Page 7 - Morticelli_et_al2016

JOURNAL OF MAPS 7
Downloaded by [Universita di Palermo] at 02:49 07 January 2016 (a) and 5(b)). We also found interbedded at different
levels decimetric thick red palaeosols (Figure 5(i) and
5(l)), made up of siltites and sandy clays with rare cen- of mostly calcareous, very coarse to medium-sized
timetric carbonatic clasts. A palaeosols layer separates
the lower cemented carbonatic breccias and megabrec-
cias (DETb) from the overlying red, not cemented
levels (DETa; Figure 5(d)), as shown along the trail
from Punta Troia to Marettimo village, in the Punta
Troia fan (Figure 5(a)), near the cemetery, and close
to the village.
4.2.2 Marine coastal deposits
Between 0 and 10 m a. s.l., we found very thin levels of
marine coastal deposits, composed of polygenic, grain-
supported, fossil-bearing (mainly bivalves and gastro-
pods) conglomerates (Figure 5(e)). They pass upwards
to micro-conglomerates and sands with reddish matrix
and faunas (Patella ferruginea, Conus testudinarius
(SIT); Figure 5(f) and 5(g)) of the MIS 5.5
(Tyrrhenian).
At Punta Troia, at Case Martorana, along the coast
between the village and the cemetery, and at Punta
Galera (Main Map), a marine coastal wedge with Tyr-
rhenian fauna is interbedded between the cemented
alluvial fan deposits and the overlying more recent
not cemented continental deposits (Figure 5(c) and 5
(h)). On the shore near Molo Nuovo a yellow fossil-
bearing calcarenitic layer underlies the older alluvial
fan cemented deposit (MRS; Figure 5(d)).
5. Marettimo offshore
The continental shelf off Marettimo Island is
bounded by a sharp shelf-break located between 80
and 140 m of depth (Main Map); it displays an
approximate rhombohedric shape in plan view that
suggests structural control by NW-SE- and WNW-
ESE-trending faults. The shelf is up to 13 km wide
southwards but only 2–3 km wide off the western,
northern and eastern coasts. This area is a very
young, undernourished platform with a number of
bathymetric breaks-of-slope and well-preserved mor-
phological features such as palaeo-cliffs, rills and iso-
lated relief (Lo Iacono, 2003).
The continental shelf is characterized by a wide-
spread surface of marine erosion, scoured on the
Meso-Cenozoic. This erosional surface, separating the
Holocene from older rocks, has a polygenetic origin
related to the last glacio-eustatic fluctuation that
occurred in the last 100 ky.
Data from seismo-acoustic profiles and scuba-div-
ing observation (www.videpi.com; Agate et al., 2005;
Catalano et al., 1993; Hermand et al., 2000) allow the
recognition of submerged outcrops of carbonate
Mesozoic rocks (MAR, MFA) and terrigenous
Oligo-Miocene rocks (FOR) unconformably covered
by Plio-Pleistocene deposits (NO, ISD, OSD).
Scattered patches of Holocene sediments unconform-
ably overlie the Meso-Cenozoic rocks. They consist
sands with gravelly lithoclasts and bioclasts made
up of algal nodules and skeletal grains (mostly
bivalves, gastropods and bryozoans).
In the innermost sector of the continental shelf (0–
20 m of water depth), a ring of the Mesozoic carbonate
rocks outcrop on the very rough sea-bed, characterized
by a number of several meter-high cliffs, at the base of
which boulders, up to 20 m in size, have accumulated
(Lo Iacono, 2003). Along the southern sector of the
island, thin beds of the Marettimo Formation can be
detected along the submerged coastal belt. Off the east-
ern coast, isolated carbonate relief of the Marettimo
Formation outcrop at Scoglio del Cimitero and il Cam-
mello. Wave cut platforms are very narrow, a few
meters wide or totally absent.
On the whole, the coast shows bluff or cliff mor-
phologies with only several very small pocket beaches.
More vertical and higher (up to some tens of meters)
cliffs coincide with the Monte Falcone Formation out-
crops (e.g. Punta Bombarda, Punta Pegna).
6. Structural analysis
Currently, the Marettimo structural edifice can be
described as a portion of a tectonic wedge, which con-
sists of two tectonic units (Bassano unit and Falcone
unit) characterized by a southeastward direction of
transport.
Folding and faulting patterns were analysed at many
sectors of the island (Main Map). The structural analy-
sis, concerning bedding, axial plane stylolite cleavage,
extensional veins, slickenlines and crystal fiber linea-
tion, allowed recognition three different tectonic events
and associated structures: the extensional, compres-
sional and transpressional events.
6.1 Extensional event
ENE-WSW normal faults, southwards-dipping and
displaying local syntectonic geometries, affect the car-
bonate rocks of MAR, around the cemetery (Figure 6
(a) and 6(b)). On the Punta Troia promontory (Main
Map), the Jurassic carbonates and dolomites of the Fal-
cone Unit are displaced by high-angle ENE-WSW nor-
mal faults. The fault planes affecting the Liassic
conglomerates and breccias (MFA1–2) are covered by
the marls and radiolaria-bearing marly limestone
(APT) along buttress unconformity surfaces (Figure 6
(c) and 6(d)). Another effect of the extensional stress
field is the ENE–WSW alignment of basaltic rocks
inside the Triassic marls of the Marettimo Formation
(MARb) in the Bassano succession (Main Map).