6. Deformation Structures

Deformation of sediments can begin during  deposition and be caused either by the depositional process itself or by other mechanisms triggered by it or by gravity. Deformational events also occur after  deposition on or below the sedimentary interface. A first distinction can thus be made between syn - and post-depositional  deformations, with the proviso made in the introduction, i.e., ignoring tectonic processes. In certain cases, however, it is not easy to discriminate between sedimentary and tectonic causes of sediment deformation, especially if tectonic stresses act on a still soft sediment. Some examples will be shown and discussed to make this point clear.

The following survey of deformative structures does not pretend to be systematic and exhaustive. It is rather aimed at exemplifying common and significant cases. I will start with smaller, gentler, and more localized structures and end with forms of larger scale and greater intensity. At one end of the spectrum, only parts of beds or bed surfaces are involved, at the other end can be seen deformation throughout packets of beds, sedimentary bodies and stratigraphic successions up to mountain size.