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SUBMERGED DEPOSITIONAL TERRACES ALONG THE ITALIAN COAST - CONCLUSION 113

static lowstand (18 ka ago); in unstable tectonics sectors, a vertical component, tectonic or volcano-
tectonic in nature, has to be added. The effect of this component is reflected both in gradual varia-
tions of the depth of the SDT (e.g. Pontine isles - quiescent at present -where in a span of coast of
18 km, the depth of all the depositional parameters of the SDT varies of about 2 meter/km), and in
the great lateral variability of the geometry of the SDT in adjacent coastal parts, but separated by
structural discontinuity and subject to differential vertical movement, e.g. Aeolian Isles - active at pre-
sent.

In some areas, SDT with features similar to the deeper ones have been observed at relative shallow
depth; most cases are located in the Aeolian Archipelago, where the SDT are present at various depth,
whose values seem to group in some classes of frequency. The main one corresponds to SDT with the
edge of about 30-40 m. At similar depths (respectively a little higher and a little lower) there are SDT
around Linosa Isle (edge at -45/55 m) and Palmarola Isle (-20/22 m); along some parts of Sardinia
coasts and of Sorrento coasts there are SDT with the edge between -55 and -95 m.

MORPHOLOGY AND INTERNAL GEOMETRY

The geometry and physical dimensions of the SDT are remarkably homogeneous: they are deposi-
tional bodies with a terraced external morphology and a wedging geometry, whose morphologic
expression is mostly evident even in the sea floor bathymetry. The maximum thickness is generally bet-
ween 10 and 30 meters. We have also obser ved low values on the west part of Sardinia edge and on
the Calabria coast (Capo Suvero). The highest thickness (more than 40 m) was found in the Pontine
and Aeolian isles (where there is a good availability of sediment).

The extension perpendicular to the coast (width) is strictly connected with the steepness and with
the width of the shelf and varies from some hundred meters to some kilometers. The extension paral-
lel to the coast (length) is more variable: near volcanic and/or insular coasts, that are uneven and cur-
vilinear and with volcanic-tectonic or structural features, there are terraces with very limited lateral
continuity (generally at least one kilometer) and great variability in the internal and external geometry,
while along tracts of rectilinear margin, the depositional terraces have been followed for many tens of
kilometers (ex. Tuscany Archipelago or Taranto Gulf), having constant characters and dimension.

We have obser ved both SDT that fade away gradually (for example due to gradient variation of the
basal surface) both with sharp lateral disappearance (for example, at the end of the abrasion platforms
or near the canyon or areas of gravitational instability).

A controlling factor in the distribution of SDT with limited extension is the presence of isolated
structures or local morphologic irregularities of the sea floor that have both a role of local source of
clastic sediment and of wave energy attenuation (for example at Sorrento Peninsula or at Capo
Suvero).

The internal structure of the SDT is always clinostratified, oblique and/or sigmoidal, sloping basin-
ward and never parallel to the coast. The foresets have inclination between 4° and 20°, often more
than 10°; such steepness can cause an apparent acoustic transparency revealed in some cases and attri-
butable to instrumental causes (see Chiocci, this volume).

The SDTs are often polyphasic, that is to say they show evidences of alternation of depositional
and erosional phases, like reactivation or erosion surfaces of the topset (Pontine Isles, Egadi, Aeolian
Isles, Sorrento). SDTs are often superimposed each other or partially coalescent, are always in retro-
gradational setting and often (not always) there is a trend to increase foreset steepness upwards.
Generally the inclination of the strata matches the inclination of the frontal slope, as evidence of a
depositional and not erosive nature of the latter; only in one case (Egadi Isles) a greater inclinations
of the frontal slope respect to the foresets has been observed, indicating postdepositional erosion due
to submarine currents.

ACOUSTIC AND LITHOLOGICAL FACIES

The textural and lithological characters of the sediment making up the SDT have been detected via
sea floor coring on Palmarola Isl. (Pontine) and Salina Isl. (Aeolian) as well as in Calabria (Capo
Suvero), Capraia shelf and Elba Ridge. Where there were no samples, the lithology has been roughly