Ball-and-pillow (pillow) structure

Definition and description

Ball-and-pillow structure is a soft-sediment deformation structure comprising rounded masses of clastic sediment (pseudonodules, q.v.) set in similar or finer grained matrix, that are vertically stacked within one horizon (Figure B2(A), (B)). Much of the discussion in the entry for pseudonodules, relating to their description and their origin through loading processes related to variations in gravitational potential energy, is relevant to ball-and-pillow structure. Distinctive features of ball-and-pillow structure include: the pseudonodules are commonly contorted into spiral or zig zag shapes; there may be very little matrix between the pseudonodules; and some ball-and-pillow horizons are consistently underlain by convolute stratification and overlain by dish structure.

Figure B2

Definition and interpretation of ball-and-pillow structure.

For simplicity, stratification is not shown in the lower, less dense layer. (A) Definition diagram for ball-and-pillow...