382
Chapter 7 Sequences, Minor Cycles, and Event Stratigraphy
laterally stacked channel systems. Lake sediments respond to (mostly irregular and nonsynchronous) lakelevel changes in a similar way as marine sediments do
to sea-level changes.
(10) The concepts and methods of cyelo- and eventstratigraphy are well established and relatively easy to
apply to field exposures and drilling cores. One has to
distinguish between cyelic (strictly periodic or quasiperiodic) and discyclic phenomena occurring at random time intervals.
- Peritidal minor carbonate cyeles and limestone-marl
successions, the latter deposited in "quiet" deeper waters (productivity, dilution, or dissolution cyeles),
mostly reflect orbital parameters (Milankovitch frequency band; about 20, 40, 100 and 400 ka). Discontinuities in shallow-water carbonate cyeles mayaiso indicate "missed beats". High-frequency coal cycles
(cyelothems) represent examples from silicic1astic environments in a humid elimate.
- Most of the discyelic depositional events (tempestites, turbidites, gravity mass flow deposits of limited
size) occur at time intervals shorter than the
Milankovitch frequencies. Some of them, such as ash
fall deposits, may be used as isochronous marker beds.
Large debris flows and floods on alluvial fans and
plains occur once in several hundreds to thousands of
years. Non-depositional event horizons, such as
paleosols, karstified surfaces, erosionallags, and various types of skeletal concentrations represent time intervals of different lengths and are normally
diachronous.
(11) The superposition of cyelic and discyc1ic (episodic) phenomena of various modes and scales sometimes creates complex successions of beds. However,
in many cases cyelo- and event-stratigraphy can be
used to refine stratigraphic correlations within thicker
sequences of longer duration (high resolution cyelic
and event stratigraphy, Kauffman et al. 1991). In sediments older than the Neogene, time scales based on
cyclostratigraphy are mostly "floating".
7.10.2 Uncertainties, Problems, and
Open Questions
(1) To what extent are sea-level changes throughout
the his tory of the Earth global, regional, or local phenomena? This question is still not sufficiently answered (e.g. Miall 1997). One of the reasons for the
ongoing debate is the problem of reliable accurate dating and long-distance correlation, in particular that of
3rd-order sequence cyeles. In this regard it is important
to note that not only glacio-eustasy, but also significant
tectonic and magmatic processes (tectono-eustasy),
affecting the volume of ocean basins, can produce coeval global sea-level changes. However, even for the
late Paleogene and Neogene, full agreement between
different "global" third-order sea-Ievel curves cannot
yet be established (e.g., between the Atlantic oxygen
isotope record of deep-water organisms and results of
sequence-stratigraphic studies of Australian shelf carbonates; McGowran et al. 1997).
(2) The number of 2nd order global sea-level changes
(period 3-50 Ma) is probably fairly well established,
but that ofthe 3rd order (0.5-3 Ma), related to certain
stratigraphic stages or epochs, seems to still be very
uncertain (cf. Fig. 7.48). The greatest frequency for a
given time span appears to occur in sedimentary sections which allow high stratigraphic resolution and
contain only short hiatuses. These correspond to specific marine depositional environments which are shallower than the deepest position of the storm-wave base
but not affected by subaerial erosion.
(3) In cyelostratigraphy, controlled by orbital parameters, it is often difficult to ascribe the sedimentary cyeles to a specific period ofthe Milankovitch frequency
band. Bundles of beds and time series analysis may
help to solve this problem. Studies in cyelostratigraphy
should be combined with those in sequence stratigraphy.
(4) The amplitudes ofglobal sea-leve1 changes are difficult to determine and are therefore mostly uncertain,
in particular those oflow-frequency changes which are
strongly affected by long-term regional tectonic subsidence or uplift. Acomparison of Jurassic and Cretaceous sea-Ievel curves derived either from passive continental margim; (the Haq et al. 1988 curve) or from
the relatively stable Russian craton demonstrates this
problem (Fig. 7.48; Sahagian et al. 1996). High-frequency sea-Ievel changes (4th and higher orders) offer
better possibilities of finding out the real eustatic amplitudes. However, one cannot expect worldwide identical amplitudes for the same oscillation. A wellknown example is the Holocene transgression, during
which the relative sea-Ievel changes varied enormously
between regions elose to or far away from the former
ice sheets (e.g. Lambeck 1993). A globally equal amplitude does not ex ist; it has to. be replaced by an
"equivalent" global amplitude. Further studies on ice
volume-controlled excursions of the oxygen isotope
ratios preserved in the shells of organisms may help to
solve this problem.
(5) The cause ofhigh-frequency sea-Ieve1 changes in a
non-glacial greenhouse state of the Earth is still not
clear. The buildup and melting of mountain glaciers, if
they existed, cannot explain sea-level fluctuations of
the order of 3-10 m (also see, e.g., Watts and Thorne
1984; Burton et al. 1987; Leinfelder and Seyfried
1993; Seibold and Berger 1996).
