Page 6 - 122789121769ClaudioCSR2008

ARTICLE IN PRESS
250 C. Lo Iacono, J. Guille´n / Continental Shelf Research 28 (2008) 245–256
Fig. 5. The main sedimentological facies observed along the Marettimo inner shelf. Textures range from very coarse sands to pebbles. In some cases
bimodal sediment distribution is evident. The boxes show the sampling sites.
The sediment is mainly composed of coarse fractions,
ranging from coarse sands to pebbles. Their composition is
mainly siliciclastic, although a bioclastic sand component is
often recognizable as a second mode (Lo Iacono, 2004).
The following different sedimentological textural groups
were recognized:
– Pebbles, gravels, and sandy gravel cover approximately
42% of the sediments present along the surveyed area on
the Marettimo inner shelf and are mainly distributed
along the western, southwestern, and northeastern inner
shelf (Fig. 4). These coarse sediments show heterogenic
mixtures in which a high percentage of pebbles (modal
diameter: 5.6–8 and 16–32 mm) is present, while the sandy
fraction, mostly bioclastic, corresponds to very coarse
(1–2 mm) and medium sands (0.3–0.5 mm) (Fig. 5).
– Gravelly sands and sands cover 58% of sediments present
along the inner shelf. The most abundant granulometric
classes correspond to coarse (0.5–0.7 mm) and very
coarse (1.4–2 mm) sands (Fig. 5). A low percentage of
gravel (2.8–4 and 5.6–8 mm) is also present. This group
mainly occurs along the eastern and northwestern
sectors of the Marettimo inner shelf, and in several
bays along the coast.
– Meadows and patches of P. oceanica seagrass were
observed on rocky and very coarse grained bottoms
throughout the study area, mostly distributed in the
southeastern and southwestern sectors, in zones shal-
lower than 30 m depth (Fig. 4).
– Rocky outcrops, mainly consisting of Triassic lime-
stones, appear as isolated morphological highs or as
seaward prolongations of the major inland structural
lineaments (Fig. 4).
4.2. Bedforms
Two large bedforms were identified on the shelf:
gravel–pebbly dunes and sorted bedforms.
Gravelly and pebbly dunes were recognized throughout
the study area. Subaqueous dunes are displayed as a
strongly reflective and contrasting acoustic facies in
SSS sonographs and correspond to the dominant bedform
along the Marettimo inner shelf (Fig. 6). The dunes
were observed for the entire depth interval of the study
area (10–50 m), with a prevalent direction parallel, or
with a low incidence angle, to the coastline. The dunes
display a symmetrical morphology (Fig. 7), and occur
in clusters with a patchy distribution or in small sandy
gravel sediment patches inside P. oceanica meadows.
They show a 2D morphology (Allen, 1968), constant
dimensional parameters, with wavelength l ranging from 1
to 2.5 m and height Z ranging from 0.15 to 0.30 m, and
slightly linear crests. Lateral extension ranges from a few
tens of meters to a maximum of 700 m observed along the
western sector. Secondary smaller features were not
observed.
The dunes with the smallest dimensions (lo1.5 m) were
observed along the southeastern and western sectors of the
study area, around Bassano Cape and from Cala Bianca to
Pegna Cape, often occurring in spatial continuity with dune
fields that show a greater wavelength (2–2.5 m, Fig. 6). They
are usually composed of mixed sediment with a texture
varying from fine sand to gravel (D50 from 0.18 to 6 mm).
The most frequent dune wavelength observed throughout
the study area ranges between 1.5 and 2 m. This class of
dunes is usually composed of sandy gravel sediments or a
mixture of gravels and pebbles (D50 ¼ 8–11 mm).