Structural style in slump sheets: Ludlow Series, Powys, Wales

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Abstract
The slump deformation in sediments of the Montgomery Trough is described and compared with tectonic deformation. The structures within each slump sheet are systematically oriented with respect to the inferred palaeoslope. The slump folds have lognormal size distributions and their range of styles closely matches that of tectonic folds. Similar folds are rare, and deformed lineations show that buckling was important during slump fold formation. Axial microfold lineations and axial plane cleavages are associated with the slump folds. Also present is a spaced cleavage, thought to have formed in soft sediment. Structural style cannot discriminate between slump and tectonic structures. The distinction may in many cases rely on subjective and uncommon features of soft-sediment deformation, such as the absence from folds of tension cracks and veins.