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246 C. Lo Iacono, J. Guille´n / Continental Shelf Research 28 (2008) 245–256

Fig. 1. Distribution of gravelly subaqueous dunes (numbers) and sorted bedforms (letters) on continental shelves.
1: Macintyre and Pilkey (1969); 2: Dyer (1971); 3: McCave (1971); 4: Newton and Werner (1972); 5: Kenyon and Belderson (1973); 6: Newton et al. (1973);
7: Werner and Newton (1975); 8: Swift and Freeland (1978); 9: Lewis (1979); 10: Tabat (1979); 11: Yorath et al. (1979); 12: Morang and Mc Master, (1980);
13: Gillie (1979, 1983); 14: Hunter et al. (1982); 15: Amos and King, (1984); 16: Langhorne et al., (1986); 17: Forbes and Boyd, (1987); 18: Berne` et al.
(1989); 19: Amos et al. (1996); 20: Durand et al. (1998); 21: Cirac et al. (2000); 22: Lobo (2000); 23: Anthony and Leth (2002); 24: Carling et al. (2006).
a: Aubrey et al. (1984); b: Cacchione et al. (1984); c: Schwab and Molnia (1987); d: Barnhardt et al. (1998); e: Black and Healy (1988); f: Siringan and
Anderson (1994); g: Hequette and Hill (1995); h: Thieler et al. (1995, 2001); i: Chin et al. (1997); j: Schwab et al. (1997); k: Boss et al. (1998); l: McQuarrie,
(1998); m: Thieler et al. (1999); n: Twichell and Paskevich (1999); o: Reed and Wells (2000); p: Schwab et al. (2000); q: McLeod and Cleary (2001);
r: Eittrem et al. (2002); s: Goff et al. (2002); t: Green et al. (2004); u: Murray and Thieler (2004); v: Ferrini and Flood (2005); w: Goff et al. (2005);
x: Gutierrez et al. (2005); y: Diesing et al. (2006); }: study area.

presence of poorly sorted sediments on a steep shelf Strait (Sicily), and have been related to strong current flows
dominated by the interaction of current and waves caused by water mass circulation or local tides (Lykousis,
(Murray and Thieler, 2004). Sorted bedforms with similar 2001; Santoro et al., 2002). However, gravelly and pebbly
characteristics (dimensions, depth of distribution and dunes and sorted bedforms have not yet been described on
acoustic facies) have been observed on a variety of Mediterranean inner continental shelves.
continental shelves at depths ranging from 15 to 80 m, set
out in a transverse direction with respect to the coastline; In the present study, we report on the gravelly–pebbly
they can be as much as several kilometers in length and dune fields and sorted bedforms on the Marettimo Island
hundreds of meters in width (Macintyre and Pilkey, 1969; inner shelf. The potential forcing mechanisms and their
Belderson et al., 1972; Wanney, 1977; Morang and Mc relict or active status are discussed in relation to the
Master, 1980; Hunter et al., 1982; Cacchione et al., 1984; present-day wave climate, potential extreme hydrodynamic
Cirac et al., 2000; Murray and Thieler, 2004; Ferrini and events, and different lower sea level conditions.
Flood, 2005; Goff et al., 2005; Diesing et al., 2006).
Therefore, it can be assumed that the mechanisms of 2. Study area
formation of these bedforms are equivalent in areas
affected by different hydrodynamic conditions. They have Marettimo Island belongs to the Egadi Islands situated
been interpreted as being related to cross-shelf flows caused in the westernmost sector of the Sicilian–Maghrebian chain
by storms that scour the seabed (Cacchione et al., 1984) or (Catalano et al., 1996, Fig. 2). The continental shelf is the
as transverse bedforms (Thieler et al., 2001; Goff et al., smallest in western Sicily, with an average area of 200 km2
2005; Ferrini and Flood, 2005). At present, sorted bed- and a maximum width of 40 km (Agate et al., 1999). It
forms are described as self-organizing transverse sedimen- displays a regular morphology, except for isolated rocky
tary structures in which the differences in roughness values outcrops and wave-cut terraces observed along the south-
in sandy and gravelly areas induce different transport rates ern outer shelf. On the eastern side, the Marettimo
and shear stress values, and favor feedback mechanisms Channel, with maximum depths of 350 m, isolates Mar-
between seabed composition and evolving morphology ettimo Island from the rest of the Egadi Islands and from
(Murray and Thieler, 2004; Coco et al., 2007a). the Sicilian shelf, probably playing an important role in the
water exchanges between the Sicily Channel and the
It is widely assumed in the environmental interpretation southern Tyrrhenian Sea (Miller, 1972; Manzella et al.,
of both present-day processes and the geological record 1988).
that the formation of coarse bedforms is related to high-
energy conditions (strong tidal currents, storm events). In Along the whole Egadi archipelago, Holocene marine
moderate-energy continental margins like the Mediterra- deposits show a reduced thickness (1–2 m) compared to the
nean, sandy–gravelly dunes have been observed in deeper usual values observed on the Sicilian shelf, due to the
areas (150–300 m) of the Aegean Sea and in the Messina reduced sedimentary supply from coastal erosion and river
input (Colantoni et al., 1993; Agate et al., 1998).