Tn. Debacker et al., Large-scale slumping deduced from structural and sedimentary features in the Lower Palaeozoic Anglo-Brabant fold belt, Belgium, J GEOL SOC, 158, 2001, pp. 341-352
Distinguishing slump folds From tectonic folds in poorly exposed areas can
be difficult, especially when the scale of the slump folds exceeds outcrop
scale. In the southeastern part of the single-phase deformed, Lower Palaeoz
oic Anglo-Brabant fold belt a comparison of cleavage/fold relationships and
stratigraphic polarity shows that a 200 m thick interval of middle Caradoc
fine-grained turbidites in the core of a large synform was overturned prio
r to tectonic deformation. This overturning is attributed to large-scale sl
umping, which was most likely a result of middle Caradoc seismic activity.
The exposed portion of the large slump sheet contains only a few small slum
p folds and intraformational breccias, making up less than 5% of the expose
d thickness. If the beds were not overturned, large-scale slumping would ne
ver be suspected and the small slump folds would probably be interpreted as
localized features in an overall 'stable' sedimentary pile. This may expla
in why so few ancient large-scale slides and slumps have been reported: the
small amount of internal deformation makes them very difficult to recogniz
e, especially when dealing with poorly exposed areas. As such, large ancien
t slides and slumps may be more common than suggested by the geological lit
erature.