Geology Reference
In-Depth Information
Fig. 5.19
(
a
) Tidal
rhythmites from a location
just seaward of the tightly
meandering reach in the
Salmon River. The section is
located at the site of Fig.
5.10d
.
Sp
= spring-tide layers;
N
= neap-tide layers. Each
sand layer was deposited by a
single flood tide. In general,
the ebb tide does not deposit
a recognizable layer. In some
of the mud drapes during
spring tides, however, a
separate silt stringer is
present in the middle of the
mud layer (highlighted by the
inscribed line in the mud
layer just below layer '16').
This was deposited by the
ebb tide. (
b
) Mudflat deposits
from the middle of the
Cobequid Bay—Salmon
River estuary, with well-
developed annual cycles.
W
= fall, winter and spring
deposits that are weakly
bioturbated and laminated.
S
= summer deposits that are
completely homogenized by
bioturbation. Note how the
annual layers become thinner
upward as the surface rises
higher in the tidal frame. The
top of the section is partially
turbated by roots of
salt-marsh plants
headwaters on land. Deposition on the point bars of
these channels generates IHS (De Mowbray
1983
;
Pearson and Gingras
2006
; Choi
2010
). Because the
position of these channels is relatively stable, the
'channel belt' that they produce is narrow, and the bulk
of the mudflat and salt-marsh deposits is horizontally
stratified.
and facies within these estuaries is predictable in
general terms, if not in detail, because of the regular
way in which the intensity of these three processes
varies along the length and across the width of the
estuary. A large amount of information exists on these
processes, because of the great amount of research that
has been done in order to understand the dynamics of
sediment transport, a topic of considerable interest
with regard to human utilization of these estuaries.
There is a growing body of research that has examined
the morphodynamics of tide-dominated estuaries, and
the broad patterns are understood reasonably well, but
more needs to be done to document the rates and pat-
terns of morphological change. In general terms, tide-
dominated estuaries can be in one of two evolutionary
5.5
Summary
Tide-dominated estuaries are dynamic environments,
because of the strong and widespread action of tidal
currents, with lesser influence from waves and river cur-
rents. The spatial organization of processes, morphology
