3 Coastal and Shallow Sea Sediments
3.2 Sediments of Tidal Flats and
Barrier Island-Lagoon Complexes
3.2.1 Tides, Tidal Ranges, and Tidal Currents
Generation ofTides
Tidal Range and Tidal Currents
Coastal Morphology and Tidal-Influenced
Environments
3.2.2 General Characteristics ofTidal Sediments
Mud Flats, Mud Deposition
Tidal Channel Sediments
Sandflats and Mixed Sand-Mudflats
Climate Control of Tidal Sediments
Response ofTidal Flats to Sea-Level Changes
3.2.3 Distinctive Features ofTidal Sediments (Summary)
3.2.4 Sediments ofBarrier Island-Lagoon Complexes
General Characteristics
Sub environments of Barrier-Island Complexes
Controls by Climate and Hydraulic Regime
Response ofBarrier Island-Lagoon Complexes to
Sea-Level Changes
Remarks to Ancient Barrier-Island Sands and
Lagoonal Sediments
3.2.5 Summary (Barrier Islands and Lagoons)
3.2.1 Tides, Tidal Ranges, and Tidal Currents
Generation of Tides
Tidal processes operate along the co asts of all large
oceans Tides and tidal waves are caused by the attraction of the Moon and, to a lesser degree, by the
Sun. On the side of the Earth facing the Moon, as
weil as on the side opposite to it, the water level of
the ocean is raised, while perpendicular to this line
the water level is depressed (Fig. 3.9a). Due to the
counter-clockwise rotation of the Earth, the piled-up
water mass dragged along by the Moon travels clockwise until it hits a continental margin and its shore,
where it is forced to flow back toward the center of
the ocean basin. This process is repeated once or
twice daily (diurnal and semi-diurnal tides) and its
intensity fluctuates in two-week periods from high
spring tides (with the Moon and Sun working in the
same direction) to low neap tides and vice versa.
Tidal processes are described in many books and special
artic1es (e.g., Dietrich 1975; Davis 1978; Klein and Ryer
1978; Pethick 1984; Carter 1988; de Boer et al. 1988;
Smith et al. 1991; Dalrymple 1992; Alexander et al. 1999).
Apart from the gravitational effect of the Moon and
the Sun, the magnitude of the tides also depends on
the period with which the water mass of an ocean, an
enclosed sea, or a bay tends to oscillate in its basin.
If this period corresponds approximately with the periodically changing gravity forces of the Moon and
Sun, the tidal range is substantially enhanced.
Tidal waves (as used here, not the erroneous synonym of storm surges or tsunamis) have a very long
wave length and therefore behave in a way similar to
wind-generated waves in shallow water (cf. Sect.
3.1). In deep water the tides are hardly noticeable,
but when a tidal wave approaches the continental
slope and shallow water, the migrating water masses
are piled up and often bundled to considerable height
(Fig. 3.9b and c).
Tides of great amplitude only develop on the
coasts of very large water bodies, i.e., at the margins
of the oceans.
Lakes and smaller sea basins separated from the open
ocean only show very small tidal effects (Fig. 3.9d). Even
the Mediterranean Sea does not have tides greater than 10
to 20 cm because its connection with the open ocean is too
narrow t~ allow tidal waves to enter from the Atlantic into
the adjacent Mediterranean basin. For other reasons, the
tides along the coasts of most oceanic islands, as weil as
along elongated continental coast lines behind narrow or
missing shelves, are also limited «I m).
From the ancient record it can be inferred that, since the
Precambrian, the Earth-Moon system must have always
operated in a similar way as it does t.oday. In addition, .it
has been tried to determine the duratJon of a ProterozOlc
year by investigating tidal cyc1es and rhythmites in glacialinfluenced ebb-tidal deposits and banded iron formations
(Sect. 6.5) in South Australia (Williarns 1989a, b). According to this study, the Proterozoic year was about 400 days
long and each day lasted approximately 22 h.
Tidal Ranges and Tidal Currents
High tides and consequently strang tidal currents are
generated under one or both of the following conditions:
- Wide shelf or continental sea (Fig. 3.9b).
- Large bay with funnel-shaped opening (Fig. 3.9c).
