Kink structures in unconsolidated fine-grained sediments

Authors:

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

Abstract

Kink structures are well known in crystals and lithified rocks. They are, however, also found in unconsolidated sandy and fine-grained deposits: it is likely that such structures even occur (though rarely) in pure clays. Especially when laminae with different grain parameters are present, kink structures may be formed. It turns out that the laminations play a most important role during kinking, just like foliation in hard-rock equivalents. The type of lamination and the grain-size differences, therefore, strongly influence the deformational process. The more regular the grain-size distribution within the sediment is, the more regular the geometry of the kink structures. The external and internal kink angles are determined by several factors, among which is variation in water pressure. Field examples of kink structures in fine-grained deposits from various countries are described and analyzed. It is concluded that they must have formed as a result of stress during early to very early stages of diagenesis. Apparently the kink structures were usually formed in so-called second- or higher-order stress systems (locally diverging from the main stress system as a result of local displacements). In a few cases, the geological context makes it possible to estimate the time-span involved in the kinking process, and it appears that it is comparable to estimates for similar consolidated structures. Since soft-sediment kink structures are good indicators of the local stress systems, it is believed that their analysis can contribute to a better understanding of various types of deformations within soft sediments. © 1985.