When the Earth was in a greenhouse state, only lirnited
amounts of water could be stored as ice in polar and
high mountain regions or as continental water in lakes
and as groundwater. However, the presence of cyclic
sediments in the Mesozoic, for example, indicates that
the astronornical parameters also operated some hundred million ofyears ago and induced rninor sea-level
and/or climatic changes.
Numerous examples of this cyclicity have been described
(e.g. Fischer 1991; Einseie and Ricken 1991; Rouse and
Gale 1995; and many others). The amplitude ofthese highfrequency sea-Ievel changes was small (some meters up to
maybe 20 m). The astronomical time scales ofthe Mesozoic
and older eras are "floating", i.e. the beginning and end of
these scales is not exactly known (Sect. 7.9.8).
In any case, the very precise astronomical time scales will
allow, in favorable cases, determination ofthe precise periods oflonger cycles. Numerical techniques, such as time series analyses, power spectra, and other experiments can help
to identify cycle periods and to better understand the processes involved (e.g. Schwarzacher 1993; Berger 1997).
7.9.3 Rhythmic (Cyclic) Bedding
Cyclic vs. Discyclic Bedding
Rhythmic bedding can be produced by two entirely
different processes:
(1) Cyclic bedding is caused by slow, gradual variations in primary sediment composition and sedimentation rates (Fig. 7.38a). These lead to a vertical sediment buildup that changes smoothly with time and is
361
characteristic for various sediment types, particularly
for calcareous and siliceous deposits. However, a
small variation in the prirnary composition, texture, or
fabric rnay be sufficient to promote a secondary differentiation into beds and interbeds accentuated by
diagenetic overprint (cf. Sect. 7.1.8). The intensity of
burrow mottling is continuous in succeeding beds.
(2) Discyclic bedding results from repeated episodic
phenomena (e.g. storrns, turbidity currents, river
floods, volcanic eruptions) and shows a very irregular
sediment buildup-time curve (Fig. 7.38b). Slow, but
more or less continuous vertical accumulation of finegrained background sediment is interrupted irregularly
by depositional (and partly erosional) events (cf. Sects.
2.2,3.1 and 5.4; Einsele et al. 1991; Einseie 1998).
Large events can wipe out the record of earlier, smaller
ones including part oftheir host sediment. As a result,
one event bed may directly follow an earlier event bed,
the top ofwhich is truncated (amalgamation). The sedimentation rates change abruptly and bioturbated surface layers of the background sediment are episodically truncated. The event bed is recolonized by specially adapted fauna burrowing from the new surface
downward. Lithographie limestones represent a specific type of discyclic bedding (Sect. 7.9.6).
The most prominent examples of cyclic bedding in the
marine environment are (cf. Sect. 5.3.7):
- Hernipelagic to pelagic limestone (or chalk)-rnarl
alternations.
- Black shale-carbonate rhythms (redox cycles).
- Pelagic banded cherts.
Anoxie intervals may modify the successions of alternating beds and their biological record. Sometimes
combinations ofboth cyclic and discyclic bedding can
be observed. Some limestone-marl sequences (see below) and strata bearing black shales, phosphorites, or
varved siliceous oozes, show both gradual cyclic variations and episodic bedding types.
Limestone-Marl Alternations
Typical deep-sea pelagic limestone-marl alternations
appeared in the geological re cord from the Upper Jurassie with the onset of substantial planktonic carbonate production. In the Paleozoic, fine-grained well-bedded or nodular limestones mainly accumulated on
shelves, upper slopes, and in shallow epicontinental
seas. Paleozoic limestones of deeper basins often consist of pellets.
To generate limestone-rnarl couplets, the rate of
(mainly planktonic) carbonate production must have
been three to four times higher than terrigenous silt
and clay input (Einsele and Ricken 1991; for more details see Ricken 1994). In shallow basins, rhythrnic
traced back from the Present into the past 5 to 6 Ma (Lourens
et al. 1996).
During the past 600 to 800 ka, the 100 ka period was
dominant (Milankovitch chron) generating high-amplitude
sea-Ievel changes and rapid ice melting events ("terminations ", Berger 1997), but in the earlier Quatemary and Pliocene the 41 ka period (Laplace chron) mainly controlled the
climatic variation with high-frequency sea-Ievel changes of
lower amplitude (Fig. 7.37e; Tiedemann et al. 1994).
Changes in aridity of North Africa (Sahel zone), however,
record precession cycles (19-23 ka) in the early to middle
Pliocene.
