130
of the interaction of two tidal wave systems operating in
the Yellow Sea. Another set of tidal current ridges is present in the northem Part of the Yellow Sea (Bohai Sea; Liu
Zhenxia et al. 1998).
Bottom currents in between the sand accumulations
commonly erode longitudinal furrows which may
collect and store coarse lag deposits, if coarsegrained material is present in the underlying beds.
Different types of ripples and current lineations provide evidence of frequently active bottom currents.
Flat ribbons or patches of sand are common features
in rather deep water. Thus, vertical sections of such a
basin fill show again a very high proportion of sand
with a variety of sedimentary structures, some of
which are not very well known. They may indicate
bidirectional current orientation, although one current direction (either the ebb or the tlood current) is
usually dominant. The fine-grained river load or
muds produced in the basin itself are mainly deposited in areas which are protected from tidal and other
bottom currents or, in the case of shelf seas, they are
transported into deep water.
Low Terrigenous Input
The second series of models shown in Figure 3.21
represents examples with low input of terrigenous
mud and sand. These models are probably realized in
nature more frequently than those discussed above.
For obvious reasons, such basins also pers ist for longer time periods than basins receiving large
terrigenous infIux.
(5) Wave-dominated, mud input. The sedimentary fill
of a low-energy, wave-dominated basin with prevailing mud input (Fig. 3.2lf) resembles that in Fig.
3.20b, but the slower silicic1astic sedimentation rate
enables higher concentrations of biogenic constituents and more intense bioturbation. For that reason,
shell accumulations in the shoreface zone and,
subordinately, in offshore tempestites are more pronounced than in model Fig. 3.20b. The sediments of
the outer shelf may become marly, because they contain relatively high proportions ofbiogenic carbonate
of both benthic and planktonic origin. Mud
tempestites tend to become completely mixed with
host sediments and thus obliterated.
A further reduction of terrigenous input to an insignificant portion of the total sediment may lead to
sediments rich in biogenie components (Fig. 3.2lg).
In this case, a favorable c1imate and sea water sufficiently rich in nutrients is needed. The latter may be
provided by river water or by oceanic currents entering the shelf sea. As a result, the sediments of the
inner shelf can again display abundant shell layers
and bioc1astic sands and silts. Larger shells are comChapter 3 Coastal and Shallow Sea Sediments
monly crushed to small pieces by predatory organisms. On the outer shelf, the carbonate content may
become so high that marls and lime muds are deposited which later form marl-limestone sequences (cf.
Sect. 7.9). If the contribution of tiny skeletons of
planktonic organisms is high, the limestones resemble deep-water pelagic limes tones which may contain
some chert. Their shallow-water origin can be inferred from alternations with other sediment types.
Bioturbation is again very intense in this environment, thus diminishing the preservation potential of
tempestites.
(6) An alternative of this model is an environment
with an oxygen minimum zone in bottom waters of
the outer shelf or in special depressions of
epicontinental seas. Such a situation may be caused
by upwelling waters rich in nutrients (cf. Sect. 5.3.4)
or by restricted water circulation. The resulting sediments are laminated bituminous c1ays and marls
which may contain some limestone beds and chert
layers. Bioturbation is limited to certain horizons or
completely missing.
(7) Storm- and tide-dominated seas. The model in
Fig. 3.2lh characterizes high-energy conditions
(storrns and tides) with low input of sand and mud.
Coastal pro gradation is limited and the slope of the
beach-shelf profile becomes rather gentle. In contrast
to the model in Fig. 3.20d, shell beds and finer
grained biogenic components may become significant contributors to the total sediment. Repeated reworking due to storm action leads to pronounced
amalgamation in the shoreface-offshore transitional
zone and to other erosional surfaces with lag deposits
and condensed beds in deeper water. Beds already
buried and somewhat indurated may become re-exposed to current action and colonized by faunal assemblages needing firm or hard grounds.
(8) Shelf seas affected by oceanic bottom currents.
The last model (Fig. 3.2li) deals with shelf seas
which are strongly intluenced by oceanic currents
entering the shelf and preventing the deposition of
fine-grained material in these regions (e.g.,
Flemming 1980). In the shoreface zone, the
depositional processes resemble those described for
models Fig. 2lf and g, but at a greater depth strong
and repeated reworking inc1uding mixing of older
and younger sands is common. Gravel may be concentrated in lag deposits, and vertical sections are
characterized by many erosional surfaces. If the
mean sedimentation rate becomes very low inc1uding
periods of non-deposition, glauconitic minerals may
form at the sedimentlwater interface (cf. Sect. 6.1).