3.2 Sediments of Tidal Flats and
Barrier Island-Lagoon Complexes
3.2.1 Tides, Tidal Ranges, and Tidal Currents
Generation ofTides
Tidal Range and Tidal Currents
Coastal Morphology and Tidal-Influenced
Environments
3.2.2 General Characteristics ofTidal Sediments
Mud Flats, Mud Deposition
Tidal Channel Sediments
Sandflats and Mixed Sand-Mudflats
Climate Control of Tidal Sediments
Response ofTidal Flats to Sea-Level Changes
3.2.3 Distinctive Features ofTidal Sediments (Summary)
3.2.4 Sediments ofBarrier Island-Lagoon Complexes
General Characteristics
Sub environments of Barrier-Island Complexes
Controls by Climate and Hydraulic Regime
Response ofBarrier Island-Lagoon Complexes to
Sea-Level Changes
Remarks to Ancient Barrier-Island Sands and
Lagoonal Sediments
3.2.5 Summary (Barrier Islands and Lagoons)
3.2.1 Tides, Tidal Ranges, and Tidal Currents
Generation of Tides
Tidal processes operate along the co asts of all large
oceans Tides and tidal waves are caused by the attraction of the Moon and, to a lesser degree, by the
Sun. On the side of the Earth facing the Moon, as
weil as on the side opposite to it, the water level of
the ocean is raised, while perpendicular to this line
the water level is depressed (Fig. 3.9a). Due to the
counter-clockwise rotation of the Earth, the piled-up
water mass dragged along by the Moon travels clockwise until it hits a continental margin and its shore,
where it is forced to flow back toward the center of
the ocean basin. This process is repeated once or
twice daily (diurnal and semi-diurnal tides) and its
intensity fluctuates in two-week periods from high
spring tides (with the Moon and Sun working in the
same direction) to low neap tides and vice versa.
Tidal processes are described in many books and special
artic1es (e.g., Dietrich 1975; Davis 1978; Klein and Ryer
1978; Pethick 1984; Carter 1988; de Boer et al. 1988;
Smith et al. 1991; Dalrymple 1992; Alexander et al. 1999).
Apart from the gravitational effect of the Moon and
the Sun, the magnitude of the tides also depends on
the period with which the water mass of an ocean, an
enclosed sea, or a bay tends to oscillate in its basin.
If this period corresponds approximately with the periodically changing gravity forces of the Moon and
Sun, the tidal range is substantially enhanced.
Tidal waves (as used here, not the erroneous synonym of storm surges or tsunamis) have a very long
wave length and therefore behave in a way similar to
wind-generated waves in shallow water (cf. Sect.
3.1). In deep water the tides are hardly noticeable,
but when a tidal wave approaches the continental
slope and shallow water, the migrating water masses
are piled up and often bundled to considerable height
(Fig. 3.9b and c).
Tides of great amplitude only develop on the
coasts of very large water bodies, i.e., at the margins
of the oceans.
Lakes and smaller sea basins separated from the open
ocean only show very small tidal effects (Fig. 3.9d). Even
the Mediterranean Sea does not have tides greater than 10
to 20 cm because its connection with the open ocean is too
narrow t~ allow tidal waves to enter from the Atlantic into
the adjacent Mediterranean basin. For other reasons, the
tides along the coasts of most oceanic islands, as weil as
along elongated continental coast lines behind narrow or
missing shelves, are also limited «I m).
From the ancient record it can be inferred that, since the
Precambrian, the Earth-Moon system must have always
operated in a similar way as it does t.oday. In addition, .it
has been tried to determine the duratJon of a ProterozOlc
year by investigating tidal cyc1es and rhythmites in glacialinfluenced ebb-tidal deposits and banded iron formations
(Sect. 6.5) in South Australia (Williarns 1989a, b). According to this study, the Proterozoic year was about 400 days
long and each day lasted approximately 22 h.
Tidal Ranges and Tidal Currents
High tides and consequently strang tidal currents are
generated under one or both of the following conditions:
- Wide shelf or continental sea (Fig. 3.9b).
- Large bay with funnel-shaped opening (Fig. 3.9c).