In an excellent record of emerged late Pliocene shallowmarine cyclic sediments of New Zealand, the 41 ka period
also predominates over the 100 ka (Naish 1997). The cycles
or cyclothems consist of clastic material, are about 50 m in
thickness, and formed in a subduction-related, rapidly subsiding basin. They could be correlated with the benthic oxygen isotope curve and magnetic reversals. Shorter climatic
cycles are briefly mentioned in Sect. 7.8.5.
During the long history of the Earth, the periods of the
orbital parameters changed, particularly that ofthe obliquity,
which was shorter in the remote past than at present. For further details see, e. g., Berger et al. (1984), Berger and Loutre
(1991), Fischer (1991), Schwarzacher (1993), de Boer and
Smith (1994), Rouse (1995), Gale (1998).
When the Earth was in a greenhouse state, only lirnited
amounts of water could be stored as ice in polar and
high mountain regions or as continental water in lakes
and as groundwater. However, the presence of cyclic
sediments in the Mesozoic, for example, indicates that
the astronornical parameters also operated some hundred million ofyears ago and induced rninor sea-level
and/or climatic changes.
Numerous examples of this cyclicity have been described
(e.g. Fischer 1991; Einseie and Ricken 1991; Rouse and
Gale 1995; and many others). The amplitude ofthese highfrequency sea-Ievel changes was small (some meters up to
maybe 20 m). The astronomical time scales ofthe Mesozoic
and older eras are "floating", i.e. the beginning and end of
these scales is not exactly known (Sect. 7.9.8).
In any case, the very precise astronomical time scales will
allow, in favorable cases, determination ofthe precise periods oflonger cycles. Numerical techniques, such as time series analyses, power spectra, and other experiments can help
to identify cycle periods and to better understand the processes involved (e.g. Schwarzacher 1993; Berger 1997).
7.9.3 Rhythmic (Cyclic) Bedding
Cyclic vs. Discyclic Bedding
Rhythmic bedding can be produced by two entirely
different processes:
(1) Cyclic bedding is caused by slow, gradual variations in primary sediment composition and sedimentation rates (Fig. 7.38a). These lead to a vertical sediment buildup that changes smoothly with time and is
361
characteristic for various sediment types, particularly
for calcareous and siliceous deposits. However, a
small variation in the prirnary composition, texture, or
fabric rnay be sufficient to promote a secondary differentiation into beds and interbeds accentuated by
diagenetic overprint (cf. Sect. 7.1.8). The intensity of
burrow mottling is continuous in succeeding beds.
(2) Discyclic bedding results from repeated episodic
phenomena (e.g. storrns, turbidity currents, river
floods, volcanic eruptions) and shows a very irregular
sediment buildup-time curve (Fig. 7.38b). Slow, but
more or less continuous vertical accumulation of finegrained background sediment is interrupted irregularly
by depositional (and partly erosional) events (cf. Sects.
2.2,3.1 and 5.4; Einsele et al. 1991; Einseie 1998).
Large events can wipe out the record of earlier, smaller
ones including part oftheir host sediment. As a result,
one event bed may directly follow an earlier event bed,
the top ofwhich is truncated (amalgamation). The sedimentation rates change abruptly and bioturbated surface layers of the background sediment are episodically truncated. The event bed is recolonized by specially adapted fauna burrowing from the new surface
downward. Lithographie limestones represent a specific type of discyclic bedding (Sect. 7.9.6).
The most prominent examples of cyclic bedding in the
marine environment are (cf. Sect. 5.3.7):
- Hernipelagic to pelagic limestone (or chalk)-rnarl
alternations.
- Black shale-carbonate rhythms (redox cycles).
- Pelagic banded cherts.
Anoxie intervals may modify the successions of alternating beds and their biological record. Sometimes
combinations ofboth cyclic and discyclic bedding can
be observed. Some limestone-marl sequences (see below) and strata bearing black shales, phosphorites, or
varved siliceous oozes, show both gradual cyclic variations and episodic bedding types.
Limestone-Marl Alternations
Typical deep-sea pelagic limestone-marl alternations
appeared in the geological re cord from the Upper Jurassie with the onset of substantial planktonic carbonate production. In the Paleozoic, fine-grained well-bedded or nodular limestones mainly accumulated on
shelves, upper slopes, and in shallow epicontinental
seas. Paleozoic limestones of deeper basins often consist of pellets.
To generate limestone-rnarl couplets, the rate of
(mainly planktonic) carbonate production must have
been three to four times higher than terrigenous silt
and clay input (Einsele and Ricken 1991; for more details see Ricken 1994). In shallow basins, rhythrnic