Geology Reference
In-Depth Information
Fig. 3.8
Photograph showing
(
a
) linear bedforms on the
Wadden Sea of Germany and
(
b
) three-dimensional
bedforms in Louisa Creek,
Queensland, Australia
sediment settling during high-tide (or low tide), slack
water conditions. Here a combination of relatively
high-energy conditions exist as tides fl ood and ebb
producing currents that move sediment, and low-
energy conditions during slack tide when fi ne sediment
can settle into bedform troughs. Sediment accumula-
tion under these circumstances incorporate the mud
and produce what is called
fl aser bedding
( Reineck
and Wunderlich
1968
) after the German word for
“fl ame”. Depending on the relative amount of mud
versus sand in these successions, wavy bedding or
lenticular bedding (Fig.
3.11
) may occur.
Because of the alternation of sand and mud on a
regular basis, tidal processes are interpreted to control
sedimentation. These types of bedding are called het-
erolithic because they contain both relatively coarse
sediment and fi ne sediment. They are very common on
intertidal environments and are present in some sub-
tidal environments such as estuaries, and the interdis-
tributaries of deltas. They are easily preserved in the
stratigraphic record (Fig.
3.12
) and are an excellent
tidal signature. However, they may also form under
non-tidal conditions, especially in fl uvial environ-
ments. The primary requirement is a combination of
