Sedimentology and magnetic susceptibility of the Upper Eifelian - Lower Givetian (Middle Devonian) in southwestern Belgium: insights into carbonate platform initiation

The major part of the Hanonet Formation is deposited on a mixed siliciclastic–
carbonate detrital ramp, whereas the top is dominated by carbonate-rimmed shelf-related
sedimentation. The transition corresponds roughly to the Eifelian–Givetian boundary. This
work is based on two stratigraphic sections located in the southern part of the Dinant
Synclinorium. Petrographic study leads to the definition of 11 microfacies, which demonstrate
important sedimentological differences existing between the sections. A curve showing
microfacies evolution is interpreted in terms of changing bathymetry. An environmental
model depicts the lateral transition from a multiclinal carbonate ramp (to the east) to a forereef
setting (to the west). Magnetic susceptibility was used to establish accurate stratigraphic
correlations between the two sections. It also leads to an appreciation of the relative importance
of eustatic sea-level change and local sedimentation rate. The combined interpretation
of the microfacies curves and the magnetic susceptibility provides a new view of the sedimentary
dynamics of the studied sections and, in a more general way, a better understanding of the
processes responsible for magnetic susceptibility variations in carbonate rocks.