Geology Reference
In-Depth Information
Fig. 3.18
Photo of tidal
bedding that is monolithic
from the Baraboo Quartzite
(Precambrian) of Wisconsin,
USA
1.0
1.0
0.5
F1
F2
0.0
0.0
E2
E1
-0.5
-0.7
0
4
8
12
16 20
Hours
24283236
0 4 8 12162024283236
Fig. 3.19
Diagram showing time-velocity curves and the reduction in individual tidal layers. The dominant current here is the fl ood
and the subordinate current is the ebb (From Archer
1998
)
records only a portion of this sequence because of the
slope of the intertidal surface (Fig.
3.21
).
Films of biological material such as bacteria and
diatoms may also play a role in tidal rhythmites. These
biofi lms cause some stabilization of the sediment surface.
Accretion by mineral sediment produces rhythmites of
light and dark material in the muddy coast of French
Guiana (Debenay et al.
2007
) . Cyanobacteria also may
produce similar rhythmic bedding (e.g. Krumbein
et al.
2003
). An excellent summary of the infl uence of
