Geology Reference
In-Depth Information
Fig. 12.15
Ground-penetrating radar transect across Old Currituck Inlet, NC. The nested channel sections suggest different periods
of excavation and fi lling (From McBride
1999
, McBride et al.
2004
)
environment, including a basal coarse sand and shell
lag that is 10-15 cm thick, unconformably overlying
very fi ne shoreface sand. Sitting on top of this basal
unit are active channel sediments, consisting of clean,
horizontal to cross-bedded medium sand with few bio-
genic structures and inactive channel deposits com-
posed of a highly burrowed, poorly-sorted, medium to
fi ne sand with numerous mud laminations (Nelligan
1983
) . Overlying the channel fi ll deposits is a fl ood
platform facies made up of medium to fi ne sand com-
pletely devoid of bedding due to intense bioturbation.
As the bar complexes migrate onshore, the entire chan-
nel sequence will be capped by a relatively coarse
facies consisting of shallow- to steeply- dipping beds
of medium to coarse sand having a high shell content.
Inlets, North Sea), much of the western and central U.S.
Gulf Coast deltas contains very muddy deltas. One
such system is the ebb-tidal delta of Barataria Pass that
is expanding due to backbarrier wetland loss and coin-
cident increasing bay tidal prism (Fig.
12.17
). As seen
in the longitudinal section of Barataria Pass
(Fig.
12.17c
), while the inlet throat enlarged between
the 1880s and 1980s, the delta prograded seaward
approximately 2 km during the same time (List et al.
1994
). The sediments comprising the ebb delta coarsen
upward and are composed of a proximal facies of up to
25% mud and a distal facies of up to 50% mud
(FitzGerald et al.
2004
). The proximal facies (1-3 m
thick) occurs on both sides of the ebb channel and con-
tains massive to laminated fi ne sand with mud layers
and is highly bioturbated. The distal facies interfi ngers
with landward proximal facies and seaward with shelf
sediment. It is relatively thin (0.4-1.2 m thick) and
consists of thinly laminated, bioturbated, muddy sand
with shell hash layers. The high mud content of this
Baratraia Pass, Louisiana
In contrast to the sand-rich tidal deltas of the U.S. East
and Gulf Coasts, and elsewhere in the world (i.e., Copper
River Delta, Alaska; Algarve Inlets, Portugal; Friesian