Chapter 7 Sequences, Minor Cycles, and Event Stratigraphy
laterally stacked channel systems. Lake sediments respond to (mostly irregular and nonsynchronous) lakelevel changes in a similar way as marine sediments do
to sea-level changes.
(10) The concepts and methods of cyelo- and eventstratigraphy are well established and relatively easy to
apply to field exposures and drilling cores. One has to
distinguish between cyelic (strictly periodic or quasiperiodic) and discyclic phenomena occurring at random time intervals.
- Peritidal minor carbonate cyeles and limestone-marl
successions, the latter deposited in "quiet" deeper waters (productivity, dilution, or dissolution cyeles),
mostly reflect orbital parameters (Milankovitch frequency band; about 20, 40, 100 and 400 ka). Discontinuities in shallow-water carbonate cyeles mayaiso indicate "missed beats". High-frequency coal cycles
(cyelothems) represent examples from silicic1astic environments in a humid elimate.
- Most of the discyelic depositional events (tempestites, turbidites, gravity mass flow deposits of limited
size) occur at time intervals shorter than the
Milankovitch frequencies. Some of them, such as ash
fall deposits, may be used as isochronous marker beds.
Large debris flows and floods on alluvial fans and
plains occur once in several hundreds to thousands of
years. Non-depositional event horizons, such as
paleosols, karstified surfaces, erosionallags, and various types of skeletal concentrations represent time intervals of different lengths and are normally
diachronous.
(11) The superposition of cyelic and discyc1ic (episodic) phenomena of various modes and scales sometimes creates complex successions of beds. However,
in many cases cyelo- and event-stratigraphy can be
used to refine stratigraphic correlations within thicker
sequences of longer duration (high resolution cyelic
and event stratigraphy, Kauffman et al. 1991). In sediments older than the Neogene, time scales based on
cyclostratigraphy are mostly "floating".
7.10.2 Uncertainties, Problems, and
Open Questions
(1) To what extent are sea-level changes throughout
the his tory of the Earth global, regional, or local phenomena? This question is still not sufficiently answered (e.g. Miall 1997). One of the reasons for the
ongoing debate is the problem of reliable accurate dating and long-distance correlation, in particular that of
3rd-order sequence cyeles. In this regard it is important
to note that not only glacio-eustasy, but also significant
tectonic and magmatic processes (tectono-eustasy),
affecting the volume of ocean basins, can produce coeval global sea-level changes. However, even for the
late Paleogene and Neogene, full agreement between
different "global" third-order sea-Ievel curves cannot
yet be established (e.g., between the Atlantic oxygen
isotope record of deep-water organisms and results of
sequence-stratigraphic studies of Australian shelf carbonates; McGowran et al. 1997).
(2) The number of 2nd order global sea-level changes
(period 3-50 Ma) is probably fairly well established,
but that ofthe 3rd order (0.5-3 Ma), related to certain
stratigraphic stages or epochs, seems to still be very
uncertain (cf. Fig. 7.48). The greatest frequency for a
given time span appears to occur in sedimentary sections which allow high stratigraphic resolution and
contain only short hiatuses. These correspond to specific marine depositional environments which are shallower than the deepest position of the storm-wave base
but not affected by subaerial erosion.
(3) In cyelostratigraphy, controlled by orbital parameters, it is often difficult to ascribe the sedimentary cyeles to a specific period ofthe Milankovitch frequency
band. Bundles of beds and time series analysis may
help to solve this problem. Studies in cyelostratigraphy
should be combined with those in sequence stratigraphy.
(4) The amplitudes ofglobal sea-leve1 changes are difficult to determine and are therefore mostly uncertain,
in particular those oflow-frequency changes which are
strongly affected by long-term regional tectonic subsidence or uplift. Acomparison of Jurassic and Cretaceous sea-Ievel curves derived either from passive continental margim; (the Haq et al. 1988 curve) or from
the relatively stable Russian craton demonstrates this
problem (Fig. 7.48; Sahagian et al. 1996). High-frequency sea-Ievel changes (4th and higher orders) offer
better possibilities of finding out the real eustatic amplitudes. However, one cannot expect worldwide identical amplitudes for the same oscillation. A wellknown example is the Holocene transgression, during
which the relative sea-Ievel changes varied enormously
between regions elose to or far away from the former
ice sheets (e.g. Lambeck 1993). A globally equal amplitude does not ex ist; it has to. be replaced by an
"equivalent" global amplitude. Further studies on ice
volume-controlled excursions of the oxygen isotope
ratios preserved in the shells of organisms may help to
solve this problem.
(5) The cause ofhigh-frequency sea-Ieve1 changes in a
non-glacial greenhouse state of the Earth is still not
clear. The buildup and melting of mountain glaciers, if
they existed, cannot explain sea-level fluctuations of
the order of 3-10 m (also see, e.g., Watts and Thorne
1984; Burton et al. 1987; Leinfelder and Seyfried
1993; Seibold and Berger 1996).