Mediterranean shelf-edge muddy contourites: examples from the Gela and South Adriatic basins |
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| Authors: | Email author" target="_blank">Giuseppe?VerdicchioEmail author Fabio?Trincardi |
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| Institution: | (1) ISMAR-CNR, Sezione Geologia Marina, Via Gobetti 101, 40129 Bologna, Italy |
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| Abstract: | We present new evidence of shallow-water muddy contourite drifts at two distinct locations in the central Mediterranean characterized
by a relatively deep shelf edge (between 170 and 300 m below sea level): the south-eastern Adriatic margin and the north-western
Sicily Channel. The growth of these shelf-edge contourite drifts is ascribed to the long-term impact of the Mediterranean
themohaline circulation. The Levantine Intermediate Water flows continuously, with annual or inter-annual variations, and
affects the shelf edge and the upper slope in both study areas. In addition, the SW Adriatic margin is impinged by the seasonally
modulated off-shelf cascading of North Adriatic Dense Water. This water mass has formed ever since the large Adriatic continental
shelf was drowned by the post-glacial sea-level rise. It energetically sweeps the entire slope from the shelf edge to the
deep basin. These bottom currents flow parallel or oblique to the depth contours, and are laterally constricted along markedly
erosional moats aligned parallel to the shelf edge where they increase in flow velocity. The internal geometry and growth
patterns of the shelf-edge contourites reflect changes in oceanographic setting affecting the whole Mediterranean Sea. In
particular, seismic correlation with published sediment cores documents that these deposits are actively growing and migrating
during the present interglacial, implying an enhancement in bottom-water formation during intervals of relative sea-level
rise and highstand. Regardless of the specific mechanisms of formation, sediment drifts in both study areas have been affected
by widespread thin-skinned mass-wasting events during post-glacial times. Repeated mass-transport processes have affected
in particular the downslope flank of the shelf-edge contourite drifts, indicating that these muddy deposits are prone to failure
during, or soon after, their deposition. |
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