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ARTICLE IN PRESS

Continental Shelf Research 28 (2008) 245–256

www.elsevier.com/locate/csr

Environmental conditions for gravelly and pebbly dunes
and sorted bedforms on a moderate-energy inner shelf

(Marettimo Island, Italy, western Mediterranean)

Claudio Lo Iaconoa,Ã, Jorge Guille´ nb

aDipartimento di Geologia e Geodesia dell’Universita` di Palermo, Via Archiraﬁ, 22, 90123 Palermo, Italy
bCSIC, Instituto de Ciencias del Mar, Paseo Marı´timo de la Barceloneta, 37-49, 08003 Barcelona, Spain

Received 8 January 2007; received in revised form 23 July 2007; accepted 27 August 2007
Available online 12 September 2007

Abstract

Side scan sonar records, sediment textural characteristics, and in-situ ﬁeld observations were used to study gravelly and pebbly dunes
and sorted bedforms on the inner shelf of Marettimo Island, along the northwestern Sicilian shelf. The dunes are composed of coarse
sands, gravels and pebbles (D50: 2–16 mm), displaying a symmetrical shape with a wavelength in the range of 1–2.5 m and a height of
0.15–0.30 m. The bedforms are distributed in a patchy pattern in a depth range of 10–50 m, and are described for the ﬁrst time on a
Mediterranean inner shelf. Sorted bedforms are linear morphological features developed almost perpendicular to the coast in the eastern
sector of the island between 15 and 50 m water depth. Bottom shear stresses required for sediment entrainment and the generation of the
shallower dunes can be reached during strong storms (Hs ¼ 5–6 m; Tp ¼ 9–11 s), which are not common in the Mediterranean Sea.
However, wave storm events recorded in the study area during the last 17 years are not able to generate the coarsest and deeper dunes,
suggesting that the stirring mechanism for dune formation is associated with severe storms that have a recurrence interval of more than
17 years. The long-term stability of the coarse bedforms is supported by the permanence of sorted bedforms without signiﬁcant
morphological changes for long periods (413 years). Therefore, it is shown that processes forming coarse bedforms can occur in tideless
and moderate-energy settings like those of the Mediterranean continental shelves, although the morphological features are probably less
dynamic and remain unaltered for longer periods than on higher-energy shelves.
r 2007 Elsevier Ltd. All rights reserved.

Keywords: Inner shelf; Gravel dunes; Sorted bedforms

1. Introduction in areas with low to moderate continental sediment inputs
and relatively high-energy conditions. In most cases, wave
Gravel dunes and sorted bedforms are coarse bedforms action on the seabed during storms is able to generate and
observed on many oceanic inner shelves around the world, maintain these bedforms (Langhorne et al., 1986; Amos et
especially on both Atlantic margins and along the western al., 1996; Cirac et al., 2000; Anthony and Leth, 2002). In
North American shelf (Fig. 1). Gravelly subaqueous dunes the case of tidal areas, the combined effect of unidirectional
(Ashley, 1990) are common features in marine environ- currents and waves promotes dune formation (Dyer, 1971;
ments and have been described on a number of continental Langhorne et al., 1986; Lobo et al., 2000; Carling et al.,
shelves of storm-dominated oceanic coasts, mostly char- 2006). Sorted bedforms (Murray and Thieler, 2004;
acterized by meso- and macrotidal regimes (Carling, 1999; Gutierrez et al., 2005) or rippled scour depressions
Flemming, 2000). In general, gravel dunes are distributed (Cacchione et al., 1984; Ferrini and Flood, 2005) are
slightly depressed, elongate features constituted by gravelly
ÃCorresponding author. CSIC, Unidad de Tecnologia Marina, Paseo and sandy gravel sediments that usually form ripples and
Marı´ timo de la Barceloneta, 37-49, 08003 Barcelona, Spain. dunes adjacent to coarse and ﬁne sand bodies that have
Tel.: +34 93 230 9500; fax: +34 93 230 9555. been deﬁned as ‘‘transversal sand patches’’ (Kenyon, 1970;
Cirac et al., 2000). Factors favoring their formation are the
E-mail address: loiacono@utm.csic.es (C. Lo Iacono).

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