Plate 117

Some details of convolute laminae

---

Convolutions are markedly and geometrically complicated structures, as can be seen in these pictures. Picture A is a section of a sandstone bed in place, picture B of a fluvial pebble collected on the bed of a river eroding similar sandstones. However a packet of convoluted laminae is cut, the patterns we see is one of convoluted and wrinkled lines with various radii of curvature, similar to those obtained by stirring two immisicible liquids in a cup or jar. It reflects many tight folds made by soft sediment laminae slipping against one another. The fold axes have a limited lateral continuity, and are folded themselves; that is why linear trends are rare and short.

A: Inoceramus beds, Cretaceous of Polish Carpathians; B: Marnoso-arenacea Formation, northern Appenines (scale in centimeters).

Glossary