Under special conditions, phosphorite nodules can
grow. Bottom life may differ from the previous examples, and the intensity of bioturbation tends to
change considerably from bed to bed.
of the interaction of two tidal wave systems operating in
the Yellow Sea. Another set of tidal current ridges is present in the northem Part of the Yellow Sea (Bohai Sea; Liu
Zhenxia et al. 1998).
Bottom currents in between the sand accumulations
commonly erode longitudinal furrows which may
collect and store coarse lag deposits, if coarsegrained material is present in the underlying beds.
Different types of ripples and current lineations provide evidence of frequently active bottom currents.
Flat ribbons or patches of sand are common features
in rather deep water. Thus, vertical sections of such a
basin fill show again a very high proportion of sand
with a variety of sedimentary structures, some of
which are not very well known. They may indicate
bidirectional current orientation, although one current direction (either the ebb or the tlood current) is
usually dominant. The fine-grained river load or
muds produced in the basin itself are mainly deposited in areas which are protected from tidal and other
bottom currents or, in the case of shelf seas, they are
transported into deep water.
Low Terrigenous Input
The second series of models shown in Figure 3.21
represents examples with low input of terrigenous
mud and sand. These models are probably realized in
nature more frequently than those discussed above.
For obvious reasons, such basins also pers ist for longer time periods than basins receiving large
terrigenous infIux.
(5) Wave-dominated, mud input. The sedimentary fill
of a low-energy, wave-dominated basin with prevailing mud input (Fig. 3.2lf) resembles that in Fig.
3.20b, but the slower silicic1astic sedimentation rate
enables higher concentrations of biogenic constituents and more intense bioturbation. For that reason,
shell accumulations in the shoreface zone and,
subordinately, in offshore tempestites are more pronounced than in model Fig. 3.20b. The sediments of
the outer shelf may become marly, because they contain relatively high proportions ofbiogenic carbonate
of both benthic and planktonic origin. Mud
tempestites tend to become completely mixed with
host sediments and thus obliterated.
A further reduction of terrigenous input to an insignificant portion of the total sediment may lead to
sediments rich in biogenie components (Fig. 3.2lg).
In this case, a favorable c1imate and sea water sufficiently rich in nutrients is needed. The latter may be
provided by river water or by oceanic currents entering the shelf sea. As a result, the sediments of the
inner shelf can again display abundant shell layers
and bioc1astic sands and silts. Larger shells are comChapter 3 Coastal and Shallow Sea Sediments
monly crushed to small pieces by predatory organisms. On the outer shelf, the carbonate content may
become so high that marls and lime muds are deposited which later form marl-limestone sequences (cf.
Sect. 7.9). If the contribution of tiny skeletons of
planktonic organisms is high, the limestones resemble deep-water pelagic limes tones which may contain
some chert. Their shallow-water origin can be inferred from alternations with other sediment types.
Bioturbation is again very intense in this environment, thus diminishing the preservation potential of
tempestites.
(6) An alternative of this model is an environment
with an oxygen minimum zone in bottom waters of
the outer shelf or in special depressions of
epicontinental seas. Such a situation may be caused
by upwelling waters rich in nutrients (cf. Sect. 5.3.4)
or by restricted water circulation. The resulting sediments are laminated bituminous c1ays and marls
which may contain some limestone beds and chert
layers. Bioturbation is limited to certain horizons or
completely missing.
(7) Storm- and tide-dominated seas. The model in
Fig. 3.2lh characterizes high-energy conditions
(storrns and tides) with low input of sand and mud.
Coastal pro gradation is limited and the slope of the
beach-shelf profile becomes rather gentle. In contrast
to the model in Fig. 3.20d, shell beds and finer
grained biogenic components may become significant contributors to the total sediment. Repeated reworking due to storm action leads to pronounced
amalgamation in the shoreface-offshore transitional
zone and to other erosional surfaces with lag deposits
and condensed beds in deeper water. Beds already
buried and somewhat indurated may become re-exposed to current action and colonized by faunal assemblages needing firm or hard grounds.
(8) Shelf seas affected by oceanic bottom currents.
The last model (Fig. 3.2li) deals with shelf seas
which are strongly intluenced by oceanic currents
entering the shelf and preventing the deposition of
fine-grained material in these regions (e.g.,
Flemming 1980). In the shoreface zone, the
depositional processes resemble those described for
models Fig. 2lf and g, but at a greater depth strong
and repeated reworking inc1uding mixing of older
and younger sands is common. Gravel may be concentrated in lag deposits, and vertical sections are
characterized by many erosional surfaces. If the
mean sedimentation rate becomes very low inc1uding
periods of non-deposition, glauconitic minerals may
form at the sedimentlwater interface (cf. Sect. 6.1).
Under special conditions, phosphorite nodules can
grow. Bottom life may differ from the previous examples, and the intensity of bioturbation tends to
change considerably from bed to bed.