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Fig. 10.24 Diagram summarizing the trends of major parameters
characterizing intertidal flats. While most parameters either
increase or decrease along the gradient between mean low tide
( MLT ) and mean high tide ( MHT ), the concentration (mass per
unit volume) of organic matter peaks in the sandy mud facies, as
would any other substance linked to the mud fraction (Modified
after Hertweck 1994 )
(mass per unit volume) of mud and any substances
linked to the mud fraction. As outlined earlier, this
would, for example, not only apply to the concentra-
tion of mud itself, but also to organic matter, heavy
metals, trace elements, organic pollutants and toxic
substances.
primary sedimentary structures (flaser, wavy and
lenticular bedding), the model is inherently incomplete
because bioturbation, shell accumulations and sedi-
mentary structures typical of intertidal creeks have
been excluded. As such it would be more applicable to
Precambrian than Phanerozoic tidal flats. However, as
shown below, it serves a very useful purpose in that it
simplifies the interpretation of generally much more
complicated real-world situations.
Such a real-world situation, in this case represent-
ing a particular location in the modern Wadden Sea, is
illustrated in Fig. 10.26 (after Chang et al. 2006c ). The
upward-coarsening sedimentary sequence recorded in
the core clearly documents a transgressive setting com-
mencing with mudflat deposits at the bottom and end-
ing with sand flat deposits at the top. A closer look at
the sequence reveals a number of features that compli-
cate the interpretation. Thus, while the mudflat deposit
in the lower core section is interspersed with thin len-
ticular beds as one would expect, the sequence does
not progressively grade upward into wavy and lenticu-
lar bedding as required by the idealized model, but is
10.5
Stratigraphic Relationships
Having discussed and illustrated a variety of typical
intertidal sedimentary structures and bedding types,
the question arises of how these might be preserved in
the rock record. Applying Walther's Law by vertically
stacking typical sedimentary facies characterizing
the intertidal gradient, a synthetic upward-coarsening
transgressive facies model has been constructed
(Fig. 10.25 ). The model is based on Reineck and
Wunderlich ( 1968 ) and includes the most characteris-
tic sedimentary structures generally observed along
the intertidal gradient from sand flats near MLT to mud
flats near MHT. While highlighting the most important
 
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