Geology Reference
In-Depth Information
8
Salt Marsh Sedimentation
Jesper Bartholdy
Abstract
This chapter deals with salt marsh sedimentation with emphasis on depositional
processes and resulting products. Salt marsh sedimentation and related dynamic
conditions are evaluated and described with examples from a wide range of loca-
tions. General mechanisms and depositional conditions are primarily illustrated
by examples from the Danish Wadden Sea based on the author's own experience.
The chapter opens with an overview over measurements of salt marsh sedimenta-
tion through time and a general description of salt marsh morphodynamics, includ-
ing an assessment of the effects of vegetation. Salt marsh sediments and
autocompaction are discussed prior to a description of salt marsh accretion
models. The latter is used to give examples of salt marsh stability in relation to
different tidal conditions and sea-level-rise scenarios. The chapter concludes with
a description of salt marshes in the geological record.
8.1
Introduction
high tide as a result of wind tide effects. Salt marshes
exist in all climate zones from the tropics to high-arctic
coastal environments. In the tropics, mangroves repre-
sent a special vegetated coastal environment which
departs from typical coastal marshes in many ways.
Part of the processes related to sedimentation in man-
groves are for obvious reasons similar to those related
to regular marshes, and no separate discussion of the
tropical zone's special conditions is included in this
chapter. See Augustinus (
1995
) for a comprehensive
description of the geomorphology and sedimentology
of mangroves. Along the banks of tidally infl uenced
rivers, there exists a gradual transition between salt
marshes in the outer part and fresh water tidal marshes
further inland. Likewise, freshwater marshes can
develop along the banks of lakes subject to wind tides.
This chapter deals with salt marshes. No separate dis-
tinction will be made in relation to these freshwater
marsh environments in which the sedimentary
As part of the coastal zone, salt marshes are defi ned
here as: 'vegetated areas located between coastal hin-
terlands and daily (or permanently) fl ooded coastal
areas'. Thus, salt marshes form a buffer zone between
areas where coastal and estuarine processes act on a
daily basis and areas that are either never fl ooded or
only fl ooded during infrequent events such as severe
storms. Most salt marsh areas are fl ooded for longer or
shorter periods in relation to high water during at least
part a normal spring-neap tidal cycle. Some, however,
can maintain a level above the highest astronomical
