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4 Favignana calcarenite

This chapter provides the results of the fieldwork and the subsequent data analysis and experiments.
Some background on sedimentary structures and how they fit into the context of the Favignana calcarenite
will be discussed first. Then the micro- and macrofacies definition and description are presented. Finally,
the experimental results regarding reservoir properties complete this chapter.

4.1 Background

The primary sedimentary structure is a very important characteristic when trying to reconstruct the
depositional environment of a sedimentary rock succession. Depending on the type of material and the
energy that was present in the system, various flow regimes can develop. Figure 4.1 shows the grain
size and flow velocity versus the sedimentary structures that can form when sediment is deposited due
to a unidirectional flow of water under given conditions. The x-axis represents the mean grain size
of the sediment that is subjected this flow, while the y-axis represents the Froude number (Fr). This

√
is a dimensionless number, defined as F r = U/ gd, where U is the mean flow velocity [m/s], g the
gravitational constant [m/s2] and d the mean flow depth [m]. This equation corresponds to the ratio
of the flow velocity and the velocity of a stationary wave inside that same flow. When Fr<1, the wave
velocity is greater than the flow velocity, allowing waves to travel upstream. A Froude number of Fr>1
represents supercritical flow conditions, where the flow velocity exceeds the wave velocity (Leeder, 1999).
When velocities are too small to move sediment, there will be no layering that is caused by the transport
mechanism of sediment. The absence of layering however does not imply that no sedimentation takes
place. Very large sedimentation rates that need a significant amount of energy still will not develop clear
lamination. In the case of Favignana it might as well be possible to have material deposited in-situ,
because it concerns the remains of living material. As velocity increases sediment will be transported on
the sea floor, causing a parallel lamination. No disruptions should be present, because this can cause
turbulence, and therefore ripples. An even higher Froude number yields the formation of dunes; first with
a linear crest, changing to an undulating crest with increasing energy. For smaller grain sizes an upper
plane bed will form at high velocity conditions. The formation of this bedform is then associated with
the erosion of existing structures because of its higher energy, but is not supercritical yet. Because of the

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