Page 34 - MSc_thesis_R A Kil

Fr = 1.0 ANTIDUNES
Fr = 0.84
gradual 3D
UPPER PLANE
FROUDE NUMBER abrubt DUNES
abrubt 2D LOWER PLANE grgardaudaulal

RIPPLES NO MOVEMENT

GRAIN SIZE

Figure 4.1 – Bed geometries as function of the grain size on the horizontal axis, and the mean
flow velocity on the vertical axis. Both axes are logarithmic, and scale of the axes has been left
out to emphasise the relative position of the flow regimes without exact numbers. Plot has been
modified after Southard & Boguchwal (1990).

high energy and the supercritical flow conditions undulated beds and antidunes can form. Antidunes are
associated with a high degree of erosion, and are therefore generally not often well preserved. A typical
phenomenon related to the formation of giant ripples and the transition to supercritical flow conditions is
a scour and fill system.

4.2 Sedimentary microfacies

The thin sections from a selected number of samples were examined with a microscope in order to describe
the microfacies of the Favignana calcarenite. Unlike the macrofacies, showing distinct differences in
sedimentary structures, the microfacies focusses more on the fossil content of the samples. Therefore, this
section gives an overview of the most common types of fossils found in the samples and in the field. The
vast majority — around 80 % — of the calcarenite matrix is made up from three types of organisms. In
order of abundance, bryozoans, red algae and foraminifera are the most common.

4.2.1 Foramol

In the industry and literature the bioclastic calcarenite as observed on Favignana is also known as foramol.
On of the first descriptions of foramol is given by Lees & Buller (1972), who defined two main types of
carbonates. The foramol differs from the chlorozoan with an abundance of animal matter, and except for

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