354
Chapter 7 Sequences, Minor Cycles, and Event Stratigraphy
transgressive and highstand systems tracts of marine
systems. Relative sea or lake-level fall is commonly
poorly recorded because the previous groundwater
highstand tends to be preserved by the onset of cementation preventing the sand grains from being eroded.
Inland dune fields (Fig. 7.34c) and their groundwater
table develop independently from the sea. Here, the
deflation surfaces mainly record tectonic movements
and/or elimate change.
Apart from deflation (Stokes) surfaces, eolian sands
often contain thin intercalations of fluvial and sabkha
sediments. Sabkha deposits (either sandy or
evaporitic), in particular, signal the former presence of
groundwater elose to the paleo-surface because they
get most of their salts from evaporating groundwater.
In a sediment buildup/time plot (Fig. 7.34a), these thin
strata normally represent more time than the episodes
of rapid sand buildup and deflation.
The Pennian of central and northwestern Europe is represented by continental sediments, including eolian dunes,
deposited in a more or less arid time. The relief of the
depositional area was probably low and comprised some
large and a number of smaller depressions occupied by
sabkhas or saline lakes. Depositional sequences are largely
controlled by climate change and cannot be explained by the
"classical" concept ofsequence stratigraphy (R. Gaupp, pers.
comrnunication; and Gaupp et al. 1993; Turner and Smith
1997). Lake level tluctuations may have been too rapid to
generate significant shifts of the facies belts. It appears that
lower frequency change from more humid to arid conditions
caused the abrupt replacement oftluvial and lake/sabkha sediments byeolian dunes and vice versa (cf. Sect. 7.7.1, Rogers
and Astin 1991). During times of increasing aridity, the river
beds and the lakes largely fell dry. As a result, the groundwater table was lowered and sand was blown out from tluvial
deposits generatingsanddunes (Fig. 7.34d). Some ephemeral
rivers may have cut deeper wadis. Later, increasing humidity
caused the lake level and groundwater table to rise up to a
"maximum tlooding surface", fixing the base of the sand
dunes and allowing the establishment of inland sabkhas at
higher elevations than the lake.
The sequence stratigraphie model of Fig. 7.34d, as proposed by Yang and Nio (1993) for the Upper Rotliegend (underlying the Zechstein evaporites in the Netherlands offshore), has been modified according to this interpretation.
7.7.4 Summary (Sequences ofLakes, Fluvial and Eolian systems)
Base-level changes of lakes, fluvial and eolian
systems follow other rules than those of the
ocean.
Closed lakes show irregular high-frequency and
often also very high-amplitude lake level
fluctions which are mainly controlled by elimate
change. Their silicielastic sediments respond to
these changes partly in a similar way as marine
sediments.
- The base-level of fluvial systems is given by the
regional water table (e.g. lake levels) or defined
by their stream equilibrium profile. Deviations
from this profile, caused by tectonic. movements
or varying sediment supply, lead to ehanges in
the staeking patterns of fluvial channels. A
7.8 Hierarchy of Sedimentary Cycles,
Their Superposition and Causes
7.8.1 General Aspects
The principal types of stratigraphie cyeles are summarized in Figure 7.35. The eyeles are listed in the order
of decreasing time period, lateral extent and (indirect1y) thiekness. Beeause eyeles of higher frequency
are superimposed on those oflower frequeney, a kind
of cycle hierarchy has been established.
The long-term cyeles of the Ist and 2nd order are
eaused either by global plate teetonics or more regional
steepening river gradient causes prograding of
coarse-grained fluvial faeies and partly valley
cutting. Either erosional surfaces and paleosols
or the turnover from increasing to decreasing
accommodation space ("maximum flooding
surface", e.g. represented by lakes or playas in
the basin center) can be used as sequence
boundaries. Decreasing accommodation space
favors lateral stacking of channel fills.
Sequences in eolian systems are bounded by
irregular non-depositional surfaces, deflation
surfaces, or wet-damp eolian intercalations (e.g.
playas). These reflect the groundwater table
which is mainly controlled by elirnate change
and subsidence.
teetonic motions (rifting, subduetion, magrnatism,
mountain building, etc.) affecting the volume of the
oeean basins. The 4th and higher order cyeles are aseribed to the buildup and melting of eontinental iee,
i.e. the change in oeeanie water volume. The meehanism responsible for the common 3rd order eyeles is
not so elear; in this case several meehanisms may be
involved (see Seet. 7.8.4).
