Geology Reference
In-Depth Information
Fig. 14.2
Simple bedform velocity matrix for deep-water
sediment movement, showing the range of common and unusual
current velocities in deep-water tides, and the potential corre-
sponding bedforms. Note that this fi gure does not take into
account either the duration of a current or sediment availability,
both of which are important controls on the development of
bedforms (Modifi ed from Stow et al.
2009
)
the normal daily velocity range of 10-50 cm/s shown
by these measurements, sediment up to fi ne gravel can
be moved, and sandy bedforms including ripples and
dunes can form, depending on sediment availability
(Fig.
14.2
) (Stow et al.
2009
) . Recognition of tidal
deposits in ancient deep marine settings, however, has
not kept up with studies of the modern, and currently
there are only a handful of papers that deal with con-
vincing deep-water tidalites (Shanmugam
2003
;
Zhenzhong and Eriksson
1991
). The purpose of this
paper is to present background from modern deep-
water tidal currents and seafl oor sediments, from out-
crops interpreted as deep-water tidal in origin, and to
discuss recognition criteria and the signifi cance of
tidalites in deep-marine rocks.
14.2
Deep-Water Processes
The major current-driven processes in operation on the
seafl oor that tend to move sediment include turbidity
currents, contour currents, wind-driven currents, inter-
nal waves, and tidal currents. In a process sense, these
all share some similarities and differences, and there
may even be signifi cant crossover in some settings.
Turbidity currents are currents driven by gravity and
