Geology Reference
In-Depth Information
9
Open-Coast Tidal Flats
Daidu Fan
Abstract
Recent research advances highlight the importance of open-coast tidal-flat
depositional system in both modern and ancient coastal environments. The system
is unique in its wave- and tide-dominated physical setting, notably distinct from
the tide-dominated barred tidal flats and the wave-dominated shorefaces.
Interactions of waves and tides over different time scales produce not only cyclic
morphologic variations in terms of erosion and deposition, but also rhythmic
depositional units consisting of storm-generated sand-dominated layers (SDLs)
and post-storm mud-dominated layers (MDLs). Ancient deposits of the open-coast
tidal flats can be distinguished by abundance of storm-generated structures and
scarcity of tidal-channel deposits from those of barred tidal flats, and by abundance
of the structures created by combined flows or the interactions of waves and tides
from those of (tidal) shorefaces. Difference is also remarkable between muddy
and sandy open-coast tidal flats. Muddy open-coast tidal flats tend to develop
along mega-river deltas and the adjacent chenier plains, have a general accretional
convex-up profile with clear zonation, and produce aggradational fining-upward
intertidal successions. Sandy open-coast tidal flats are common in the open-mouth
estuaries of small rivers and the adjacent strand plains, usually develop an erosional
concave-up profile with common presence of inner swash bars having the coarsest
sediment near the high water, and produce coarsening-upward retrogradational
successions. The vertical successions of sandy open-coast tidal flats generally
contain more storm-generated beds volumetrically than those of muddy open-coast
tidal flats. Notably, there are some accretional sandy open-coast tidal flats, lying in
between the above two settings. A new spectrum of coastal morphodynamic
settings is therefore proposed to change from the tide-dominated barred tidal flats,
the wave-influenced and tide-dominated muddy open-coast tidal flats, the wave-
and tide-dominated accretional sandy open-coast tidal flats, the wave-dominated
erosional sandy open-coast tidal flats, to the wave-dominated tidal shorefaces.
9.1
Introduction
Tidal flats can be developed in numerous environments,
like lagoons, embayments, estuaries, deltas, and coastal
plains, ranging from sheltered environments to those
 
Search WWH ::




Custom Search