Page 58 - MSc_thesis_R A Kil

a wind has the possibility to create waves — is the largest at a northwestern wind. More than 700
kilometres of open sea are situated between western Sicily and the Ligurian coast in the northern part of
Italy. The regional name for the strong north-south wind is the Mistral (It: Maestrale), which can be
remarkably powerful and can therefore potentially transport coarse grained sediments in case of major
storm events. The impact of the Mistral winds on eastern Favignana can potentially be intensified when
water pushes itself through the channel between the Levanzo and Favignana limestone platforms.

The hypothesis of storm-related events as a main driving force of sediment transport is reflected in the
outcrop data. As mentioned earlier, predominant directions are observed to be around southeast to
south (figure 4.12). Outcrops show very few subsequent palaeo-directions, approximately opposite to the
main orientation, indicating minor storm events from the south occurred during the sedimentation of the
calcarenite complex. Another explanation can be found in the fact that some of the subsequent directions
are found in sequences that show upper plane flow regimes. This can lead to an interpretation where the
structures are seen as backsets of antidunes. At this stage it is not certain what process caused the —
apparent — reversal of the flow direction.

A summary of observed palaeo-transport directions and possible locations of cool water carbonate factories
is provided in figure 5.1. An important observation in here is the orientation of the flow with respect to
the other Aegadian islands and the mainland of Sicily. The southeast direction is more or less aligned
with the channel between Levanzo and Monte Santa Caterina. Moreover, the other dominant southwest
direction shows transport parallel to the coast. This indicates alongshore currents to have played a role
in the system.

Outcrop analysis shows that also gravity processes most likely had an important role in the transport of
sediment. In particular the large scour systems may have been favoured and/or generated by gravity
processes. It is therefore reasonable that the start of erosion at the crest of a calcarenite wedge started a
self-inducing process driven by gravity, scouring into the earlier deposited sediments.

5.3 Depositional environment

The character of the internal sedimentary structures and the processes that formed the Favignana
calcarenite are fairly complex. The base of the Lower Pleistocene system on Favignana is the top of the
Trubi clay, which can be found at several locations on the island, in particular Cala Rossa and Cala
Azzurra (figures 4.9e and 4.9f). The top of the clay is both bioturbated and eroded, but bioturbation did
not continue across the boundary between the clay and the bioclastic Favignana deposits. This indicates
either a stop in sedimentation or an erosive event at this stage — no deposits dating from the uppermost
Pliocene (Piacenzian stage) are found — which also confirms the difference in age between the Zanclean
Trubi Formation and the Favignana calcarenite.

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