14
Marine deltas represent a transitional, highly variable depositional environment between continental
and marine conditions (Fig. 1.8a). The subaerial part
of such a delta is controlled by fluvial and possibly
lacustrine processes, whereas its coastal and subaqueous regions are dominated by the hydrodynamic and
chemical properties of the sea. Large terrigenous sediment supply causes prograding of the deltaic complex
toward the sea; high sedimentation rates and subsidence enhanced by the sediment load enable the formation of thick, widely extended deltaic sequences.
Marine delta complexes provide a particularly good
example of depositional environments which are controlled predominantly by various exogenic factors
(Sect. 3.4).
Acijacent sea basins and epicontinental seas are
connected with the open sea and therefore exchange
water with the ocean (Fig. l.7c and d). The extent of
this water exchange and thus the salinity of the basin
water strongly depend on the width and depth of the
opening to the ocean. In humid regions, adjacent basins with a limited opening tend to develop brackish
conditions, while arid basins frequently become more
saline than normal sea water (Sect. 4.2). Adjacent basins and epicontinental seas on continental crust are
commonly shallow, but basins on oceanic or mixed
crust mayaiso be deep. The shapes of these basins
largely vary; some of them show symmetric or asymmetric cross sections; some represent basins subdivided by shallow swells into several subbasins (segmented basins). In the latter case, markedly differing
depositional subenvironments have to be taken into
account. Most of these adjacent basins are strongly
influenced by the climate and relief of the peri-basin
land regions (cf. Fig. 1. 7b), which control the influx of
terrigenous material from local andlor distal sources.
In summary, adjacent basins may exhibit a particularly
great variety of sedimentary facies (Sect. 4.3).
The sediments of shallow seas and continental
shelves (Fig. 1.8b) are also considerably affected by
processes operating in neighboring land regions. These
generally provide sufficient material to keep these basins shallow. Strong waves, surface and bottom currents usually tend to distribute the local influx of
terrigenous sediment over large areas. Especially in
shallow water, high-energy conditions prevent the deposition of fine-grained materials, partially including
sands. Therefore, such environments often pers ist over
long time periods without being filled up to sea level
(Fig. l.6). This is also true for widely extended
shallow-marine basins, as long as excess sediment volurne (in relation to space provided by subsidence) can
be stored in special depressions (Fig. 1.8b and d) or be
swept into a neighboring deeper ocean basin. The margin of such basins is commonly characterized by a
kind of ramp morphology.
Deeper marine basins are usually bordered by a
shelf zone of varying width followed by a wide and
normally gentle slope (continental slope, Fig. l.8c).
Chapter 1 Basin Classification
The foot of the slope in deep water (continental rise) is
still gently inclined basinward; it is built up to a large
extent by redeposited material derived directly from the
slope (slope apron) or by sediments funnelled by submarine valleys and canyons into the deep sea (deep-sea
fans). The terms continental slope and continental rise
are commonly used to describe corresponding features
of the present-day passive, Atlantic-type continental
margins. These terms, however, imply a plate-tectonic
interpretation. Deep-sea basins or basin plains are the
deepest parts of marine environments except deep-sea
trenches and some other special features associated
with the behavior of oceanic crust (see below).
Large volumes of terrigenous material can be co llected by the troughs in a submarine horst and graben
topography bordering the continent (Fig. l.8e). Similady, deep-sea trenches at the foot of relatively steep
slopes and slope basins are sites of preferential sediment accumulation (Fig. l.8g). Thick, ancient flysch
sequences are mostly interpreted as depositions in such
basins. Less important sediment accumulation systems
are small basins ("ponds"), which occur along oceanic
ridges, and infillings of narrow troughs due to fracturing ofthe oceanic crust (Fig. l.8f).
The thin, frequently incomplete sedimentary records
on the tops of submarine ridges, platforms, and
seamounts (Fig. J.8j) strongly contrast with all other
marine sediments. These deposits are mostly biogenic,
chemically or biochemically precipitated and usually
contain only very small proportions of terrigenous or
volcanoclastic materials. Although such lirnited sediment accumulations can hardly be referred to as basin
fills, they do constitute an important and diagnostically
significant part of larger marine depositional environments.
The direct influence of tectonic basin evolution on
sedimentary facies is only evident in areas, where tectonic movements are rapid and nonuniform, such as at
the basin margins, or where sediment accumulation
lags far behind subsidence faulting, or thrusting. This
situation is common in continental riß and pull-apart
basins during their early stages of evolution, in
subduction-related settings, in renmant and foreland
basins, and in deep marine environments along oceanic
ridges or trans form faults far away from large land
masses. These problems are further discussed in Chapter 12.