Long-term cyelie phenomena had a profound impaet
on the evolution of the oeean basins, elirnate, nature
and distribution of sediments, as well as the evolution
of life. They can be reeonstrueted only by the study of
the geological history of large areas (eontinents) and
long-distanee eorrelation. What we norrnally observe
Chapter 7 Sequences, Minor Cycles, and Event Stratigraphy
transgressive and highstand systems tracts of marine
systems. Relative sea or lake-level fall is commonly
poorly recorded because the previous groundwater
highstand tends to be preserved by the onset of cementation preventing the sand grains from being eroded.
Inland dune fields (Fig. 7.34c) and their groundwater
table develop independently from the sea. Here, the
deflation surfaces mainly record tectonic movements
and/or elimate change.
Apart from deflation (Stokes) surfaces, eolian sands
often contain thin intercalations of fluvial and sabkha
sediments. Sabkha deposits (either sandy or
evaporitic), in particular, signal the former presence of
groundwater elose to the paleo-surface because they
get most of their salts from evaporating groundwater.
In a sediment buildup/time plot (Fig. 7.34a), these thin
strata normally represent more time than the episodes
of rapid sand buildup and deflation.
The Pennian of central and northwestern Europe is represented by continental sediments, including eolian dunes,
deposited in a more or less arid time. The relief of the
depositional area was probably low and comprised some
large and a number of smaller depressions occupied by
sabkhas or saline lakes. Depositional sequences are largely
controlled by climate change and cannot be explained by the
"classical" concept ofsequence stratigraphy (R. Gaupp, pers.
comrnunication; and Gaupp et al. 1993; Turner and Smith
1997). Lake level tluctuations may have been too rapid to
generate significant shifts of the facies belts. It appears that
lower frequency change from more humid to arid conditions
caused the abrupt replacement oftluvial and lake/sabkha sediments byeolian dunes and vice versa (cf. Sect. 7.7.1, Rogers
and Astin 1991). During times of increasing aridity, the river
beds and the lakes largely fell dry. As a result, the groundwater table was lowered and sand was blown out from tluvial
deposits generatingsanddunes (Fig. 7.34d). Some ephemeral
rivers may have cut deeper wadis. Later, increasing humidity
caused the lake level and groundwater table to rise up to a
"maximum tlooding surface", fixing the base of the sand
dunes and allowing the establishment of inland sabkhas at
higher elevations than the lake.
The sequence stratigraphie model of Fig. 7.34d, as proposed by Yang and Nio (1993) for the Upper Rotliegend (underlying the Zechstein evaporites in the Netherlands offshore), has been modified according to this interpretation.
7.7.4 Summary (Sequences ofLakes, Fluvial and Eolian systems)
Base-level changes of lakes, fluvial and eolian
systems follow other rules than those of the
ocean.
Closed lakes show irregular high-frequency and
often also very high-amplitude lake level
fluctions which are mainly controlled by elimate
change. Their silicielastic sediments respond to
these changes partly in a similar way as marine
sediments.
- The base-level of fluvial systems is given by the
regional water table (e.g. lake levels) or defined
by their stream equilibrium profile. Deviations
from this profile, caused by tectonic. movements
or varying sediment supply, lead to ehanges in
the staeking patterns of fluvial channels. A
7.8 Hierarchy of Sedimentary Cycles,
Their Superposition and Causes
7.8.1 General Aspects
The principal types of stratigraphie cyeles are summarized in Figure 7.35. The eyeles are listed in the order
of decreasing time period, lateral extent and (indirect1y) thiekness. Beeause eyeles of higher frequency
are superimposed on those oflower frequeney, a kind
of cycle hierarchy has been established.
The long-term cyeles of the Ist and 2nd order are
eaused either by global plate teetonics or more regional
steepening river gradient causes prograding of
coarse-grained fluvial faeies and partly valley
cutting. Either erosional surfaces and paleosols
or the turnover from increasing to decreasing
accommodation space ("maximum flooding
surface", e.g. represented by lakes or playas in
the basin center) can be used as sequence
boundaries. Decreasing accommodation space
favors lateral stacking of channel fills.
Sequences in eolian systems are bounded by
irregular non-depositional surfaces, deflation
surfaces, or wet-damp eolian intercalations (e.g.
playas). These reflect the groundwater table
which is mainly controlled by elirnate change
and subsidence.
teetonic motions (rifting, subduetion, magrnatism,
mountain building, etc.) affecting the volume of the
oeean basins. The 4th and higher order cyeles are aseribed to the buildup and melting of eontinental iee,
i.e. the change in oeeanie water volume. The meehanism responsible for the common 3rd order eyeles is
not so elear; in this case several meehanisms may be
involved (see Seet. 7.8.4).
Long-term cyelie phenomena had a profound impaet
on the evolution of the oeean basins, elirnate, nature
and distribution of sediments, as well as the evolution
of life. They can be reeonstrueted only by the study of
the geological history of large areas (eontinents) and
long-distanee eorrelation. What we norrnally observe