Structural analysis of kink bands in unconsolidated sands

Authors:

• Antonius Van Loon,
• K. Brodzikowski,
• R. Gotowała

Abstract

Kink structures frequently occur in lithified sediments, but they are scarce in soft rocks. Nevertheless they can be found in various types of deposits, formed under different conditions. In such unconsolidated materials the bedding (or better: the lamination) acts in the same way as foliation in, for instance, metamorphic rocks. The type of lamination therefore influences the kink-band formation. Where alternations of lithologically different laminae exist, this may play an important role. Especially in " mixed" deposits the type of kink structures may be different from what it tends to be in lithified material. For that reason this paper is restricted to more or less lithologically uniform deposits, mainly composed of sand. Some characteristic structures are described, depicted and analyzed. It is concluded that they cannot be regarded as features arising from brittle behaviour and that they must have formed in relatively early stages of deformation. They frequently seem to be the result of local stress systems which occur as a result of displacements due to larger-scale deformations (with different stress systems). Variations in the pore-water pressure within the sediments influence the strain conditions and therefore probably determine parameters like the external and internal kink angles. From the sedimentary context a strain rate is deduced of 2.5 · 10^-6 to 1 · 10^-10 s^-1. © 1984.