536
These and many other minor facies assoeiations described in Part 11 are particularly useful for the identification of depositional environments.
Lateral Facies Associations
Successions similar to those mentioned above also
occur as lateral facies associations:
- Alluvial fan - braidplain - (playa) lake ± eolian
sands (cf. Figs. 2.8 and 2.32).
- Alluvial plain - tidal flats (lagoon) - shallow marine - deeper marine.
- Alluvial plain (red beds, eolian sands) - coastal
sabkha - lagoonal carbonates and evaporites - reef -
forereef - carbonate slope - slope apron (partially
shown in Fig. 6.8e).
- Clastic shelf - slope and slope channels deep-sea
fan- basin plain
(cf. Fig. 5.18).
- Mid-oceanic ridge - deep-sea pelagic and
hemipelagic environments (below and above CCD)deep-sea trench - accretionary wedge with slope basins. (Sect. 12.5, Fig. 12.19).
Proximal-distal trends in relation to the sediment
souree also lead to distinct lateral facies associations,
for example:
- Slope channel deposits - upper and lower deep-sea
fan - overbank deposits - basin plain, displaying
channel, proximal and distal turbidites (Sect. 5.4.2,
Fig.5.18).
- Lava flows - pyroclastic flows and ignimbrites -
ash falls with decreasing grain size - fluvial-transported tephra - ash turbidites in lakes and in the deep
sea (Sect. 2.4.2, Fig. 2.24).
- Relatively coarse fluvial sand - fine eolian sand -
eolian dust (loess, Fig. 2.1).
Further examples of facies aSSOCIatlOns in various
tectonically defined basin types are described in
Chapter 12.
11.7 Preservation and Recycling
of Older Sediments
11.7.1 Tbe Survival Rate of Sediment
A general, global problem is the preservation and
recycling of sediments in the geological record. Due
to uplift and erosion as weIl as subduction at convergent plate boundaries, only part of the ancient sediments still exists. Old mountain ranges, such as the
Caledonian and Hercynian fold-thrust belts, are
Chapter 11 Sediment Supply, Subsidence, and Basin Fill
largely stripped of their sedimentary cover and exhibit their "roots" at the present land surface. By contrast, pre- and synorogenic sediments of younger
orogenic belts are still in the process of being rapidly
eroded. Considering the state of erosion of presentday mountain ranges, we observe that, for example in
the Himalayas, Paleozoic metamorphic and nonmetamorphic rocks as weIl as Mesozoic and some
Tertiary sediments are presently exposed to coeval
weathering and denudation. In the Alps, Triassic to
Cretaceous sediments as weIl as older metamorphic
rocks of the central crystalline zones are widely subjected to present-day erosion, but some Tertiary sediments also contribute to the modem sediment yield
of this region.
These examples and the fact that mountain ranges
have sediment yields about two orders of magnitude
greater than lowlands demonstrate that modem sediments are derived from rocks of a wide range in age.
Their terrestrial proportion mainly consists of recycled older sediments including metamorphic rocks.
One can define a kind of mean residence time of sedimentary rocks, i.e. the time span between their formation and erosion. Similarly, the "half-life" (' "&"50) of
sediments of a certain time period can be determined
which is the time after which 50% of the initial sediment volume has been eroded (Fig. 11.33a).
A rough estimate for the sediments of Alpine orogenie
belts renders a mean residenee time on the order of 200 to
300 Ma. Immature orogenie belts exhibit a sediment halflife of 78 Ma, mature orogenie belts with exhumed "roots"
one of -350 Ma (Veizer et al. 1989). Aetive margin basins
tend to be rapidly destroyed ('50 = 25 Ma), whereas the
sediments of passive margins live longer ('so = 75 Ma).
Sediments on eontinental platforms reaeh a half-live of
-350 Ma. For the post-Devonian time, the average half-life
of all types of sediment was found to be 130 Ma (Gregor
1985). For all ages ofsediment, including the Preeambrian,
the half-life is longer. Total sediment produetion for the
last 3000 Ma is estimated to have been about 5 to 6 times
the mass· of the presently existing sediment. The average
sediment yield of the Phanerozoie was probably in the order of7 to 10 x 10 9 tlyear (Gregor 1985; Tardy et al. 1989;
see also Wold and Hay 1990).
To define the remaining sedimentary mass of an
older time period, the term "survival rate" was proposed (e.g. Gregor 1985). This is the present-day
surviving mass (or volume) of sedimentary rocks of a
given time span per unit time of deposition (e.g.
tonsIMa). The volume of sediments preserved from a
certain time period, including some metamorphosed
material, generally decreases with their age. For the
Phanerozoic this decline in sediment mass can be
approximated by an exponential curve (Fig.
11.34a,b). However, the masses of preserved Precambrian rocks are greater than predicted by this
rule, because they are predominantly cratonic. Even
in the Phanerozoic, there are many deviations from
These and many other minor facies assoeiations described in Part 11 are particularly useful for the identification of depositional environments.