1.4.5 Some General Trends for Sediment
Accumulation and Facies
From the previous discussion one can draw some general, straightforward rules for the sediment accumulation and facies in various depositional environments:
- The influence of terrigenous sediment sources on
basin fillings decreases in the following order: high-
Marine deltas represent a transitional, highly variable depositional environment between continental
and marine conditions (Fig. 1.8a). The subaerial part
of such a delta is controlled by fluvial and possibly
lacustrine processes, whereas its coastal and subaqueous regions are dominated by the hydrodynamic and
chemical properties of the sea. Large terrigenous sediment supply causes prograding of the deltaic complex
toward the sea; high sedimentation rates and subsidence enhanced by the sediment load enable the formation of thick, widely extended deltaic sequences.
Marine delta complexes provide a particularly good
example of depositional environments which are controlled predominantly by various exogenic factors
(Sect. 3.4).
Acijacent sea basins and epicontinental seas are
connected with the open sea and therefore exchange
water with the ocean (Fig. l.7c and d). The extent of
this water exchange and thus the salinity of the basin
water strongly depend on the width and depth of the
opening to the ocean. In humid regions, adjacent basins with a limited opening tend to develop brackish
conditions, while arid basins frequently become more
saline than normal sea water (Sect. 4.2). Adjacent basins and epicontinental seas on continental crust are
commonly shallow, but basins on oceanic or mixed
crust mayaiso be deep. The shapes of these basins
largely vary; some of them show symmetric or asymmetric cross sections; some represent basins subdivided by shallow swells into several subbasins (segmented basins). In the latter case, markedly differing
depositional subenvironments have to be taken into
account. Most of these adjacent basins are strongly
influenced by the climate and relief of the peri-basin
land regions (cf. Fig. 1. 7b), which control the influx of
terrigenous material from local andlor distal sources.
In summary, adjacent basins may exhibit a particularly
great variety of sedimentary facies (Sect. 4.3).
The sediments of shallow seas and continental
shelves (Fig. 1.8b) are also considerably affected by
processes operating in neighboring land regions. These
generally provide sufficient material to keep these basins shallow. Strong waves, surface and bottom currents usually tend to distribute the local influx of
terrigenous sediment over large areas. Especially in
shallow water, high-energy conditions prevent the deposition of fine-grained materials, partially including
sands. Therefore, such environments often pers ist over
long time periods without being filled up to sea level
(Fig. l.6). This is also true for widely extended
shallow-marine basins, as long as excess sediment volurne (in relation to space provided by subsidence) can
be stored in special depressions (Fig. 1.8b and d) or be
swept into a neighboring deeper ocean basin. The margin of such basins is commonly characterized by a
kind of ramp morphology.
Deeper marine basins are usually bordered by a
shelf zone of varying width followed by a wide and
normally gentle slope (continental slope, Fig. l.8c).
Chapter 1 Basin Classification
The foot of the slope in deep water (continental rise) is
still gently inclined basinward; it is built up to a large
extent by redeposited material derived directly from the
slope (slope apron) or by sediments funnelled by submarine valleys and canyons into the deep sea (deep-sea
fans). The terms continental slope and continental rise
are commonly used to describe corresponding features
of the present-day passive, Atlantic-type continental
margins. These terms, however, imply a plate-tectonic
interpretation. Deep-sea basins or basin plains are the
deepest parts of marine environments except deep-sea
trenches and some other special features associated
with the behavior of oceanic crust (see below).
Large volumes of terrigenous material can be co llected by the troughs in a submarine horst and graben
topography bordering the continent (Fig. l.8e). Similady, deep-sea trenches at the foot of relatively steep
slopes and slope basins are sites of preferential sediment accumulation (Fig. l.8g). Thick, ancient flysch
sequences are mostly interpreted as depositions in such
basins. Less important sediment accumulation systems
are small basins ("ponds"), which occur along oceanic
ridges, and infillings of narrow troughs due to fracturing ofthe oceanic crust (Fig. l.8f).
The thin, frequently incomplete sedimentary records
on the tops of submarine ridges, platforms, and
seamounts (Fig. J.8j) strongly contrast with all other
marine sediments. These deposits are mostly biogenic,
chemically or biochemically precipitated and usually
contain only very small proportions of terrigenous or
volcanoclastic materials. Although such lirnited sediment accumulations can hardly be referred to as basin
fills, they do constitute an important and diagnostically
significant part of larger marine depositional environments.
The direct influence of tectonic basin evolution on
sedimentary facies is only evident in areas, where tectonic movements are rapid and nonuniform, such as at
the basin margins, or where sediment accumulation
lags far behind subsidence faulting, or thrusting. This
situation is common in continental riß and pull-apart
basins during their early stages of evolution, in
subduction-related settings, in renmant and foreland
basins, and in deep marine environments along oceanic
ridges or trans form faults far away from large land
masses. These problems are further discussed in Chapter 12.
1.4.5 Some General Trends for Sediment
Accumulation and Facies
From the previous discussion one can draw some general, straightforward rules for the sediment accumulation and facies in various depositional environments:
- The influence of terrigenous sediment sources on
basin fillings decreases in the following order: high-