Geology Reference
In-Depth Information
Brett, C.E., Baird, G.C. (eds., 1997): Paleontological events:
stratigraphical, ecological, and evolutionary implications.
- 604 pp., New York (Columbia University Press)
Dodd, J.R., Stanton, R.J. (1990): Paleoecology. Concepts and
applications. Second edition. - 502 pp., New York (Wiley)
Etter, W. (1994): Palökologie. Eine methodische Einführung.
- 294 pp., Basel (Birkhäuser)
Fischer, G., Wefer, G. (1999): Use of proxies in paleoceano-
graphy. - 735 pp., Berlin (Springer)
Fürsich, F.T. (1995): Approaches to paleoenvironmental re-
constructions. - Geobios, Mem. Spec.,
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, 183-195
Martin, R.E. (1999): Taphonomy. A process approach. -
524 pp., Cambridge (Cambridge University Press)
Nybakken, J.W. (1993): Marine biology. An ecological ap-
proach. Third edition. - 462 pp., New York (Harper Collins
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Further reading
: K109
Box 12.1.
Terms used for discussing depositional water
energy.
•
Depositional interface:
Interface between the water
and the bottom where sediments are deposited in rela-
tion to the energy level at the interface.
•
Energy index:
Inferred degree of water agitation in
the sedimentary environment of deposition.
•
Energy level:
The kinetic energy (due to wave or cur-
rent action) that existed or exists in the water of a sedi-
mentary environment either at the interface of deposi-
tion or above it. Depending on the water depth, wave
amplitude and storm activity, the energy level at the depo-
sitional interface may be fairly constant, or may range
within wide limits as a function of time.
•
High-energy environment:
An aqueous sedimentary
environment characterized by a high energy-level and
by turbulent action (such as that created by waves, cur-
rents or surf) that prevents the settling and accumula-
tion of fine-grained sediment.
•
Low-energy environment:
An aqueous sedimentary
environment characterized by a low-energy level and by
standing water or a general lack of wave and current
action, thereby permitting fine-grained sediment to settle
and accumulate.
•
Quiet-water sedimentation:
Deposition within a near
zero energy level at the depositional interface. Quiet-
water does not necessarily imply the complete absence
of water movement or the existence of stagnant condi-
tions.
•
Storm wave base:
The water depth down to which
storm-generated waves and resulting bottom currents
rework bottom sediments (generally lime mudstones and
wackestones) and produce specific texture types (tem-
pestites, see Sect. 12.1.2.1). The depth of the storm wave
base varies strongly (about 50 m down to 250 m in shelf
seas, and about 20 to 30 m in epicontinental seas).
•
Surf:
(a) The wave activity in the area between the
shoreline and the outermost limit of breakers. (b) A col-
lective term for breakers.
•
Wave base:
The water depth below which surface
wave action no longer stirs and moves the sediment. Also
called fair-weather wave base. The wave base ranges
widely, depending on wave amplitude and fetch, bottom
topography and activity of storms.
•
Tsunami:
A gravitational sea wave produced by large-
scale, short-duration disturbance of the ocean floor, prin-
cipally by earthquakes. Characterized by great speed of
propagation, long wave lengths and long periods. May
pile up waves of 30 m height and more, causing much
damage in shallow-marine water, along coasts, and on
land. Ancient tsunami deposits may be recognized by
extended sheets of marine sand overlying terrestrial or
lacustrine sequences (Minoura et al. 1994; Shiki et al.
2000).
12.1.1 Hydrodynamic Controls
Paleoenvironmental interpretations of carbonate depos-
its rely strongly on estimations of hydrodynamic con-
ditions and processes, whose definitions are listed in
Box 12.1. The effects of severe storms are discussed in
Sect. 12.1.2.
The kinetic energy of motion existing in the water
at the depositional interface or a few tens of centime-
ters below it is caused by waves or current action.
Mechanisms that drive the flow of water across the sedi-
ment-water interface and within the pore spaces include
wave-induced advection, density driven convection,
groundwater seepage and active pumping by benthic
organisms (Libelo et al. 1994). Movement of water
across the sediment-water interface and within near
surface sediments control the cycling of nitrogen, phos-
phorus, carbon, sulfur and trace metals between sedi-
ment and the water column.
Low-energy and high-energy levels
: Depending on
various oceanographic factors (e.g. water depth, wave
amplitude) the energy level may be fairly constant or
may vary strongly over time (e.g. in tidal zones or in
areas affected by storms). The energy of a water mass
capable of moving sedimentary particles varies between
low (low-energy sediments) and high (high-energy
deposition).
Generally high-energy environments include the in-
tertidal zone, shallow-marine open platforms, inner
ramps and the leeward parts of framework reefs. Low-
energy environments occur in protected areas, such as
enclosed bays, estuaries, lagoons, inner platform areas,
outer ramps and in deeper-water settings. Benthic or-
ganisms exhibit specific adaptions to high or low-en-
ergy conditions (Riedl 1969; see Nybakken 1993 for a
review). High-energy conditions provide a constant
source of nutrients and oxygenated seawater and re-
duce the settling rate of fine-grained sediment.
The reconstruction of water energy is based on sedi-
mentological and paleontological criteria. Paleontologi-
cal criteria include specific morphologies of skeletal