Lateral Facies Associations
Successions similar to those mentioned above also
occur as lateral facies associations:
- Alluvial fan - braidplain - (playa) lake ± eolian
sands (cf. Figs. 2.8 and 2.32).
- Alluvial plain - tidal flats (lagoon) - shallow marine - deeper marine.
- Alluvial plain (red beds, eolian sands) - coastal
sabkha - lagoonal carbonates and evaporites - reef -
forereef - carbonate slope - slope apron (partially
shown in Fig. 6.8e).
- Clastic shelf - slope and slope channels deep-sea
fan- basin plain
(cf. Fig. 5.18).
- Mid-oceanic ridge - deep-sea pelagic and
hemipelagic environments (below and above CCD)deep-sea trench - accretionary wedge with slope basins. (Sect. 12.5, Fig. 12.19).
Proximal-distal trends in relation to the sediment
souree also lead to distinct lateral facies associations,
for example:
- Slope channel deposits - upper and lower deep-sea
fan - overbank deposits - basin plain, displaying
channel, proximal and distal turbidites (Sect. 5.4.2,
Fig.5.18).
- Lava flows - pyroclastic flows and ignimbrites -
ash falls with decreasing grain size - fluvial-transported tephra - ash turbidites in lakes and in the deep
sea (Sect. 2.4.2, Fig. 2.24).
- Relatively coarse fluvial sand - fine eolian sand -
eolian dust (loess, Fig. 2.1).
Further examples of facies aSSOCIatlOns in various
tectonically defined basin types are described in
Chapter 12.
11.7 Preservation and Recycling
of Older Sediments
11.7.1 Tbe Survival Rate of Sediment
A general, global problem is the preservation and
recycling of sediments in the geological record. Due
to uplift and erosion as weIl as subduction at convergent plate boundaries, only part of the ancient sediments still exists. Old mountain ranges, such as the
Caledonian and Hercynian fold-thrust belts, are
Chapter 11 Sediment Supply, Subsidence, and Basin Fill
largely stripped of their sedimentary cover and exhibit their "roots" at the present land surface. By contrast, pre- and synorogenic sediments of younger
orogenic belts are still in the process of being rapidly
eroded. Considering the state of erosion of presentday mountain ranges, we observe that, for example in
the Himalayas, Paleozoic metamorphic and nonmetamorphic rocks as weIl as Mesozoic and some
Tertiary sediments are presently exposed to coeval
weathering and denudation. In the Alps, Triassic to
Cretaceous sediments as weIl as older metamorphic
rocks of the central crystalline zones are widely subjected to present-day erosion, but some Tertiary sediments also contribute to the modem sediment yield
of this region.
These examples and the fact that mountain ranges
have sediment yields about two orders of magnitude
greater than lowlands demonstrate that modem sediments are derived from rocks of a wide range in age.
Their terrestrial proportion mainly consists of recycled older sediments including metamorphic rocks.
One can define a kind of mean residence time of sedimentary rocks, i.e. the time span between their formation and erosion. Similarly, the "half-life" (' "&"50) of
sediments of a certain time period can be determined
which is the time after which 50% of the initial sediment volume has been eroded (Fig. 11.33a).
A rough estimate for the sediments of Alpine orogenie
belts renders a mean residenee time on the order of 200 to
300 Ma. Immature orogenie belts exhibit a sediment halflife of 78 Ma, mature orogenie belts with exhumed "roots"
one of -350 Ma (Veizer et al. 1989). Aetive margin basins
tend to be rapidly destroyed ('50 = 25 Ma), whereas the
sediments of passive margins live longer ('so = 75 Ma).
Sediments on eontinental platforms reaeh a half-live of
-350 Ma. For the post-Devonian time, the average half-life
of all types of sediment was found to be 130 Ma (Gregor
1985). For all ages ofsediment, including the Preeambrian,
the half-life is longer. Total sediment produetion for the
last 3000 Ma is estimated to have been about 5 to 6 times
the mass· of the presently existing sediment. The average
sediment yield of the Phanerozoie was probably in the order of7 to 10 x 10 9 tlyear (Gregor 1985; Tardy et al. 1989;
see also Wold and Hay 1990).
To define the remaining sedimentary mass of an
older time period, the term "survival rate" was proposed (e.g. Gregor 1985). This is the present-day
surviving mass (or volume) of sedimentary rocks of a
given time span per unit time of deposition (e.g.
tonsIMa). The volume of sediments preserved from a
certain time period, including some metamorphosed
material, generally decreases with their age. For the
Phanerozoic this decline in sediment mass can be
approximated by an exponential curve (Fig.
11.34a,b). However, the masses of preserved Precambrian rocks are greater than predicted by this
rule, because they are predominantly cratonic. Even
in the Phanerozoic, there are many deviations from