Geology Reference
In-Depth Information
6
Stratigraphy of Tide-Dominated
Estuaries
Bernadette Tessier
Abstract
Tide-dominated estuaries have received less attention than wave-dominated
estuaries due mainly to the fact that they are less common coastal systems.
Consequently, the data available on the sedimentary infi ll of tide-dominated estu-
aries are limited. The present chapter describes several modern (Holocene) exam-
ples for which seismic, sediment core and 14C age data are available, allowing
reconstruction of sediment fi lls. Some ancient examples are also given. The distri-
bution and preservation of some key features such as systems tracts and ravine-
ment surfaces are discussed in light of the different examples, as well as the
controlling factors of infi lling. Only a few features and factors can fi nally be
assigned specifi cally to tide-dominated estuary infi lls. However, two points must
be emphasized: (1) wave-built bodies are common features preserved within tide-
dominated estuary infi lls; and (2) the potential for preservation of estuarine sedi-
mentary bodies is primarily controlled by tidal accommodation, defi ned by the
depth of the main tidal channel belt.
6.1
Introduction
Additionally, since estuaries are known as ephemeral
coastal systems, sensitive to sea-level and climate
fl uctuations (Masselink and Hughes
2003
) , many
projects have been devoted over the last decades to
study their sedimentary infi lling for defi ning the forc-
ing factors of their evolution. As a consequence, a
huge amount of data has been published on the stra-
tigraphy of estuarine fi lls, both from modern and
ancient examples. Literature on tide-dominated or
tide-infl uenced sedimentary coastal systems, and
more generally on estuaries, is particularly vast. The
most common classifi cation of estuaries used by sedi-
mentologists is that defi ned by Dalrymple et al.
(
1992
), and slightly revised recently (Dalrymple
2006
). According to the prevailing hydrodynamics at
the mouth of the estuary, waves or tidal currents, two
Estuaries are usually defi ned as the seaward portion of
a drowned incised valley (Dalrymple et al.
1992
).
Interest in the study of incised-valley systems increased
tremendously in the 1990s both because they represent
key objects for a better understanding of sequence
stratigraphy of marine-to-continental successions,
and they potentially constitute good clastic oil reser-
voirs (Dalrymple et al.
1994
; Zaitlin et al.
1994
).
