ABSTRACTS / RESUMES - Comitato Glaciologico Italiano

GIOVANNI GABBIANELLI 1
& PAOLO COLANTONI 2
Palinuro Seamount: a large open-sea volcano
in the Tyrrhenian Sea partially modelled
by Late Quaternary glacio-eustatic sea level changes
1 Dipartimento di Scienze della Terra e Geologico-Ambientali,
Universita di Bologna, via Zamboni, 27, 40127 Bologna, Italy
2 Istituto di Geodinamica e Sedimentologia,
Universita di Urbino, ex-Sogesta, Urbino, Italy
The Palinuro Seamount, located in the southeast Tyrrhenian
sea (Central Mediterranean) about 80 km offshore the
coasts of Campania Region, is a wide volcanic complex
due to Plio-Quaternary faults connected to the extension
of the Tyrrhenian basin (Barberi & alii, 1974; Beccaluva &
alii, 1984; Serri 1990). Detailed informartions on the volcanic
morphology and on discovered ore deposits (mainly
Mn and some metallic sulphides) were obtained by means
of direct inspections carried out by manned and un- manned
submersibles, narrow beam echosounding, side scan
sonar surveys, high resolution seismic profiling and bottom
sampling (Selli & Gabbianelli, 1979; Rossi & alii, 1980;
Minniti & Bonavia 1984). Its sampled lavas are mainly tholeitic.
Some calc- alkaline samples collected on its summital
area showed an age of about 350 ky B.P. (Colantoni &
alii, 1981).
The seamount is marked by an E-W prevailing extension
(about 55 km of length Vs. about 30 km of width) and rises
from the over 3200 m deep tyrrhenian Bathyal Plain up
to 80 metres. In addition to the main and shallowest summit,
other eight E-W ranging peaks with a clear conical
morphology and all corresponding to single eruptive centers,
are encountered at depth between about 1300 and
500 m. The main summit itself is composed at least of two
different eruptive features separated by a little sill lying at a
maximum depth of 180 m. The minor and western one is
clearly cone- shaped and shows, at its narrow top about
136 m deep, radial little ridges and a well recognizable erateric
morphology, while the major and eastern feature is
characterized by a general more complex and rough
morphology.
It presents a wide plateau (about 3 km of radius) whose
depth ranges from less than 80 m at the center to 100-120
m at the external edges. A number of small reliefs raise
above the plateau and represent relics of wave erosion; to
one of these corresponds the shalloweat depth of 70 m
(Colantoni & alii, 1981). At major depths the slopes deep
rapidly at a rate of 1 to 2.
The summit of the volcano has been visited by divers that
observed a clear erosional surface, covered by organogeneous
sands, with rough outcrops of hard lavas surrounded
by large cobbles up to 30 em in diameter, indicative of
an old and strong wave action. The debris pulled away
from the eroded surface fed a depositional wedge on the
western edge of the platform, similar to the low-stand de-
posits described in the classic model of the sequence stratigraphy.
The wedge, whose thickness is up to 40 m, shows
clear downlap terminations and internal foresets lying on a
slant surface of unconformity which stretch forth the erosional
surface.
The Palinuro Seamount is therefore the first documented
example in the Mediterranean of an open-sea seamount,
where the morphology of the top has been largely controlled
by the late Pleistocene glacio-eustatic variations that
about 18 ky B.P. brought the sea level down to 110-130 m
below the present level, triggering widespread erosions.
GIOVANNI GABBIANELLI & CARLOELMI
Submerged evidences of the Roman delta of the Po River
near the Reno River mouth (North Adriatic italian coast)
Dipartimento di Scienze della Terra e Geologico- Ambientali,
Universita di Bologna, via Zamboni, 67, 40127 Bologna, Italy
The Reno River is a minor Apennine river that debouches
into the Adriatic sea, North of Ravenna. The area of its modern
mouth represented in historical times the place of two
wide cuspidate deltas of another river, the Po River, that
followed each other in the complex evolution of its dispersing
system. In the last 2500 years and before the formation
of the modern Po bird-foot delta (17 th century to present),
at least ten distinct major cuspidate subdeltas developed,
following the repeated shifting of the distributary channels
and the increasing man's control on the Padan hydrographic
system (Ciabatti, 1966; Roncuzzi & alit: 1970; Fabbri
1985, Bondesan 1989). These delta bodies, largely reconstructed
on the basis of inland geomorphologic elements
(buried barriers island, lagoon remains etc.) and of
historical-archaeological information, generally did not
prograde far out from the shorelines for two main causes:
- the rivers flow was distributed along a wide frontal area
and through small outlets, delta interlagoonal areas, interdistributary
bay etc. (Nelson, 1970);
- the sediment supply was lower than the present one, due
to the low man's impact on the natural system.
Their largest extension generally never reached nor passed
the present coast line, with the exceptions of: i) the late
173