The Sicilian gateway: anatomy of the deep-water connection between East and West Mediterranean basins

Abstract

The Sicilian gateway is a narrow, deep, interconnected series of basins, sill valleys and passageways that cuts across the broad, shallow Sicilian-Tunisian Platform in the Central Mediterranean. This deep connection allows dense Levantine Intermediate Water (LIW) formed in the Eastern Mediterranean to flow in a westerly direction through the gateway and exit into the Tyrrhenian and Balearic basins of the Western Mediterranean. LIW is replaced by a strong surface flow of Modified Atlantic Water (MAW). A complex and still active tectonic regime has been an important control on the development of physiography and on the style and distribution of sediments across the Platform.Within the deep gateway basins, turbidites, debrites and megabeds are intercalated with a background of predominantly muddy and calcareous, hemipelagic and contourite sediments. Evidence for the influence of bottom currents on sedimentation is seen in the construction of small mounded drifts and irregular patch drifts, in zones of scouring and non-deposition, in local photographic evidence of a current-smoothed or rippled seafloor, and as a subtle combination of features present in the background sediments. These include: extensively reworked microfossil assemblages, rare diffuse lamination, coarse lenses of mixed composition within a pervasively bioturbated sediment, and relatively high rates of accumulation.

Contour current imprints and contourite drifts in the Bahamian archipelago

“…Detached drifts usually form at a bend of the margin and prograde downslope and perpendicular to the margin. Channel‐related drifts form in large deep‐channels in which current velocity is locally increased. Contourites are thus deposited as convex, low‐topography, patch drifts in the channel axis or along their sides and as contourite lobes at the channel mouth (Howe et al ., ; McCave & Carter, ; Reeder et al ., ). Confined drifts form in narrow channels, gateways or gaps, and show vertical stacking of contourites with very restricted lateral migration. Localized patch drifts with limited extension. Infill drift usually filling a failure scar or any other topographic low. Fault‐controlled drift related to a fault scar and mixed drift related to current interaction. Recently Lüdmann et al . () introduced a point‐sourced fed, channel related, drift type named delta drift that occurred attached to the slope of a Miocene carbonate platform in the Inner Sea of the Maldives.…”

Short-distance variability in slope bed-forms along the Southwestern Adriatic Margin (Central Mediterranean)

“…Clear evidence of bottom current deposits and correlative erosional features in the Mediterranean come from restricted sub-basins, such as the South Adriatic (Verdicchio et al, in press) and the Alboran Sea (Ercilla et al, 2002), or from passageways as the Corsica Channel (Roveri, 2002), the Sicily Strait (Reeder et al, 2002) and the Otranto Strait , where local topography is likely to induce flow restriction and bottom current acceleration. All these areas show examples of simple, asymmetric mounded drifts or upslope migrating sediment waves that are very similar to some of the contourite deposits of the Atlantic Ocean, but are typically smaller in size and seem to encompass a more reduced time interval, implying faster growth rates.…”

Seafloor evidence for the interaction between cascading and along‐slope bottom water masses

“…Beyond the Adriatic slope, other areas of deep water formation, such as the Gulf of Lions, provide increasing evidence for the seafloor impact of cascading cold waters on the upper slope [Gaudin et al, 2006] and in canyons [Canals et al, 2006]. Elsewhere, several margins of the Mediterranean are impacted by intermediate or deep water masses that flow along the contour and allow formation of several examples of bottomcurrent deposits and accompanying erosional features, especially where straits and sills between different sub-basins constrain and focus the flowing bottom water masses [Marani et al, 1993;Reeder et al, 2002;Roveri, 2002]. These latter cases documented the interaction of a single water mass flowing along the regional contour and against local morphological relief, resulting in relatively large but geometrically simple sediment drifts (as described by Faugères et al [1999]).…”